WO2025165217A1 - Process for producing magnesium hydroxide and potassium chloride of high purity from a carnallite treatment brine - Google Patents

Abstract

The invention relates to an efficient and economical process for recovering magnesium and potassium from a brine effluent. In particular, the magnesium and potassium are recovered sequentially as magnesium hydroxide and potassium chloride, from a carnallite (KCl.MgCl2.6H2O) treatment brine, with qualities that enable them to be commercially upgraded.

Description

PROCESS FOR PRODUCING HIGH PURITY MAGNESIUM HYDROXIDE AND POTASSIUM CHLORIDE FROM CARNALLITE TREATMENT BRINE

FIELD TO WHICH THE INVENTION RELATES

The present invention relates to a process for producing high purity magnesium hydroxide and potassium chloride from brine generated by the upgrading process, in other words from treating carnallite (KCI. MgCI ₂ . 6 H ₂ O) or a potash ore containing carnallite.

PREVIOUS ART

Potassium chloride, commonly known as potash or muriate of potash (MOP), is mainly used in the agricultural sector. This vital nutrient is recognized as one of the three main macronutrients (NPK) to improve agricultural production and ensure global food security. The deposits exploited worldwide are mainly composed of sylvinite (mixture of sylvite KCI and halite NaCI) contained in a NaCI salt gangue. The presence of carnallite (KCI, MgCI ₂ , 6H ₂ O) in these minerals causes a disruption in the conventional potash processing process and its valorization poses a number of challenges.

Currently, under the pressure of an increasingly strong demand for this critical element for global food security, and to enable the development of new carnallite valorization projects, it would be crucial to develop an integrated process to recover magnesium and potassium chloride as marketable products in order to align with the concept of zero liquid discharge in a sustainable development approach.

According to the literature reviewed, few patents have been devoted to investigating the possibility of recovering valuable products from brine generated by the potash industry in order to maximize the cost-benefit of the plant and mitigate the environmental impacts associated with conventional brine disposal methods.

U.S. Pat. No. 4,162,297 (Aubry et al.) describes a method for recovering magnesium chloride from brine produced during the cold decomposition of carnallite ore. The method involves the use of dioxane to selectively precipitate magnesium chloride. The appropriate volume concentration of dioxane is between 10 and 25% of the initial brine volume. Room temperature, i.e., about 21-26 °C, is preferred for the precipitation of magnesium chloride from brine.

US Pat. No. 4,495,160 (Moote et al.) presents an effective method for removing magnesium from brine using calcium hydroxide at temperatures above 80 °C. This forms a precipitate of insoluble magnesium hydroxide and soluble strontium hydroxide. The magnesium hydroxide precipitate settles rapidly above 90 °C, allowing easy filtration. The remaining brine is cooled to precipitate strontium hydroxide, which can be recovered by filtration. Carbon dioxide gas can aid in the precipitation of strontium hydroxide if necessary.

EP3771690A1 (Cipollina A. et al.) describes a method for extracting minerals from seawater and brine from treatment plants. Magnesium is first recovered as magnesium hydroxide using a reactive crystallization method using an alkaline solution of KOH and NaOH or a mixture of the two solutions. The other trace elements are subsequently recovered by the same method in another crystallization using an acidic solution and finally an electrodialysis step. The final discharge from the operation is recycled to evaporation ponds or discharged into the sea.

U.S. Pat. No. 2010/0233767A1 describes a method for recovering magnesium from a liquid waste solution by including a pretreatment step. It highlights the importance of pretreatment to prepare the solution and optimize the recovery process. Various methods such as precipitation, solvent extraction, and ion exchange are discussed for magnesium recovery. The patent highlights the importance of specific conditions during recovery, such as temperature and pH, to improve recovery efficiency.

Most of these patents use reagents which can themselves generate additional effluents and do not propose an integrated global scheme which would make it possible to respond to the problem in a sustainable manner.

Currently, under the pressure of an increasingly strong demand for this critical element for global food security, and to enable the development of new carnallite valorization projects, it would be crucial to develop an integrated process to recover magnesium and potassium chloride as marketable products in order to align with the concept of zero liquid discharge in a sustainable development approach.

BRIEF DESCRIPTION OF THE INVENTION

Given the exceptional challenges associated with the industrial exploitation of potash, and to address the associated social and societal impacts, the present invention proposes a method;

• New and extrapolable “scalable” to obtain high purity magnesium hydroxide and potassium chloride and thus solve the problems linked to the exploitation of potash, and in particular carnallite (KCI. MgCI ₂ . 6 H ₂ O).

• Versatile production of high purity magnesium hydroxide and potassium chloride from brine waste regardless of its quality in terms of concentration of valuable elements

• Sustainable, which allows the recovery of the entire value of an industrial discharge by aiming for a Zero Liquid Discharge or ZLD objective with the objective of recycling all of the discharged water The invention relates in particular to a process for the sequential production of magnesium hydroxide (Mg(0H)2) and potassium chloride (KCI) from a carnallite treatment brine (KCI.MgCI2.6H2O) comprising the steps defined in claims 1 and following.

The above stated and other objects of the invention will become apparent from a review of the description, drawings, and examples presented. It should be noted that the description, drawing, and examples are presented for illustrative purposes only and should not be construed as limiting the scope of the invention.

Advantageously, the process includes several stages which will allow the recovery of magnesium in the form of magnesium hydroxide (Mg(0H)2) and potassium in the form of potassium chloride (KCI) commonly called potassium muriate (MOP) with the advantage of recycling the exhausted solution upstream of the process to close the loop.

Initially, an alkaline precipitation step allows the recovery of magnesium hydroxide with a yield exceeding 90%. A solid-liquid separation step, such as filtration, allows the recovery of the product in the form of a white powder.

Subsequently, the remaining liquid from the previous step, called mother liquor, is heated to a temperature ranging from 90 °C to 100 °C for a specific period. Then, the mother liquor is subjected to a cooling process, leading to crystallization and the formation of potassium chloride. These potassium chloride crystals are then recovered by employing a suitable solid-liquid separation technique, such as filtration, but not limited to.

Since the brine waste has been effectively depleted of magnesium and potassium as magnesium hydroxide and potassium chloride, respectively, the residual mother liquor stream can be recycled to the carnallite cold decomposition unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, for the understanding of which reference will be made to the appended drawings in which:

• Figure 1 is a schematic representation of the continuous process for recovering magnesium hydroxide and potassium chloride from brine waste in accordance with the present invention.

• Figure 2 shows another embodiment of the device according to which the precipitation step is carried out in a device which allows simultaneous addition of the brine solution and the precipitant solution • Figure 3 is a schematic representation, by way of non-limiting example, and illustrating an example in which the solution resulting from crystallization is recycled at the level of carnallite decomposition.

The present invention will be better understood by studying a particular embodiment taken as a non-limiting example and illustrated by the appended drawings, in which:

• Figure 4 shows an X-ray diffractogram carried out on the product obtained from magnesium hydroxide. This diffractogram demonstrates the production of magnesium hydroxide and the chemical quality of which is confirmed in the example given in Table 1

• Figure 5 shows an X-ray diffractogram made on the product obtained from potassium chloride. This diffractogram demonstrates the production of potassium chloride and the chemical quality of which is confirmed in the example given in Table 1

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1, the process according to the invention comprises a succession of steps which allow the recovery of magnesium and potassium contained in the brine solution. This scheme allows the recovery of 90% of the magnesium contained in the brine with a hydroxide quality of at least 95%. The potassium chloride KCI obtained by crystallization showed a product quality which assays at least 99% KCI.

The brine subjected to the treatment according to the invention may be of natural origin, such as brine extracted or obtained from a salt lake, a marine lagoon or a marsh highly concentrated in sought-after minerals; it may also be obtained via the “solution mining” process.

As shown in Figure 1, the method comprises a precipitation step (1) which results from the contact of the alkaline precipitant solution with the brine solution. Initially, a brine solution is combined with potassium hydroxide at a temperature approximately in the range of 20°C and 60°C, preferably at room temperature. The resulting mixture is subjected to vigorous stirring for a predetermined time. As a result, a white suspension composed of magnesium hydroxide is formed. A predetermined amount of an organic flocculant is introduced into the magnesium suspension to improve the filtration efficiency.

The recovery of high purity magnesium hydroxide and potassium chloride from the brine solution produced by decomposition of a carnallite ore was carried out in the same manner as in Example 1.

The brine solution generated by the cold decomposition of a carnallite ore, having the following chemical composition: 55.6 g/l of Mg2+, 15.5 g/l of Na+; 28.7 g/l of K+ and 212.4 g/l of CI-, The purity of magnesium hydroxide and potassium chloride is 99% (Figure 4 and 5) with an overall recovery of 94.5% and 49%, respectively.

In this example, the quality of magnesium hydroxide is consistent with market specifications for flame retardants while the quality of potassium chloride crystals is consistent with the market for electrochemistry such as electroplating or electrolysis.

Note that the potassium recovery yield could be improved by multiplying the crystallization steps because this step is carried out on an industrial scale in at least 5 crystallizations (five successive steps).

According to various features of the invention and in accordance with the example given in Figure 3, a device could be used to control this precipitation step. Indeed, a simultaneous addition of the brine solution with the precipitant solution according to predefined flow rates based on the stoichiometry of the chemical precipitation reaction significantly improves the efficiency of the process.

This precipitation step could be done in more than one step/stage, if necessary, to recover another element than magnesium, and using one or a mixture of alkaline precipitants. Indeed, depending on the origin of the brine solution, other chemical species such as iron (Fe2+ or Fe3+), calcium (Ca2+), lithium (Li+) or beryllium (Be2+), could be eliminated according to the said method by adjusting the precipitation conditions for each of these species.

Subsequently, the precipitate is allowed to settle and a solid-liquid separation process is used to recover the resulting precipitate. The remaining liquid, called mother liquor, is heated to a temperature ranging from 90°C to 100°C for a specific period to allow its saturation with potassium. Then, the mother liquor is subjected to a cooling process to a temperature between 40°C and 20°C, leading to the crystallization of potassium chloride. These potassium chloride crystals are then obtained by employing an appropriate technique such as filtration.

In another example, the brine solution generated by the cold decomposition of a carnallite ore, and having undergone a subsequent crystallization step in an evaporation pond, and having a higher concentration of magnesium (68.5 g/l) and lower potassium (1.87 g/l) and sodium (2.9 g/l). This solution is treated according to the scheme described in Figure 3 and allowed a recovery of magnesium hydroxide exceeding 95%, with a product quality of 96%.

Also, the quality of potassium chloride crystals is in line with market specifications for MOP 60 muriates of potash which require a quality of 60% K2O.

In the diagram presented in Figure 3, the solution depleted in magnesium and potassium is recycled in the cold decomposition stage of carnallite to reduce the consumption of fresh water at this stage and to recycle all the brine discharge, with the aim of environmental protection and sustainable development. INDUSTRIAL APPLICATION

The process and method according to the invention is particularly intended for the industrial recovery of a carnallite recovery reject or a carnallite-rich potash ore or a solution resulting from a "solution mining" process applied to rocks or terrains containing high concentrations of Mg and K. The steps described in this invention refer to mature processes on an industrial scale (chemical precipitation, solid-liquid separation, crystallization) and industrial extrapolation would not pose any technical or technological limitations.

In addition, the present invention provides a versatile process for producing high-purity magnesium hydroxide and potassium chloride from a brine solution regardless of its quality in terms of concentration of valuable elements. The precipitation conditions can, in fact, be adapted to accommodate any change in the concentration of these elements.

REFERENCES

Andre Aubry, Michel Bichara, RECOVERY OF MAGNESIUM CHLORIDE FROM BRINES, US patent 4,162,297 (1979)

Truman P. Moote, Robert L. Reed, REMOVAL AND RECOVERY OF MAGNESIUM, STRONTIUM AND BARIUM FROM BRINES, US patent 4,495,160 (1983)

Cipollina Andrea, Bevacqua Maurizio, Micale Giorgio, Papapetrou Michael, Tamburini Alessandro, PROCEDURE FOR THE EXTRACTION OF MINERALS FROM SEA WATER, PLANT FOR EXTRACTION AND MINERALS OBTAINED THROUGH THE EXTRACTION PROCEDURE, EP3771690A1 (2019)

David McMurran, PROCESS FOR THE RECOVERY OF MAGNESUMI FROM A SOLUTION AND PRETREATMENT, US 2010/0233767 Al (2010).

Claims

Claims 1. A process for the sequential production of magnesium hydroxide (Mg(OH)2) and potassium chloride (KCI) from a carnallite treatment brine (KCI.MgCI2.6H2O) comprising the following steps: a) preparing an aqueous solution of a precipitating agent based on KOH, NaOH or CaO, or a mixture of two or three of said components, with a concentration ranging from 1M to 5M; b) adding said precipitating agent solution to an aqueous brine solution, stirred and heated to a temperature ranging from 20°C to 60°C; c) maintaining mechanical stirring of the mixture for a period ranging from 15 min to 60 min; d) separating the magnesium hydroxide precipitate (Mg(OH)2) from the mother solution by means of a solid-liquid separation system; e) heating the mother solution to between 90°C and 100°C followed by cooling it to a temperature between 20°C and 40°C causing the crystallization of potassium chloride, and f) collecting the potassium chloride using a solid-liquid separation system. 2. Method according to claim 1, in which a flocculating agent solution is added to the suspension resulting from step b. 3. Method according to claim 2, in which the flocculating agent is a synthetic or bio-sourced polymer of the Polyethylene-oxide (PEO) type. 4. The method of claim 1, wherein said brine solution is a waste product from a carnallite decomposition process or a sylvite flotation process present in a potash ore. 5. The method of claim 1, wherein said brine solution is from a natural source such as a salt lake or from brine obtained from a "solution mining" technique. 6. Method according to at least one of claims 1 to 5, in which the brine solution may contain a concentration of Mg2+ which varies from 2 g/l to 200 g/l. 7. Method according to at least one of claims 1 to 6, in which the method of adding the precipitating agent according to step b) is direct, inverse, or simultaneous with flow rates corresponding to the stoichiometry of the chemical reaction. 8. Method according to at least one of claims 1 to 7, in which the mother liquor resulting from the magnesium hydroxide precipitation process generates a concentration of K+ which varies between 20g/l and 120g/l. 9. Method according to at least one of claims 1 to 8, characterized in that the number of potassium chloride crystallization stages is 1 to 6 to maximize the recovery of potassium chloride. 10. Method according to at least one of claims 1 to 9, comprising an additional step of fractional precipitation in the presence of other elements. in the carnallite treatment brine such as iron, calcium, lithium or beryllium. 11. Method according to at least one of claims 1 to 10, comprising a phase of recycling the aqueous solution resulting from the potassium chloride crystallization step for carrying out a previous step of decomposition of carnallite or flotation of sylvite.