HK1261100A1

HK1261100A1 - Process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate

Info

Publication number: HK1261100A1
Application number: HK19120965.9A
Authority: HK
Inventors: N·C·内尔森; H·瑞普; W·克罗伊格
Original assignee: Omya国际股份公司
Priority date: 2016-02-05
Filing date: 2017-02-03
Publication date: 2019-12-27

Description

Process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate

Technical Field

The present invention relates to a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate, a process for the mineralization and/or stabilization of water and the use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by this process for the mineralization and/or stabilization of water.

Background

Drinking water has become scarce. Even in water-rich countries, not all water sources and reservoirs are suitable for producing drinking water, and many water sources today are threatened by a drastic deterioration of the water quality. The feed water originally used for drinking purposes was primarily surface water and ground water. However, for environmental and economic reasons, the treatment of seawater, brine, brackish water, wastewater and contaminated discharge water is becoming increasingly important.

In order to recover water (for drinking) from sea water or brackish water, several apparatuses and methods are known which are of considerable importance for arid areas, coastal areas and islands in the sea, and these generally include distillation, electrolysis and osmotic or reverse osmosis methods. The water obtained from these processes is very soft and has a low pH due to the lack of pH buffering salts, and therefore the water obtained from these processes tends to be highly reactive and unless treated, can create severe corrosion difficulties during its distribution in conventional pipelines. Furthermore, untreated desalinated water cannot be used directly as a source of drinking water. To prevent the dissolution of undesirable substances in pipeline systems, to avoid corrosion of water supply equipment such as pipes and valves and to make water palatable, it is necessary to increase the mineral and alkalinity content of the water.

The traditional method and corresponding equipment mainly used for water mineralization is lime addition by carbon dioxide and limestone bed filtration (also called calcite contactor) and dissolution with partial carbonation. Other less common methods of mineralization include, for example, the addition of slaked lime and sodium carbonate, the addition of calcium sulfate and sodium bicarbonate, or the addition of calcium chloride and sodium bicarbonate.

The lime process involves the use of CO₂Acidifying water to treat lime solutions, wherein the following reactions are involved:

from the above reaction scheme, it can be concluded that two equivalents of CO are required₂One equivalent of Ca (OH)₂Conversion to Ca²⁺And bicarbonate for mineralization. The process depends on two equivalents of CO₂To convert alkaline hydroxide ions into the buffer species HCO₃ ^-. For the mineralization of water, a saturated calcium hydroxide solution, commonly referred to as lime water, is prepared from lime milk (usually up to 5% by weight), based on the total weight, in an amount of 0.1-0.2% by weight. It is therefore necessary to use a saturator that produces lime water and a large volume of lime water is required to achieve the target levels of minerals and alkalinity content. Another drawback of this method is that the slaked lime is corrosive and requires appropriate handling and special equipment. Furthermore, an improperly controlled addition of hydrated lime to soft water may result in an undesirable pH change due to the fact that lime does not have buffering properties.

The limestone bed filtration process includes the step of passing soft water through a bed of granular limestone to dissolve calcium carbonate in the water stream. Limestone and CO are reacted according to₂Contact of acidified water to mineralize water:

unlike the lime process, only one equivalent of CO is stoichiometrically required₂Namely, one equivalent of CaCO₃Conversion to Ca²⁺And bicarbonate for mineralization and alkalinity addition. Furthermore, limestone is non-corrosive and is due to CaCO₃Prevents large pH variations. However, as the pH increases, the reaction slows, making it necessary to add additional CO₂Metering to ensure sufficient CaCO₃Is dissolved. Unreacted CO₂And then removed by stripping or neutralization with sodium hydroxide.

Methods and systems for water mineralization using milk or slurry of lime are described in US 7,374,694 and EP 0520826. US 5,914,046 describes a method for reducing the acidity of wastewater discharge using a pulsed limestone bed.

US 7,771,599 describes a method of mineralising process water in a desalination system. The process separates carbon dioxide gas from seawater or the concentrate (brine) of a desalination process via a gas transfer membrane. The separated carbon dioxide gas is then used to produce soluble calcium bicarbonate (Ca (HCO)₃)₂). WO 2012/020056 a1 is directed to a method of mineralising water comprising the steps of providing feed water and injecting gaseous carbon dioxide and a slurry into the feed water, wherein the slurry comprises micronized calcium carbonate. WO 2010/023742 a2 describes a method and an apparatus for producing drinking water by post-processing (post-treatment) desalinated water obtained by desalinating seawater via distillation or reverse osmosis. The method includes a carbon dioxide absorption process of excessively supplying carbon dioxide to desalted water to absorb the carbon dioxide, a mineralization process of passing desalted water adsorbed by the carbon dioxide through a limestone filter in which limestone is filled to form calcium ions and bicarbonate ions, and a carbon dioxide discharge process of supplying air to desalted water passed through the mineralization process to discharge the carbon dioxide and the air to obtain drinking water. WO 2012/113957 a1 relates to a method for remineralizing a fluid, wherein the final turbidity is controlled. The method comprises the steps of reagent dosing, remineralization and filtration. EP 2565165 a1 relates to a water mineralization method comprising the steps of: providing a feed water, providing an aqueous calcium carbonate solution, wherein the aqueous calcium carbonate solution comprises dissolved calcium carbonate and reactive species thereof, and combining the feed water and the aqueous calcium carbonate solution. EP 2623466 a1 relates to a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate and the use thereof. The process may be carried out in a reactor system comprising a tank equipped with an agitatorAt least one filtering device and a grinding device. EP 2623467 a1 relates to a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate and the use thereof. The process is carried out in a reactor system comprising a tank equipped with an agitator and at least one filtration device. EP 2623564 a1 relates to an apparatus for purifying minerals, pigments and/or fillers and/or for producing precipitated alkaline earth metal carbonates and/or water mineralization and the use of such an apparatus for purifying minerals, pigments and/or fillers and/or for water mineralization and/or for producing precipitated alkaline earth metal carbonates. WO 2013/132399 a1 relates to water mineralization by: mixing carbonate in powder form into water in a rapid process, generating CO in water₂But increases its turbidity. The treated water is then transported through a reactor with granular carbonates, wherein the CO in the water₂The additional carbonate is dissolved in a slow manner. The reactor simultaneously adds additional minerals and alkalinity to the water and removes the turbidity of the water by dissolving the residual powder and filtering insoluble particles. CN 102826689A 1 relates to a post-treatment process of desalted seawater, which comprises the following steps: (1) introducing CO₂Adding into desalted seawater and mixing thoroughly; and (2) adding CO₂The desalted seawater is mineralized in a mineralization pool; arranging a calcium carbonate filter bed in the mineralization pond; and adding CO₂The desalinated seawater of (a) is passed through a calcium carbonate filter bed to effect substantial contact and reaction with the calcium carbonate. WO 2013/014026 a1 relates to a method for treating water and the use of calcium carbonate in such a method. In particular, it relates to a process for remineralisation of water comprising the steps of: (a) providing a feed water having a carbon dioxide concentration of at least 20mg/l, preferably in the range of 25 to 100mg/l, and more preferably in the range of 30 to 60mg/l, (b) providing an aqueous slurry comprising micronized calcium carbonate, and (c) combining the feed water of step (a) with the aqueous slurry of step (b) to obtain remineralized water. WO 2014/187666a1 relates to a multi-batch system for preparing a solution of calcium bicarbonate and to the use of such a two-batch system for preparing a solution of calcium bicarbonate. WO 2014/187613A 1 relates to a device for preparing calcium bicarbonate solutionsAnd the use of such a device for the continuous preparation of a solution of calcium bicarbonate and the use of such a device for the remineralization of water.

US 2009/0101573 a1 relates to a wastewater treatment plant and method, a mineral mixing tank receiving biologically treated water, sludge produced by biological treatment and mineral sludge containing calcium etc. from a settling tank. The mineral pump returns the sludge and treated water from the mineral mixing tank to the raw water tank. An air lift pump circulates the treated water between a re-aeration tank having a semi-anaerobic section and a denitrification tank. The semi-anaerobic stage mitigates environmental changes of the microorganisms during circulation of the treated water between the re-aeration tank and the denitrification tank, and thereby achieves an environment required to promote the propagation of the microorganisms. The air lift pump enables stirring with low energy consumption even when the microorganisms are cultured to their high concentration. WO 2006/128730 a1 describes a process for treating a feed stream of an aqueous medium of a given composition, the feed stream comprising components which may form scale dissolved in a Reverse Osmosis (RO) system under given process conditions, thereby providing a permeate stream and a retentate (concentrate) stream comprising components which may form scale in concentrations high enough to cause scale formation in those parts of the RO system which are in contact with said retentate in the absence of a scale inhibitor, in which process (a) the retentate is continuously monitored for the presence of particles of components which may form scale in said retentate and readings of one or more physical parameters of the retentate relating to the presence of these particles are continuously recorded; (b) continuously comparing the recorded readings with measured values of said one or more parameters of a retentate obtained from an aqueous medium of the same composition under the same process conditions, the values of said process conditions being empirically predetermined; and (c) once the recorded readings of said one or more parameters differ from said predetermined measurements, adding an amount of scale inhibitor to the RO system upstream of the membrane, said amount of scale inhibitor having been empirically predetermined to prevent scale formation under said conditions. WO 98/46533 a1 relates to a system for purifying water to remove at least one of natural organic matter, colour, turbidity, bacteria, cysts and oocysts, viruses, arsenic compounds and insoluble impurities. The system comprises the following steps: providing a water body to be purified; controlling the pH value of the water body to be in the range of 5 to 8; and adding a coagulant to the body of water to provide floes. The floe is maintained in the water body at a concentration of 1-6 for the purpose of adsorbing at least one of natural organic matter, color, turbidity, and bacteria to provide treated water. Thereafter, a first portion of the treated water and floes is removed from the body of water. US 6,027,649 a relates to a system for purifying water to remove at least one of natural organic matter, color, turbidity, bacteria, cysts and oocysts, viruses, arsenic compounds and insoluble impurities. The system comprises the following steps: providing a water body to be purified; controlling the pH value of the water body within the range of 5-8; and adding a coagulant to the body of water to provide floes. The floe is maintained in the water body at a concentration of 1-6 for the purpose of adsorbing at least one of natural organic matter, color, turbidity, and bacteria to provide treated water. Thereafter, a first portion of the treated water and floes is removed from the body of water. A submerged semi-permeable membrane is provided in the body of water for removing a second portion of the treated water. The membrane has a pore size of 0.02-1 μm to provide a permeate consisting of purified water and a retentate comprising floes. The water is treated by mixing to minimize membrane fouling and to allow for thorough mixing of the floes in the water. US 2010/0224541 a1 describes a small bubble diffuser tube capable of producing small bubbles uniformly and consistently, even when the diffuser tube has a long length; a small bubble diffusing device and an immersed membrane separation apparatus using such a tube were manufactured. US 2013/0064741 a1 relates to a system for fixing carbon dioxide. The system includes a first reactor for extracting an alkali metal component from the slag and a second reactor for carbonating the extracted alkali metal component with carbon dioxide. With such a system, carbon dioxide can then be fixed in a simpler and cost-effective manner.

However, the described method has the following disadvantages: mineralization of water and in particular production of aqueous solutions (for mineralization of water) comprising at least one earth alkali bicarbonateShow CO that is still improvable₂Efficiency and/or excessive energy consumption.

In view of the above, it would still be of interest to the skilled person to improve the mineralization of water. It would be particularly desirable to provide an alternative or improved process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate which can be prepared in a more efficient, economical and ecological manner, in particular for which the CO can be increased₂The efficiency of the consumption and without excessive energy consumption for the method and the corresponding device.

Disclosure of Invention

It is therefore an object of the present invention to provide a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate. Another object may be seen to provide a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate which increases the CO used in the process₂The consumption efficiency. Another object may be seen to provide a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate which enables to reduce the total energy consumption for the process and the corresponding plant. Another object may be seen to be to provide a process for the preparation of an aqueous solution comprising at least one earth alkali bicarbonate, wherein the production of sludge is reduced compared to the typical lime systems of the prior art.

One or more of the foregoing and other problems are solved by the subject matter defined herein in the independent claims. Advantageous embodiments of the invention are defined in the respective dependent claims.

A first aspect of the invention relates to a process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate. The method comprises the following steps:

a) providing water;

b) providing at least one alkaline earth metal carbonate-containing material;

c) providing CO₂Or pK_aValue of<5 with an acid;

d) mixing the water of step a) with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids are combined in any order, for example to obtain an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate;

e) filtering at least part of the aqueous suspension S1 obtained in step d) by passing the aqueous suspension S1 through at least one submerged membrane module (submerged membrane module) to obtain an aqueous solution S2 comprising at least one alkaline earth metal bicarbonate,

wherein the at least one submerged membrane module is located in a container (container).

According to another aspect of the present invention, there is provided a method for the mineralization and/or stabilization of water, the method comprising the steps of:

i) providing the water to be mineralized with water,

ii) providing an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by a process as defined herein,

iii) combining the water to be mineralized of step (i) with the aqueous solution comprising at least one alkaline earth metal bicarbonate of step (ii) to obtain mineralized water.

According to one embodiment of the method of the invention for the mineralization of water, the method comprises the further step (iv): (iv) adding a base, preferably sodium hydroxide or calcium hydroxide, to the mineralized water of step (iii).

According to another aspect of the present invention, there is provided the use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by a process as described herein for the mineralization and/or stabilization of water or as mineralized water. According to one embodiment of the present use, the water is desalinated or naturally soft water.

According to one implementation of the method of the inventionScheme, step d) includes the following steps: i1) mixing the water of step a) with the CO of step c)₂Or acid combining, and i2) combining the mixture of i1) with the at least one alkaline earth metal carbonate-containing material of step b); or ii1) combining the water of step a) with the at least one alkaline earth metal carbonate-containing material of step b), and ii2) combining the mixture of ii1) with the CO of step c)₂Or a combination of acids.

According to another embodiment of the process according to the invention, process steps d) and e) are carried out in the same vessel, preferably in a reactor tank.

According to yet another embodiment of the method of the present invention, the at least one submerged membrane module has a pore size of preferably <1 μm and more preferably <0.1 μm.

According to one embodiment of the method of the present invention, air or process fluid is preferably recirculated through at least a portion of the surface of the at least one submerged membrane module, more preferably the CO of step c), from the bottom to the top direction of the at least one submerged membrane module and/or vessel₂Or acid is added to the air or process fluid.

According to another embodiment of the method of the invention, the container is sealed and the air at the top of the container is used as feed and reintroduced into the bottom of the container.

According to another embodiment of the process of the invention, the process comprises a further step f): backwashing the at least one submerged membrane module, optionally CO, with water₂Or pK_aValue of<5 acid was added to the water.

According to one embodiment of the process of the present invention, the at least one alkaline earth metal carbonate-containing material of step b) is selected from precipitated calcium carbonate, modified calcium carbonate, ground calcium carbonate and mixtures thereof, preferably, the at least one alkaline earth metal carbonate-containing material of step b) is selected from ground calcium carbonate.

According to another embodiment of the process of the present invention, the at least one alkaline earth metal carbonate-containing material of step b) is ground calcium carbonate selected from the group consisting of marble, limestone, chalk and mixtures thereof.

According to yet another embodiment of the process of the present invention, the at least one alkaline earth metal carbonate-containing material of step b) is provided in dry form or in the form of an aqueous suspension; and/or the at least one earth alkali hydrogen carbonate obtained in step d) comprises, preferably consists of, calcium hydrogen carbonate.

According to one embodiment of the process of the present invention, the acid provided in step c) has<pK of 4_aThe acid and/or the acid is selected from sulphuric acid, hydrochloric acid, nitric acid or citric acid and/or mixtures thereof.

According to another embodiment of the process of the invention, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) has an earth alkali metal concentration, expressed as earth alkali hydrogen carbonate, of from 20 to 1000mg/l and more preferably from 50 to 600mg/l and most preferably from 80 to 400 mg/l; and/or has a pH value of 6.1 to 8.9 and preferably 6.5 to 8.5.

It is to be understood that for purposes of the present invention, the following terms have the following meanings.

The term "alkaline earth metal carbonate-containing material" may refer to a material comprising at least 50.0% by weight of alkaline earth metal carbonate, based on the total dry weight of the alkaline earth metal carbonate-containing material.

By "calcium carbonate-containing material" in the meaning of the present invention is meant a material as a source of calcium carbonate, preferably selected from the group consisting of ground calcium carbonate, precipitated calcium carbonate, surface-reacted calcium carbonate, dolomite and mixtures thereof.

The term "mineralization" as used herein means the addition of essential mineral ions and alkalinity to water that is completely free or contains insufficient mineral or alkalinity to obtain palatable water. Mineralization can be achieved by adding at least a specific alkaline earth carbonate, such as calcium carbonate, as the only raw material to the water to be treated. Optionally, for example, to obtain health-related benefits to ensure proper uptake of some essential minerals and trace elements, additional substances such as magnesium salts may be mixed into or with alkaline earth metal carbonates such as calcium carbonate and subsequently added to the water during the mineralization process. The mineralized product may comprise additional minerals selected from magnesium sulfate, potassium or sodium, potassium bicarbonate, sodium bicarbonate or other minerals containing essential trace elements and mixtures thereof, according to national guidelines for human health and drinking water quality. Preferably, the mineralized product comprises additional minerals selected from the group consisting of magnesium sulfate, potassium bicarbonate, sodium bicarbonate, and mixtures thereof.

The term "stabilization" as used in the present invention refers to increasing mineral content and alkalinity to neutralize or remove remaining "aggressive" carbon dioxide and/or to raise pH to achieve a stable and balanced final water quality. This stabilization is preferably achieved by: stripping aggressive carbon dioxide, adding a base to the mineralized water obtained by the inventive apparatus, or a combination of both.

The expression "CO" in the meaning of the present invention₂By efficiency is meant the CO in the process₂(additional CO initially in the feed water provided in step (a) and provided in step (c)₂(measured in mmol/l)) to the amount (measured in mmol/l) of alkaline earth carbonate (provided in step (b)) that is converted to alkaline earth bicarbonate with increasing feed water from step (a) to the alkaline earth carbonate of the aqueous solution S2 produced in step (e).

The expression "acidified" or "acid" in the meaning of the present invention relates to bronsted-lowry (r) ((r))Lowry) theory, and thus involving H₃O⁺An ion donor. In addition, the pH of the acid may be>7, for example in>7 to 7.5, provided that there is a suitable corresponding base to receive the H supplied by the acid₃O⁺Ions.

In accordance with the inventionPurpose, "pK_aThe value "indicates the acid dissociation constant associated with a given ionizable hydrogen in a given acid and indicates the natural degree of dissociation of this hydrogen from such acid at equilibrium in water at a given temperature. Such a pK_aValues can be found in reference texts such as: harris, d.c. "Quantitative Chemical Analysis: 3 rd edition, 1991, w.h&Co.(USA)，ISBN 0-7167-2170-8。pK_aThe values can be determined according to prior art methods well known to those skilled in the art. pK of acid_aThe values depend on the temperature, unless explicitly stated otherwise, the pK according to the invention_aThe values relate to a temperature of 25 ℃.

When the term "comprising" is used in the present description and claims, it does not exclude other elements. For the purposes of the present invention, the term "consisting of … … (of) is to be considered as a preferred embodiment of the term" comprising or comprising ". If in the following it is defined that a group set (group) comprises at least a certain number of embodiments, this is also to be understood as disclosing a group set, which preferably only consists of these embodiments.

Where an indefinite or definite article is used when referring to a singular noun e.g. "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated.

Terms such as "available" or "definable" and "obtained" or "defined" are used interchangeably. This for example means that unless the context clearly dictates otherwise, the term "obtained" is not meant to indicate that for example an embodiment must be obtained by, for example, a sequence of steps following the term "obtained", although the term "obtained" or "defined" always includes such a restrictive understanding as a preferred embodiment.

Details and preferred embodiments of the process according to the invention for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate will be described in more detail hereinafter. It is to be understood that these technical details and embodiments also apply, where applicable, to the inventive method and use for the mineralization and/or stabilization of water.

The process of the invention is used to prepare an aqueous solution comprising at least one earth alkali hydrogen carbonate. In particular, the process of the invention is used for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate suitable for the mineralization and/or stabilization of water.

The term "aqueous" solution refers to a system wherein the aqueous solvent comprises or preferably consists of water. However, the term does not exclude that the aqueous solvent comprises a minor amount of at least one water miscible organic solvent selected from the group consisting of methanol, ethanol, acetone, acetonitrile, tetrahydrofuran and mixtures thereof. Preferably, the aqueous solvent comprises at least 80.0% by weight, preferably at least 90.0% by weight, more preferably at least 95.0% by weight, still more preferably at least 99.0% by weight of water, based on the total weight of the aqueous solvent. For example, the aqueous solvent consists of water.

The term aqueous "solution" in the meaning of the present invention refers to a system comprising an aqueous solvent and particles of alkaline earth carbonate and/or alkaline earth bicarbonate, wherein the particles of alkaline earth carbonate and/or alkaline earth bicarbonate are dissolved in the aqueous solvent. The term "dissolved" in the meaning of the present invention refers to a system wherein no discrete solid particles are observed in the aqueous solvent.

The term "at least one" alkaline earth hydrogen carbonate in the meaning of the present invention means that the alkaline earth hydrogen carbonate comprises, preferably consists of, one or more alkaline earth hydrogen carbonates.

In one embodiment of the present invention, the at least one earth alkali hydrogen carbonate comprises, preferably consists of, one earth alkali hydrogen carbonate. Further optionally, the at least one earth alkali hydrogen carbonate comprises, preferably consists of, two or more earth alkali hydrogen carbonates. For example, the at least one earth alkali hydrogen carbonate comprises, preferably consists of, two earth alkali hydrogen carbonates.

Preferably, the at least one earth alkali hydrogen carbonate comprises, more preferably consists of, one earth alkali hydrogen carbonate.

In one embodiment of the invention, the at least one earth alkali hydrogen carbonate is selected from the group consisting of calcium hydrogen carbonate, magnesium hydrogen carbonate and mixtures thereof. Preferably, the at least one earth alkali hydrogen carbonate comprises, preferably consists of, calcium hydrogen carbonate.

Step a): providing water

According to step a) of the method of the invention, water is provided.

The water provided in step a) may come from various sources and may be selected from distilled water, tap water, industrial water, desalinated water such as desalinated seawater, brackish water (brackish water), treated wastewater, water treated by reverse osmosis or natural soft water such as ground water, surface water or rainfall. It may also contain 10-2000 mg/l NaCl. Preferably, the water provided in step a) is desalted water, such as permeate or distillate obtained from a desalination process.

In one embodiment of the process of the invention, the water provided in step a) is water to be mineralized. That is, the water provided in step a) is water that is completely free or contains an insufficient amount of minerals or alkalinity.

The water provided in step a) may be pre-treated. Pretreatment may be necessary, for example, in the case of water originating from surface water, ground water or rainwater. For example, to meet drinking water guidelines, water needs to be treated to remove contaminants, such as organics or undesirable minerals, through the use of chemical or physical techniques. For example, ozonation may be used as a first pretreatment step, followed by coagulation, flocculation, or sedimentation as a second treatment step. For example, iron (III) salts such as FeClSO₄Or FeCl₃Or aluminumSalts such as AlCl₃、Al₂(SO₄)₃Or polyaluminium may be used as a flocculating agent. The flocculated material may be removed from the water, for example, by a sand filter or a multi-layer filter. Other water purification methods that can be used to pretreat water are described in e.g. EP 1975310, EP 1982759, EP 1974807 or EP 1974806.

If seawater or brackish water is provided in step a), the seawater or brackish water is first pumped out of the sea by subsurface intake water such as wells or open ocean intake water, and then subjected to physical pretreatment such as screening, sedimentation or sand removal methods. Depending on the desired water quality, additional processing steps such as coagulation and flocculation may be required to reduce potential fouling on the membrane. The pretreated seawater or brackish water can then be distilled, for example, by using: multi-stage flash evaporation, multi-effect distillation, or membrane filtration such as nanofiltration or reverse osmosis to remove remaining particulates and dissolved materials.

It is noted that the water provided in step a) is preferably provided in the main process stream (17) and in the at least one side stream (15).

That is, a part of the water provided in step a) forms the main process stream (17) and the remaining part of the water becomes the at least one side stream (15). Thus, the main process stream (17) and the at least one side stream (15) are connected to each other, preferably the at least one side stream (15) is connected to the main process stream (17) (through its inlet and outlet).

In one embodiment, the at least one lateral stream (15) may comprise a main branch (15a) of the lateral stream and one or more lateral branches (15b) of the lateral stream. For example, the at least one side stream (15) may be branched into a side branch (15b) of the side stream, which provides water for the preparation of the aqueous suspension S1, and a main branch (15a) of the side stream, which provides water for the dilution of the aqueous suspension S1 prepared in the side branch (15b) of the side stream. In other words, the side branch (15b) of the side stream provides water for the aqueous suspension S1, while the main branch (15a) of the side stream provides water directly in the vessel, preferably the reactor tank (1).

The term "at least one" side stream means that one or more side process streams may be provided in the process of the present invention.

In one embodiment of the invention, the process comprises, preferably consists of, a main process stream (17) and a side stream (15). Further optionally, the process comprises, preferably consists of, a main process stream (17) and two or more side streams (15a), (15b), etc. Preferably, the process comprises a main process stream (17) and one side stream (15), more preferably consists of the main process stream (17) and one side stream (15). Further optionally, the water provided in step a) is provided only in the main process stream (17). That is, this method does not include at least one side stream. Thus, in one embodiment, the process comprises, preferably consists of, a main process stream (17).

In one embodiment, the main process stream (17) may comprise a main branch (17a) of the main process stream and one or more side branches (17b) of the main process stream. For example, the at least main process stream (17) may be branched into a side branch (17b) of the main process stream, which provides water for preparing the aqueous suspension S1, and a main branch (17a) of the main process stream, which provides water for diluting the aqueous suspension S1 prepared in the side branch (17b) of the main process stream. In other words, the side branch (17b) of the main process stream provides water for the aqueous suspension S1, whereas the main branch (17a) of the main process stream provides water directly in the vessel, preferably the reactor tank (1).

It should be noted that a side branch is considered as a side branch (17b) of the main process stream if the main branch (17a) and the one or more side branches of the main process stream merge together before the aqueous suspension S1 is directed into the vessel, preferably the reactor tank (1). That is, the aqueous suspension S1 is prepared in the side branch (17b) of the main process stream and is then conducted into the main branch (17a) of the main process stream, for example for diluting the aqueous suspension S1, and the diluted aqueous suspension S1 is then conducted into the vessel, preferably reactor tank (1), via the main branch (17a) of the main process stream.

If the side stream (S) (15) and the main process stream (17) are combined after the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate has been released from the vessel, preferably the reactor tank (1), the side stream (15) is considered to be a side stream (15).

Step b): providing at least one alkaline earth metal carbonate-containing material

According to step b) of the process of the present invention, at least one alkaline earth metal carbonate-containing material is provided.

The term "at least one" alkaline earth metal carbonate-containing material in the meaning of the present invention means that the alkaline earth metal carbonate-containing material comprises, preferably consists of, one or more alkaline earth metal carbonate-containing materials.

In one embodiment of the present invention, the at least one alkaline earth metal carbonate-containing material comprises, preferably consists of, an alkaline earth metal carbonate-containing material. Further optionally, the at least one alkaline earth metal carbonate-containing material comprises, preferably consists of, two or more alkaline earth metal carbonate-containing materials. For example, the at least one alkaline earth metal carbonate-containing material comprises, preferably consists of, and more preferably consists of two or three alkaline earth metal carbonate-containing materials.

Preferably, the at least one alkaline earth metal carbonate-containing material comprises, more preferably consists of, an alkaline earth metal carbonate-containing material.

For example, the at least one alkaline earth metal carbonate-containing material comprises, more preferably consists of, a calcium carbonate-containing material.

According to one embodiment of the process of the present invention, the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) in step b) is selected from the group consisting of precipitated calcium carbonate, modified calcium carbonate, ground calcium carbonate and mixtures thereof.

Preferably, the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) in step b) is ground calcium carbonate.

"Ground Calcium Carbonate (GCC)" in the meaning of the present invention is calcium carbonate obtained from natural sources, including marble, chalk or limestone, and processed via processes such as grinding, screening and/or by wet and/or dry subdivision, for example by cyclones.

"Precipitated Calcium Carbonate (PCC)" in the meaning of the present invention is a synthetic substance, usually by precipitation after reaction of carbon dioxide with lime in an aqueous environment or by precipitation of calcium and carbonate sources in water or by addition of calcium ions and carbonate ions (e.g. CaCl)₂And Na₂CO₃) Precipitating from the solution. Precipitated calcium carbonate exists in three primary crystalline forms: calcite, aragonite and vaterite, and there are many different polymorphs (crystal habit) for each of these crystal forms. Calcite has a triangular structure with typical crystallographic habit such as scalenohedral (S-PCC), rhombohedral (R-PCC), hexagonal prismatic, axial, colloidal (C-PCC), cubic and prismatic (P-PCC). Aragonite is a orthorhombic structure with a typical crystal habit of paired hexagonal prisms, and a variety of classifications for the forms of elongated prisms, curved leaves, steep pyramids, chisel pointed crystals, furcated trees, and coral or worm shapes.

"modified calcium carbonate" in the meaning of the present invention is a surface-reacted natural calcium carbonate which is obtained by the following process: in this process, natural calcium carbonate is mixed with pK at 25 ℃_aOne or more H of 2.5 or less than 2.5₃O⁺The ion donor reacts with gaseous CO formed in situ and/or from an external supply₂Reacted and optionally at least one aluminium silicate and-Or at least one synthetic silica and/or at least one calcium silicate and/or at least one silicate of a monovalent salt (such as sodium silicate and/or potassium silicate and/or lithium silicate) and/or at least one aluminium hydroxide and/or at least one sodium silicate and/or potassium silicate. Further details regarding the preparation of surface-reacted natural calcium carbonate are disclosed in WO 00/39222, WO 2004/083316 and US 2004/0020410A 1, the contents of which references are incorporated herein by reference.

The alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, is preferably Ground Calcium Carbonate (GCC).

For example, the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) of step b) is selected from marble, limestone, chalk, half-burnt lime, dolomitic limestone, calcareous dolomite, half-burnt dolomite, and precipitated alkaline earth metal carbonates such as precipitated calcium carbonate, for example having calcite, aragonite and/or vaterite mineral crystal structure, for example from addition of Ca (OH)₂The de-hardening of the water. The use of marble, limestone and/or chalk is preferred because they are naturally occurring minerals and the turbidity of the final drinking water quality is ensured by using clear aqueous solutions comprising at least one earth alkali bicarbonate produced by using these naturally occurring minerals. Natural marble deposits contain mostly acid-insoluble silicate impurities. However, when using the product prepared by the process of the present invention, this acid-insoluble material (sometimes a colored silicate) does not affect the final water quality in terms of turbidity.

Thus, preferably, the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, of step b) is Ground Calcium Carbonate (GCC) selected from marble, limestone, chalk and mixtures thereof.

According to one embodiment of the invention, the at least one alkaline earth metal carbonate-containing material comprises, preferably consists of: the particles consist of an alkaline earth carbonate in an amount of ≥ 40.0% by weight, preferably 90.0% by weight, more preferably ≥ 95.0% by weight and most preferably ≥ 97.0% by weight, based on the total dry weight of the at least one alkaline earth carbonate-containing material.

For example, the at least one calcium carbonate-comprising material comprises, preferably consists of: the particles consist of calcium carbonate in an amount of ≥ 40.0% by weight, preferably 90.0% by weight, more preferably ≥ 95.0% by weight and most preferably ≥ 97.0% by weight, based on the total dry weight of the at least one calcium carbonate-containing material.

Further preferably, the at least one alkaline earth metal carbonate-containing material of step b) is a micronized alkaline earth metal carbonate-containing material (preferably a calcium carbonate-containing material).

For the purposes of the present invention, the term "micronized" means that the particle size is in the micrometer range, for example, from 0.1 to 50.0 μm. Micronized particles may be obtained by techniques based on friction and/or impact (e.g. milling or grinding under wet or dry conditions). However, the micronized particles may also be produced by any other suitable method, such as precipitation, rapid expansion of supercritical solutions, spray drying, classification or differentiation of naturally occurring sands or muds, filtration of water, sol-gel methods, spray reaction synthesis, flame synthesis or liquid foaming synthesis.

For example, the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) of step b) has a weight median particle size d of from 0.1 to 50.0 μm, preferably from 0.2 to 25.0 μm, more preferably from 0.3 to 10.0 μm and most preferably from 0.5 to 5.0 μm₅₀。

Throughout this document, the "particle size" of alkaline earth metal carbonate-containing materials and other materials is described by their particle size distribution.

Here, the value d_xThe following diameters are indicated: x% by weight of the particles, relative to the diameter, having a value of less than d_xOf (c) is measured. This means for example d₂₀The value is the particle size below which 20% by weight of all particles are smaller. d₅₀The value is thus the weight median particle size, i.e. 50% by weight of all particles are larger than this particle size and the remaining 50% by weight are smaller than this particle size. For the purposes of the present invention, unless otherwise indicated, the particle size is specified as the weight median particle size d₅₀。d₉₈The values are particle sizes wherein 98% by weight of all particles are smaller than the particle size. The particle size was determined by using a sedigraph (TM) 5100 or 5120 from Micromeritics Instrument Corporation. Methods and apparatus are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments. At 0.1% by weight Na₄P₂O₇Is measured in an aqueous solution of (a). The samples were dispersed using a high speed stirrer and ultrasound.

In one embodiment of the invention, the alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) of step b) has a thickness of 0.01 to 200.0m²A/g and preferably from 1.0 to 100.0m²BET specific surface area/g, measured by nitrogen adsorption using the BET isotherm (ISO9277: 2010).

Additionally or alternatively, the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) of step b) may comprise 0.02 to 50.0 wt. -%, 0.03 to 25.0 wt. -% or 0.05 to 10.0 wt. -% of HCl insoluble content, based on the total weight of the at least one alkaline earth metal carbonate-containing material (preferably calcium carbonate-containing material) of step b). Preferably, the HCl insoluble content of the at least one alkaline earth metal carbonate-containing material does not exceed 1.0 wt%, based on the total weight of the calcium carbonate. The HCl insoluble content may be, for example, minerals such as quartz, silicates, or mica.

The at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, of step b) is provided in dry form or in aqueous form.

If the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, of step b) is added in dry form, the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, may be in powder form or in pellet form.

The term "dry" in relation to the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, is understood to mean a material having less than 0.3% by weight of water relative to the weight of the at least one alkaline earth metal carbonate-containing material. The water% was determined according to the Coulometric Karl Fischer measurement method, wherein the at least one alkaline earth metal carbonate-containing material was heated to 220 ℃ and the water content released as steam and separated using a nitrogen stream (100ml/min) was determined in a Coulometric Karl Fischer unit.

If the at least one alkaline earth metal carbonate-containing material of step b) is provided in dry form, the dry alkaline earth metal carbonate-containing material may be dosed into a slurry compression (make-down) system, which is then combined with water in step d). Alternatively, the dried alkaline earth metal carbonate-containing material is combined with water in step d). For example, the dried alkaline earth metal carbonate-containing material is combined with water in a vessel, preferably a reactor tank (1), or the dried alkaline earth metal carbonate-containing material is dosed into the water stream.

If the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, of step b) is added in aqueous form, the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, added in step d) is in the form of an aqueous suspension having a solids content of 0.01-20.0% by weight, more preferably 1.0-15.0% by weight and most preferably 2.0-10.0% by weight, based on the total weight of the suspension. Such a slurry is preferably produced on site by: a highly concentrated slurry having a solids content of, for example, 30.0-60.0% by weight, for example, about 40% by weight, or an alkaline earth metal carbonate-containing material (preferably a calcium carbonate-containing material) in, for example, a solid form such as a powder or pellet form, is used without any dispersant.

For the purposes of the present invention, a "suspension" or "slurry" refers to a system comprising a solvent (i.e., an aqueous solvent) and particles comprising an alkaline earth carbonate material and/or an alkaline earth bicarbonate, wherein at least a portion of the particles comprising the alkaline earth carbonate material and/or the alkaline earth bicarbonate are present in the aqueous solvent in the form of insoluble solids. The term does not exclude that a portion of the alkaline earth metal carbonate-containing material and/or alkaline earth metal bicarbonate particles is dissolved in the aqueous solvent.

The suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, may comprise in addition to the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, further micronized mineral. According to one embodiment, the suspension comprising the at least one alkaline earth metal carbonate-containing material (preferably a calcium carbonate-containing material) may comprise micronized calcium magnesium carbonate such as dolomitic limestone, calcareous dolomite or half-burnt dolomite, magnesium oxide such as burnt dolomite, magnesium sulphate, potassium bicarbonate, sodium bicarbonate and/or other minerals containing the necessary trace elements.

For example, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, of step b) is provided in a storage tank (13), which storage tank (13) is connected to a receiving means (14) suitable for preparing a suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material. Preferably, the containing means (14) is connected to the side stream (15), or if the side stream comprises side branches, the containing means (14) is preferably connected to the side branch (15b) of the side stream, such that water provided in the side stream (15) or the side branch (15b) of the side stream is used for preparing the suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably the calcium carbonate-containing material. The suspension (16) comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, is then preferably transferred into a vessel, preferably a reactor tank (1), for carrying out process step c). If the side stream (15) comprises side branches, the suspension comprising at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, prepared in the side branch (15b) of the side stream can also be first conducted into the main branch (15a) of the side stream and the diluted suspension comprising at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, obtained in the main branch (15a) of the side stream is then transferred into a vessel, preferably a reactor tank (1), for carrying out process step c). Thus, the reservoir (13) and the holding means (14) may be part of the side stream (15).

In one embodiment, the alkaline earth metal carbonate-containing material can be combined with water in a vessel, preferably a reactor tank (1). That is, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, in step b) may be provided in a storage tank (13), which storage tank (13) is directly connected to the vessel, preferably to the reactor tank (1).

The at least one alkaline earth metal carbonate-containing material, e.g. calcium carbonate-containing material, is preferably dosed into the water stream via a dosing unit (25) or directly into the tank. The dosing unit (25) may be any kind of dosing unit known to the person skilled in the art and typically used for dosing alkaline earth carbonate containing material.

In a further alternative embodiment, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, of step b) is provided in a reservoir (13), which reservoir (13) is directly connected to a side stream (15), or if the side stream comprises a side branch, the reservoir (13) is directly connected to the side branch (15b) of the side stream, such that the water provided in the side stream (15) or the side branch (15b) of the side stream is used for preparing a suspension comprising at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material. In this embodiment, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, of step b) is thus dosed directly into the side stream (15) or into the side branch (15b) of the side stream, for example before the suspension (16) comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, is transferred into a vessel, preferably a reactor tank (1), for carrying out process step c). Further optionally, if the side stream (15) comprises side branches, the suspension comprising at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, prepared in the side branch (15b) of the side stream can also be first conducted into the main branch (15a) of the side stream and the diluted suspension comprising at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, obtained in the main branch (15a) of the side stream is then transferred into a vessel, preferably a reactor tank (1), for carrying out process step c).

If the process consists of a main process stream (17), i.e. does not comprise at least one side stream (15), the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material, in step b) is provided in a storage tank (13), which storage tank (13) is preferably connected to a holding vessel (14) suitable for preparing a suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably calcium carbonate-containing material. Preferably, the containing means (14) is connected to the main process stream (17) such that water provided in the main process stream (17) is used for preparing the suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material. The suspension (16) comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, is then preferably transferred into a vessel, preferably a reactor tank (1), for carrying out process step c).

In one embodiment, the alkaline earth metal carbonate-containing material can be combined with the water of the main process stream (17) in a vessel, preferably a reactor tank (1). That is, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, in step b) may be provided in a storage tank (13), which storage tank (13) is directly connected to the vessel, preferably to the reactor tank (1).

In a further alternative embodiment, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, in step b) may be provided in a storage tank (13), which storage tank (13) is directly connected to the main process stream (17), such that the water provided in the main process stream (17) is used for preparing the suspension comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material. In this embodiment, the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, in step b) is thus dosed directly into the main process stream (17), for example before the suspension (16) comprising the at least one alkaline earth metal carbonate-containing material, preferably a calcium carbonate-containing material, is transferred into a vessel, preferably a reactor tank (1), for carrying out process step c).

If the main process stream (17) comprises one or more side branches, the calcium carbonate-comprising material may be dosed directly into the side branch (17b) of the main process stream, or a containing means (14) may be connected to the side branch (17b) of the main process stream.

₂Step c): supplying CO or acids

According to step c) of the process of the invention, CO is provided₂Or pK_aValue of<5, or a salt thereof.

Preferably, pK_aValue of<5 was determined at 25 ℃.

The carbon dioxide used is selected from gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide and gaseous mixtures of carbon dioxide with other gases, for example carbon dioxide-containing flue gases emitted from industrial processes, such as combustion processes or calcination processes or the like. Preferably, the carbon dioxide is gaseous carbon dioxide. When a gaseous mixture of carbon dioxide and other gases is used, then the carbon dioxide is present in a range of from 90.0% to about 99.0% by volume, and preferably from 95.0% to 99.0% by volume, based on the total volume of the gaseous mixture. For example, carbon dioxide is present in an amount of at least 97.0% by volume based on the total volume of the gaseous mixture.

The acid used in the process of the invention preferably has a pK at 25 ℃_aValue of<4, or a salt thereof. For example, the acid of step c) is selected from sulfuric acid, hydrochloric acid, nitric acid or citric acid and mixtures thereof. In one embodiment, the acid will be selected from acids having a pK at 25 ℃_aAcids having a value less than or equal to 0 and more particularly selected from sulfuric acid, hydrochloric acid or mixtures thereof. Alternatively, the acid may be a salt having an acidic pH, e.g. an alkali metal salt, e.g. NaHSO₄And/or KHSO₄。

Preferably, CO₂Provided in step c).

In one embodiment, the CO is added₂Or pK_aValue of<5 into the vessel (1). Preferably, the container (1) is connected to a recirculation air flow (5). The recirculation air flow (5) is arranged, for example, such that the air flow is recirculated from the bottom to the top direction of the container (1). In one embodiment, the CO of step c)₂Or pK_aValue of<5 is injected into the recirculating air stream (5). That is to say, CO in step c)₂Or pK_aValue of<5 is added to the air or process fluid of the recirculating air stream (5).

₂Step d): combining water with at least one alkaline earth metal carbonate-containing material and CO or an acid

According to step d) of the process of the present invention, the water of step a) is mixed with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids may be combined in any order.

The water of step a) according to process step d) is mixed with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the combination of acids may be accomplished by any conventional means known to those skilled in the art. Preferably, the combining may be performed under mixing and/or homogenization conditions. The person skilled in the art will adapt these mixing and/or homogenizing conditions, such as mixing speed and temperature, according to his process equipment.

For example, the combination can be carried out in a vessel, preferably a reactor tank (1). Such tanks are well known to those skilled in the art and are available from a wide range of suppliers.

In particular, the water of step a) is mixed with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids are combined in any order, for example to obtain an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate.

It is to be understood that if the process consists of the main process stream (17), the at least one alkaline earth metal carbonate-containing material of step b) may be added to water provided in the main process stream (17) or in a side branch (17b) of the main process stream. Further optionally, the at least one alkaline earth metal carbonate-containing material of step b) may be added to water provided in the side stream (15) or in a side branch (15b) of the side stream. Thus, if the process comprises a side stream (15), the at least one alkaline earth metal carbonate-containing material of step b) is preferably added to the water provided in the side stream (15). If the side stream (15) comprises side branches, the at least one alkaline earth metal carbonate-containing material of step b) is preferably added to the water provided in the side branches (15b) of the side stream. If the main process stream (17) comprises a side branch, the at least one alkaline earth metal carbonate-containing material of step b) is preferably added to the water provided in the side branch (17b) of the main process stream.

Preferably, the at least one alkaline earth metal carbonate-containing material of step b) is added to water provided in the side stream (15) or in a side branch (15b) of the side stream (if the side stream comprises a side branch) or in the main process stream (17) or in a side branch (17b) of the main process stream (if the method does not comprise a side stream (15) such that an aqueous suspension comprising at least one alkaline earth metal carbonate-containing material is obtained.

The aqueous suspension comprising at least one alkaline earth metal carbonate-containing material obtained in the side stream (15) or in a side branch (15b) of the side stream (15) if the side stream comprises side branches or in the main process stream (17) or in a side branch (17b) of the main process stream if the process does not comprise side streams (15) preferably has a solids content of 0.01-20.0% by weight, more preferably 1.0-15.0% by weight and most preferably 2.0-10.0% by weight, based on the total weight of the suspension.

Carbon dioxide or pK_aValue of<5 (at 25 ℃) of an acid may be injected at a controlled rate into the side stream (15) or into a side branch (15b) of the side stream (if the side stream includes a side branch) or into the main process stream (17) or a side of the main process streamIn the aqueous suspension comprising at least one alkaline earth metal carbonate-containing material obtained in branch (17b), if the process does not comprise a side stream (15), a dispersion of carbon dioxide bubbles in the stream is formed and the bubbles are dissolved therein. For example, carbon dioxide or pK_aValue of<5 (at 25 ℃) of an acid is injected into the water so that the concentration of carbon dioxide in the water is between 10 and 1500mg/l and preferably between 50 and 500mg/l (depending on the starting CO)₂Concentration) to reach the final target pH (excess CO)₂) And final target calcium concentration (as CaCO)₃Added).

According to one embodiment of the process of the invention, process step d) comprises the following steps:

ii1) combining the water of step a) with the at least one alkaline earth metal carbonate-containing material of step b), and

ii2) mixing the mixture of ii1) with the CO of step c)₂Or a combination of acids.

In this embodiment, the aqueous suspension comprising at least one alkaline earth metal carbonate-containing material obtained in the side stream (15) or in a side branch (15b) of the side stream (15) if the side stream comprises a side branch or in the main process stream (17) or in a side branch (17b) of the main process stream if the process does not comprise a side stream (15) is preferably transferred (16) to a plant into which carbon dioxide or pK is injected_aValue of<5 (at 25 ℃) in a container of acid, preferably a reactor tank (1). More preferably, CO of step c)₂Or pK_aValue of<5 is injected into the vessel (1) via a recirculation air stream (5). Thus, CO of step c)₂Or pK_aValue of<5 is preferably added to the air or process stream of the recycle air stream (5).

Alternatively, carbon dioxide or pK_aValue of<5 (at 25 ℃) of acid is added to the water provided in the side stream (15) or in the side branch (15b) of the side stream (if the side stream comprises a side branch) or in the main process stream (17) or in the side branch (17b) of the main process stream (if the process does not comprise a side stream (15)), so that the adjustment is in the range of 2.5 to 7.5The pH value of (1). Preferably, the pH is adjusted to a range of 3.0-7.0 and preferably 4.0-5.0.

Adding carbon dioxide or pK_aValue of<5 (at 25 ℃) into the water provided in the side stream (15) or in the side branch (15b) of the side stream (if the side stream comprises a side branch) or in the main process stream (17) or in the side branch (17b) of the main process stream (if the process does not comprise a side stream (15)) thus resulting in acidified water being obtained.

Carbon dioxide or pK_aValue of<Acid of 5 (at 25 ℃) may be injected at a controlled rate into water provided in the side stream (15) or side branch (15b) of the side stream (if the side stream includes a side branch) or in the main process stream (17) or side branch (17b) of the main process stream (if the process does not include a side stream (15)), forming a dispersion of carbon dioxide bubbles in the stream and dissolving the bubbles therein. For example, carbon dioxide or pK_aValue of<5 (at 25 ℃) of an acid is injected into the water so that the concentration of carbon dioxide in the water is between 10 and 1500mg/l and preferably between 50 and 500mg/l (depending on the starting CO)₂Concentration) to reach the final target pH (excess CO)₂) And final target calcium concentration (as CaCO)₃Added).

Carbon dioxide or pK in water supplied in the side stream (15) or in a side branch (15b) of the side stream if the side stream comprises a side branch or in the main process stream (17) or in a side branch (17b) of the main process stream if the process does not comprise a side stream (15)_aValue of<The amount of acid of 5 (at 25 ℃) will depend on the amount of carbon dioxide already present in the water provided in the side stream (15) or side branch (15b) of the side stream or in the main process stream (17) or side branch (17b) of the main process stream. The amount of carbon dioxide already present in the water will in turn depend on, for example, upstream treatment of the water. For example, water that has been desalinated by flash evaporation will contain an additional amount of carbon dioxide and thus an additional pH compared to water that has been desalinated by reverse osmosis. For example, water that has been desalinated by reverse osmosis may have a pH of about 5.3 and about 10mg/l CO₂The amount of (c).

Thus, the at least one alkaline earth metal carbonate-containing material of step b) in dry form or in aqueous suspension is injected into acidified water.

Thus, in this embodiment, method step d) comprises the steps of:

i1) mixing the water of step a) with the CO of step c)₂Or the acids are combined, and

i2) combining the mixture of i1) with the at least one alkaline earth metal carbonate-containing material of step b).

In this embodiment, carbon dioxide or pK_aValue of<5 (at 25 ℃) is thus added to the water provided in the side stream (15) or in the side branch (15b) of the side stream (if the side stream comprises a side branch) or in the main process stream (17) or in the side branch (17b) of the main process stream (if the process does not comprise a side stream (15)), and the acidified water obtained is transferred into a vessel, preferably a reactor tank (1). Additionally, the aqueous suspension comprising at least one alkaline earth metal carbonate-containing material obtained in the side stream (15) or in a side branch (15b) of the side stream (if the side stream comprises a side branch) or in the main process stream (17) or in a side branch (17b) of the main process stream (if the process does not comprise a side stream (15)) is also transferred (16) to a vessel, preferably a reactor tank (1), to combine the acidified water with the aqueous suspension comprising at least one alkaline earth metal carbonate-containing material.

Preferably, method step d) is carried out by:

In one embodiment of the process of the invention, step d) is preferably carried out at a temperature of from 5 to 55 deg.C, more preferably from 15 to 30 deg.C, to ensure that the water of step a) is mixed with stepThe at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids are combined thoroughly.

It will be appreciated that the dissolution rate of the at least one alkaline earth metal carbonate-containing material in the liquid phase (i.e. water) to obtain a solution S1 comprising at least one alkaline earth metal bicarbonate depends on the dosed carbon dioxide or pK_aValue of<5, but also on temperature, pH, pressure, initial alkaline earth carbonate concentration in the suspension, and carbon dioxide or pK_aValue of<5 (at 25 ℃) to the aqueous suspension comprising the at least one alkaline earth metal carbonate-containing material.

Preferably, the concentration of carbon dioxide in the aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate obtained in step d) is in the range of from 10 to 1500mg/l, more preferably from 20 to 1000mg/l and most preferably from 50 to 400 mg/l.

Additionally or alternatively, the CO used to generate 1mol of the at least one alkaline earth bicarbonate in the aqueous suspension S1 obtained in step d)₂The amount (in mol) is from 1.0 to 6.0mol, preferably from 1.0 to 3.0mol and most preferably from 1.0 to 2.0 mol.

It is to be noted that the kind of the at least one alkaline earth metal bicarbonate in the aqueous suspension obtained in step d) depends on the at least one alkaline earth metal carbonate-containing material provided in step b) of the process of the present invention. Thus, if the at least one alkaline earth metal carbonate-containing material comprises a calcium carbonate-containing material, the at least one alkaline earth metal bicarbonate in the aqueous suspension S1 obtained in step d) comprises calcium bicarbonate. Further alternatively, if the at least one alkaline earth metal carbonate-containing material consists of calcium carbonate, the at least one alkaline earth metal bicarbonate in the aqueous suspension S1 obtained in step d) consists of calcium bicarbonate.

It is to be understood that the aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate obtained in step d) preferably has an earth alkali metal concentration, calculated as earth alkali hydrogen carbonate, of from 20 to 1000mg/l, preferably from 50 to 600mg/l and most preferably from 80 to 400 mg/l. In one embodiment of the process of the invention, the aqueous suspension S1 comprising at least one alkaline earth metal bicarbonate (being calcium bicarbonate) obtained in step d) has a calcium metal concentration, calculated as calcium bicarbonate, of between 20 and 1000mg/l, preferably between 50 and 600mg/l and most preferably between 80 and 400 mg/l.

As described above, an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate is obtained in step d).

The aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate obtained in step d) also comprises undissolved solid particles of the at least one earth alkali carbonate-containing material, and thus the aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate is subjected to a filtration step e).

In view of this, the aqueous suspension S1 comprising at least one alkaline earth bicarbonate obtained in step d) preferably has a turbidity value of more than 10NTU, more preferably the aqueous suspension S1 comprises visible solids, i.e. is opaque.

"turbidity" in the meaning of the present invention describes the blurring or turbidity of a fluid caused by individual particles (suspended solids) that are not normally visible to the naked eye. The measurement of turbidity is a key test of water quality and can be performed with a turbidimeter. The Turbidity Units from a calibrated turbidimeter for use in the present invention are defined as Nephelometric Turbidity Units (NTU).

In one embodiment of the present invention, the aqueous suspension S1 comprising at least one alkaline earth metal bicarbonate obtained in step d) preferably has a solids content of 0.01 to 10.0% by weight, more preferably 0.5 to 10.0% by weight and most preferably 1.2 to 8.0% by weight, based on the total weight of the aqueous suspension S1.

Step e): filtering at least a portion of the aqueous suspension S1

According to step e) of the process of the invention, at least part of the aqueous suspension S1 obtained in step d) is filtered by passing the aqueous suspension S1 through at least one submerged membrane module, so as to obtain an aqueous solution S2 comprising at least one alkaline earth metal bicarbonate.

The filtration step e) is preferably carried out in a vessel, preferably a reactor tank (1).

In one embodiment of the process of the present invention, step e) is preferably carried out at a temperature of 5-55 ℃, more preferably 15-45 ℃ to ensure that the water of step a) is contacted with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids are combined thoroughly.

It is to be understood that process steps d) and e) can be carried out separately or simultaneously, i.e. in different vessels or in the same vessel. Thus, process steps d) and e) can be carried out in one or more vessels.

For example, if process steps d) and e) are carried out in different vessels, i.e. separately, process steps d) and e) are carried out in two or more vessels, preferably in two vessels. In this embodiment, it is understood that process step e) is carried out after process step d).

Alternatively, process steps d) and e) are carried out in the same vessel. In this embodiment, it is understood that process steps d) and e) are carried out simultaneously.

In view of reduced overall energy consumption and higher cost efficiency, it is preferred that process steps d) and e) are carried out in the same vessel, i.e. simultaneously, preferably in reactor tank (1).

If process steps d) and e) are carried out simultaneously, steps d) and e) are preferably carried out at a temperature of from 5 to 55 deg.C, more preferably from 15 to 45 deg.C.

One particular requirement of the process of the invention is that: at least a portion of the aqueous suspension S1 is filtered through at least one submerged membrane module (2). Preferably, the entire amount of the aqueous suspension S1 is filtered through at least one submerged membrane module (2).

The at least one submerged membrane module (2) is thus located in a vessel, preferably a reactor tank (1).

The at least one submerged membrane module may be any type of submerged membrane module known to the person skilled in the art and typically used for filtering sludge and aqueous suspensions containing minerals, pigments and/or fillers. For example, submerged membrane modules from Toray Industries, Inc.

The at least one submerged membrane module (2) (i.e. membrane) preferably has a pore size of<1 μm, and more preferably<0.1 μm, such as 0.04-0.9 μm, for example about 0.04 μm or 0.08 μm. The membrane of the at least one submerged membrane module (2) may be made of ceramic, polymer or other synthetic material. For example, the at least one submerged membrane module (2) comprises a membrane made of a material selected from the group consisting of: sintered materials, porous ceramics, synthetic polymers such as polyethylene, polypropylene, polyvinylsulfone, polyvinylidene fluoride (PVDF) orAnd mixtures thereof. In one embodiment, the at least one submerged membrane module (2) further comprises fibers or non-woven fabrics, such as fibers or non-woven fabrics made of materials selected from the group consisting of: synthetic polymers such as polyethylene, polypropylene, polyester or mixtures thereof.

It is understood that the number of the at least one submerged membrane module (2) depends on the size of the process. One skilled in the art can adapt this number of submerged membrane modules depending on the particular process size used.

The at least one submerged membrane module (2) preferably has a high flux, i.e. a high flow rate per unit membrane area and time (flux ═ l/[ m ] m²*h]). For example, the at least one submerged membrane module (2) has a value ≧ 10 l/(m)²h) Preferably 20 to 100 l/(m)²h) And most preferably 40 to 100 l/(m)²h) The flux of (c).

Preferably, the at least one submerged membrane module (2) is arranged such thatAir or process fluid is recirculated (5) through at least a portion of the surface of the at least one submerged membrane module. This has the advantage that: CO 2₂Can be efficiently introduced into the vessel, preferably the reactor tank (1), for increasing the efficiency of the formation of the aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate. Furthermore, such an arrangement may result in cleaning of the at least one submerged membrane module (2), which is achieved by cross-flow aeration, which may reduce fouling of the at least one submerged membrane module (2). Furthermore, this arrangement has the benefit of maintaining a uniform suspension and preventing undissolved particles from settling.

In one embodiment, air or process fluid is recirculated (5) through at least a portion of the surface of the at least one submerged membrane module (2) from the bottom to the top direction of the at least one submerged membrane module (2) and/or the vessel, preferably reactor tank (1), preferably the at least one submerged membrane module (2) and the vessel, preferably reactor tank (1).

It is understood that CO of step c)₂Or acid (4) is preferably added to the air or process fluid which is recirculated (5) through at least a portion of the surface of the at least one submerged membrane module (2).

If air or process fluid is recirculated through at least a part of the surface of the at least one submerged membrane module, preferably the vessel, preferably the reactor tank (1), is sealed and air at the top of the vessel, preferably the reactor tank (1), is used as feed and reintroduced (5) at the bottom of the vessel, preferably the reactor tank (1).

Thus, the process steps d) and e) are preferably carried out in the same vessel, preferably in the reactor tank (1), and air or process fluid is recirculated (5) through at least a portion of the surface of the at least one submerged membrane module (2) from the bottom to the top direction of the at least one submerged membrane module (2) and the vessel, preferably the reactor tank (1). More preferably, process steps d) and e) are carried out in the same vessel, preferably in a reactor tank(1) And CO of step c)₂Or acid (4) is added to the air or process fluid that is recirculated (5) through at least a portion of the surface of the at least one submerged membrane module (2) and the vessel, preferably the reactor tank (1).

It is to be understood that the recirculation air stream (5) is preferably independent of the side stream (15) or the main process stream (17) (if the process does not comprise a side stream (15)), i.e. the inlet and outlet of the recirculation air stream (5) are connected to the vessel (preferably reactor tank (1)) at a different location than the inlet and outlet of the side stream (15) or the main branch (15a) of the side stream or the side branch (15b) of the side stream or the main process stream (17) or the main branch (17a) of the main process stream or the side branch (17b) of the main process stream.

In addition to the cleaning as described above, the method may further comprise the step of cleaning the at least one submerged membrane module (2).

For example, the process of the invention comprises a further step f): backwashing the at least one submerged membrane module.

The term "backwashing" in the meaning of the present invention refers to the addition of water and/or chemicals from the other side of the at least one submerged membrane module (2), i.e. from the permeate side, to the feed side of the at least one submerged membrane module and/or vessel for cleaning the at least one submerged membrane module (2).

For example, backwashing of the at least one submerged membrane module (2) may be performed using water. If the method of the invention comprises the further step f) of backwashing the at least one submerged membrane (2) with water, the backwashing may be performed every 5 to 60 minutes, such as 10 to 15 minutes.

Additionally, CO may be reacted₂Or pK_aValue of<5 (at 25 ℃) of an acid was added to the water. In such embodiments, backwashing may be performed once or twice per week.

It is to be understood that the present process can be carried out as a batch process, a semi-continuous or a continuous process.

The expression "semi-continuous process" in the meaning of the present application refers to at least one process step which is carried out in continuous form.

The aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the invention preferably has a carbon dioxide concentration of from 0.001 to 300mg/l, more preferably from 0.1 to 150mg/l, most preferably from 0.5 to 50.

It is to be understood that the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) preferably has an earth alkali metal concentration, calculated as earth alkali hydrogen carbonate, of 20-1000 mg/l. Preferably, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) has an earth alkali metal concentration, calculated as earth alkali hydrogen carbonate, of 50-500mg/l and more preferably 80-300 mg/l.

In one embodiment of the process of the invention, the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) comprises calcium bicarbonate, the solution having a calcium metal concentration, calculated as calcium bicarbonate, of between 20 and 1000mg/l, preferably between 50 and 500mg/l and more preferably between 80 and 300 mg/l.

In a further alternative embodiment of the process of the invention, the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) comprises magnesium bicarbonate, the solution having a magnesium metal concentration, calculated as magnesium bicarbonate, of between 20 and 1000mg/l, preferably between 50 and 400mg/l and more preferably between 80 and 300 mg/l.

Further optionally, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) comprises calcium hydrogen carbonate and magnesium hydrogen carbonate, the solution having a total calcium and magnesium metal concentration, calculated as calcium magnesium hydrogen carbonate, of 20-1000mg/l, preferably 50-500mg/l and more preferably 80-300 mg/l.

In one embodiment of the present invention, the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) has a dissolved content of the at least one alkaline earth metal bicarbonate of from 0.001 to 2.0% by weight, more preferably from 0.001 to 0.05% by weight and most preferably from 0.001 to 0.03% by weight, based on the total weight of the aqueous solution.

Additionally or alternatively, the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) preferably has a turbidity value lower than 0.5NTU and more preferably lower than 0.3 NTU. For example, the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) has a turbidity value below 0.2NTU or below 0.1 NTU.

It is to be understood that the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) preferably has a pH value of 6.1-8.9 and preferably 6.5-8.5.

According to one embodiment of the process of the invention, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) has a german hardness of 1 to 55 ° dH, preferably 3 to 30 ° dH and most preferably 4.5 to 17 ° dH.

For the purposes of the present invention, the German hardness is expressed in "degree German hardness, ° dH". In this respect, the german hardness refers to the total amount of alkaline earth metal ions in the aqueous solution comprising the alkaline earth metal bicarbonate.

Preferably, the aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process of the present invention has a german hardness that is at least 3 ° dH, more preferably at least 5 ° dH, higher than the german hardness of the water provided in step a).

In one embodiment, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the invention is suitable as mineralized water. This is preferably the case if the method does not comprise at least one side stream (15) or if the at least one side stream (15) does not comprise side branches. That is to say that the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the invention is mineralized water if the process consists of a main process stream (17).

Alternatively, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the invention is suitable for the mineralization and/or stabilization of water. For example, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the invention is suitable for desalination or mineralization and/or stabilization of natural soft water. This is preferably the case if the method comprises at least one side stream (15) or if the at least one side stream (15) comprises side branches.

For example, the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) is transferred (9) from the side stream (15) to the main process stream (17) for the mineralization and/or stabilization of water.

The water which can be mineralized by using the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the present invention can be derived from various sources and can be selected from distilled water, industrial water, tap water, desalinated water such as desalinated sea water, brackish water or brine, treated wastewater or natural soft water such as groundwater, surface water or rainfall. Preferably, the water mineralized by using the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained by the process of the present invention is desalinated water, such as permeate or distillate obtained from a desalination process.

In view of the good results obtained, the present application further relates in another aspect to a method for the mineralization and/or stabilization of water, comprising the steps of:

i) providing the water to be mineralized with water,

ii) providing an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process described herein,

With regard to the definition of the water to be mineralized and/or stabilized, the aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by this process and preferred embodiments thereof, reference may be made to the explanations provided above in the discussion of the technical details of the process of the invention for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate.

Preferably, the aqueous solution comprising at least one earth alkali hydrogen carbonate provided in step ii) has a german hardness which is at least 3 ° dH, more preferably at least 5 ° dH, higher than the german hardness of the water to be mineralized provided in step i).

In order to neutralize any remaining "aggressive" carbon dioxide and/or to increase the pH to obtain a stable and balanced final water quality, it is preferred to strip the aggressive carbon dioxide, add a base to the mineralized water obtained in step iii), or a combination of both.

Thus, the method for mineralization and/or stabilization of water preferably comprises a further step (iv): by stripping aggressive CO₂(iv) adding a base to the mineralized water of step (iii), and performing pH adjustment by stripping and adding a base to the mineralized water.

In one embodiment, the base (preferably provided in water) is added to the mineralized water in the main process stream (17) to adjust the pH of the mineralized water to a range of 7.0 to 9.0 and form mineralized water having an alkaline earth metal concentration of 10-300mg/l as alkaline earth metal bicarbonate.

Thus, preferably, a base such as Ca (OH)₂(21) Is added to the main process stream (17).

The base is preferably an alkali metal hydroxide and/or an alkaline earth metal hydroxide. More preferably, the base is an alkali metal hydroxide and/or an alkaline earth metal hydroxide selected from calcium hydroxide and/or magnesium hydroxide and/or sodium hydroxide, such as calcium hydroxide or magnesium hydroxide or sodium hydroxide. The base as alkaline earth metal hydroxide preferably consists of calcium hydroxide.

According to one embodiment of the process of the present invention, the base as alkali metal hydroxide and/or alkaline earth metal hydroxide is preferably micronized alkali metal hydroxide and/or alkaline earth metal hydroxide.

For example, the alkali as an alkaline earth metal hydroxide has a weight median particle size d₅₀Is 0.1 to 100.0. mu.m, preferably 0.2 to 50.0. mu.m, more preferably 0.3 to 25.0. mu.m, and most preferably 0.5 to 10.0. mu.m.

In one embodiment of the invention, the base as alkaline earth metal hydroxide has a thickness of 0.01 to 200.0m²A/g and preferably from 1.0 to 100.0m²BET specific surface area/g, measured by nitrogen adsorption using the BET isotherm (ISO9277: 2010).

The base is preferably added as alkali metal hydroxide and/or alkaline earth metal hydroxide so that the concentration of alkali metal hydroxide and/or alkaline earth metal hydroxide added to the mineralized water is 0.1-100mg/l and preferably 0.5-10 mg/l.

The base is preferably provided in water. It will therefore be appreciated that the base is preferably in the form of a solution or suspension.

If the base as alkali metal hydroxide and/or alkaline earth metal hydroxide is in the form of a solution or suspension, the content of the alkali metal hydroxide and/or alkaline earth metal hydroxide is preferably from 0.5% by weight to 50% by weight, preferably about 20% by weight, based on the total weight of the solution or suspension.

The alkali metal hydroxide and/or alkaline earth metal hydroxide solution or suspension may be produced in situ or separately from the process of the invention. If the alkali metal hydroxide and/or alkaline earth metal hydroxide solution or suspension is prepared separately from the process according to the invention, the alkali metal hydroxide and/or alkaline earth metal hydroxide solution or suspension is preferably not prepared from the water provided in step a). Alternatively, the water provided in method step a) is used to prepare the alkali metal hydroxide and/or alkaline earth metal hydroxide solution or suspension.

The pH of the mineralized water is adjusted to 7.0-9.0 by adding a base, preferably an alkali metal hydroxide and/or an alkaline earth metal hydroxide, to the mineralized water in the main process stream (17). Preferably, the pH of the mineralized water is adjusted to 7.2-8.9 and preferably 7.8-8.4. It is understood that pH adjustment depends on the level of remineralization and the target final water quality.

In one embodiment, a part of the water provided in step a) forms the main process stream (17) and the remaining part of the water forms the at least one side stream (15). Thus, the at least one side stream (15) is connected to the main process stream (17), preferably the at least one side stream (15) is connected to the main process stream (17) via an inlet and an outlet.

In one embodiment, the outlet of the at least one side stream (15) is preferably located at the main process stream (17) after the inlet of the at least one side stream (15).

The term "after" in the meaning of the present invention refers to a subsequent position after another unit of the device.

If the method further comprises adding a base such as Ca (OH)₂(21) Into the main process stream (17), the base is then preferably injected into the mineralized water, i.e. after the outlet of the at least one side stream (15). If the alkali metal hydroxide and/or alkaline earth metal hydroxide solution or suspension is prepared with the water provided in process step a), it is preferably formed in the side stream (21). This side stream is preferably connected to the main process stream (17) via an inlet and an outlet.

Another aspect of the invention relates to the use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by a process as defined herein for the mineralization and/or stabilization of water. The water is preferably desalinated or naturally soft water. Further alternatively, the present invention relates to the use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process as defined herein as mineralized water. This is preferably the case if the process does not comprise at least one side stream (15). That is, the at least one alkaline earth metal carbonate-containing material of step b) is added to the main process stream (17).

With regard to the definition of the water to be mineralized, the aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by this process and preferred embodiments thereof, reference may be made to the explanations provided above in the discussion of the technical details of the process of the invention for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate.

The following examples additionally illustrate the invention but are not meant to limit the invention to the illustrated embodiments.

Drawings

List of reference symbols:

(1): reactor tank

(2): immersed membrane (Module)

(3): product storage tank

(4): carbon dioxide injection

(5): recirculating air

(6): pressure measurement of recirculated air

(7): pressure measurement in a reaction tank

(8): pressure measurement in aqueous solutions

(9): aqueous solution S2

(10): flow measurement of aqueous solutions

(11): level measurement in a reactor tank

(12): turbidity measurement in aqueous solutions

(13): calcium carbonate storage silo with dosing screw feeder

(14): receptacle for preparing calcium carbonate suspensions

(15): side stream, water supply to the process

(16): suspensions of micronized calcium carbonate

(17): main process stream

(17a) The method comprises the following steps Main branch of main process stream

(17b) The method comprises the following steps Side branch of main process stream

(18): pH measurement of mixed water stream

(19): conductivity measurement of mixed water streams

(20): for Ca (OH)₂Storage tank of

(21)：Ca(OH)₂Dosing process stream

(22): pH measurement of the final water stream

(23): final water flow conductivity measurement

(24): final treated water stream

(25): calcium carbonate dosing screw feeder

Fig. 1 relates to an apparatus suitable for carrying out the general process according to the invention.

Figure 2 relates to an apparatus suitable for carrying out the mineralization method according to the present invention.

Figure 3 relates to an apparatus suitable for carrying out mineralization with a pH adjustment method according to the present invention.

Fig. 4 relates to a schematic of a process comprising only a main process stream (17) and wherein calcium carbonate is dosed into a vessel (1) comprising an immersed membrane module (2).

Fig. 5 relates to a schematic of a process which comprises only a main process stream (17) and in which calcium carbonate is dosed directly into the main process stream (17).

Fig. 6 relates to a schematic illustration of a process which comprises only the main process stream (17) and in which calcium carbonate is dosed directly to a holding vessel (14) for preparing a calcium carbonate suspension.

Fig. 7 relates to a schematic illustration of a process comprising a main branch (17a) of a main flow and one side branch (17b) of the main flow, wherein calcium carbonate is dosed into a receptacle (14) for preparing a calcium carbonate suspension, the receptacle (14) being located in the side branch (17b) of the main flow.

Fig. 8 relates to a schematic of a process comprising a main branch (17a) of the main flow and one side branch (17b) of the main flow, wherein calcium carbonate is dosed directly into the side branch (17b) of the main flow.

Fig. 9 relates to a schematic of a process comprising a main stream (17) and a side stream (15), wherein calcium carbonate is dosed directly into a container (1) comprising an submerged membrane module (2), which container (1) is located in the side stream (15).

Fig. 10 relates to a schematic of a process comprising a main stream (17) and a side stream (15), wherein the container (1) comprising the submerged membrane module (2) is located in the side stream (15) and calcium carbonate is dosed into the side stream (15).

Fig. 11 relates to a schematic illustration of a process comprising a main stream (17) and a side stream (15), wherein a container (1) comprising an immersed membrane module (2) and recirculation air (5) is located in the side stream (15) and calcium carbonate is dosed into a receptacle (14) for preparing a calcium carbonate suspension, which receptacle (14) is located in the side stream (15). The figure also shows Ca (OH)₂Dosing a process stream (21).

Fig. 12 relates to a schematic representation of a process comprising a main flow (17), a main branch of a side stream (15a) and a side branch of a side stream (15b), wherein calcium carbonate is dosed into a receptacle (14) for preparing a calcium carbonate suspension, the receptacle (14) being located in the side branch of the side stream (15 b). The figure also shows a container (1) comprising submerged membrane modules (2) and recirculation air (5), and Ca (OH) located in the main branch (15a) of the side stream₂Dosing a process stream (21).

Fig. 13 relates to a schematic of a process comprising a main flow (17), a main branch of a lateral flow (15a) and a side branch of a lateral flow (15b), wherein calcium carbonate is dosed directly into the side branch of the lateral flow (15 b). The figure also showsA container (1) comprising submerged membrane modules (2) and recirculation air (5) located in the main branch (15a) of the side stream, and Ca (OH)₂Dosing a process stream (21).

Figure 14 relates to the results of the graphs produced in test 3 (example of magnesium hydroxide dissolution using the method according to the invention).

Detailed Description

The scope and benefits of the present invention will be better understood based on the following examples, which are intended to illustrate certain embodiments of the invention and are not limiting.

Examples

1. Measuring method

The measurement method used in the examples is described below.

pH of aqueous suspensions or solutions

The pH of the suspension or solution was measured using a WTWMulti 3420pH meter with integrated temperature compensation and WTWWTW SenTix 940pH probe. Calibration of the pH electrodes was performed using standards at pH 4.01, 7.00, and 9.21. The reported pH value is the endpoint value detected by the instrument (endpoint when the measured signal differs from the average over the first 6 seconds by less than 0.1 mV).

Solids content of aqueous suspensions

Moisture Analyser

The solids content (also referred to as "dry weight") was determined using the Moisture Analyser HR73 from Mettler-Toledo, Switzerland under the following settings: 3, standard drying and 5-20g of product are automatically cut off at the temperature of 120 ℃.

Particle size distribution (diameter) of particulate material<Mass% of particles of X) and weight median diameter (d)₅₀)

The weight particle diameter and the particle diameter mass distribution of the particulate material are measured by sedimentation, which is an analysis of the sedimentation behavior in a gravitational field. The Sedigraph from Micromeritics Instrument Corporation was used^TM5120 or Sedigraph^TM5100 measurement is carried out.

Methods and apparatus are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments. At 0.1% by weight Na₄P₂O₇Is measured in an aqueous solution of (a). The samples were dispersed using a high speed stirrer and ultrasound.

Turbidity of aqueous suspension of solution

Turbidity was measured using a Hach Lange 2100AN IS laboratory turbidimeter and calibrated using stabcl turbidity standards <0.1, 20, 200, 1000, 4000, and 7500NTU (Formazine standards).

Hardness of aqueous solution

Determination of the ion involved in the hardness of the water, Ca, by titration with the chelating agent ethylenediaminetetraacetic acid (EDTA-disodium salt 0.01M)²⁺(aq) and Mg²⁺(aq). To buffer the pH constant at 10, NH was used₃-NH₄And (4) Cl buffer solution. Titration using Eriochrome Black T as indicator confirmed the results due to Ca²⁺(aq) and Mg²⁺(aq) total hardness caused by ions until the solution changed from wine red to sky blue. The amount of total hardness is calculated by the following equation:

hardness (EDTA volume (ml) × 0.01 × 100.08 × 1000/(sample volume (ml))

Magnesium hardness was calculated by determining the total concentration of calcium and magnesium ions and the concentration of calcium ions. The concentration of calcium ions is first completely precipitated as Mg (OH)₂The magnesium ion is counted to determine: add 50% w/v NaOH solution, swirl the solution and wait until complete precipitation. Hydroxynaphthol blue was then added and the sample was titrated with 0.01M EDTA until the solution became sky blue.

Electrical conductivity of

Conductivity at 25 ℃ Using a cell equipped with a corresponding Mettler Toledo conductivity expansion cell and Mettler ToledoMettler Toledo Seven Multi Instrument of 741 conductivity probe.

The instrument was first calibrated in the relevant conductivity range using a commercially available conductivity calibration solution (from mettler toledo). The effect of temperature on conductivity is automatically corrected by a linear correction mode. The measured conductivity is reported as a reference temperature of 20 ℃. The conductivity values reported are the endpoint values detected by the instrument (endpoint when the measured conductivity differs from the average value in the last 6 seconds by less than 0.4%).

Temperature of

The temperature was measured using a handheld WTW probe from Xylem Analytics.

Alkalinity of aqueous solution

The alkalinity of the aqueous solution was determined by titrating the sample with a 0.1M hydrochloric acid solution. The endpoint of the titration was reached at a constant pH of 4.3. The amount of alkalinity is calculated by the following equation:

alkalinity ═ acid volume (ml) x 0.1x 100.08x 1000/(2 x sample volume (ml))

Acidity of aqueous solution

By titration of free CO with 0.01M sodium hydroxide solution₂To determine the acidity of the aqueous solution. The endpoint of the titration was reached at a constant pH of 8.3. Free CO₂The amount of (d) is calculated by the following equation:

free CO₂NaOH volume (ml) x 0.01x 44.01x 1000/sample volume (ml)

Langlier Saturation Index (LSI)

The Langelier Saturation Index (LSI) describes the tendency of an aqueous liquid to form scale or become corrosive, with positive LSI indicating a tendency to form scale and negative LSI indicating a corrosive nature. The equilibrium langeril saturation index (i.e., LSI ═ 0) thus means that the aqueous liquid is in chemical equilibrium. LSI is calculated as follows:

LSI＝pH–pH_s，

wherein the pH is the actual pH of the aqueous liquid and the pH is_sIs CaCO₃pH of the aqueous liquid at saturation. The pH can be estimated as follows_s：

pH_s＝(9.3+A+B)-(C+D)，

Wherein A is a numerical indicator of the Total Dissolved Solids (TDS) present in the aqueous liquid, B is a numerical indicator of the temperature of the aqueous liquid in K, C is CaCO in mg/l₃A numerical indicator of the calcium concentration of the aqueous liquid, and D is as mg/l CaCO₃A numerical indicator of the alkalinity of the aqueous liquid. The parameters a to D are determined using the following equations:

A＝(log₁₀(TDS)–1)/10,

B＝-13.12×log₁₀(T+273)+34.55,

C＝log₁₀[Ca²⁺]–0.4,

D＝log₁₀(TAC)，

wherein TDS is total dissolved solids in mg/l, T is temperature in ℃, [ Ca ]²⁺]In mg/l CaCO₃Calcium concentration of the aqueous liquid and TAC in mg/l CaCO₃The alkalinity of the aqueous liquid is measured.

2. Examples of the embodiments

The equipment of the invention-preparation of calcium bicarbonate water solution

The general process flow of a plant according to the invention is shown in FIG. 1A flow chart. The device comprises an inner part with a thickness of 50m²A reactor tank (1) for submerged membranes (2), a calcium carbonate storage silo (13) with a dosing screw feeder and a holding device (14) for preparing a calcium carbonate suspension.

A solution of calcium bicarbonate (9) is produced in the permeate stream and this can be used to increase the mineral content and alkalinity of the other stream.

Feed water is obtained from a reverse osmosis system, producing water having the following water specifications:

sodium: <1mg/l

Chloride: <2mg/l

Calcium: 8mg/l

Magnesium: <1mg/l

Alkalinity: 12mg/l (as CaCO)₃Meter)

^odH：1.12

pH value: 6.9

Conductivity: 24 mu S/cm

The calcium bicarbonate solution can be produced using the above-described apparatus in the following manner: the reactor tank (1) is initially filled with a 5.0% by weight calcium carbonate suspension to a defined volume, determined by level measurement (11) in the reactor tank, which covers the surface of the submerged membrane. The blower begins to recirculate a volume of air (5) from the top of the reactor tank (1) to the diffuser located at the bottom of the submerged membrane (2) to ensure that a uniform suspension is maintained within the reactor tank (1) and to provide some cleaning effect to the submerged membrane (2). The air volume (5) is recirculated at a rate of about 200 times per hour. A controlled amount of carbon dioxide is added to the air stream at (4). The carbon dioxide-loaded recirculation air creates turbulence through the submerged membrane (2) from the bottom to the top of the reactor tank (1) and the carbon dioxide is transferred from the air stream to the calcium carbonate suspension, increasing the amount of carbon dioxide dissolved in the suspension. The reaction between calcium carbonate and dissolved carbon dioxide allows the formation of an alkaline calcium bicarbonate solution in the reactor tank (1). At the same time, calcium carbonate is added from the storage silo (13) to the containing vessel (14) for preparing a calcium carbonate suspension within the containing vessel (14). A loss-in-weight screw feeder was used to accurately measure the amount of calcium carbonate added. Water was also added to the tank and a mixer was used to produce a homogeneous suspension of known solids content. The suspension (16) of micronized calcium carbonate is then transferred into the reactor tank (1) at a rate equal to the amount of calcium carbonate dissolved by reaction with carbon dioxide, so that the total amount of calcium carbonate not dissolved inside the reactor tank (1) remains unchanged. An aqueous solution of filtered permeate S2(9) was extracted from the reactor tank (1) through the submerged membrane (2).

Pilot run Unit (Start-up pilot unit)

Using natural calcium carbonate powder (From Omya International AG, OrgonFance, d₅₀3 μm) as starting material in a pilot plant of the plant according to the invention. The reactor (1) was filled with 900l of the prepared 5% by weight suspension of calcium carbonate powder, which was carried out by means of a level control (11). Recirculating air flow (5) fan at 10m³H starts for regeneration of the membrane by turbulent flow. The overpressure of the air flow is measured by (6).

Example 1:

to produce a high load of concentrate (-250 mg/l alkalinity), 99g of carbon dioxide (4) was dosed into the recirculating air stream over 1 hour. Continuous production was started at the end of the first hour recycle time. During continuous production, 250mg/l calcium carbonate suspension (16) was added to the reactor (1) for continuous dissolution of calcium carbonate in the reactor tank (1). At the same time, a clear aqueous solution S2(9) was extracted through the submerged membrane (2) at a concentration of 250mg/l calcium bicarbonate, measured as calcium carbonate, using a two-way dosing pump. The two ratios (suspension of micronized calcium carbonate (16) and aqueous solution (9)) are controlled by level measurement (11) in the reactor tank (1) and flow meter measurement (10) of the aqueous solution S2 (9). The initial setting of the ratio depends on the achievable membrane flux rate and is measured as the transmembrane pressure (8). The quality of the aqueous solution S2(9) was controlled by turbidity measurements (12) and titration.

The operating conditions and water quality results are given in tables 1 and 2 below.

Table 1: the process stream of example 1.

Process stream	(16)	(9)	(5)
				Description of the invention	Calcium carbonate suspension	Calcium bicarbonate solution S2	Recirculating air
Flow rate (l/h)	1 250	1 250	20 000
				Solid content (% by weight)	0.025	0	0
Concentration (mg/l)	0	220	110^a

^a: carbon dioxide is dosed into the reactor in equivalents based on the flow rate of water through the reactor.

Table 2: water quality of example 1

Process stream	(9)
		Description of the invention	Calcium bicarbonate solution S2
Alkalinity (mg/l, as CaCO)₃Meter)	220
		Hardness (mg/l, as CaCO)₃Meter)	214
pH	7.4
		Temperature [ deg.C ]]	21.5
Turbidity [ NTU]	0.1

The above-described method using the apparatus according to the invention has a much better energy efficiency than the patent application EP 2623467 a 1. According to Table 4 of EP 2623467A 1, 35l/h of permeate were produced in 4 different experiments from a tubular membrane Module (Microdyne-Module MD063 TP 2N). The suspension in these tests was circulated through the tubular module at a rate of 3200 l/h at a pressure of 1.5 bar to produce this permeate flow. The hydraulic energy required to produce this permeate is thus:

hydraulic energy (W) V x ρ x p

Wherein:

fluid flow velocity (m)³/s)

Rho fluid density (kg/m)³)

Static pressure at pump outlet (kPa)

For the example from patent application EP 2623467 a1, the following inputs are available:

V＝3 200l/h＝8.8e-04m³/s

ρ＝1 000kg/m³(for water, without any other details)

This produced an average of 54l/h of permeate and therefore the power consumption per cubic meter of permeate produced can be calculated as follows:

power/cubic meter 0.133 kW/0.035 m³/h＝3.8kW.h/m³。

Using the apparatus according to the invention and as shown in FIG. 1, a pressure of 50kPa was produced of 1250 l/h-3.47 e-04m³Permeate in s.

The hydraulic energy is thus calculated as follows:

the hydraulic energy (W) is V x ρ x p — 3.47e-04x 1000 x 50 — 17.4W.

This produced an average of 1250l/h of permeate and therefore the power consumption per cubic meter of permeate produced can be calculated as follows:

power/cubic meter 0.0174 kW/1.25 m³/h＝0.014kW.h/m³

The specific power consumption (power consumption per cubic meter of permeate produced) of the invention is therefore more than 270 times less than in the case of patent application EP 2623467 a 1.

CO according to tests with the inventive device described by EP 2623467A 1 and shown in FIG. 1₂Efficiency is calculated as follows:

(free CO in Water₂+ CO dosed₂)/CO₂Molecular weight (final basicity-initial basicity)/CaCO₃Molecular weight

＝(2+110)/44.01g/mol：(220-12)/100.08g/mol＝2.54：2.08＝1.22：1。

CO according to a test carried out with a device according to patent application EP 2623467A 1₂The efficiency is shown as:

110/44.01g/mol：170/100.08g/mol＝2.5：1.7＝1.47：1。

apparatus of the invention-preparation and dosing of an aqueous solution of calcium bicarbonate to increase the mineral and alkalinity content of desalinated water

A general process flow diagram of an apparatus according to the present invention is shown in fig. 2. The device comprises an inner part with a thickness of 50m²A reactor tank (1) for submerged membranes (2), a product reservoir (3), a calcium carbonate storage silo (13) with a dosing screw feeder and a holding device (14) for preparing a calcium carbonate suspension.

A calcium bicarbonate solution is produced in aqueous solution S2(9) and dosed into the main process stream (17) to increase the mineral content and alkalinity of the main process stream.

sodium: <1mg/l

Chloride: <2mg/l

Calcium: 8mg/l

Magnesium: <1mg/l

Alkalinity: 12mg/l (as CaCO)₃Meter)

^odH：1.12

pH value: 6.9

Conductivity: 24 mu S/cm

The calcium bicarbonate solution can be produced in a side stream using the above described apparatus in the following manner: the reactor tank (1) is initially filled with a 5.0% by weight calcium carbonate suspension to a defined volume, measured by a level measurement (11) in the reactor tank (1), which covers the surface of the submerged membrane (2). The blower begins to recirculate a volume of air (5) from the top of the reactor tank (1) to the diffuser located at the bottom of the submerged membrane (2) to ensure that a uniform suspension is maintained within the reactor (1) and to provide some cleaning effect to the membrane. The air volume (5) is recirculated at a rate of about 200 times per hour. A controlled amount of carbon dioxide is added to the air stream at, for example, location (4). The carbon dioxide-laden recycled air creates turbulence through the submerged membrane (2) from the bottom to the top of the reactor and the carbon dioxide is transferred from the air stream to the calcium carbonate suspension, increasing the amount of carbon dioxide dissolved in the suspension. The reaction between calcium carbonate and dissolved carbon dioxide allows the formation of a calcium bicarbonate solution within the reactor tank. At the same time, calcium carbonate is added from the storage silo (13) to the containing vessel (14) for preparing a calcium carbonate suspension within the containing vessel (14). A loss-in-weight screw feeder was used to accurately measure the amount of calcium carbonate added. Water is also added to the holding vessel (14) and a mixer is used to produce a homogeneous suspension of known solids content. The suspension (16) of micronized calcium carbonate is then transferred into the reactor tank (1) at a rate equal to the amount of calcium carbonate dissolved by reaction with carbon dioxide, so that the total amount of calcium carbonate not dissolved inside the reactor tank (1) remains unchanged. An aqueous solution of filtered permeate S2(9) as a clear concentrated calcium bicarbonate solution is used to add calcium and bicarbonate to the main process stream line (17) by means of a bi-directional dosing pump. The product reservoir (3) is used as a buffer also for the backwash sequence every 10 minutes.

Pilot unit for pilot run

Using natural calcium carbonate powder (From Omya International, Orgon France, d₅₀3 μm) as starting material in a pilot plant. The reactor tank (1) was filled with 900l of the prepared 5% by weight suspension of calcium carbonate powder, which was carried out by level measurement (11) in the reactor tank (1). Recirculating air flow (5) fan at 10m³H starts for regeneration of the membrane by turbulent flow. The overpressure of the air flow is measured by (6).

Example 2:

to produce a high load of concentrate (-250 mg/l alkalinity), 99g of carbon dioxide (4) was dosed into the recirculating air stream over 1 hour. Continuous production was started at the end of the first hour recycle time. During continuous production, 250mg/l calcium carbonate suspension (16) was added to the reactor (1) for continuous dissolution of calcium carbonate in the reactor tank (1). At the same time, a clear aqueous solution S2(9) was extracted at a concentration of 250mg/l of calcium bicarbonate (measured as calcium carbonate) by means of an immersed membrane and discharged into the main stream (17) through the product reservoir (3) via a two-way dosing pump. The two ratios (suspension of micronized calcium carbonate (16) and aqueous solution S2(9)) are controlled by level measurement (11) and flow measurement (10) in the reactor tank (1). The initial setting of the ratio depends on the achievable membrane flux rate and is measured as the transmembrane pressure (8). The quality of the aqueous solution S2(9) was controlled by turbidity measurements (12) and titrations in the aqueous solution (9). The mass of the first blend is measured by pH (18), conductivity (19) and titration of the blended water stream.

The operating conditions and water quality results are given in tables 3 and 4 below.

Table 3: the process stream of example 2.

Table 4: water quality results of example 2

Process stream	(9)	(24)
			Description of the invention	Calcium bicarbonate solution S2	Final water
Alkalinity (mg/l, as CaCO)₃Meter)	220	81
			Hardness (mg/l, as CaCO)₃Meter)	214	85
pH	7.4	7.25
			Temperature [ deg.C ]]	21.5	21
Turbidity [ NTU]	0.1	0

The inventive device-preparation and dosing of an aqueous solution of calcium bicarbonate followed by pH adjustment to increase the mineral and alkalinity content of the desalinated water and to stabilize it in terms of its saturation index

A general process flow diagram of an apparatus according to the present invention is shown in fig. 3. The device comprises an inner part with a thickness of 50m²A reactor tank (1) for submerged membranes (2), a product storage tank (3), a calcium carbonate storage silo (13) with a dosing screw feeder and a holding device (14) for preparing a calcium carbonate suspension, as well as a calcium hydroxide storage tank (20) and a dosing system.

A calcium bicarbonate solution is produced in aqueous solution S2(9) and dosed into the main process stream (17) to increase the mineral content and alkalinity of the main process stream (17). After dosing the calcium bicarbonate solution, a 5.0% by weight and high purity calcium hydroxide suspension (21) is dosed in the main process stream (17) to produce the desired final water quality of the final treated water stream (24).

Feed water is provided in all process streams, the feed water being obtained from a reverse osmosis system, yielding water with the following water specifications:

sodium: <1mg/l

Chloride: <2mg/l

Calcium: 8mg/l

Magnesium: <1mg/l

Alkalinity: 12mg/l (as CaCO)₃Meter)

^odH：1.12

pH value: 6.9

Conductivity: 24 mu S/cm

The calcium bicarbonate solution can be produced in a side stream using the above described apparatus in the following manner: the reactor tank (1) is initially filled with a 5.0% by weight calcium carbonate suspension to a defined volume, measured by a level measurement (11) in the reactor tank (1), which covers the surface of the submerged membrane (2). The blower begins to recirculate a volume of air (5) from the top of the reactor tank (1) to the diffuser located at the bottom of the submerged membrane (2) to ensure that a uniform suspension is maintained within the reactor tank (1) and to provide some cleaning effect to the submerged membrane (2). The volume was recirculated at a rate of about 200 times per hour. A controlled amount of carbon dioxide is added (4) to the air stream. The carbon dioxide-loaded recirculation air creates turbulence through the submerged membrane (2) from the bottom to the top of the reactor tank (1) and the carbon dioxide is transferred from the air stream to the calcium carbonate suspension, increasing the amount of carbon dioxide dissolved in the suspension. The reaction between calcium carbonate and dissolved carbon dioxide allows the formation of a calcium bicarbonate solution in the reactor tank (1). At the same time, calcium carbonate is added from the storage silo (13) to the containing vessel (14) for preparing a calcium carbonate suspension within the containing vessel (14). A loss-in-weight screw feeder was used to accurately measure the amount of calcium carbonate added. Water was also added to the tank and a mixer was used to produce a homogeneous suspension of known solids content. The suspension (16) of micronized calcium carbonate is then transferred into the reactor tank (1) at a rate equal to the amount of calcium carbonate dissolved by reaction with carbon dioxide, so that the total amount of calcium carbonate not dissolved inside the reactor tank (1) remains unchanged. An aqueous solution of filtered permeate S2(9) as a clear concentrated calcium bicarbonate solution is used to add calcium and bicarbonate to the main process stream (17) by a bi-directional dosing pump. The product reservoir (3) is used as a buffer also for the backwash sequence every 10 minutes. A second dosing pump is used to add the calcium hydroxide suspension stored in a storage tank (20), for example at location (21), to the main process stream (17).

Pilot unit for pilot run

Using natural calcium carbonate powder (From Omya International, Orgon France, d₅₀3 μm) and calcium hydroxide suspension (d: (d)Precal 72, concentration in water 20% by weight) as starting material in the pilot plant.The product (Precal 72) is a highly reactive 20% by weight calcium hydroxide suspension, diluted to 5% by weight (21) and dosed directly into the final treated water stream (24) for efficient pumping. The reactor tank (1) was filled with 900l of the prepared 5% by weight suspension of calcium carbonate powder, which was carried out by level measurement (11) in the reactor tank 1. Recirculating air flow (5) fan at 10m³H starts for regeneration of the membrane by turbulent flow. The overpressure of the air flow is measured by (6).

Example 3:

to produce a high load of concentrate (-250 mg/l alkalinity), 99g of carbon dioxide (4) was dosed into the recirculating air stream over 1 hour. Continuous production was started at the end of the 1h recycle time. During continuous production, 250mg/l micronized calcium carbonate suspension (16) was added to the reactor tank (1) for continuous dissolution of calcium carbonate within the reactor tank (1). At the same time, a clear aqueous solution (9) was extracted at a concentration of 250mg/l of calcium bicarbonate (measured as calcium carbonate) by means of an immersed membrane (2) and discharged via a two-way dosing pump through a product reservoir (3) into the main process stream (17). The two ratios (suspension of micronized calcium carbonate (16) and aqueous solution S2(9)) were controlled by level measurement (11) in the reactor tank (1) and flow measurement (10) of aqueous solution S2 (9). The initial setting of the ratio depends on the achievable membrane flux rate and is measured as the transmembrane pressure (8). The quality of the aqueous solution (9) is controlled by turbidity measurements (12) and titrations. The mass of the first blend was measured by pH (18), conductivity (19) and titration. In order to achieve the desired final water quality with a langelier saturation index of 0 for the final treated stream (24), a calcium hydroxide suspension (21) from the tank (20) is also dosed into the final treated stream (24).

The operating conditions and water quality results are given in tables 5 and 6 below.

Table 5: the process stream of example 3.

Table 6: water quality results of example 3

Process stream	(9)	(24)
			Description of the invention	Calcium bicarbonate solution S2	Final water
Alkalinity (mg/l, as CaCO)₃Meter)	220	88.5
			Hardness (mg/l, as CaCO)₃Meter)	214	92.5
pH	7.4	7.95
			Temperature [ deg.C ]]	21.5	21
Turbidity [ NTU]	0.1	0

Embodiment 4 of the present invention: dissolution of magnesium hydroxide by using the method given in figure 1

4.1 devices

The following devices were used for testing:

● 2150 liter "membrane calcite reactor" (MCR) consisted of:

○ cylindrical stainless steel reactor with ○ volume of 2150l, with the required connections,

○ Microdyn Bio-cel BC-50 submerged membrane unit installed in the reactor,

the lid of the reactor is sealed off,

instruments for level control and pressure monitoring,

● a blower system configured to form a blower recirculation loop, consisting of:

a blower operated by a variable speed drive,

○ blower piping connected from the top of the reactor (connected to the lid)

an exhaust piping system, a diffuser manifold connected to the bottom of the submerged membrane unit,

● osmotic pump to extract concentrated solution through membrane, having flow meter to measure flow rate

● A carbon dioxide dosing system, comprising:

○ carbon dioxide bottle

pressure regulator to reduce the pressure from 50 to 5 bar of the bottle

Mass flow meter and control valve to regulate and measure the dosing of carbon dioxide

○ dosing connection to the blower discharge piping system

● slurry compression (SMD) system consisting of:

slurry compression (SMD) tank, with electric stirrer and tank level instrumentation,

feed water to the tank, controlled to maintain a level in the tank

o loss-in-weight dosing feed system to accurately add the required amount of micronized calcium carbonate to the SMD tank,

○ hopper for supplying micronized calcium carbonate to a loss-in-weight feeder,

○ slurry feed pump for dosing the calcium carbonate suspension produced in the SMD tank into a 2150l reactor,

dosing hose for connecting the slurry feed pump to the 2150l reactor

● magnesium hydroxide dosing system, comprising:

storage tank for suspension containing 25% magnesium hydroxide

○ Prominent Gamma L dosing pump

○ discharge hose from dosing pump, connected to dosing hose between slurry feed pump and 2150l reactor (part of SMD system)

the magnesium dosing system is configured such that magnesium hydroxide is dosed into the suspension of micronized calcium carbonate (16).

4.2 procedure:

the following procedure was used for the experiments:

SMD tanks were filled with water and calcium carbonate was dosed into the tanks to produce suspension S1 (according to the setup provided in section 4.3).

2. The SMD control was placed in an automatic mode so that water would be continually replenished in the SMD tank as the suspension was removed from the tank and calcium carbonate would be continuously dosed to ensure that a consistent suspension of the concentration provided in section 4.3 was produced.

3. The suspension S1 containing 5% micronized calcium carbonate was charged into a 2150l reactor. Technical details of micronized calcium carbonate are provided in section 4.3.

4. The lid of the reactor was closed and a tight seal was ensured.

5. The blower was operated electrically to maintain the micronized calcium carbonate in suspension S1.

6. Carbon dioxide was dosed into the blower recirculation loop according to the setup provided in section 4.3.

7. The osmotic pump was operated at the set rate to provide the desired flow rate and to extract the clarified solution S2 from the reactor tank according to the settings provided in section 4.3.

8. The slurry feed pump was operated at a set speed to ensure that the level within the reactor tank remained constant.

9. According to the test setup provided in section 4.3, the magnesium hydroxide dosing pump was set to change speed to dose the required amount of magnesium hydroxide into the process.

10. A sample of the concentrated solution S2 extracted by the osmotic pump was analyzed for the following water qualities by the method described above:

a. alkalinity (mg/l)

b. Total hardness (mg/l)

c. Magnesium hardness (mg/l)

d. Acidity (in mg/l CO)₂Meter)

pH, conductivity, temperature & turbidity

4.3 test setup

The following test set-up was used during the experiment:

table 7: test setup

4.4 results of measurement

Table 8: results of measurement for test 1

Table 9: results of measurement for test 2

Table 10: results of measurement for test 3

The results provided in test 1 (table 8) show that very stable values can be generated for the alkalinity of the concentrated solution S2 without magnesium hydroxide dosing. Stable values were also generated for total hardness and magnesium concentration.

The results provided in test 2 (Table 9) show that dosing of 30mg/l magnesium hydroxide provides about 10-14mg/l magnesium. This is expected because magnesium hydroxide has a molecular weight of 58.3g/mol, with 24.3g/mol or 41.7% of this amount.

The results provided in test 3 (table 10) show that during the course of the experiment very stable results were achieved for all values, in particular for the basicity and the magnesium concentration. For this test, 60mg/l of magnesium hydroxide were dosed. This should ideally add 25Mg/l Mg²⁺Ions. This is consistent with the following results: the results show that the concentrated stream withdrawn from the reactor contains on average 25.8mg/l magnesium, which ranges from 23.6 to 27.2mg/l magnesium. The results are also summarized in fig. 14.

In all cases, the turbidity of the concentrate stream was measured at 0.01 NTU.

And (4) conclusion: from these experiments it can be concluded that the method of the invention, which has been developed for dissolving micronized calcium carbonate, can also be used for efficiently dissolving magnesium (in the form of magnesium hydroxide). The results were very stable, indicating that the process could also be precisely controlled. This method has the advantages that: it produces a haze-free concentrate stream in the absence of unwanted anions.

In summary, it has been shown that this approach provides a cost effective alternative to the current approach. Furthermore, the process can be effectively controlled to dose the required amount of calcium and, if desired, magnesium.

Claims

1. A process for preparing an aqueous solution comprising at least one earth alkali hydrogen carbonate, comprising the steps of:

a) providing water;

b) providing at least one alkaline earth metal carbonate-containing material;

c) providing CO₂Or pK_aValue of<5 with an acid;

d) mixing the water of step a) with the at least one alkaline earth metal carbonate-containing material of step b) and the CO of step c)₂Or the acids are combined in any order to obtain water comprising at least one earth alkali hydrogen carbonateAn aqueous suspension S1;

e) filtering at least a portion of the aqueous suspension S1 obtained in step d) by passing the aqueous suspension S1 through at least one submerged membrane module to obtain an aqueous solution S2 comprising at least one alkaline earth metal bicarbonate,

wherein the at least one submerged membrane module is located in the container.

2. The method of claim 1, wherein step d) comprises the steps of:

i1) mixing the water of step a) with the CO of step c)₂Or acid combining, and i2) combining the mixture of i1) with the at least one alkaline earth metal carbonate-containing material of step b); or

ii1) combining the water of step a) with the at least one alkaline earth metal carbonate-containing material of step b), and ii2) combining the mixture of ii1) with the CO of step c)₂Or a combination of acids.

3. The process according to claim 1 or 2, wherein process steps d) and e) are carried out in the same vessel, preferably in a reactor tank.

4. The method according to any one of claims 1-3, wherein the at least one submerged membrane module has a pore size of preferably <1 μm and more preferably <0.1 μm.

5. The method according to any one of claims 1-4, wherein air or process fluid is recycled through at least a part of the surface of the at least one submerged membrane, preferably from the bottom to the top direction of the at least one submerged membrane module and/or vessel, more preferably the CO of step c)₂Or acid is added to the air or process fluid.

6. A method according to claim 5, wherein the container is sealed and air at the top of the container is used as feed and reintroduced to the bottom of the container.

7. The method according to any one of claims 1-6, wherein the method comprises the further step f): backwashing the at least one submerged membrane module, optionally CO, with water₂Or pK_aValue of<5 acid was added to the water.

8. The process according to any one of claims 1 to 7, wherein the at least one alkaline earth metal carbonate-containing material of step b) is selected from the group consisting of precipitated calcium carbonate, modified calcium carbonate, ground calcium carbonate and mixtures thereof, preferably the at least one alkaline earth metal carbonate-containing material in step b) is ground calcium carbonate.

9. The process according to any one of claims 1-8, wherein the at least one alkaline earth metal carbonate-containing material of step b) is ground calcium carbonate selected from the group consisting of marble, limestone, chalk and mixtures thereof.

10. The process according to any one of claims 1-9, wherein the at least one alkaline earth metal carbonate-containing material of step b) is provided in dry form or in the form of an aqueous suspension; and/or

The at least one earth alkali hydrogen carbonate obtained in step d) comprises, preferably consists of, calcium hydrogen carbonate.

11. The process according to any one of claims 1-10, wherein the acid provided in step c) has<pK of 4_aThe acid and/or the acid is selected from sulphuric acid, hydrochloric acid, nitric acid or citric acid and/or mixtures thereof.

12. The process according to any one of claims 1 to 11, wherein the aqueous solution S2 comprising at least one alkaline earth metal bicarbonate obtained in step e) has an alkaline earth metal concentration, expressed as alkaline earth metal bicarbonate, of from 20 to 1000mg/l and more preferably from 50 to 600mg/l and most preferably from 80 to 400 mg/l; and/or has a pH value of 6.1 to 8.9 and preferably 6.5 to 8.5.

13. A method for the mineralization and/or stabilization of water, the method comprising the steps of:

i) providing the water to be mineralized with water,

ii) providing an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process as defined in any one of claims 1 to 12,

14. The method according to claim 13, comprising the further step (iv): (iv) adding a base, preferably sodium hydroxide or calcium hydroxide, to the mineralized water of step (iii).

15. Use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process according to any one of claims 1 to 12 for the mineralization and/or stabilization of water or as mineralized water.

16. Use according to claim 15, wherein the water is desalinated or naturally soft water.