Method for removing magnesium in saline water

Abstract

The present embodiment relates to a method for removing magnesium from brine, and specifically, may provide a method for removing magnesium from brine including a step of preparing concentrated brine, a step of stepwise adding an alkaline substance to the concentrated brine to precipitate a precipitate having a controlled particle size, and a step of separating the precipitate.

Description

Technical Field

[0001] This embodiment relates to a method for removing magnesium from brine. Specifically, by gradually adding an alkaline substance to the brine to control the particle size of the precipitate, magnesium in the brine is removed. Background Art

[0002] Lithium compounds are widely used for various purposes in various industries such as secondary batteries, ceramics, glass, alloys, pharmaceuticals, etc. With the commercialization of electric vehicles and the increasing demand for energy storage in recent years, it is expected that the demand for lithium materials will also increase significantly in the future.

[0003] Raw materials for preparing lithium materials include minerals, brines, and seawater. Among these raw materials, minerals such as spodumene, petalite, and lepidolite contain about 1% to 1.5% lithium, which is relatively high. However, in order to extract lithium from minerals, numerous processes such as flotation, high-temperature roasting, crushing, acid mixing, extraction, refining, concentration, precipitation, etc. must be carried out. Therefore, the recovery process is complex, energy consumption is high, the cost is high, and the use of acid in the process of extracting lithium has caused serious environmental pollution problems.

[0004] In addition, it is known that a total of 2.5×1011 tons of lithium is dissolved in seawater. Currently, the main technology is to put a recovery device containing an adsorbent into seawater, selectively adsorb lithium, and then extract lithium through acid treatment. However, since the concentration of lithium in seawater is only 0.17 ppm, the efficiency of extracting lithium from seawater is very low, and there is a problem of low economy.

[0005] Due to these problems, currently lithium is mainly extracted from brines, which come from natural salt lakes. More than 70% of the world's lithium reserves are distributed in South American regions including Argentina, Chile, Bolivia, etc.

[0006] In the brine containing lithium, the lithium concentration level of commercially developed brine is 0.3 g / L to 2 g / L. In addition to lithium, salts such as Mg, Ca, B, Na, K, SO4, etc. are also dissolved.

[0007] The lithium contained in the brine is mainly extracted in the form of lithium carbonate. In the commercial process, in order to extract lithium carbonate from the lithium-containing brine, wells are first drilled in natural highland salt lakes above 3000 meters above sea level, and then the brine is pumped into evaporation ponds. After several months to one year of long-term natural evaporation, the lithium is concentrated several times to dozens of times. Then, impurities such as Mg, Ca, and B are removed by precipitation, and the content of lithium carbonate exceeds the solubility to recover lithium. However, this traditional method consumes a large amount of energy and time in the evaporation and concentration process of the brine, resulting in a significant reduction in production efficiency; at the same time, during the evaporation and concentration process of the brine, lithium precipitates in the form of salt together with other impurities, resulting in lithium loss. In addition, during the rainy season, its utilization is restricted. On the other hand, in order to remove Mg and Ca in the impurities, during the solid-liquid separation process, lithium will co-precipitate, reducing the lithium recovery rate. Since Mg and Ca are mixed and precipitated with each other, they need to be separated again, which is a cumbersome task and makes it difficult to be used as a resource. In addition, the amount of precipitate generated to remove Mg and Ca is large, causing various problems in the solid-liquid separation process.

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

[0009] However, in the process of preparing lithium compounds from the brine, one of the most prominent problems is the process of removing Mg contained in the concentrated brine. Since in most salt water resources, the content of Mg is much higher than that of Li, the amount of precipitate generated during the Mg removal process exceeds the output of the final product Li. In addition, the generated Mg precipitate particles are small and have strong agglomeration, making the subsequent efficient separation process unable to proceed smoothly, seriously reducing the productivity of the entire plant.

[0010] Therefore, there is a current need to develop a technology for removing magnesium from brine that can effectively separate the Mg component in the concentrated brine and smoothly carry out the efficient separation process. Summary of the Invention

[0011] Technical Problem

[0012] In one embodiment of the present invention, it aims to provide a method for removing magnesium from brine. Specifically, this method controls the particle size of the precipitate by gradually adding an alkaline substance, thereby achieving the removal of magnesium in the brine.

[0013] Technical Solution

[0014] A method for removing magnesium from brine according to an embodiment of the present invention includes the steps of preparing concentrated brine; gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size; and separating the precipitate.

[0015] The step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size includes a first step of adding an alkaline substance and a second step of adding an alkaline substance. The alkaline substances in the first step and the second step are added in a molar ratio range of 1:0.5 to 1:20.

[0016] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size, the particle size (D10) at which the cumulative volume in the particle size distribution of the precipitate reaches 10% is in the range of 7.0 μm to 9.0 μm.

[0017] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size, the spread (D50 / D10) in the particle size distribution of the precipitate is in the range of 3 to 4.

[0018] The step of preparing concentrated brine is to prepare brine with a lithium (Li) component concentration in the range of 0.5 g / L to 20 g / L, a magnesium (Mg) component concentration in the range of 2 g / L to 40 g / L, and a sulfur (S) component to magnesium (Mg) component concentration ratio in the range of 0.5 to 2.

[0019] In the step of separating the precipitate, the magnesium (Mg) component concentration in the brine after separating the precipitate is 0.003 g / L or less.

[0020] After adding the alkaline substance in the first step, the pH value is in the range of 8 to 9.5, and after adding the alkaline substance in the second step, the pH value is in the range of 11 to 12.

[0021] In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size, the alkaline substance is a calcium-containing substance.

[0022] Advantages of the Invention

[0023] According to an embodiment of the present invention, it has the advantage of improving the magnesium removal rate in brine.

[0024] According to an embodiment of the present invention, the service life of the solid-liquid separation device for separating the precipitate can be extended, and the economy of the entire process can be improved. Brief Description of the Drawings

[0025] Figure 1 Generally shows a method for removing magnesium from brine according to an embodiment of the present invention.

[0026] Figure 2 Shows the SEM image of the sediment precipitated according to Embodiment 4 of the present invention.

[0027] Figure 3 Shows the SEM image of the precipitate precipitated according to Comparative Example 2 of the present invention. Detailed Description of the Invention

[0028] In the description of the present invention, terms such as first, second, third, etc. are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, and / or segment described below can also be described as the second part, component, region, layer, and / or segment.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise clearly indicated to the contrary in the context, the singular forms used are also intended to include the plural forms. It should also be understood that the term "comprising" used in the specification can specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, fields, integers, steps, actions, elements, and / or components.

[0030] If a part is described as being above another part, there may be other parts directly above or between the other part. When a part is described as being directly above another part, there will be no other parts therebetween.

[0031] Although not otherwise defined, the meanings of all terms (including technical terms and scientific terms) used herein are the same as those commonly understood by those of ordinary skill in the art to which the present invention pertains. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0032] The embodiments of the present invention will be described in detail below. However, this is only provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

[0033] Figure 1 Generally shows a method for removing magnesium from brine according to an embodiment of the present invention.

[0034] Refer to Figure 1, according to an embodiment of the present invention, the method for removing magnesium from brine may include a step of preparing concentrated brine (S1), a step of gradually adding an alkaline substance (S2), and a step of separating the precipitated sediment (S3).

[0035] First, the step of preparing concentrated brine (S1) is to prepare concentrated brine containing lithium with a pH in the range of 5.5 to 7.5. The concentration of lithium (Li) component in the concentrated brine may be in the range of 0.5 g / L to 20 g / L, the concentration of magnesium (Mg) component may be in the range of 2 g / L to 40 g / L, and the concentration of calcium (Ca) component may be below 1 g / L. Meanwhile, the concentration ratio of sulfur (S) component to magnesium (Mg) component may be in the range of 0.1 to 3.0, specifically, in the range of 0.5 to 2.0.

[0036] The step of gradually adding an alkaline solution (S2) refers to the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate, specifically, it may be a step of precipitating a precipitate with a controlled particle size.

[0037] The alkaline substance may be an oxide or hydroxide including any one or more of sodium (Na), potassium (K), or calcium (Ca), specifically, it may be an oxide of calcium (Ca) or a hydroxide of calcium (Ca).

[0038] When the alkaline substance is added to the concentrated brine, the magnesium (Mg) component contained in the concentrated brine may form a magnesium hydroxide (Mg(OH)2) precipitate.

[0039] On the other hand, when an alkaline substance containing calcium (Ca) is added to the concentrated brine, the reaction shown in the following chemical equation may occur.

[0040] Ca 2+ (aq) + 2OH -1 (aq) + Mg 2+ (aq) + SO4 2- (aq) + 2H2O(l) → Mg(OH)2(s) + CaSO4·2H2O(s) (1)

[0041] As described above, adding a calcium-containing substance to the concentrated brine can form a slurry. In the initial low pH region, mainly calcium sulfate (CaSO4) precipitate is formed. As the pH value increases, magnesium hydroxide (Mg(OH)2) precipitate precipitates out, and the precipitation amount gradually increases. In order to improve the removal rate of the impurity magnesium (Mg) component in the brine, it is necessary to control the amount of alkaline substance added and the reaction time so that the pH value reaches above 11.

[0042] Specifically, in the low pH region, various forms of calcium sulfate (CaSO4) precipitates in the shape of large-sized needles or plates are formed. As the addition amount of calcium-containing alkaline substances increases, the pH value of the slurry gradually rises. When the pH value exceeds 9.5, an inter-cross reaction occurs among calcium sulfate (CaSO4), calcium hydroxide (Ca(OH)2), and magnesium hydroxide (Mg(OH)2). Therefore, the particles of the large-sized calcium sulfate (CaSO4) precipitates generated in the low pH region become fine, and moreover, the generation of calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2) with fine particle sizes can also proceed actively. On the other hand, as the pH value increases, the refinement trend of these precipitates accelerates. These fine precipitates adhere to the pores of the filter cloth of the filtration device used to separate subsequent precipitates, resulting in clogging. Therefore, this not only reduces the filtration speed of the filtration device and the service life of the filter cloth, but also becomes the main reason for reducing the operating efficiency of the entire process.

[0043] To solve the above problems, in one embodiment of the present invention, the alkaline substances can be added to the concentrated brine in more than two steps. Specifically, it can include a first step of adding alkaline substances and a second step of adding alkaline substances, and in the first step and the second step, the alkaline substances can be added in a ratio of 1:0.5 to 1:20. When the alkaline substances are added within the above range, not only can the removal efficiency of magnesium in the brine be improved, but also the particle size of the precipitates can be controlled within the target range, thereby preventing the reduction of the separation speed in the subsequent precipitate separation step and being conducive to preventing the shortening of the service life of the precipitate separation device.

[0044] By adding the alkaline substances in two steps, namely the first step and the second step, the pH value of the concentrated brine added with the alkaline substances in the first step can be controlled within the range of 8 to 9.5, while the pH value of the concentrated brine added with the alkaline substances in the second step can be controlled within the range of 11 to 12. In this way, by reducing the pH value of the starting step compared with the existing process, the generation of calcium sulfate (CaSO4) nuclei in the initial stage of the reaction is induced more actively, and by increasing the growth time of the reaction particles in the relatively low pH region compared with the existing process, there is an advantage that the size of the residual particles in the final slurry after the reaction increases.

[0045] In one embodiment of the present invention, the alkaline substances can be added in a range of 1.2 times to 2.0 times the theoretically calculated value, where the theoretically calculated value is the alkaline component required to completely convert the magnesium (Mg) component contained in the concentrated brine into magnesium hydroxide (Mg(OH)2). Specifically, it can be added in a range of 1.5 times to 1.7 times. That is, it can be added in a range of 1.2 equivalents to 2.0 equivalents of the theoretically calculated value of the alkaline substances, specifically, in a range of 1.5 equivalents to 1.7 equivalents.

[0046] On the other hand, the basic substance can be added to the concentrated brine and stirred for a certain period of time. Specifically, after adding the basic substance in the first step, stirring can be carried out for 10 minutes to 1 hour; after adding the basic substance in the second step, stirring can be carried out for 30 minutes to 3 hours. In addition, after adding the basic substance in the second step, the stirring time can be about 2 to 3 times the stirring time after adding the basic substance in the first step. This is beneficial to effectively precipitate magnesium while controlling the particle size of the precipitate.

[0047] For the precipitate formed by adding the basic substance to the concentrated brine, the particle size (D10) at which the cumulative volume distribution in the particle size distribution reaches 10% may be in the range of 7.0 μm to 9.0 μm, and the dispersion degree (D50 / D10) may be in the range of 3 to 4.

[0048] Next, in the step of separating the precipitate (S3), the precipitate is separated by using the filter cloth of the filtration separation device, and the brine filtrate after removing magnesium can be obtained. The filtration separation device or the filter cloth can be the filtration separation device or the filter cloth used in the conventional lithium recovery process or impurity removal process in brine, and is not limited thereto.

[0049] On the other hand, in the step of separating the precipitate (S3), the concentration of magnesium (Mg) in the brine solution remaining after separating the precipitate can be 0.003 g / L or less.

[0050] Next, the preferred embodiments and comparative examples of the present invention will be described. However, the following embodiments are only the preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0051] First, concentrated brine containing the components in Table 1 below was prepared.

[0052]

Table 1

[0053]

[0054] (Example 1)

[0055] Using the concentrated brine 2 in Table 1 as the raw material, Ca(OH)2 was used as the basic substance, and Ca(OH)2 was added to the concentrated brine 2 in two steps. The total amount of Ca(OH)2 added to the concentrated brine 2 in two steps was 1.6 times (1.6 equivalents) of the theoretically calculated value of Ca(OH)2 required when all the Mg components contained in the concentrated brine 2 reacted to form Mg(OH)2.

[0056] Here, in the first step, after adding 0.1 times (0.1 equivalent) of the theoretically calculated value of Ca(OH)2, stirring is carried out for 30 minutes; in the second step, after adding 1.5 times (1.5 equivalents) of the theoretically calculated value of Ca(OH)2, stirring is carried out for 1 hour and 30 minutes, and then the reaction is terminated. After the reaction is completed, the precipitated final product is separated into solid and liquid by a pressurized solid-liquid separation device, and an experiment for removing magnesium from the concentrated brine is carried out.

[0057] (Examples 2 to 5)

[0058] In the first step, Ca(OH)2 is added at 0.3 equivalents (Example 2), 0.5 equivalents (Example 3), 0.7 equivalents (Example 4), and 0.9 equivalents (Example 5) of the theoretically calculated value respectively. In the second step, Ca(OH)2 is added at 1.3 equivalents (Example 2), 1.1 equivalents (Example 3), 0.9 equivalents (Example 4), and 0.7 equivalents (Example 5) of the theoretically calculated value respectively. Except for this, an experiment for removing magnesium from the concentrated brine is carried out in the same manner as in Example 1.

[0059] (Examples 6 to 8)

[0060] Except for using concentrated brine 1, concentrated brine 3, and concentrated brine 4 in Table 1, magnesium is also removed from the concentrated brine in the same manner as in Example 3.

[0061] (Examples 9 to 11)

[0062] Except for using concentrated brine 1, concentrated brine 3, and concentrated brine 4 in Table 1, an experiment for removing magnesium from the concentrated brine is also carried out in the same manner as in Example 5.

[0063] (Comparative Examples 1 to 4)

[0064] Using concentrated brine 1 to 4 in Table 1 as the raw material concentrated brine, and using Ca(OH)2 as the alkaline substance. For each concentrated brine, 1.6 times (1.6 equivalents) of the theoretically calculated value of Ca(OH)2 is added so that all the Mg components contained therein react to form Mg(OH)2, and the reaction is terminated after stirring for 2 hours. After the reaction is completed, the final product of the precipitated precipitate is separated into a solid phase and a liquid phase using a pressurized solid-liquid separation device.

[0065] According to Examples 1 to 11 and Comparative Examples 1 to 3, after the reaction is completed, samples of the generated final products are taken, and analysis is carried out using the particle size of the precipitate, which is summarized in Table 2 below. In the present invention, the particle size analysis of the precipitate is carried out using Mastersizer 3000 of Malvern Company, and the sampled slurry is analyzed by wet laser particle size analysis method.

[0066] In addition, according to Embodiments 1 to 11 and Comparative Examples 1 to 3, after the reaction was completed, the weight of the final product was measured, and then the filtration rate was calculated by dividing the time required to completely separate the solid phase and the liquid phase by the filter cloth area of the pressure solid-liquid separation device, and the results are presented in Table 2.

[0067] Through the pressure type solid-liquid separation device, the liquid substance is collected by an independent collection device, and the solid substance remains on the surface of the filter cloth in the form of a cake. By applying a certain impact to the cake, it can fall off from the filter cloth. During this process, the detachability of the cake was evaluated by observing the microscopic structure of the filter cloth surface after detachment.

[0068] The detachability was rated as Δ: average, ○: excellent, ◎: very excellent.

[0069] The detachability of the cake was relatively compared by visually observing whether the cake could be well separated from the surface of the filter cloth when removing the cake on the surface of the filter cloth after the solid-liquid separation was completed. If the cake particles adhered to the surface of the filter cloth, it was judged as average or below; if the cake was smoothly removed and there was almost no residue on the surface of the filter cloth, it was judged as excellent; and when there was no residue on the surface of the filter cloth after the cake was removed and there was no trace of the cake adhering to the surface of the filter cloth, it was judged as very excellent.

[0070] In addition, the Mg residual concentration of the filtrate separated by the pressure type solid-liquid separation device was measured by ICP analysis.

[0071]

Table 2

[0072]

[0073]

[0074] Referring to the results of Example 6, Example 9 and Comparative Example 1 using concentrated brine 1 as the raw material, it can be confirmed that the filtration rate was increased by about 53% and about 37% respectively, and the cake detachment performance was improved.

[0075] If referring to the results of Examples 1 to 5 and Comparative Example 2 using concentrated brine 2 as the raw material, in the case of Examples 1 to 5, compared with Comparative Example 2, it can be confirmed that the filtration rate was increased by about 30% to 74%, and the cake detachability was also improved.

[0076] Referring to the results of Example 7, Example 10 and Comparative Example 3 using concentrated brine 3 as the raw material, it can be confirmed that in Example 7 and Example 10, compared with Comparative Example 3, the filtration rate was increased by about 63% and about 39% respectively, and the cake detachment performance was also improved.

[0077] Referring to the results of Example 8, Example 11 and Comparative Example 4 using concentrated brine 4 as the raw material, it was found that compared with Comparative Example 3, the filtration rates of Example 7 and Example 10 increased by approximately 47% and 36% respectively, and the filter cake release property was also improved.

[0078] Figure 2 The SEM image of the precipitate precipitated according to Example 4 of the present invention is shown, Figure 3 The SEM image of the precipitate precipitated according to Comparative Example 2 of the present invention is shown.

[0079] Referring to Figure 2 and Figure 3 , it can be confirmed that the precipitate precipitated according to Example 4 of the present invention has a relatively larger particle diameter compared to the precipitate precipitated according to Comparative Example 2.

[0080] From the experimental results, it can be confirmed that by adjusting the addition ratio of the alkaline substance to control the initial pH value at a lower level, the filtration rate of the precipitate increased by approximately 30% to 80%, and the filter cake release performance was also improved.

[0081] Therefore, by increasing the filtration rate and improving the filter cake release performance, the cycle time of the magnesium removal process in the brine can be shortened, and the replacement cycle of the filtration membrane can be extended. In addition, not only can the productivity of the magnesium removal process in the brine be improved, but also the economy of the entire process can be improved.

[0082] The present invention is not limited to the above embodiments, but can be implemented in various different forms, and those skilled in the art to which the present invention pertains should understand that the present invention can be implemented in other specific forms without changing the technical idea or basic characteristics of the present invention. Therefore, it should be understood that the above embodiments are exemplary in all aspects and not restrictive.

Claims

1. A method for removing magnesium from brine, comprising: A step of preparing concentrated brine; A step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size; And A step of separating the precipitate.

2. The method for removing magnesium from brine according to claim 1, wherein The step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size comprises: A first step of adding an alkaline substance and a second step of adding an alkaline substance.

3. The method for removing magnesium from brine according to claim 2, wherein In the first step of adding an alkaline substance and the second step of adding an alkaline substance, The alkaline substance is added in a molar ratio range of 1:0.5 to 1:20 in the first step and the second step.

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

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

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

7. The method for removing magnesium from brine according to claim 1, wherein In the step of separating the precipitate, the magnesium (Mg) component concentration in the brine after separating the precipitate is 0.003 g / L or less.

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

9. The method for removing magnesium from brine according to claim 1, wherein In the step of gradually adding an alkaline substance to the concentrated brine to precipitate a precipitate with a controlled particle size, The alkaline substance is a calcium-containing substance.

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