How to remove magnesium from saltwater

Abstract

This embodiment relates to a method for removing magnesium from brine, and specifically, the method can include the steps of preparing concentrated brine, gradually adding an alkaline solution to the brine to form a precipitate having a controlled particle size, and separating the generated precipitate.

Description

[Technical Field]

[0001] The present invention relates to a method for removing magnesium from saltwater, and more particularly to a method for removing magnesium from saltwater by gradually adding an alkaline substance to saltwater to control the particle size of the precipitates that are deposited. [Background technology]

[0002] Lithium compounds are used in a wide range of applications across a wide range of industries, including secondary batteries, ceramics, glass, alloys, and pharmaceuticals. With the recent commercialization of electric vehicles and the increasing need for energy storage, demand for lithium materials is expected to grow significantly in the future.

[0003] The raw materials for producing lithium materials include mineral ores, brine, and seawater. Among these, ores such as spodumene, petalite, and lepidolite contain a relatively high amount of lithium, at about 1 to 1.5%. However, extracting lithium from minerals requires numerous steps, including flotation, high-temperature calcination, crushing, acid mixing, extraction, refining, concentration, and precipitation, making the recovery process complicated and costly due to high energy consumption. Furthermore, the use of acid in the lithium extraction process causes severe environmental pollution.

[0004] In addition, seawater contains a total of 2.5 x 10 11 It is known that lithium is dissolved in seawater in an amount of 100 tons. The main technique is to insert a recovery device containing an adsorbent into seawater to selectively adsorb lithium, and then extract the lithium by treating it with acid. However, the concentration of lithium in seawater is only 0.17 ppm, so extracting lithium from seawater is very inefficient and uneconomical.

[0005] Due to these issues, lithium is currently mainly extracted from brine, which is produced from natural salt lakes, with over 70% of the world's reserves located in South America, including Argentina, Chile, and Bolivia.

[0006] Among lithium-containing brines, commercially developed brines have a lithium concentration of 0.3g / L to 2g / L, and contain dissolved salts such as Mg, Ca, B, Na, K, and SO4, excluding lithium.

[0007] Lithium contained in brine is primarily extracted in the form of lithium carbonate. Commercially available processes for extracting lithium carbonate from lithium-containing brine involve drilling tube wells in natural salt lakes at altitudes of over 3,000 meters above sea level, pumping the brine into evaporation ponds, and allowing it to evaporate over a period of several months to a year to concentrate the lithium several to several tens of times. Impurities such as magnesium, calcium, and boron are then precipitated and removed, resulting in the precipitation of lithium in an amount exceeding the solubility of lithium carbonate. However, this conventional method requires significant energy and time to evaporate and concentrate the brine, significantly reducing productivity. Furthermore, lithium is lost during the evaporation and concentration process, resulting in limited use during the rainy season. Furthermore, lithium co-precipitation during the solid-liquid separation of magnesium and calcium to remove impurities reduces the lithium recovery rate. Mg and Ca are mixed and precipitated together, which requires a tedious process of separating them again, making it difficult to utilize as a resource. In addition, the amount of precipitate generated during the removal of Mg and Ca is large, causing various problems in the solid-liquid separation process.

[0008] To solve the above problems, a process has been developed in which brine is concentrated to a level of 4 g / L, Mg, Ca, etc. are removed, NaOH and phosphoric acid are added to recover lithium phosphate, and then lithium hydroxide is produced through subsequent electrolysis and crystallization.

[0009] However, one of the biggest problems in the process of producing lithium compounds from brine is the process of removing Mg from the concentrated brine. Since most brine resources contain far more Mg than Li, the amount of precipitate generated in the Mg removal process is greater than the amount of Li produced as the final product. Furthermore, the resulting Mg precipitates are very fine and highly cohesive, which hinders the subsequent solid-liquid separation process, significantly reducing the productivity of the entire plant.

[0010] Therefore, it is necessary to develop a magnesium removal technology in brine that can effectively separate the Mg components contained in concentrated brine and smoothly carry out the solid-liquid separation process. Summary of the Invention [Problem to be solved by the invention]

[0011] In one embodiment of the present invention, there is provided a method for removing magnesium from saltwater, specifically, a method for removing magnesium from saltwater, in which an alkaline substance is added in stages to control the particle size of precipitates. [Means for solving the problem]

[0012] A method for removing magnesium from brine according to an embodiment of the present invention may include preparing concentrated brine, gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size, and separating the precipitate.

[0013] The step of gradually adding an alkaline substance to the concentrated brine to deposit a precipitate with a controlled particle size includes a first alkaline substance addition step and a second alkaline substance addition step, and the alkaline substance may be added in a molar ratio of 1:0.5 to 1:20 in the first and second steps.

[0014] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size, the particle size distribution of the precipitate may be such that the particle size (D10) at which the cumulative volume becomes 10% is in the range of 7.0 μm to 9.0 μm.

[0015] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size, the particle size distribution of the precipitate may have a variation (D50 / D10) in the range of 3 to 4.

[0016] In the step of preparing the concentrated brine, brine having a lithium (Li) concentration in the range of 0.5 g / L to 20 g / L, a magnesium (Mg) concentration in the range of 2 g / L to 40 g / L, and a sulfur (S) to magnesium (Mg) concentration ratio in the range of 0.5 to 2 may be prepared.

[0017] In the step of separating the deposited precipitate, the saltwater from which the precipitate is separated may have a magnesium (Mg) concentration of 0.003 g / L or less.

[0018] After adding the alkaline material in the first step, the pH value may be in the range of 8 to 9.5, and after adding the alkaline material in the second step, the pH value may be in the range of 11 to 12.

[0019] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size, the alkaline substance may be a calcium-containing substance. [Effects of the Invention]

[0020] According to one embodiment of the present invention, there is an advantage that the removal rate of magnesium from saltwater can be improved.

[0021] According to one embodiment of the present invention, the useful life of the solid-liquid separator that separates the deposited precipitate can be extended, and there is an advantage in that the economy of the entire process can be improved. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating a method for removing magnesium from saltwater according to an embodiment of the present invention. [Figure 2] 1 shows an SEM image of the precipitate formed in Example 4 of the present invention. [Figure 3] 1 shows an SEM image of the precipitate formed in Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] In describing the present invention, terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0024] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0025] When a part is referred to as being "on" another part, it can mean that it is directly on top of the other part, or there can be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0026] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or very formal meaning unless defined.

[0027] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is given by way of example only, and the present invention is not limited thereto, but is defined only by the scope of the claims set forth below.

[0028] FIG. 1 is a schematic diagram illustrating a method for removing magnesium from saltwater according to one embodiment of the present invention. Referring to FIG. 1, a method for removing magnesium from brine according to one embodiment of the present invention may include a step of preparing concentrated brine (S1), a step of gradually adding an alkaline substance (S2), and a step of separating the deposited precipitate (S3).

[0029] First, in the step (S1) of preparing concentrated brine, concentrated brine containing lithium and having a pH in the range of 5.5 to 7.5 may be prepared. The concentration of lithium (Li) in the concentrated brine may be in the range of 0.5 g / L to 20 g / L, the concentration of magnesium (Mg) in the concentrated brine may be in the range of 2 g / L to 40 g / L, and the concentration of calcium (Ca) may be 1 g / L or less. Meanwhile, the concentration ratio of sulfur (S) to magnesium (Mg) may be in the range of 0.1 to 3.0, specifically in the range of 0.5 to 2.0.

[0030] The step of gradually adding an alkaline solution (S2) is a step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate, and specifically, may be a step of precipitating a precipitate with a controlled particle size.

[0031] The alkaline substance may be an oxide or hydroxide containing one or more selected from sodium (Na), potassium (K), and calcium (Ca), and specifically may be calcium (Ca) oxide or calcium (Ca) hydroxide.

[0032] When the alkaline substance is added to the concentrated brine, the magnesium (Mg) component contained in the concentrated brine can form a magnesium hydroxide (Mg(OH)2) precipitate.

[0033] Meanwhile, when an alkaline substance containing calcium (Ca) is added to the concentrated brine, a reaction represented by the following chemical formula may occur. Ca 2+ (aq)+2OH -1 (aq)+Mg 2+ (aq)+SO4 2- (aq)+2H2O(l)→Mg(OH)2(s)+CaSO4·2H2O(s) (1)

[0034] As mentioned above, adding calcium-containing substances to concentrated brine can form a slurry. Initially, calcium sulfate (CaSO4) precipitates primarily in the low pH range, and as the pH increases, magnesium hydroxide (Mg(OH)2) precipitates, with the amount of precipitation gradually increasing. To improve the removal rate of magnesium (Mg), an impurity in brine, the amount of alkaline substance added and the reaction time must be controlled to maintain a pH value of 11 or higher.

[0035] Specifically, in the low pH range, coarse calcium sulfate (CaSO4) precipitates in various shapes, such as needles or plates. The pH value of the slurry gradually increases with the amount of calcium-containing alkaline material added. However, at pH values ​​above 9.5, cross-reactions occur between calcium sulfate (CaSO4), calcium hydroxide (Ca(OH)2), and magnesium hydroxide (Mg(OH)2). Therefore, the coarse calcium sulfate (CaSO4) precipitates formed in the low pH range become finer, and the formation of fine-sized calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2) can actively occur. Meanwhile, as the pH increases, the tendency for the precipitates to become finer can accelerate. These fine precipitates adhere to the pores of the filter cloth used in the subsequent sediment separation process, resulting in pore clogging. This not only reduces the filtration speed of the filter and shortens the service life of the filter cloth, but also reduces the operational efficiency of the entire process.

[0036] To solve the above-mentioned problems, in one embodiment of the present invention, the alkaline substance may be added to the concentrated brine in two or more stages. Specifically, the process may include a first alkaline substance addition stage and a second alkaline substance addition stage, and the alkaline substance may be added in a ratio of 1:0.5 to 1:20 in the first and second stages. Adding the alkaline substance in this range not only improves the efficiency of magnesium removal from the brine, but also controls the particle size of the precipitate to a desired range, thereby preventing a decrease in the separation speed in the subsequent sediment separation stage and shortening the life of the sediment separation device.

[0037] As described above, by adding the alkaline material separately in the first and second stages, the pH value of the concentrated brine to which the alkaline material is added in the first stage can be controlled to a range of 8 to 9.5, and the pH value of the concentrated brine to which the alkaline material is added in the second stage can be controlled to a range of 11 to 12. In this way, by lowering the pH in the initial stage compared to conventional processes, the nucleation of calcium sulfate (CaSO4) is more actively induced at the beginning of the reaction, and the time for reaction particles to grow in the relatively low pH range is increased compared to conventional processes, which has the advantage of increasing the size of particles remaining in the final slurry after the reaction is completed.

[0038] In one embodiment of the present invention, the alkaline substance may be added in an amount 1.2 to 2.0 times, specifically 1.5 to 1.7 times, the theoretical amount of alkaline substance required to completely convert the magnesium (Mg) contained in the concentrated brine to magnesium hydroxide (Mg(OH)2). In other words, the alkaline substance may be added in an amount 1.2 to 2.0 equivalents, specifically 1.5 to 1.7 equivalents.

[0039] Meanwhile, the alkaline substance can be added to the concentrated brine and stirred for a predetermined period of time. Specifically, after adding the first-stage alkaline substance, stirring can be performed for 10 minutes to 1 hour, and after adding the second-stage alkaline substance, stirring can be performed for 30 minutes to 3 hours. The stirring time after adding the second-stage alkaline substance may be approximately 2 to 3 times the stirring time after adding the first-stage alkaline substance. This is advantageous for effectively precipitating magnesium while controlling the particle size of the precipitate.

[0040] The precipitate precipitated by adding an alkaline substance to the concentrated brine may have a particle size (D10) of 7.0 μm to 9.0 μm, where the cumulative volume is 10%, in the particle size distribution, and the variation (D50 / D10) may be in the range of 3 to 4.

[0041] Next, in the step of separating the precipitate (S3), the precipitate is separated using a filter cloth of a filtration separator, thereby obtaining a brine filtrate from which magnesium has been removed. The filtration separator or filter cloth may be any filtration separator or filter cloth used in a typical process for recovering lithium from brine or a process for removing impurities, and is not particularly limited.

[0042] Meanwhile, in the step of separating the precipitate (S3), the concentration of magnesium (Mg) in the brine filtrate remaining after separating the precipitate may be 0.003 g / L or less. [Example]

[0043] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0044] First, a concentrated salt solution containing the components shown in Table 1 below was prepared.

[0045] [Table 1]

[0046] Example 1 Concentrated brine 2 in Table 1 was used as the raw material, and Ca(OH)2 was used as the alkaline substance, and Ca(OH)2 was added to the concentrated brine 2 in two stages. The total amount of Ca(OH)2 added to the concentrated brine 2 in the two stages was 1.6 times (1.6 equivalents) the theoretical amount of Ca(OH)2 required to completely react all of the Mg components contained in the concentrated brine 2 with Mg(OH)2.

[0047] In the first step, 0.1 times (0.1 equivalents) the theoretical amount of Ca(OH)2 was added and stirred for 30 minutes, and in the second step, 1.5 times (1.5 equivalents) the theoretical amount of Ca(OH)2 was added and stirred for 1 hour and 30 minutes before the reaction was terminated. After the reaction was completed, the final product containing precipitate was separated into solid and liquid using a pressurized solid-liquid separator, and an experiment was conducted to remove magnesium from the concentrated brine.

[0048] Examples 2 to 5 An experiment to remove magnesium from concentrated brine was carried out in the same manner as in Example 1, except that in the first step, 0.3 equivalents (Example 2), 0.5 equivalents (Example 3), 0.7 equivalents (Example 4), and 0.9 equivalents (Example 5) of Ca(OH)2 were added, respectively, based on the theoretical calculation, and in the second step, 1.3 equivalents (Example 2), 1.1 equivalents (Example 3), 0.9 equivalents (Example 4), and 0.7 equivalents (Example 5) of Ca(OH)2 were added, respectively, based on the theoretical calculation.

[0049] Examples 6 to 8 An experiment to remove magnesium from concentrated brine was carried out in the same manner as in Example 3, except that concentrated brine 1, concentrated brine 3 and concentrated brine 4 in Table 1 were used.

[0050] Examples 9 to 11 An experiment to remove magnesium from concentrated brine was carried out in the same manner as in Example 5, except that concentrated brine 1, concentrated brine 3 and concentrated brine 4 in Table 1 were used.

[0051] (Comparative Examples 1 to 4) Concentrated brines 1 to 4 in Table 1 were used as the raw concentrated brines, and Ca(OH)2 was used as the alkaline substance. 1.6 times (1.6 equivalents) of the theoretical amount of Ca(OH)2 needed to completely convert the contained Mg into Mg(OH)2 was added to each concentrated brine, and the reaction was terminated after stirring for 2 hours. After the reaction, the final product, which contained precipitate, was separated into solid and liquid using a pressurized solid-liquid separator.

[0052] In Examples 1 to 11 and Comparative Examples 1 to 3, the final products produced after the reaction were sampled and analyzed based on the particle size of the precipitates, and the results are summarized in Table 2. In the present invention, the particle size analysis of the precipitates was carried out by introducing the sampled slurry into a Malvern Mastersizer 3000 using a wet laser particle size analysis method.

[0053] In addition, in Examples 1 to 11 and Comparative Examples 1 to 3, the weight of the final product produced after the reaction was completed was measured, and then the time required for complete separation into solid and liquid and the filtration rate were calculated by dividing the area of ​​the filter cloth of the pressurized solid-liquid separator. The results are summarized in Table 2.

[0054] Through the pressurized solid-liquid separator, liquid materials are collected by a separate collector, and solid materials remain on the surface of the filter cloth in the form of a cake. The cake can be peeled off from the filter cloth by applying a predetermined impact. At this time, the releasability of the cake was evaluated by observing the microstructure of the filter cloth surface from which the cake was peeled.

[0055] The peelability was evaluated as follows: Δ: average, ○: excellent, ⊚: extremely excellent.

[0056] Cake releasability was evaluated by visual observation of whether the cake was easily separated from the surface of the filter cloth when the cake was removed after the completion of solid-liquid separation. If cake particles were found on the surface of the filter cloth, it was judged to be below average. If the cake was smoothly removed with almost no residue on the surface of the filter cloth, it was judged to be excellent. If no residue was found on the surface of the filter cloth after the cake was removed and there were no traces of cake adhering to the surface of the filter cloth, it was judged to be extremely excellent.

[0057] In addition, the filtrate separated using the pressurized solid-liquid separator was subjected to ICP analysis to measure the residual Mg concentration.

[0058] [Table 2]

[0059] Referring to the results of Examples 6, 9, and Comparative Example 1, in which Concentrated Brine 1 was used as the raw material, it was confirmed that the filtration rate increased by approximately 53% and approximately 37%, respectively, and that the cake peelability was improved.

[0060] Referring to the results of Examples 1 to 5 and Comparative Example 2, which used concentrated brine 2 as a raw material, it can be seen that in Examples 1 to 5, the filtration rate increased by about 30% to 74% compared to Comparative Example 2, and cake peelability was also improved.

[0061] Referring to the results of Examples 7, 10, and Comparative Example 3, which used Concentrated Brine 3 as the raw material, it can be seen that in Examples 7 and 10, the filtration rate increased by about 63% and about 39%, respectively, compared to Comparative Example 3, and cake peelability was also improved.

[0062] Referring to the results of Examples 8, 11, and Comparative Example 4, which use concentrated brine 4 as the raw material, it can be seen that in Examples 7 and 10, the filtration rate increased by about 47% and about 36%, respectively, compared to Comparative Example 4, and cake peelability was also improved.

[0063] FIG. 2 shows an SEM image of the precipitate deposited in Example 4 of the present invention, and FIG. 3 shows an SEM image of the precipitate deposited in Comparative Example 2 of the present invention.

[0064] 2 and 3, it can be seen that the particle size of the precipitate deposited in Example 4 of the present invention is relatively larger than that of the precipitate deposited in Comparative Example 2.

[0065] From the experimental results, it was confirmed that when the initial pH was controlled low by adjusting the alkaline substance input ratio, the filtration rate of the precipitate increased by about 30% to 80%, and the cake peelability was also improved.

[0066] Therefore, it can be confirmed that the cycle time of the magnesium removal process from brine can be shortened and the filter cloth replacement period can be extended by increasing the filtration speed and cake peelability. Furthermore, it is believed that not only can the productivity of the magnesium removal process from brine be improved, but also the economy of the entire process can be improved.

[0067] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting.

Claims

1. providing a concentrated brine; gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size; and Separating the deposited precipitate; How to remove magnesium from saltwater.

2. The step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size includes: Including a first alkaline substance injection stage and a second alkaline substance injection stage; The method for removing magnesium from saltwater according to claim 1.

3. The first alkaline substance introduction step and the second alkaline substance introduction step are In the first and second steps, the alkaline material is added in a molar ratio of 1:0.5 to 1:

20. The method for removing magnesium from saltwater according to claim 2.

4. The step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size includes: In the particle size distribution of the precipitate, the particle size (D10) at which the cumulative volume becomes 10% is in the range of 7.0 μm to 9.0 μm. The method for removing magnesium from saltwater according to claim 1.

5. The step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size includes: In the particle size distribution of the precipitate, the variation (D50 / D10) is in the range of 3 to 4. The method for removing magnesium from saltwater according to claim 1.

6. The step of preparing the concentrated brine includes: The concentration of the lithium (Li) component is in the range of 0.5 g / L to 20 g / L, The concentration of the magnesium (Mg) component is in the range of 2 g / L to 40 g / L, Preparing salt water having a concentration ratio of sulfur (S) component to magnesium (Mg) component in the range of 0.5 to 2; The method for removing magnesium from saltwater according to claim 1.

7. The step of separating the deposited precipitate includes: the saltwater from which the precipitate was separated has a magnesium (Mg) concentration of 0.003 g / L or less; The method for removing magnesium from saltwater according to claim 1.

8. After adding the first alkaline material, the pH value is in the range of 8 to 9.5; After adding the second alkaline material, the pH value is in the range of 11 to 12. The method for removing magnesium from saltwater according to claim 2.

9. adding an alkaline substance to the concentrated brine step by step to precipitate a precipitate having a controlled particle size; The alkaline substance is a calcium-containing substance. The method for removing magnesium from saltwater according to claim 1.

Images