RU2758643C2 - Preparation of suspension of red iron oxide pigment - Google Patents

Abstract

FIELD: chemical industry; environmental protection.

SUBSTANCE: plant for the preparation of a suspension of red iron oxide pigments includes reactor (1) for the preparation of iron nitrate, reactor (2) for the preparation of a suspension of hematite cores, reactor (3) for the preparation of hematite pigment, scrubbers (4) and/or (6). Reactors (1) and (3) are made with the possibility of communication with scrubber (4) and/or (6) via lines (L-3a) and (L-3b), respectively. Reactor (2) is made with the possibility of communication via line (L-4) with oxidative unit (5) made with the possibility of communication via line (L-5) with scrubber (4) and/or (6). The plant also contains unit for purifying waste gas (9) made with the possibility of communication via line (L-8) with heater (8) communicated via line (L-7) with scrubber (4) and/or (6). The plant can be equipped with several scrubbers (4 and 6) and additionally – with a unit for purifying waste water communicated with reactor (3) or with a separating device; with a heat exchanger communicated with scrubbers (4) and (6), with heater (8) and with unit for purifying waste gas (9). The separating device can be communicated with reactor (3).

EFFECT: plant provides for effective and environmentally friendly Penniman process, i.e. nitrate process with obtaining red iron oxide pigments of a wide color spectrum and with high yield, with minimal release of by-products into the environment.

5 cl, 12 dwg

Description

The present invention relates to an improved process for the production of red iron oxide pigments by the Penniman process with nitrate (also called the nitrate process or the Congo red process) and a plant for carrying out this process, as well as the use of a plant for the production of red iron oxide pigments by the Penniman process using nitrate.

Iron oxides are used in many industrial areas. They are used, for example, as coloring pigments in ceramics, building materials, plastics, inks, paints and paper, they serve as a base for various catalysts or substrates, and are capable of adsorbing or absorbing pollutants. Magnetic iron oxides find use in magnetic storage devices, toners or ferromagnetic fluids, or in medical applications such as, for example, as a contrast agent for magnetic resonance imaging.

Encyclopedia of Industrial Chemistry, VCH Weinheim 2006, Глава 3.1.1. Iron Oxide Pigments, стр. 61-67). Железоокисные пигменты посредством процесса осаждения получают из растворов солей железа и щелочных соединений в присутствии воздуха. Благодаря целевому контролю реакции также возможно таким образом получить мелкоизмельченные частицы гетита, магнетита и маггаемита. Однако красные пигменты, полученные этим процессом, проявляют относительно низкую интенсивность цвета и, следовательно, используются главным образом в промышленности строительных материалов.Iron oxides can be obtained by water precipitation and by hydrolysis reactions of iron salts (

Encyclopedia of Industrial Chemistry, VCH Weinheim 2006, Chapter 3.1. Iron Oxide Pigments, pp. 61-67). Iron oxide pigments are obtained through a precipitation process from solutions of iron salts and alkaline compounds in the presence of air. Due to the targeted control of the reaction, it is also possible in this way to obtain fine particles of goethite, magnetite and maggaemite. However, the red pigments produced by this process exhibit relatively low color intensity and are therefore mainly used in the building materials industry.

However, the water production of finely divided hematite corresponding to the α-Fe ₂ O ₃ modification is much more difficult. As a result of using the aging step, it is also possible to obtain hematite by direct water deposition by adding finely ground iron oxide in the modification of maggaemite, γ-Fe ₂ O ₃ , or modification of lepidocrocyte, γ-FeOOH, as a nucleating material [US 5421878; EP 0645437; WO 2009/100767].

An additional method for producing red iron oxide pigments is the Penniman process (US 1327061; US 1368748; US 2937927; EP 1106577A; US 6503315). In this process, an iron oxide pigment is obtained by dissolving and oxidizing metallic iron with the addition of a core of iron salt and iron oxide. Accordingly in SHEN, Qing; SUN, Fengzhi; Wujiyan Gongye 1997, (6), 5-6 (CH), Wujiyan Gongye Bianjib, (CA 128: 218378n) discloses a process in which dilute nitric acid acts on iron at elevated temperatures. This produces a suspension of hematite cores. This slurry is formed in a conventional manner to form a slurry of red pigment, and the pigment is isolated from this slurry, if desired, in a manner that is conventional in itself. The color intensity of the red pigments produced by this process, however, is relatively low, similar to the color intensity of the commercial product grade 130, and therefore these pigments are mainly used in the building materials industry. EP 1106577A discloses a variant of the Penniman process involving exposing iron to dilute nitric acid at elevated temperatures in order to obtain nuclei, i. E. finely divided iron oxides having a particle size less than or equal to 100 nm. The interaction of iron with nitric acid is a complex reaction and, depending on the experimental conditions, can lead either to passivation of iron and, consequently, to termination of the reaction, or to dissolution of iron with the formation of dissolved iron nitrate. Both variants of the development of the reaction are undesirable, and the production of finely ground hematite is carried out only under certain conditions. EP 1106577A describes similar conditions for the preparation of finely divided hematite. Here iron is reacted with dilute nitric acid at temperatures between 90 and 99 ° C. WO 2013/045608 describes a process for the production of red iron oxide pigments in which the reaction step for the production of cores is improved, i. E. finely ground hematite having a particle size less than or equal to 100 nm.

These essentially efficient processes, which allow the direct production of high quality red iron oxides with a large variation in color values, nevertheless suffer from the following disadvantages:

1. The release of nitrogen oxides of the formula NO _m , in which nitrogen can have different oxidation states between +1 and +5. Nitrogen oxides can be toxic (examples are nitrous gases NO, NO ₂ and N ₂ O ₄ , also generally identified as "NO _x "); they generate smog, destroy the atmospheric ozone layer by UV radiation and are greenhouse gases. Specifically, dinitrogen monoxide is a potent greenhouse gas than carbon dioxide by a factor of about 300. In addition, dinitrogen monoxide is currently considered to be the most potent ozone depleter. In the case of the Penniman process with nitric acid, nitrous gases NO and NO ₂ , as well as dinitrogen monoxide, are formed in significant quantities.

2. The Penniman process with nitric acid produces nitrogen-containing wastewater that contains significant amounts of nitrates, nitrites and ammonia compounds.

3. The Penniman process with nitric acid is very energy intensive as it involves heating large volumes of aqueous solutions to temperatures between 60 ° C and 120 ° C by means of an external power supply. In addition, by introducing oxygen-containing gases as oxidants into the reaction mixture, energy carriers are removed from the reaction mixture (steam stripping) and must be supplied again in the form of heat.

Therefore, the aim was to provide an efficient and environmentally friendly process for the production of red iron oxide pigments that avoids the above disadvantages, with on the one hand red iron oxide pigments are obtained with a wide color spectrum in high yields, and on the other hand, the fraction of nitrogen-containing by-products is minimized. released into the environment.

A process for producing red iron oxide pigments has been discovered that achieves this goal and also provides a facility in which this process can be carried out on an industrial scale.

The method according to the invention comprises at least the steps

a) obtaining a solution of iron (II) nitrate by reacting iron with nitric acid, thereby producing a first nitrogen oxide-containing stream and optionally further separating any unreacted iron from the iron (II) nitrate solution thus obtained,

b) preparing an aqueous slurry of hematite cores by reacting iron with nitric acid, thereby producing a second nitrogen oxide-containing stream, and optionally further separating any unreacted iron from the slurry of hematite cores thus obtained,

c) obtaining an aqueous suspension of hematite pigment by

I. interaction of an aqueous suspension of hematite cores from step b) with a solution of iron (II) nitrate from step a) and at least one alkaline precipitant in the presence of at least one oxygen-containing gas, and / or by reaction

II. interaction of an aqueous suspension of hematite cores from step b) with a solution of iron (II) nitrate from step a), iron and at least one oxygen-containing gas,

thus obtaining a third nitrogen oxide-containing stream.

d) isolating the hematite pigment present in the aqueous suspension of the hematite pigment from the aqueous phase,

e) oxidizing the second nitrogen oxide containing stream from step b) to obtain an oxidized second nitrogen oxide containing stream.

f) contacting the first nitrogen oxide-containing stream and / or the third nitrogen oxide-containing stream and / or the oxidized second nitrogen oxide-containing stream from step e) with an aqueous wash phase, thus obtaining a pre-purified gas stream and a wash phase rich in nitric acid.

g) Removing dinitrogen monoxide and / or nitrous gases from the pre-purified gas stream from step f) by heating to a temperature of 200 to 1400 ° C, optionally in the presence of at least one catalyst, preferably from 250 to 500 ° C in the presence of at least one catalyst and / or from 800 to 1400 ° C in the absence of a catalyst, thus obtaining a purified gas stream.

In one preferred embodiment, the process according to the invention comprises, in addition to steps a) to g), step

h) removing at least ammonia compounds and / or nitrite compounds and / or nitrate compounds, in particular at least ammonia compounds, nitrate compounds and nitrite compounds from the aqueous phase from step d) by means of methods known to those skilled in the art, obtaining a purified waste water and optionally salt-enriched waste water.

In a further preferred embodiment, the process according to the invention comprises, in addition to steps a) to g) or a) to h), one or more steps of

i) recycling the nitric acid-rich aqueous phase formed in step f) to step a) and / or b) and / or c) and / or

j) using the heated purified gas stream from step g) to preheat the pre-purified gas stream from step f) to form a preheated pre-purified gas stream and cooled purified waste gas.

At this point, it can be noted that the scope of the invention encompasses all desirable and possible combinations of these components, ranges of values and / or process parameters, which are given above and presented below, or basic or stated in the preferred ranges.

The commonly used iron contains iron in the form of wires, sheets, nails, knots, or coarse sawdust. The individual pieces in this case have any desired shape and traditionally have a thickness (measured, for example, as wire diameter or sheet thickness) from about 0.1 millimeter up to about 10 millimeters. The size of the coils of wire or sheets used in the process is mainly determined by practical reasons. Therefore, it should be possible to load the reactor with raw material without difficulty, usually through an inspection hatch. Such iron is produced, among other processes, as scrap or as a by-product in the metalworking industry, examples of which are perforated metal sheets.

The iron used in the process according to the invention generally has an iron content of> 90%. The impurities found in this iron are usually foreign metals such as, for example, manganese, chromium, silicon, nickel, copper, and other elements. However, high-purity iron can also be used without detriment.

The nitric acid used in steps a) and b) in the process according to the invention has a concentration of 10 to 67 wt. % HNO ₃ , preferably from 20 to 67 wt. % HNO ₃ . In steps b) and / or c), in addition to nitric acid, it is also possible to use another acid, such as, for example, hydrochloric acid or sulfuric acid. Preferably no additional acid other than nitric acid is used in these process steps. This is the advantage that the aqueous suspension of hematite cores obtained by the process according to the invention and the hematite have a very low sulfur and chlorine content. This is an advantage for the use of catalysts, since sulfur and chlorine are known catalyst poisons for certain reactions.

Iron (II) nitrate solutions generally have concentrations of 50 to 300 g / L Fe (NO ₃ ) ₂ (number based on anhydrous solid). In addition to Fe (NO ₃ ) ₂ , iron (II) nitrate solutions can also contain amounts from 0 to 50 g / L Fe (NO ₃ ) ₃ . However, a very low amount of Fe (NO ₃ ) _{3 is} beneficial.

Nitrogen oxides for the purposes of the present invention are nitrogen and oxygen containing compounds of the general formula NO _y . This group includes nitrous gases (also called NO _x ) of the general formula NO _m , where nitrogen can have different oxidation states between +1 and +5. Examples of these are NO (nitrogen monoxide, m = 1, oxidation state +2), NO ₂ (nitrogen dioxide, m = 2, oxidation state +4), and N ₂ O ₅ (m = 2.5, oxidation state +5 ). NO ₂ is in temperature and pressure dependent equilibrium with its dimer N ₂ O ₄ (the oxidation state of both is + IV). Hereinafter, NO ₂ will refer to both NO ₂ itself and its dimer N ₂ O ₄ . N ₂ O (dinitrogen monoxide, laughing gas, m = 0.5, oxidation state +1) also belongs to the group of nitrogen oxides of the general formula NO _y , but does not belong to the group of nitrous gases.

The first nitrogen oxide-containing stream from step a) or the third nitrogen oxide-containing stream from step c) of the process according to the invention generally contains from 1 to 200 g / m ³ nitrous gases (calculated as g / m ³ NO ₂ ) and / or from 0 , 5 to 50 g / m ³ N ₂ O. The amount of nitrous gases and dinitrogen monoxide in these streams can vary in wide ranges. Stage a) of the process according to the invention generally produces small amounts of nitrous gases and dinitrogen monoxide, which usually accumulate over the reaction mixture in the reactor, since these reactors are usually closed. The introduction of air or inert gases such as nitrogen, also called external air, into the reactor by suction or blowing produces a first nitrogen oxide-containing stream.

In step b) of the process according to the invention, as a rule, according to the reaction conditions, significantly higher quantities of nitrous gases and dinitrogen monoxide are produced than in the case of step a), and these quantities are likewise accumulated over the reaction mixture in the reactor if these reactors closed, or directed to lines connected to the reactor, if the reactors are open, when, for example, the permissible pressures are exceeded. By introducing air or inert gases, for example nitrogen, also called external air, into the reactor by suction or purging, streams with defined levels of nitrous gases and dinitrogen monoxide can then be generated. Then the amount of nitrous gases and dinitrogen monoxide in these streams depends on the amount of these gases generated during the interaction and on the amount of external air charged into the installation and on the duration of the external air charging, and can therefore be adjusted to the desired levels beneficial for additional technological stages. It may be advantageous to combine the first and second nitrogen oxide containing streams after leaving the reactors or to introduce the first nitrogen oxide containing stream as a substitute for external air into the reactor for step b). The resulting combined first and second nitrogen oxide containing streams generally contain from 1 to 50 g / m ^{3 of} nitrous gases (calculated as g / m ³ NO ₂ ) and / or from 1 to 50 g / m ³ of dinitrogen monoxide.

The second nitrogen oxide-containing stream from step b) of the process according to the invention generally has a concentration of from 1 to 2000 g / m ^{3 of} nitrous gases (calculated as g / m ³ NO ₂ ) and from 0.5 to 2000 g / m ³ of dinitrogen monoxide. By introducing at least one oxygen-containing gas into the reactor during the reaction, a second nitrogen oxide-containing stream is generated. The amount of nitrous gases and dinitrogen monoxide can therefore also be controlled via the flow rate of the at least one oxygen-containing gas.

The oxidized second nitric oxide-containing stream obtained after step e) generally contains no more than 50%, preferably less than 30%, more preferably less than 15% of the original nitrogen monoxide fraction, i. E. fraction present before stage f).

The aqueous suspension of hematite cores obtained in step b) generally has a concentration of from 50 to 300 g / l of hematite, preferably from 80 to 150 g / l of hematite. The hematite cores obtained according to step b) and present in the aqueous suspension of the hematite cores have a particle size of, for example, less than or equal to 100 nm and / or a BET specific surface area of 40 m ² / g to 150 m ² / g ... This hematite (α-Fe ₂ O ₃ ) may also contain fractions of other phases, for example goethite (α-FeOOH) and / or ferrihydrite (5 Fe ₂ O ₃ ⋅9 H ₂ O).

At least one alkaline precipitant from step c) in embodiment I. is, for example, NaOH, KOH, Na ₂ CO ₃ , K ₂ CO ₃ , NH ₃ or NH ₄ OH, or other hydroxides and carbonates of alkali metals and alkaline earth metals or any desired mixtures thereof. Preference is given to the use of alkali metal hydroxides or alkali metal carbonates, especially the use of NaOH.

At least one oxygen-containing gas from step c) in embodiment I. or II. represents, for example, air, oxygen, NO, NO ₂ , O _3, or mixtures of these gases. Air is preferred.

The separation of the hematite pigment present in the aqueous suspension of the hematite cores from the aqueous phase according to step d) is preferably carried out by sedimentation, filtration or centrifugation. The removed aqueous phase contains, among other components, nitrate compounds, nitrite compounds and ammonia compounds and thus generally has a total nitrogen content of 0.2 to 10 g / l nitrogen, preferably 0.2 to 5 g / l nitrogen ( calculated in each case for elemental nitrogen).

The red iron oxide pigment obtained by the process according to the invention is also referred to alternatively as hematite pigment in connection with this invention, preferably contains from 80 to 100 wt. % α-Fe ₂ O ₃ , the crystal lattice of α-Fe ₂ O ₃ containing from 0 to 10 wt. % crystalline water. The hematite obtained by the process according to the invention has a wide color spectrum. The color of hematite is influenced by particle size, particle size distribution, amount of crystalline water and / or the introduction of external atoms. Color values are measured by methods known in the art.

The aqueous wash phase is mainly water or dilute nitric acid, preferably dilute nitric acid, more preferably nitric acid, which moves in a circular motion.

The nitric acid-rich wash phase generally has an HNO ₃ content of from 1 to 67 wt. %, preferably from 5 to 67 wt. %.

The catalysts are preferably alternatively catalysts for the decomposition of nitrous gases and / or for the decomposition of dinitrogen monoxide. Examples of catalysts are activated carbons, silica gel, molecular sieves, vanadium-zinc catalysts or chromium-zinc catalysts.

The pre-purified gas stream generally has a temperature of from 20 to 90 ° C, preferably from 30 to 80 ° C, and contains preferably not more than 50%, more preferably less than 30%, very preferably less than 15% of the initial fraction of nitrous gases ( calculated as NO ₂ ), i.e. fraction present before stage f).

Preheated pre-heated from 250 to 500 ° C, more preferably from 300 to 450 ° C and from 0.5 to 20 g / m ³ nitrous gases (calculated as g / m ³ NO ₂ ), preferably from 0.5 to 20 g / m ³ nitrous gases (calculated as g / m ³ NO ₂ ) and / or from 1 to 40 g / m ³ N ₂ O.

The cleaned exhaust gas generally has a temperature of 150 to 1500 ° C, preferably 150 to 500 ° C. The cleaned flue gas mainly contains 0.001 to 0.3 g / m ³ nitrous gases (calculated as g / m ³ NO ₂ ), preferably 0.005 to 0.3 g / m ³ nitrous gases (calculated as NO ₂ ) and / or from 0.001 to 0.3 g / m ³ N ₂ O, preferably from 0.005 to 0.3 g / m ³ N ₂ O.

The cooled cleaned exhaust gas generally has a temperature of from 80 ° C to 450 ° C, preferably from 150 to 350 ° C. The cooled cleaned exhaust gas mainly contains 0.001 to 0.3 g / m ³ nitrous gases (calculated as g / m ³ NO ₂ ), preferably 0.005 to 0.3 g / m ³ nitrous gases (calculated as NO ₂ ) and / or from 0.001 to 0.3 g / m ³ N ₂ O, preferably from 0.005 to 0.3 g / m ³ N ₂ O.

Treated waste water contains only small residual amounts of dissolved nitrogen compounds. The purified waste water generally has a total nitrogen content of not more than 0.2 g / L nitrogen, preferably not more than 0.1 g / L nitrogen, more preferably not more than 0.02 g / L nitrogen (calculated in each case on elemental nitrogen).

Salt-enriched wastewater mainly contains salts that have not been removed in the previous treatment steps. The salt-enriched waste water preferably contains sulphate.

Steps a) and / or b) can take place in any way known to the skilled person for reacting iron with nitric acid.

For example, in step a), 0.4 to 10 moles of iron per mole of nitric acid are reacted at a temperature of 60 ° C or less, preferably 10 to 60 ° C, to obtain an iron (II) nitrate solution. If an excess of iron is used, the iron (II) nitrate solution can be easily separated from the unreacted iron. In the next portion, additional iron and / or additional nitric acid are optionally added.

Steps b) and c) of the process according to the invention can be carried out in any way known to the person skilled in the art. Steps b) and c) are preferably carried out in accordance with the processes described in EP 1106577 A or WO 2013/045608.

This is accomplished, for example, by using step b) of the process according to the invention with the generation of a suspension of hematite cores, the reaction temperature of the action of nitric acid on the iron being at least 90 ° C, preferably between 90 and 99 ° C.

In another preferred embodiment of step b), an aqueous suspension of hematite cores is generated, the nitric acid having a concentration of 2 to 6 wt. % HNO ₃ and is used in a molar reaction ratio of iron to nitric acid (HNO ₃ ) from 1.5 to 16. In a further preferred embodiment of step b) an aqueous suspension of hematite cores is generated, the nitric acid having a concentration of 2 to 15 wt. % HNO ₃ . In a further preferred embodiment of step b), a molar reaction ratio of iron to nitric acid (HNO ₃ ) of 1.0 to 16 is used.

In a further preferred embodiment of step b) aqueous suspensions of hematite cores are prepared, wherein the hematite cores present in the aqueous suspension of hematite cores have a particle size of less than or equal to 100 nm and a BET specific surface area of 40 m ² / g to 150 m ² / g, measured according to DIN 66131, the preparation comprising at least the steps:

i) providing a mixture of iron and water having a temperature of 60 to 120 ° C,

ii) adding nitric acid to the mixture from step i), and

iii) optionally further separating any unreacted iron from the aqueous suspension of the hematite cores thus obtained.

In a further preferred embodiment, in step ii), nitric acid is added to the mixture from step i) at a rate such that the reaction mixture is preferably heated by at least 15 ° C. in less than 120 minutes after the addition of nitric acid is complete, even without an external heat source ... Likewise, it is preferred that the reaction mixture in step ii) reaches a maximum temperature of 105 to 160 ° C. Likewise, it is preferred that steps i) and ii) take place in a pressure vessel. Likewise, it is preferred that after completion of the addition of nitric acid in step ii), a drop in the reaction temperature to less than 100 ° C. is expected before carrying out step iii).

In one preferred embodiment of variant I. of step c), the temperature during the reaction is from 70 to 100 ° C, preferably from 75 to 90 ° C. The iron (II) nitrate solution from step a) and at least one alkaline precipitant are dosed and the reaction mixture is oxidized with at least one oxygen-containing gas, preferably 0.2 to 100 liters of at least one oxygen-containing gas, preferably air, per hour and per liter of suspension until the red iron oxide pigment reaches the desired color shade.

In one preferred embodiment of Option II. stage c) a suspension of hematite pigment is obtained by reacting a suspension of hematite cores with iron and a solution of iron (II) nitrate at temperatures from 70 to 100 ° C, preferably from 75 to 90 ° C, and oxidation with 0.2 to 100 liters at least as much as one oxygen-containing gas, preferably air, per hour and per liter of slurry, until the red iron oxide pigment reaches the desired hue.

In a further preferred embodiment of option II. step c) an aqueous suspension of hematite cores from step b) is reacted with a solution of iron (II) nitrate from step a) and iron, at least one oxygen-containing gas and at least one sulfate salt, such as iron (II) sulfate, and / or sulfate of an alkali metal or alkaline earth metal, preferably iron (II) sulfate and / or sodium sulfate, to obtain a red iron oxide pigment. The reaction temperature is 70 to 100 ° C, preferably 75 to 90 ° C. The at least one oxygen-containing gas used is preferably air, the amount being preferably 0.2 to 50 liters of air per hour and per liter of suspension until the iron oxide red pigment reaches the desired color shade.

In a further preferred embodiment of step c), an aqueous suspension of hematite cores from step b) is reacted with an iron (II) nitrate solution from step a), at least one alkaline precipitant, iron, at least one oxygen-containing gas and optionally at least a sulfate salt such as iron (II) sulfate and / or alkali metal sulfate or alkaline earth metal sulfate, preferably iron (II) sulfate and / or sodium sulfate, to form a red iron oxide pigment. The reaction temperature is 70 to 100 ° C, preferably 75 to 90 ° C. At least one alkaline precipitant is added to the reaction mixture, more preferably at the end of the reaction, such as when the residual concentration of iron (II) ions is less than or equal to 10 g / l, very preferably when the residual concentration of iron (II) ions is less than or equal to 5 g / l, while the supply of oxygen-containing gas is continued. The oxygen-containing gas used preferably contains air, the amount being preferably 0.2 to 50 liters of air per hour and per liter of suspension until the iron oxide red pigment reaches the desired color shade.

The supply of at least one oxygen-containing gas can be started in all preferred embodiments or during the heating phase of the reaction mixture consisting of a slurry of hematite cores from step b), an iron (II) nitrate solution from step a) and iron, or at the end heating phases.

At least one sulfate salt, for example iron (II) sulfate or alkali metal sulfate or alkaline earth sulfate, preferably iron (II) sulfate and / or sodium sulfate, can in all preferred embodiments be used in the form of a solution, suspension or solid ... The solid in this case is in the form of an anhydrous compound or various modifications containing crystalline water. Iron (II) sulfate is preferably used in the form of an aqueous solution or in the form of solid iron (II) sulfate heptahydrate or suspensions thereof.

In another preferred embodiment of step c) at least one sulfate salt, for example iron (II) sulfate or alkali metal sulfate or alkaline earth metal sulfate, preferably iron (II) sulfate and / or sodium sulfate, is added to the reaction mixture before and / or after starting the supply of oxygen-containing gas. The advantage is that less iron (II) nitrate solution should be used and that precipitation of the hematite pigment formed during the reaction from the hematite pigment suspension is accelerated. This facilitates the subsequent separation of the hematite pigment in step d) of the process according to the invention.

In step d) of the process according to the invention, the separation of the red iron oxide pigment present in the suspension is carried out, preferably by filtration and / or sedimentation and / or centrifugation. Likewise, preferably the filter cake is washed and then the filter cake is dried. Likewise, one or more screening steps are preferably carried out prior to separating the red iron oxide pigment from the aqueous phase, more preferably using sieves of various sizes and with decreasing sieve sizes. The advantage is that by means of these means external substances, for example metal particles, which would otherwise contaminate the hematite pigment, are removed from the hematite pigment suspension.

To separate the hematite pigment from the aqueous phase, it is possible to carry out all methods known to those skilled in the art, for example, precipitation followed by removal of the aqueous phase or filtration using filter presses, such as the use of membrane filter presses.

In one preferred embodiment of step d), at least one sulfate salt, for example iron (II) sulfate or alkali metal sulfate or alkaline earth metal sulfate, preferably iron (II) sulfate and / or sodium sulfate, can be added to the hematite pigment suspension in time or before screening and / or during or before separation. The advantage is that precipitation of the hematite pigment from the hematite pigment suspension is accelerated. This facilitates the subsequent separation of the red iron oxide pigment in step d) of the process according to the invention.

Further, optionally, at least one purification of the filter cake or the cake thus separated is present. After separation and / or purification, the optionally red iron oxide pigment thus separated is dried, for example, using filter dryers, belt dryers, kneading dryers, rotary spray dryers, drying chambers or spray dryers. Drying preferably takes place using belt dryers, disc dryers, kneading dryers and / or spray dryers.

The oxidation of the second nitric oxide-containing stream from step b) to step e) is carried out, for example, by contacting the second nitric oxide-containing stream with at least one oxidizing agent, optionally in the presence of one or more catalysts and / or high energy radiation, for example UV radiation. Oxidants are mainly air, oxygen, ozone or hydrogen peroxide, preferably air.

Oxidation occurs, for example, at temperatures between 20 and 300 ° C.

Oxidation occurs, for example, at a pressure of 0.08 MPa to 2 MPa (0.8 to 20 bar). Preferably, oxidation takes place at pressures between 0.08 MPa and 1 MPa (0.8 to 10 bar). In general, oxidation is accelerated by higher pressures. One of the reactions during the oxidation of the second nitrogen oxide-containing stream is the oxidation of NO to NO ₂ .

In step f) the first nitrogen oxide-containing stream - and, if step c) is carried out, according to embodiment II. also the third nitrogen oxide containing stream - as well as the oxidized second nitrogen oxide containing stream from step e) are contacted with an aqueous wash phase to obtain a pre-purified gas stream and a nitric acid-rich wash phase. In this operation, in particular from the nitrogen oxide-containing streams of steps a) and c) or from the oxidized nitrogen oxide-containing stream from step e), NO _{2 is} removed.

During the reaction of NO ₂ with the aqueous wash phase, nitric acid is formed and thus the concentration of HNO _{3 of the} aqueous wash phase is continuously increased during the purification of the NO _2- containing stream until the desired final concentration is reached. The final concentration of HNO ₃ is preferably 10 to 67 wt. %, more preferably from 20 to 67 wt. %. When the desired final concentration of HNO _{3 is} reached, the nitric acid formed is removed from the flush loop and replaced with water or nitric acid below the desired final concentration of HNO ₃ .

The pre-purified gas stream obtained according to step f) of the process according to the invention contains, for example, not more than 50%, preferably less than 30%, more preferably less than 15% of the original NO ₂ fraction present before step f). The NO present in the streams used in step f) dissolves in the aqueous phase to a much lesser extent than NO ₂ , but the NO content changes even during purification, in part through equilibrium reactions or oxidation. N ₂ O is soluble in the aqueous phase to a significantly lower degree than NO ₂ . The effect of cleaning on the N ₂ O concentration of the gas stream is generally very small.

Stage g) is preferably carried out in the presence of one or more catalysts. Relevant processes are fairly well known to those skilled in the art as DeNOx processes or even SCR (Selective Catalytic Reduction) or NSCR (Non Selective Catalytic Reduction) processes. Also known is a process for the thermal decomposition of dinitrogen monoxide called the DeN2O® process.

The pre-purified gas stream is here mainly in contact with ammonia or a chemical compound that decomposes to form ammonia, for example urea, in the presence of one or more catalysts, which may optionally be supported on at least one support. The catalysts generally include titanium dioxide, vanadium pentoxide and tungsten oxide and / or zeolites and / or platinum and / or oxides of other metals. Nitrous gases and ammonia react here in a coproportionation reaction with the formation of nitrogen and water, or with the formation of nitrogen, carbon dioxide and water in the case of using urea, rather than ammonia. At the same time, depending on the catalyst used, dinitrogen monoxide is thermally decomposed into nitrogen and oxygen (decomposition catalysis). However, dinitrogen monoxide can also be decomposed thermally without a catalyst before or after the removal of other nitrogen oxides. For this purpose, dinitrogen monoxide can be heated indirectly or directly to the desired temperature. Direct heating takes place by burning carbonaceous fuels such as natural gas or gasoline in the presence of waste gas containing dinitrogen monoxide. In this case, carbon dioxide and nitrogen are formed directly. Stage g) is preferably carried out in one stage and in the presence of at least one catalyst and in the presence of ammonia or at least one chemical compound which decomposes to form ammonia, for example urea. At this stage, the temperature of the pre-purified gas stream rises to a temperature of from 250 to 500 ° C, more preferably from 300 to 450 ° C.

In another embodiment, step g) is carried out in two steps. In this case, the pre-purified gas stream from stage f)

i) heated to a temperature of from 250 to 500 ° C, more preferably from 300 to 450 ° C, and further

ii) heated to a temperature of 800 to 1400 ° C.

In this case, there is a catalytic reaction DeNOx, in which nitrogen oxides such as nitrogen monoxide and nitrogen dioxide are decomposed, and in the second stage, non-catalytic thermal decomposition of dinitrogen monoxide occurs.

In step h) of the process according to the invention, mainly iron-containing compounds, for example, iron salts, especially iron (II) salts, and / or nitrogen-containing compounds, for example, ammonia compounds, nitrate compounds or nitrite compounds, and / or sulfur-containing compounds, for example, sulfate compounds are removed from the aqueous phase from step d), for example, by oxidative precipitation and / or denitration and / or coagulation and / or flocculation and / or precipitation and / or filtration and / or ultrafiltration and / or reverse osmosis. The treated waste water can be used again for chemical operations in reactors or for other stages, for example, as wash water for filtration operations.

For these purposes, the waste water from step d) of the process according to the invention is denitrized and / or subjected to at least one coagulation step and / or undergoes at least one flocculation step and / or undergoes at least one precipitation step and / or undergoes at least one stage of filtration and / or is subjected to at least one stage of ultrafiltration and / or further purified by at least one stage of reverse osmosis.

The removal of ammonia compounds, nitrite compounds and nitrate compounds from the aqueous phase from step d) can take place in different ways, such as by biological denitration or by a process known as the Anammox process.

In the case of biological denitration, nitrate compounds dissolved in waste water are reduced to molecular nitrogen under anaerobic conditions, i.e. with the exclusion of oxygen through specific microorganisms. One particular biological denitration option is the Anammox process, in which microorganisms absorb the carbon required for denitration in the form of carbon dioxide. In other processes, microorganisms must be provided with other carbon sources, for example, alcohols such as methanol or ethanol.

Ammonia compounds and nitrite compounds dissolved in waste water can be additionally oxidized to nitrate compounds (nitrification) under aerobic conditions, i.e. in the presence of oxygen, through specific microorganisms. The stages of nitrification (aerobic) and denitrification (anaerobic) can be combined. For this purpose, they can be carried out one after the other, in which case nitrification can take place after denitrification and / or denitrification can take place after nitrification. In preferred embodiments, the nitrification and denitrification steps are carried out sequentially several times. This has the advantage that, as a result, the amount of nitrogen compounds dissolved in the waste water can be further reduced.

This step is preferably followed by at least one coagulation and at least one flocculation. In this case, the solids suspended in the waste water preferably aggregate into larger particles and are removed by flocculation. In the flocculation step, chemicals are added to the waste water to help flocculate particles previously coagulated, examples of such chemicals are organic or inorganic polymers. In these stages, the iron ions present in the waste water are also removed by precipitation.

This step is preferably followed by at least one sedimentation in which the particles, which are flocculated, settle to the bottom of the suspension and can be removed continuously or intermittently. The sludge thus separated can be compressed, dried and then sent for recycling.

This step is preferably followed by at least one filtration. In this case, the aqueous phase of the waste water treated in this way is filtered through one or more stages. This step is preferably followed by at least one ultrafiltration, in which specific membranes separate particles in the range from 0.1 to 0.001 μm - for example, high molecular weight substances, colloidal substances, polymeric substances - from the aqueous phase.

This step is preferably followed by at least one reverse osmosis. Here, ions or larger molecules are held on semi-permeable membranes so that only water in a nearly pure form passes through the semi-permeable membrane. In the process according to the invention, reverse osmosis preferably separates salts from waste water, for example phosphates, chlorides and / or sulfates, which after reverse osmosis are located in the salt-rich waste water. In one preferred embodiment, if step c) and / or step d) is carried out using sulfate salts, the salt-rich waste water is returned to step c) and / or step d). This is the advantage that the sulfate present in the process is reused to a large extent and there is no need to introduce sulfate into the process as an external raw material.

The waste water purified in stage h) of the process according to the invention can be reused for chemical operations in reactors or for other stages, for example as wash water for filtration operations. As an alternative to wastewater treatment, wastewater from step d) containing the recited ammonia compounds, nitrite compounds and nitrate compounds can be tried on alone or in admixture as fertilizer optionally with other suitable components and / or after concentration by reverse osmosis or evaporation.

In a further preferred embodiment of the process according to the invention in step j), for preheating the pre-purified gas stream from step f), a heated pre-purified gas stream obtained after step g) is used with temperatures generally from 200 to 1400 ° C, preferably from 250 up to 500 ° C, in the case of carrying out stage g) in the presence of at least one catalyst, or preferably from 800 to 1400 ° C, in the case of carrying out stage g) in the absence of a catalyst.

The invention further encompasses a plant suitable for carrying out the process according to the invention. This setting is explained in more detail below using shapes:

Figure 1 shows an illustration of a simple plant according to the invention comprising three reactors, an oxidation plant, a scrubber, a heater and an exhaust gas purification unit.

Figure 2 shows an illustration of an installation according to the invention, which, in comparison with Figure 1, additionally comprises an additional scrubber, a heat exchanger and a waste water treatment unit.

Figure 2a shows an illustration of a plant according to the invention which, in contrast to Figure 2, comprises a separate separating device 34 between the reactor 3 and the waste water treatment unit 10.

Figure 3 shows a typical embodiment of reactor 1.

Figure 4 shows a typical embodiment of reactor 2.

Figure 5 shows a typical embodiment of reactor 3.

Figure 6 shows a typical embodiment of the separating device 34.

Figures 7 and 7a show typical embodiments of the oxidation unit 5.

Figures 8 and 8a show typical embodiments of a scrubber 4 or 6.

Figure 9 shows a typical embodiment of a heat exchanger 7.

Figure 10 shows a typical embodiment of a heater 8.

Figures 11, 11a and 11b show typical embodiments of an exhaust gas purification unit 9.

Figure 12 shows a typical embodiment of a wastewater treatment unit 10.

The symbols in the figures are as follows:

A gas containing oxygen

AQ-1 waste water from hematite pigment slurry production

AQ-2 Purified waste water obtained from biological wastewater denitration AQ-1

AQ-3 Purified waste water from coagulation, flocculation and / or sedimentation of waste water AQ-2

AQ-4 salt-enriched waste water

AQ-EX treated waste water

Fe iron

AQ-Fe (NO ₃ ) ₂ iron (II) nitrate solution

P-Fe ₂ O ₃ pigment

S-Fe ₂ O ₃ suspension of hematite cores

PAQ-Fe ₂ O ₃ hematite pigment suspension

G-1 purified waste gas

G-EX cooled cleaned waste gas

H ₂ O water

HNO ₃ nitric acid

L-1 to L-x lines 1 to x

NOX-1 first stream containing nitrogen oxide (waste gas from the preparation of iron (II) nitrate solution)

NOX-2 first stream containing nitrogen oxide (waste gas from the production of a suspension of hematite cores)

NOX-2-OX oxidized second nitrogen oxide-containing stream (oxidized waste gas from the production of hematite core slurry)

NOX-3 third stream containing nitrogen oxide (waste gas from the production of hematite pigment slurry)

NOX-4 pre-treated gas stream (waste gas from cleaning NOX-1, NOX-2-OX and NOX-3)

NOX-5 preheated pre-treated gas stream (waste gas from preheating NOX-4)

NOX-6 heated pre-treated gas stream (waste gas from heating NOX-4 or NOX-5)

NOX-7 NOX-6 enriched with U

OXM oxidizer

U ammonia or urea

WP water wash phase

WP-1 HNO-enriched ₃ rinsing phase WP

1 reactor for obtaining a solution of iron (II) nitrate

11 reaction vessel

12 stirrer

13 cooling block

111 inlet for iron, HNO ₃ and H ₂ O

112 outlet for NOX-1

113 outlet for iron (II) nitrate solution

2 reactor for obtaining a suspension of hematite nuclei

21 reaction vessels

22 stirrer

23 cooling block

24 heater

211 inlets for iron, HNO ₃ and H ₂ O

212 outlet for NOX-2

213 outlet for suspension of hematite cores

3 reactor for obtaining a suspension of hematite pigment

31 reaction vessels

32 stirrer

33 heater

34 separating device

311 inlet for a solution of iron (II) nitrate, a suspension of hematite cores, oxygen-containing gas and water

312 outlet for NOX-3

313 hematite pigment suspension outlet

341 hematite pigment slurry inlet

342 separation kit

343 hematite pigment outlet

344 waste water outlet AQ-1

4 scrubber

41 absorption columns

42 valve

411 inlet for NOX-1, NOX-3 and / or NOX-2-OX

412 inlet for water rinsing phase WP

413 outlet for NOX-4

414 outlet for HNO _3- enriched flushing phase WP-1

5 oxidation block

51 inlet for NOX-2

52 outlet for NOX-2-OX

53 drying plant

54 oxidation catalyst

55 oxidizer inlet

56 oxidizing vessel

6 scrubber

61 absorption columns

62 valve

611 NOX-1, NOX-3 and / or NOX-2-OX

612 inlet for water rinsing phase WP

613 outlet for NOX-4

614 outlet for HNO _3- enriched flushing phase WP-1

7 heat exchanger

71 inlet for NOX-4

72 outlet for NOX-5

73 inlet for G-1

74 outlet for G-EX

8 heater

81 inlet for NOX-4 or NOX-5

82 outlet for NOX-6

83 heating chamber

84 heating element

9 block for cleaning waste gas

91 evaporator

92 reactor

911 inlet for NOX-6

912 inlet for U

913 liquid distributor

914 outlet for NOX-7

921 inlet for NOX-6 or NOX-7

922 catalyst

923 catalyst

924 outlet for G-1

10 block for purification of waste water

101 biological denitration units

102 block for coagulation / flocculation / sedimentation

103 filtration / ultrafiltration / reverse osmosis unit

1011 inlet for AQ-1

1012 outlet for AQ-2

1021 inlet for AQ-2

1022 outlet for AQ-3

1031 inlet for AQ-3

1032 outlet for AQ-EX

One embodiment of the installation according to the invention includes at least

- at least one reactor (1) and

- at least one reactor (2), at least one reactor (3),

- at least one scrubber (4), preferably two scrubbers (4 and 6), where

(a) at least one reactor (1) is connected via at least one line (L-3a) to at least one scrubber (4) or (6), and

(b) at least one reactor (3) is connected via at least one line (L-3b) to at least one scrubber (4) or (6), and

(c) at least one reactor (2) is connected through at least one line (L-4) to at least one oxidation unit (5), and at least one oxidation unit (5) is connected through at least one line (L-5) with at least one scrubber (4) or (6), and

- at least one waste water treatment unit (10), and at least one heater (8), at least one waste gas treatment unit (9), connected through at least one line (L-8) along with at least one heater (8), and at least one heater (8) connected through at least one line (L-7) to at least one scrubber (4) or (6).

In addition to the plant described above, one alternative embodiment of the plant according to the invention includes at least one waste water treatment unit (10), which is connected via at least one line (L-10) to at least one reactor (3 ) or with at least one separating device (34).

In addition to one of the plants described above, one alternative embodiment of the plant according to the invention includes at least one heat exchanger (7), preferably a heat exchanger (7), which is connected via at least one line (L-6a) to at least one scrubber (4), through at least one line (L-6b) with at least one scrubber (6), through at least one line (L-7) with at least one heater (8) and at least through one line (L-9) with at least one waste gas treatment unit (9).

In addition to one of the above-described installations, one alternative embodiment of the installation according to the invention includes at least one separating device (34), preferably a filtering device (34), which is connected via at least one line (L-10) at least with one unit for waste water treatment (10) and through at least one line (L-32) with at least one reactor (3).

The individual block and process steps carried out in this document are described in detail below.

It may be noted at this point that the scope of the invention encompasses all desirable and possible combinations of plant embodiments given below, including their preferred ranges, in combination with any combination of the above process according to the invention and its preferred embodiments.

In at least one reactor 1, in step a), a solution of iron (II) nitrate is obtained by reacting iron with nitric acid to obtain a first nitrogen oxide-containing stream.

As at least one reactor 1, it is possible to use reactors of the type widely known to those skilled in the art for such types of interactions. Reactors 1 for reacting iron with nitric acid to produce an aqueous solution of iron (II) nitrate mainly include reaction vessels made of materials that are resistant to the starting materials iron and nitric acid, as well as to the reaction products of iron nitrate and nitrogen oxides. The simplest reactors can be, for example, vessels with fixed walls or lined with tiles and installed in the ground. Reactors also encompass, for example, reaction vessels made of glass, nitric acid-resistant plastics such as polytetrafluoroethylene (PTFE), for example, steel, enamelled steel, plastic-coated or lacquered steel, and stainless steel, for example with code material 1.44.01. The reaction vessels are preferably vessels made of stainless steel, enamelled steel, more preferably stainless steel material code 1.44.01. The reaction vessels can be open or closed. In preferred embodiments of the invention, the reaction vessels are closed. Reaction vessels are generally designed for temperatures between 0 and 150 ° C and for pressures from 0.05 MPa (0.05 megapascals corresponds to 0.5 bar) to 1.5 MPa (1.5 megapascals corresponds to 15 bar).

One preferred embodiment of reactor 1 is shown in Figure 3. Reactor 1 comprises at least a reaction vessel 11, a mixer 12, a cooling block 13, an inlet 111 for HNO ₃ and iron, an outlet 112 for a first nitrogen oxide-containing stream NOX-1, and outlet 113 for iron (II) nitrate solution AQ-Fe (NO ₃ ) ₂ . Alternatively, the inlet 111 and / or the outlet 112 and / or the outlet 113 in the reaction vessel 11 can also be designed to be provided with the same orifice, one inlet for each individual reactant and / or product, or any the desired combination. In the preferred embodiment of Figure 3, mixer 12 and cooling block 13 are connected via line L-11, in which the iron (II) nitrate solution is circulated, to the reaction vessel 11. In another preferred embodiment, the mixer 12 can also take the form of a mechanical stirrer, for example , propeller stirrer, in the reaction vessel 11. In a further preferred embodiment, the cooling unit 13 can be implemented directly in the reaction vessel 11, for example, in the form of a cooling jacket or in the form of a cooling coil.

The text below describes the implementation of step a) of the process according to the invention by way of example in the reactor 1. To carry out step a) of the process according to the invention, the starting materials iron, water and HNO ₃ are introduced into the reaction vessel 11 through the inlet 111. When the liquid phase is in contact with iron, an exothermic reaction begins. Mainly iron and water are charged into the reactor. Nitric acid can be added quickly if exothermic reaction allows, or over a period of up to 10 hours. The reaction temperature is here maintained at or less than 60 ° C. by means of a cooling device 13. At the same time, the liquid phase is stirred by means of a stirrer 12 to obtain a uniform distribution of the liquid phase around the iron. Stirrer 12 serves to generate turbulence in the liquid phase of the reaction mixture, and is basically a pump that circulates the solution of iron nitrate AQ-Fe (NO ₃ ) ₂ or a mechanical stirrer that mixes the liquid phase, for example, using a propeller. The conversion is determined by the amount of HNO ₃ in relation to iron. The solution of iron (II) nitrate AQ-Fe (NO ₃ ) ₂ , thus obtained temporarily, is either stored in a vessel or for back-up storage or for sedimentation (not shown in FIG. 1 or 2) and / or transferred directly to at least one reactor 3, preferably via line L-1, which is connected to inlet 311.

In reactor 2, in step b), an aqueous slurry of hematite cores is obtained by reacting iron with nitric acid to produce a second nitrogen oxide-containing stream.

As at least one reactor 2, it is possible to use reactors of the type well known to those skilled in the art for similar types of reactors. The reactors 2 generally contain one or more reaction vessels made and materials that are resistant to the feedstock. The simplest reaction vessels can be containers having, for example, fixed walls or tiles and set in the ground. Reactors are also vessels, for example made of glass, nitric acid-resistant plastics such as polytetrafluoroethylene (PTFE), for example, steel, for example, steel, enamelled steel, plastic-coated or lacquered steel, or stainless steel, for example, with material code 1.44.01. The reaction vessels can be open or closed. In preferred embodiments, the reaction loans are closed. Reaction vessels are generally designed for temperatures between 0 and 150 ° C and for pressures from 0.05 MPa (0.05 megapascals corresponds to 0.5 bar) to 1.5 MPa (1.5 megapascals corresponds to 15 bar).

One preferred embodiment of reactor 2 is shown in Figure 4. Reactor 2 comprises at least a reaction vessel 21, a stirrer 22, a cooling block 23, a heater 24, an inlet 211 for Fe and HNO ₃ , an outlet 212 for a second nitrogen oxide containing NOX stream. -2, as well as the outlet 213 for a suspension of hematite cores S-Fe ₂ O ₃ . In one alternative embodiment, inlet 211 and / or outlet 212 and / or outlet 213 may also be designed to be provided with the same orifice, one inlet or outlet for each individual reactant or product, or any desired. combination. In a preferred embodiment according to Figure 4, the agitator 22, the cooling block 23 and the heater 24 are connected via a line L-21, in which the hematite core slurry circulates, to the reaction vessel 21. In a further preferred embodiment, the agitator 22 can also be implemented in the form of a mechanical agitator, for example, in the form of a propeller agitator, in the reaction vessel 11. In a further preferred embodiment, the cooling unit 23 and / or the heater 24 can be realized directly in the reaction vessel 11, for example, in the form of a cooling jacket and / or heating jacket or by direct introduction of a stream or the form of a cooling cartridge or heating cartridge, or direct injection of cold or hot water. In the following, this document describes the implementation of step b) of the process according to the invention by way of example in the reactor 2. To carry out step b) of the process according to the invention, the feedstock iron, water and HNO ₃ are introduced into the reaction vessel 21 through the inlet 211. Here, the reaction is carried out as observed above under the conditions of step b). By means of the heater 24, the reaction mixture consisting of iron and water is heated to the desired reaction temperature (in this respect, see observations under the conditions of step b) of the process according to the invention). When the desired initial temperature has been reached, HNO _{3 is} added in the manner described under the conditions of step b), initiating an exothermic reaction which causes an additional increase in the temperature of the reaction mixture. In another preferred embodiment, at the same time, the liquid phase is stirred by means of a stirrer 22 to obtain a uniform distribution of the liquid phase around the iron. Stirrer 22 serves to generate turbulence in the liquid phase of the reaction mixture, and is basically a pump that circulates a suspension of hematite cores S- (Fe ₂ O ₃ ) or a mechanical agitator that mixes the liquid phase, for example, using a propeller. The degree of conversion is determined by the amount of HNO ₃ in relation to iron and by the temperature profile during the reaction. During the interaction, a steady drop in the concentration of HNO ₃ is observed. The suspension of hematite cores S- (Fe ₂ O ₃ ) thus obtained is either temporarily stored in a vessel or for back-up storage or for sedimentation (not shown in FIG. 1, 2 or 4) through the outlet 213, and / or transferred directly through outlet 213 to reactor 3, preferably via line L-2, which connects to inlet 311. Unreacted iron remains in reaction vessel 21 until the next reaction when water and fresh iron are added again.

In at least one reactor 3 in step c), an aqueous suspension of hematite pigment is obtained by

I. interaction of an aqueous suspension of hematite cores from step b) with a solution of iron (II) nitrate from step a) and at least one alkaline precipitant in the presence of at least one oxygen-containing gas, or by

II. reacting an aqueous slurry of hematite cores from step b) with an iron (II) nitrate solution from step a) and iron and at least one oxygen-containing gas to form a third nitrogen oxide-containing stream.

As at least one reactor 3, it is possible to use reactors of the type well known to those skilled in the art for similar types of reactions. The reactors 3 generally contain one or more reaction vessels made and materials that are resistant to the feedstock. The simplest reaction vessels can be containers having, for example, fixed walls or tiles and set in the ground. Reactors are also vessels, for example made of glass, nitric acid-resistant plastics such as polytetrafluoroethylene (PTFE), for example, steel, for example, steel, enamelled steel, plastic-coated or lacquered steel, or stainless steel, for example, with material code 1.44.01. The reaction vessels can be open or closed. In preferred embodiments, the reaction vessels are closed. Reaction vessels are generally designed for temperatures between 0 and 150 ° C and for pressures from 0.05 MPa (0.05 megapascals corresponds to 0.5 bar) to 1.5 MPa (1.5 megapascals corresponds to 15 bar).

One preferred embodiment of the reactor 3 is shown in Figure 5. The reactor 3 comprises at least a reaction vessel 31, a stirrer 32, a heater 33, an inlet 311 for a solution of iron (II) nitrate, a suspension of hematite cores, an oxygen-containing gas and water, an outlet 312 for the third nitrogen oxide-containing stream NOX-3, and an outlet 313 for the hematite pigment slurry. In one alternative embodiment, the inlet 311 and / or the outlet 312 and / or the outlet 313 in the reaction vessel 311 can also be designed to be provided with the same orifice, one inlet or outlet for each individual reactant or product. or any combination you desire. In a preferred embodiment according to Figure 5, agitator 32 and heater 33 are connected via line L-31, in which the hematite pigment suspension circulates, to the reaction vessel 31. In another preferred embodiment, the agitator 32 can also take the form of a mechanical agitator, for example a propeller agitator. in the reaction vessel 31. In a further embodiment, the heater 33 can be implemented directly in the reaction vessel 31, for example in the form of a heating jacket, heating cartridge and / or heating coil, or by direct steam injection by direct supply of hot water.

The following describes the implementation of step c) of the process according to the invention by way of example in reactor 3. To carry out step c) of the process according to the invention, in the "acid precipitation" embodiment, the starting materials iron, water, iron (II) nitrate solution and a suspension of hematite cores are introduced into the reaction vessel 31 through inlet 311. A heater 33 heats the reaction mixture to a temperature of from 70 to 100 ° C, preferably from 75 to 90 ° C (in this regard, see observations under the conditions of step c) of the process according to the invention). At the same time, by oxidation with 0.2 to 50 liters of air per hour and per liter of suspension, hematite is deposited on the hematite cores and coarsens during the interaction until the red iron oxide pigment reaches the desired color shade ("acid precipitation" embodiment). In another preferred embodiment, at the same time, the liquid phase is agitated by means of a stirrer 32, obtaining a uniform distribution of the liquid phase, which, as the reaction proceeds more and more, contains suspended hematite pigments around the iron. Stirrer 32 serves to generate turbulence in the liquid phase of the reaction mixture, and is basically a pump that circulates a suspension of hematite pigment PAQ-Fe ₂ O ₃ or a mechanical agitator that mixes the liquid phase, for example, using a propeller. The PAQ-Fe ₂ O ₃ hematite pigment suspension thus obtained is either temporarily stored in a vessel or for back-up storage or for sedimentation (not shown in Figure 1, 2, 6 or 6), and / or transferred directly to the separating device 34 via the outlet 313 through a line L-32 that connects to the inlet 341.

In at least one separating device 34 in step d) the hematite pigment present in the aqueous hematite pigment suspension is separated from the aqueous phase, preferably by filtration and / or precipitation of the hematite pigment suspension and / or washing the filter cake obtained by filtration and / or precipitation ...

As the at least one separating device 34 it is possible to use devices of a type well known to those skilled in the art for such separation stages. The separating device 34 can be implemented directly in the reactor 3 or as a separate device. If the separating device 34 is implemented as a separate unit, it is connected via line L-32 to the reactor 3 (see also Figure 2a).

A preferred embodiment of the separating device 34 is shown in Figure 6. The separating device 34 comprises at least an inlet 341 for a hematite pigment suspension, a separating kit 342, an outlet 343 for a hematite pigment, and an AQ-1 wastewater outlet 344. The constituents of the AQ-1 waste water include nitrate compounds, nitrite compounds and ammonia compounds, and therefore this waste water generally has a total nitrogen content of 0.2 to 10 g / L nitrogen, preferably 0.2 to 5 g / L nitrogen (calculated in each case based on elemental nitrogen). In one alternative embodiment, inlet 341 and / or outlet 343 and / or outlet 344 in separator 34 may also be designed to be provided with the same orifice, one inlet or outlet for each individual reactant and / or product, or any desired combination thereof. In a further alternative embodiment, the separating device 34 can be integrated in one piece in the reactor 3; in this case, line L-10 connects directly to reactor 3 (as also shown in Figure 2).

The following describes the implementation of step d) of the process according to the invention by way of example on a separating device 34.

To carry out step d) of the process according to the invention, the hematite pigment suspension is introduced through inlet 341 into a separating set 342. In this set, the solid constituents are separated from the liquid constituents. Prior to this, it is optionally possible to carry out one or more screening steps, more preferably with different sieve sizes and with decreasing sieve sizes. The separation of the pigment from the liquid phase is carried out, for example, by filtration. The liquid phase is separated, and optionally, the washing liquid obtained after washing the separated solid, referred to collectively hereinafter as waste water AQ-1, is transferred through the outlet 344 to the waste water treatment unit 10 via line L-10. The wet filter cake is removed from the separating set 342 through the outlet 343 and then dried. In an alternative embodiment, the red iron oxide pigment is dried directly in the separating set 342 and then removed in dried form from the outlet 343.

In at least one oxidation unit 5, in step e), the second nitrogen oxide-containing stream from step b) is oxidized.

As the at least one oxidation unit 5, it is possible to use oxidation units of the type well known to those skilled in the art for this type of reaction.

The oxidation unit 5 for oxidizing nitrogen oxides mainly comprises pipelines or an oxidizing vessel in which the gas phase containing the gas to be oxidized is brought into contact with an oxidizing agent, optionally using one or more catalysts and / or high energy radiation, for example UV radiation, an inlet for a second nitrogen oxide-containing stream, an inlet for an oxidant, an outlet for an oxidized second stream, optionally a source of high energy radiation, such as a UV lamp, and / or optionally at least one catalyst. Oxidants are mainly air or other oxygen-containing gases, ozone or hydrogen peroxide. Air is preferred. The oxidation catalysts are mainly activated carbon, silica gel, molecular sieves, vanadium-zinc or chromium-zinc catalysts, or titanium dioxide. In a further preferred embodiment, one or more UV lamps located within the oxidation vessel can accelerate oxidation. The oxidation units 5 are preferably conduits, more preferably in spiral embodiments, in which the UV radiation sources are positioned such that the stream to be oxidized is in contact with the UV light source as intensely and for as long as possible.

Preferred embodiments of the oxidation unit 5 are shown in Figures 7 and 7a. Oxidation unit 5 comprises at least an inlet 51 for a second nitrogen oxide-containing stream, an outlet 52 for an oxidized second nitrogen oxide-containing stream NOX-2, an oxidant inlet 55, and an oxidation vessel 56. The oxidation unit 5 optionally further comprises an emitting unit 53 , preferably a UV emitting unit and / or one or more oxidation catalysts 54. In one alternative embodiment, inlet 51 and / or inlet 55 and / or outlet 52 in reaction vessel 56 may also be designed to be the same the same hole, one inlet or outlet for each individual reagent or product, or any desired combination thereof.

The following describes the implementation of step e) of the process according to the invention by way of example on the oxidation unit 5. To carry out step e) of the process according to the invention, the second nitrogen oxide-containing stream NOX-2 from the reactor 2 is transferred to the oxidation unit 5 through the outlet 212 via line L-4, which connects to inlet 51. Oxidation of the second nitrogen oxide-containing stream NOX-2 takes place in an oxidation vessel 56. For oxidation, it is advantageous to have a second nitrogen oxide-containing stream NOX-2 with a temperature of 20 to 300 ° C. Either the stream to be oxidized is brought to the required temperature for oxidation by heating, or the stream to be oxidized is actually already at the required temperature as a result of the previous process step. Oxidation is usually carried out under atmospheric pressure, but it can also be accelerated by increased gas pressure in the oxidizer. In general, the oxidation is carried out at pressures from 0.08 MPa to 2 MPa, preferably from 0.08 MPa to 1 MPa. Through inlet 55, the oxidant enters the oxidation vessel 56. During the oxidation of NO in the second nitrogen oxide-containing stream, NOX-2 is oxidized to NO2, giving an oxidized second nitrogen oxide-containing stream NOX-2-OX. After oxidation, the oxidized second nitrogen oxide containing stream NOX-2-OX moves from outlet 52 through line L-5, which connects to inlet 41 or 61, to scrubber 4 or 6 (see Figure 1).

In at least one scrubber 4 and / or 6 according to step f), the first nitrogen oxide-containing stream and, when step c) was carried out according to variant II., Also the third nitrogen oxide-containing stream as well as the oxidized second nitrogen oxide-containing stream from step e ) contact with an aqueous wash phase to generate a pre-purified gas stream and a wash phase enriched in nitric acid.

As at least one scrubber 4 and / or 6, it is possible to use scrubbers of the type well known to those skilled in the art for similar waste gas purification steps. Scrubbers 4 or 6 comprise at least one inlet for a first nitrogen oxide containing stream and / or for an oxidized second nitrogen oxide containing stream and / or for a third nitrogen oxide containing stream, an inlet for an aqueous scrubbing phase, an outlet for an enriched HNO ₃ a flushing phase and an outlet for a pre-purified gas stream.

Scrubbers 4 or 6 are generally scrubbers in which the gas phase is in contact with a liquid phase, preferably an aqueous scrubbing phase. One of the components of the gas phase is gas, which must be removed from the gas phase. The gas to be removed dissolves well in the liquid phase or reacts with the liquid phase to form a dissolved reaction product. The liquid phase is mainly water, aqueous solutions of hydroxides of alkali metals and alkaline earth metals, dilute hydrogen peroxide solution or nitric acid.

The liquid phase is either at the bottom of the scrubber or is introduced into the interior of the scrubber in such a way as to greatly increase the surface area of the liquid phase, for example, by spraying or spraying. Examples of such scrubbers are spray scrubbers, spray condensation scrubbers, crossflow scrubbers or counterflow scrubbers. If the liquid phase is at the bottom of the scrubber, the gas phase is introduced into the liquid phase so that the gas phase has a maximum contact area, for example, by introduction using a special nozzle or by substantially mixing the two phases. Examples of such scrubbers are packed scrubbers.

Preference is given to scrubbers 4 and / or 6 which operate with a neutral medium such as water or an acidic medium such as nitric acid or mixtures thereof as the aqueous phase. This is the advantage that nitrogen dioxide or dinitrogen pentoxide produces nitric acid that can be recycled to the process.

Preferred embodiments of the scrubber 4 or 6 are shown in Figures 8 and 8a. In one embodiment, scrubbers 4 or 6 comprise at least one inlet for a first nitrogen oxide containing stream and / or for an oxidized second nitrogen oxide containing stream and / or for a third nitrogen oxide containing stream, a scrubber column, an inlet for an aqueous wash phase , an outlet for a nitric acid-rich wash phase and an outlet for a pre-purified gas stream. A further embodiment of the scrubber 4 or 6 further comprises a control valve which is connected to the inlet of the aqueous wash phase and to the outlet for the nitric acid-rich wash phase.

The following describes the implementation of step f) of the process according to the invention in a scrubber 4 or 6. The aqueous wash phase WP is introduced through inlet 412 or 612 into the scrubber column 41 or 61, where it is well distributed by means of suitable devices over the interior of the scrubber column 41 or 61. First nitrogen oxide-containing stream NOX-1 and / or oxidized second nitrogen oxide-containing stream NOX-2-OX and / or third nitrogen oxide containing stream NOX-3 are introduced through inlet 411 or 611 into scrubber column 41 or 61, where they contact water wash phase WP. The nitric acid-enriched wash phase WP-1, obtained after contact of the nitric acid-containing streams NOX-1, NOX-2-OX and / or NOX-3, is either transferred through the line to the vessel and / or transferred again as an aqueous wash phase WP through an inlet 412 or 612 to the scrubber column, where it is once again in contact with the NOX-1, NOX-2-OX and / or NOX-3 containing nitrogen oxide streams. This results in a continuous increase in the nitric acid content of the nitric acid-rich wash phase WP-1 until the content reaches the desired value. Then, in a further preferred embodiment, the washing phase WP-1, thus rich in nitric acid, is recycled according to step i) of the process according to the invention in step a) and / or b) and / or c). In a further preferred embodiment of the process, the nitric acid-rich wash phase WP-1 is stored in one or more vessels until its next use. In a further preferred embodiment of the process, the nitric acid-rich wash phase WP-1 is transferred from the outlet 414 or 614 of the scrubber column 41 or 61 and moves again through line L-41 or L-61 and through inlet 412 or 612 into the scrubber column. The multi-position valve is connected to line L-41 or L-61, which makes it possible to meter the water flush phase WP into line L-41 or L-61, and makes it possible to remove the nitric acid-rich flush phase WP-1 from the line L-41 or L -61. In a further embodiment of the scrubber 4, the inlet 411 and / or the inlet 412 and / or the outlet 413 and / or the outlet 414 can also be designed to be formed with the same opening, one inlet or outlet for each individual reagent or product; or any desired combination thereof. In a further embodiment of the scrubber 6, the inlet 611 and / or the inlet 612 and / or the outlet 613 and / or the outlet 614 can also be designed to be provided with the same opening, one inlet or outlet for each individual reagent or product; or any desired combination thereof.

After flushing, in one embodiment, the pre-purified NOX-4 gas stream is transferred from outlet 413 or 613 through line L-7, which connects to inlet 81, to heater 8 (see Figure 1). In a further embodiment, the pre-purified gas stream NOX-4, after flushing, is transferred from outlet 413 or 613 through line L-6a or L-6b, which connects to inlet 71, to heat exchanger 7 (see Figure 2).

In one preferred embodiment, the heat exchanger 7 is connected between the scrubbers 4 and / or 6 and the heater 8.

In the heat exchanger 7, in step g) i) in a preferred embodiment of the process according to the invention, the pre-purified gas stream is preheated to a temperature of from 250 to 500 ° C, more preferably from 300 to 450 ° C.

As the at least one heat exchanger 7, it is possible to use heat exchangers of a type well known to those skilled in the art for such technological stages. The at least one heat exchanger 7 comprises at least one inlet for a pre-cleaned gas stream, an outlet for a pre-heated pre-cleaned gas stream, an inlet for a cleaned waste gas, and an outlet for a cooled cleaned waste gas.

Heat exchangers 7 are generally devices in which there is heat transfer from a stream with a higher temperature to a stream with a lower temperature and vice versa. This heat transfer can be direct, indirect, or semi-indirect. A typical example of direct heat transfer is, for example, a cooling tower. A typical example of indirect heat transfer is, for example, a recuperator. A typical example of semi-indirect heat transfer is, for example, a rotary heat exchanger. The heat exchangers used are mainly tube or plate type heat exchangers. In such heat exchangers, the geometrical flow of the various flows can be counter-flow, co-flow or cross-flow.

One preferred embodiment of the heat exchanger 7 is shown in Figure 9. The heat exchanger 7 comprises at least an inlet 71 for a pre-treated NOX-4 gas stream, an outlet 72 for a pre-heated pre-treated NOX-5 gas stream, an inlet 73 for a purified waste gas G-1 and outlet 74 for cooled purified waste gas G-EX.

The following describes the implementation of step g) i) of the process according to the invention by way of example on a heat exchanger 7. The pre-purified gas stream NOX-4 moves from the outlet 413 of the scrubber 4 and / or the outlet 613 of the scrubber 6 through at least one line L-6a and / or L-6b to the inlet 71 in the heat exchanger 7. In the heat exchanger 7, heat from the cleaned waste gas G-1, which moves from the outlet 924 of the waste gas cleaning device 9 (a detailed description of this waste gas cleaning device 9 follows or below) through line L-9 to the inlet 73 of the heat exchanger 7, is used to heat the pre-purified NOX-4 gas stream. The pre-treated gas stream, thus pre-heated, NOX-5, leaves the heat exchanger 7 through the outlet 72 and moves through the line L-7 to the inlet 81 of the heater 8. As a result of the passage of heat from the purified waste gas G-1 to the pre-treated gas stream NOX-4, the purified exhaust gas G-1 is cooled and leaves the heat exchanger 7 through the outlet 74 as cooled purified exhaust gas G-EX, which can then be discharged into the ambient air, preferably through a pipe.

In at least one heater according to step g), the pre-purified gas stream from step f) is heated to a temperature of 200 to 1400 ° C. In this regard, a certain amount of nitrogen oxides, preferably dinitrogen monoxide, has already been removed from the previously purified gas stream.

As the at least one heater 8, it is possible to use heaters of a type well known to those skilled in the art for such steps.

Heaters are mainly devices that raise the temperature of the flow. The stream can be heated directly or indirectly. An example of direct heating is a gas fan burner in which hot combustion gases cause direct heating of the gas stream mixed therewith. The indirect heating device is, for example, an electrical heating element such as a heating coil. Heaters 8 generally comprise at least one inlet for a pre-purified gas stream, an outlet for a pre-heated pre-purified gas stream, a heating chamber and at least one heating element, preferably a fan burner.

One preferred embodiment of the heater 8 is shown in Figure 10. The heater 8 comprises at least one inlet 81 for a pre-purified NOX-4 gas stream or a pre-heated pre-purified NOX-5 gas stream, at least one outlet 82 for a pre-heated purified gas stream NOX-6, at least one heating chamber 83 and at least one heating element 84, preferably a gas fan burner.

The heating of the pre-purified gas stream to a temperature of 200 to 1400 ° C in accordance with step g) of the process according to the invention by way of example on a heater 8 is described below. (see Figure 1), the pre-treated NOX-4 gas stream is transferred from the outlet 413 and / or 613 of the scrubbers 4 and / or 6 through the line L-7, which is connected to the inlet 81, to the inlet 81 of the heater 8. B In a further embodiment (see Figure 2), the preheated pre-treated NOX-5 gas stream is moved from the outlet 72 of the heat exchanger via line L-7, which connects to the inlet 81, to the inlet 81 of the heater 8. Direct heating of the preheater is preferred. purified gas stream NOX-4 or preheated pre-purified gas stream NOX-5 according to by means of a gas fan burner. The pre-purified NOX-4 gas stream or the pre-heated pre-purified NOX-5 gas stream is heated here to the temperature required in the waste gas purification unit 10, from 250 to 500 ° C in the presence of at least one catalyst and / or from 800 to 1400 ° C in the absence of a catalyst and then in the form of a heated pre-purified gas stream NOX-6, leaves the heater 8 through the outlet 82 and moves through the line L-8 to the inlet 911 of the unit for cleaning waste gas 9.

In at least one waste gas purification unit 9, according to step g), nitrogen oxides are removed from the pre-purified gas stream from step f) by heating to a temperature of 200 to 1400 ° C, optionally in the presence of a catalyst, preferably 250 to 500 ° C in the presence of a catalyst or from 800 to 1400 ° C in the absence of a catalyst, obtaining a purified gas stream.

As at least one treatment gas purification unit 9, it is possible to use treated gas purification units well known to those skilled in the art for such purification operations.

The treated gas purification units 9 are generally devices that remove unwanted gaseous substances such as nitrous gases, for example, by catalytic reduction and / or that remove dinitrogen monoxide by thermal decomposition over one or more catalysts. These treated gas treatment units are also called SCR reactors (SCR = Selective Catalytic Reduction).

At least one treated gas purification unit 9 generally comprises at least one reactor, at least one inlet for a heated pre-purified gas stream, at least one catalyst and at least one outlet for a purified gas stream.

In a further preferred embodiment, at least one treated gas purification unit 9 further comprises an evaporator with an inlet for a heated pre-purified gas stream, a liquid distributor for urea and / or ammonia, and an outlet for a heated pre-purified gas stream that is enriched in urea and / or ammonia, and which in this preferred embodiment is connected through a line to the inlet in the reactor.

One preferred embodiment of an exhaust gas purification unit 9 is shown in Figure 11. At least one exhaust gas purification unit 9 comprises at least one reactor 92, at least one inlet 921 for a heated pre-purified NOX-6 gas stream, at least one catalyst 922; and at least one outlet 924 for the purified gas stream G-1. Catalyst 922 can be either a catalyst for the decomposition of nitrous gases and / or for the decomposition of dinitrogen monoxide.

A further preferred embodiment of the waste gas purification unit 9 is shown in Figure 11a. At least one unit for purifying waste gas 9 further comprises an evaporator 91 with an inlet 911 for a heated pre-treated NOX-6 gas stream, an inlet 912 for urea and / or ammonia U, a liquid distributor 913 for urea and / or ammonia U, and an outlet 914 for a heated pre-treated NOX-7 gas stream that is enriched in urea and / or ammonia and is connected via line L-91 to inlet 921 in reactor 92.

A further preferred embodiment of the waste gas purification unit 9 is shown in Figure 11b. At least one unit for purifying waste gas 9 further comprises a catalyst 923. The catalyst 923 can be either a catalyst for the decomposition of nitrous gases and / or for the decomposition of dinitrogen monoxide.

The following describes the execution of step g) of the process according to the invention by way of example using the waste gas purification unit 9 in accordance with Figure 11b. To carry out step g) of the process according to the invention, the heated pre-treated NOX-6 gas stream from the heater 8 is transferred from the outlet 82 through the line L-8 and the inlet 911 to the evaporator 91 of the waste gas purification unit 9. At the same time, through the inlet orifice 912, ammonia or urea U is sprayed through liquid distributor 913 into evaporator 91, and thereby mixed with heated pre-purified NOX-6 gas stream. The ammonia-rich or urea-rich NOX-7 gas stream flows through outlet 914 from evaporator 9 through line L-91 and inlet 921 to reactor 92. Here, the ammonia-rich or urea-rich NOX-7 gas stream contacts catalyst 922 and / or catalyst 923. The amount of nitrous gases and dinitrogen monoxide is reduced in this step, as described above under the conditions of step g). The purified stream G-1 leaves the reactor 92 through outlet 924 and moves through line L-9 and inlet 73 to heat exchanger 7, in which, according to step i) of the process according to the invention, it leaves some of its heat to the pre-purified NOX- gas stream. 4, which as a result becomes preheated. By transferring the heat of the purified waste gas G-1 to the pre-purified gas stream NOX-4, the purified waste gas G-1 is cooled and leaves the heat exchanger 7 through the outlet 74 in the form of cooled purified waste gas G-EX.

The cooled cleaned exhaust gas G-EX that exits the outlet 74 of the heat exchanger 7 contains only a small residual fraction of nitrous gases and dinitrogen monoxide. In addition, most of the heat stored in it is returned back to the process, i.e. to the pre-purified gas stream NOX-4. The cooled, cleaned G-EX flue gas can therefore be vented to the ambient air through a chimney, chimney or other suitable device.

In at least one wastewater treatment unit 10, according to step h), ammonia compounds, nitrite compounds and nitrate compounds are removed from the aqueous phase from step d). As at least one waste water treatment unit 10, it is possible to use waste water treatment units well known to those skilled in the art for such technological stages.

In at least one wastewater treatment unit 10, according to step h), ammonia compounds, nitrite compounds and nitrate compounds are removed from the aqueous phase from step d).

As at least one wastewater treatment unit 10, it is possible to use wastewater treatment units well known to those skilled in the art for such purification stages. At least one wastewater treatment unit 10 comprises at least one biological denitration unit and / or a coagulation unit and / or a flocculation unit and / or a sedimentation unit. Biological denitration units are generally vessels or reservoirs in which the waste water to be treated comes into contact with microorganisms under conditions in which the microorganisms are capable of modifying nitrogen-containing impurities in a desirable manner.

Coagulation units are basically vessels or reservoirs in which waste water to be treated is mixed with coagulants. Coagulants are chemical compounds that neutralize the electrical charge on some of the impurities present in the wastewater. By neutralizing the electrical charge, finely suspended, ground solids are able to adhere to each other. This step requires preferably intensive mixing of the waste water with the coagulants, preferably by means of high-speed stirrers. Coagulants are, for example, aluminum chlorides, aluminum sulfate, sodium aluminate, ferric chloride, ferrous sulfate, calcium hydroxide or cationic polyelectrolytes, preferably polyamines and polyaluminium chlorides.

Flocculation units are basically vessels or reservoirs in which waste water to be treated is mixed with flocculating agents. The flocculating agents are preferably organic or inorganic polymers that promote the flocculation of previously coagulated particles, more preferably polyacryl amides.

Sedimentation units are generally vessels or tanks in which waste water is mixed with flocculating agents for optional purification. The flocculating agents are preferably organic or inorganic polymers that promote the flocculation of previously coagulated particles, more preferably polyacrylamides.

One preferred embodiment of a wastewater treatment unit 10 is shown in Figure 12. A wastewater treatment unit 10 comprises at least one biological denitration unit 101, a coagulation, flocculation and sedimentation unit 102, and a filtration, ultrafiltration and reverse osmosis unit 103. ... The biological denitration unit 101 contains at least one inlet 1011 for waste water AQ-1, which is obtained from the preparation of a pigment suspension, and an outlet 1012 for waste water AQ-2, which is obtained from the biological denitration of waste water AQ-1.

The unit 102 for coagulation, flocculation and sedimentation contains at least one inlet 1021 for waste water AQ-2, and outlet 1012 for waste water AQ-3, which is obtained from coagulation, flocculation and / or sedimentation of waste water AQ-2.

The unit 103 for filtration, ultrafiltration and reverse osmosis contains at least one inlet 1031 for waste water AQ-3, and outlet 1032 for treated waste water AQ-EX, which is obtained from filtration, ultrafiltration and reverse osmosis of waste water AQ-3 ...

The outlet 1012 and the inlet 1021 are connected to each other via line L-101. The outlet 1022 and the inlet 1031 are connected to each other via a line L-102.

The following describes the implementation of step h) by way of example on a waste water treatment unit 10.

To carry out step h) of the process according to the invention, waste water AQ-1 from the preparation of the pigment slurry is transferred from the reactor 3 through the outlet 343 of the separating device 34 through the line L-10 and the inlet 1011 to the biological denitration unit 101. Here, as described under the conditions of step h), the ammonia compounds present in the wastewater AQ-1 are oxidized to nitrate under aerobic conditions, and the nitrate compounds are reduced by enzymes in a subsequent step under non-aerobic conditions to form molecular nitrogen to obtain purified wastewater. water AQ-2.

Waste water AQ-2, thus purified, leaves unit 101 through outlet 1012 and travels through line L-101 to inlet 1021 to coagulation / flocculation / sedimentation unit 102 where it is further purified as described for step h), with the receipt of treated waste water AQ-3.

Waste water AQ-3, thus purified, leaves unit 102 through outlet 1022 and moves through line L-102 to inlet 1031 to unit 103 for filtration, ultrafiltration and reverse osmosis, where it is further purified as described for step h) , with the receipt of treated waste water AQ-EX.

The treated AQ-EX waste water that comes out of the outlet 1032 of the filtration / ultrafiltration / reverse osmosis unit 103 now contains only a small fraction of the impurities it originally contained. The treated AQ-EX wastewater can therefore be discharged through wastewater pipes to wastewater systems, or stored temporarily in vessels until it returns to the last point in time back to one of the process steps requiring water.

With the process according to the invention and the plant according to the invention, in which the process according to the invention is carried out, by means of the Penniman process using nitrate it is possible to obtain red iron oxide pigments of high quality, in high yields, with optimal energy consumption and with the prevention of waste gases and waste water containing undesirable reaction products such as nitrous gases, nitrogen monoxide, iron-containing compounds and sulfur-containing compounds.

Claims (13)

1. Installation for obtaining a suspension of red iron oxide pigments, including at least one reactor (1) for producing a solution of iron (II) nitrate, and at least one reactor (2) for producing a slurry of hematite cores, and at least one reactor (3) for producing a hematite pigment slurry, and at least one scrubber (4) and / or (6), where (a) said at least one reactor (1) is configured to communicate through at least one line (L-3a) with said at least one scrubber (4) and / or (6), and (b) said at least one reactor (3) is configured to communicate through at least one line (L-3b) with said at least one scrubber (4) and / or (6), and (c) said at least one reactor (2) is configured to communicate through at least one line (L-4) with at least one oxidation unit (5), and said at least one oxidation unit (5) is configured with the possibility of communication through at least one line (L-5) with the specified at least one scrubber (4) and / or (6), and at least one unit for cleaning waste gas (9), and at least one heater (8), and said at least one unit for cleaning waste gas (9) is configured to communicate through at least one line (L- 8) with the specified at least one heater (8) and the specified at least one heater (8) is configured to communicate through at least one line (L-7) with the specified at least one scrubber (4) and / or (6). 2. Installation according to claim 1, characterized in that it includes two scrubbers (4 and 6). 3. Installation according to claim 1, further comprising at least one waste water treatment unit (10), which is configured to communicate through at least one line (L-10) with at least one reactor (3) or with at least one separating device (34). 4. Installation according to claim. 1, further comprising at least one heat exchanger (7), which is configured to communicate through at least one line (L-6a) with the specified at least one scrubber (4), through at least one line (L-6b) with at least one scrubber (6), through at least one line (L-7) with the specified at least one heater (8) and through at least one line (L-9) with the specified at least one unit for cleaning waste gas (9). 5. Installation according to any one of paragraphs. 1-4, additionally containing at least one separating device (34), which is configured to communicate through at least one line (L-10) with the specified at least one waste water treatment unit (10) and at least through one line (L-32) with the specified at least one reactor (3).

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