Pretreatment method and application of high-magnesium boron-containing brine

Abstract

The invention relates to the technical field of extraction of lithium from brine, and provides a pretreatment method of high-magnesium boron-containing brine and application thereof. Before entering an electrodialysis lithium extraction device, the high-magnesium boron-containing brine is pretreated, and the method comprises the following steps: diluting the high-magnesium boron-containing brine with water to obtain diluted high-magnesium boron-containing brine; adding a seed crystal into the diluted high-magnesium boron-containing brine, stirring, standing and settling, and taking supernate to obtain first pretreated high-magnesium boron-containing brine; and adding acid into the first pretreated high-magnesium boron-containing brine to adjust the pH value to 5.0-6.5. Through the mode, the concentration of boron ions in the brine can be reduced, the influence of precipitation of magnesium borate on an electrodialysis membrane is reduced, and the stability and continuity in the electrodialysis lithium extraction process can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium extraction from brine, and in particular to a pretreatment method for high-magnesium and boron-containing brine and application thereof. Background Art

[0002] More than 70% of the world's industrial lithium reserves come from salt lakes. With the development of new energy vehicles, the demand for lithium resources has grown rapidly, making the salt lake lithium extraction technology receive greater attention. The technologies for extracting lithium from salt lake brine include evaporation crystallization, precipitation, extraction, adsorption, calcination, electrodialysis, and electrochemical deintercalation. Electrodialysis is a lithium extraction operation that uses potential difference as a driving force and the selective permeability of ion exchange membranes to separate or enrich ions from lithium-containing solutions. At present, the use of electrodialysis to extract lithium has been industrialized, with stable production and good economic benefits.

[0003] The electrodialysis method uses lithium-containing old brine as raw material for electrodialysis operation. Usually, lithium-containing old brine contains more magnesium ions and boron ions (high-magnesium boron-containing brine). During the electrodialysis process, magnesium borate salts often precipitate to contaminate the electrodialysis membrane, resulting in decreased current efficiency, increased energy consumption, reduced lithium extraction efficiency, and reduced membrane life, which seriously affects the stability and continuity of the electrodialysis lithium extraction process. In order to solve the problem of magnesium borate salt precipitation and contamination of the electrodialysis membrane, high-concentration acid is usually added to adjust the pH of high-magnesium boron-containing brine to 1-2 for acidification and boron removal. However, this method consumes a large amount of high-concentration acid, which is not only costly but also environmentally polluting.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a pretreatment method for high-magnesium boron-containing brine and its application. The method aims to reduce the boron content in high-magnesium boron-containing brine and inhibit the precipitation of magnesium borate, thereby reducing the precipitation of magnesium borate in the process of electrodialysis lithium extraction, preventing the contamination of the electrodialysis membrane, extending the service life of the electrodialysis membrane, and facilitating the improvement of the stability and continuity in the process of electrodialysis lithium extraction.

[0006] In a first aspect, the present invention provides a method for pretreating high-magnesium boron-containing brine, the pretreatment method comprising the following steps: S1: diluting the high-magnesium boron-containing brine with water to obtain diluted high-magnesium boron-containing brine; S2: adding seed crystals to the diluted high-magnesium boron-containing brine, stirring and then standing to settle, taking the supernatant to obtain the first pretreated high-magnesium boron-containing brine; S3: adding acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 5.0-6.5 to obtain a second pretreated high-magnesium boron-containing brine.

[0007] In an optional embodiment, the volume ratio of the high-magnesium boron-containing brine to water dilution is 1:(0.1-2).

[0008] In an optional embodiment, the seed crystal is a magnesium borate salt, including at least one of kieserite, kieserite, magnesium hexaborate, kieserite, kieserite and kieserite.

[0009] In an optional embodiment, the ratio of the mass of boron in the seed crystal to the mass of boron in the diluted high-magnesium boron-containing brine is (0.001-0.05):1.

[0010] In an optional embodiment, the stirring time is 1h-48h, and the stirring temperature is -15°C to 25°C; The static sedimentation time is 7 days to 60 days, and the static sedimentation temperature is -15°C to 25°C.

[0011] In an optional embodiment, the step S2 comprises: adding seed crystals to the diluted high-magnesium boron-containing brine, stirring and then allowing to settle, taking the supernatant for ultrafiltration treatment, and obtaining a first pretreated high-magnesium boron-containing brine.

[0012] In an alternative embodiment, the acid comprises at least one of hydrochloric acid, sulfuric acid and nitric acid.

[0013] In a second aspect, the present invention provides an application of a pretreatment method for high-magnesium boron-containing brine as described in the first aspect, wherein the pretreatment method for high-magnesium boron-containing brine is used in the technical field of electrodialysis lithium extraction, and the high-magnesium boron-containing brine is a magnesium saturated solution containing lithium.

[0014] The present invention has the following beneficial effects: the pretreatment method of high-magnesium boron-containing brine can reduce the boron content of the brine, thereby effectively inhibiting the precipitation of solid magnesium borate salt from the brine during the electrodialysis process. The high-magnesium boron-containing brine is diluted and seed crystals are added, and the synergistic effect of the two accelerates the precipitation of solid magnesium borate salt in the brine and reduces the concentration of boron ions and magnesium ions in the brine; then the brine is adjusted to be weakly acidic by adding acid, so that part of the magnesium borate salt is converted into boric acid, and the precipitation of magnesium borate salt is further inhibited. The method is simple, efficient, energy-saving and environmentally friendly, can extend the service life of the electrodialysis membrane, and is conducive to improving the stability and continuity of the electrodialysis lithium extraction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 is a process flow chart of an embodiment of the present invention; Figure 2 This is a graph showing the change in current density during the electrodialysis lithium extraction process of Example 1 of the present invention; Figure 3 This is a graph showing the change in current density during the electrodialysis lithium extraction process of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below. The techniques, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the techniques, methods and equipment should be regarded as part of the specification. If the specific conditions are not specified in the embodiments, they are carried out according to the normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0018] The pretreatment method and application of high-magnesium boron-containing brine provided by the present invention are specifically described below.

[0019] The present invention provides a pretreatment method for high-magnesium boron-containing brine, the treatment method comprising the following steps: S1: diluting the high-magnesium boron-containing brine with water to obtain diluted high-magnesium boron-containing brine; S2: adding seed crystals to the diluted high-magnesium boron-containing brine, stirring and then standing to settle, taking the supernatant to obtain the first pretreated high-magnesium boron-containing brine; S3: adding acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 5.0-6.5 to obtain a second pretreated high-magnesium boron-containing brine.

[0020] Specifically, the present invention will explain each of the above steps one by one to obtain the treated high-magnesium boron-containing brine.

[0021] In some embodiments, the volume ratio of the high-magnesium boron-containing brine to water dilution is 1:(0.1-2), preferably 1:(0.5-1).

[0022] There are abnormal phenomena such as "supersaturated solubility" and "dilution to form salts" in the high-magnesium boron-containing brine system. The present invention promotes the precipitation of magnesium borate by diluting the high-magnesium boron-containing brine. The principle is that after evaporation and concentration, the boron-containing magnesium brine forms a high-concentration brine (high-magnesium boron-containing brine), and the borate anions mainly exist in the form of highly polymerized boron-oxygen complex anions, which are not easy to precipitate with magnesium ions to form salts; dilution with water causes the highly polymerized boron-oxygen complex anions in the solution to depolymerize with water to form low-polymerized boron-oxygen complex anions, which are easier to crystallize with magnesium ions to form salts. At the same time, according to the acid-base equilibrium theory, magnesium borate, as a strong base and weak acid salt, has a greater solubility in an acidic environment; the highly polymerized boron-oxygen complex anions release OH during the depolymerization process of adding water. - ions increase the pH of the brine system, the solubility of magnesium borate in the diluted high-magnesium borate-containing brine becomes smaller, and it is easier to precipitate magnesium borate solids.

[0023] The volume ratio of high-magnesium boron-containing brine and water dilution will affect the precipitation of magnesium borate. When there is too much water in the mixed dilution, the boron concentration in the diluted high-magnesium boron-containing brine decreases, resulting in a decrease in supersaturation concentration and a slow precipitation rate of magnesium borate; when there is too little water in the mixed dilution, the viscosity of the diluted high-magnesium boron-containing brine is large, the diffusion effect is weakened, and the precipitation rate of magnesium borate slows down.

[0024] In some embodiments, the seed crystal is a magnesium borate salt, including at least one of kieserite, kieserite, magnesium hexaborate, kieserite, kieserite and kieserite.

[0025] In some embodiments, the mass ratio of boron in the seed crystal to the mass ratio of boron in the diluted high-magnesium boron-containing brine is (0.001-0.05):1, preferably (0.001-0.01):1.

[0026] In some embodiments, the stirring time is 1h-48h, for example, it can be any one of 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 20h, 28h, 38h, 48h, or a range between any two of them; the stirring temperature is -15°C to 25°C, for example, it can be any one of -15°C, -10°C, -5°C, 0°C, 4°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range between any two of them.

[0027] In some embodiments, the standing time is 7d-60d, for example, it can be any one of 7d, 10d, 15d, 20d, 25d, 30d, 35d, 60d, or a range between any two of them; the standing temperature is -15°C to 25°C, for example, it can be any one of -15°C, -10°C, -5°C, 0°C, 4°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range between any two of them.

[0028] A lower stirring temperature or standing temperature will lead to a decrease in the solubility of magnesium borate in the diluted high-magnesium boron-containing brine, which is conducive to the crystallization and precipitation of magnesium borate salt. However, if the stirring temperature or standing temperature is too low, impurity salts such as magnesium sulfate and magnesium chloride are easily precipitated, which will cause the loss of lithium in the brine during the precipitation of impurity salts. Dilution to salt often requires a long period of standing to promote the precipitation of magnesium borate salt. The present invention adds seed crystals to the diluted high-magnesium boron-containing brine, which can further accelerate the precipitation of magnesium borate salt.

[0029] In some embodiments, seed crystals are added to the diluted high-magnesium boron-containing brine, stirred and then allowed to stand for sedimentation, and the supernatant is subjected to ultrafiltration to obtain a first pretreated high-magnesium boron-containing brine.

[0030] In some embodiments, acid is added to the first pretreated high-magnesium boron-containing brine to adjust its pH to 5.0-6.5. For example, the pH can be any one of 5.0, 5.2, 5.4, 5.8, 6.0, 6.2, 6.4, 6.5 or a range between any two of them.

[0031] Similarly, according to the acid-base balance theory, the solubility of magnesium borate can be greatly improved in an acidic environment, thereby effectively reducing the precipitation of magnesium borate in the electrodialysis lithium extraction process of high-magnesium borate brine. Therefore, adding a small amount of acid to the first pre-treated high-magnesium borate brine to make the system weakly acidic with a pH of 5.0-6.5 can reduce the occurrence of problems such as membrane pollution, reduced membrane life, and membrane performance degradation caused by the precipitation of magnesium borate.

[0032] In some embodiments, the acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0033] The present invention also provides an application of a pretreatment method for high-magnesium boron-containing brine in the field of electrodialysis lithium extraction technology. The pretreated high-magnesium boron-containing brine is placed in an electrodialysis lithium extraction device to perform electrodialysis separation to prepare a solution with a high lithium content, and then the solution with a high lithium content is subjected to deep impurity removal, concentration, lithium precipitation, demagnetization, drying and other steps to obtain lithium carbonate.

[0034] In some embodiments, the high-magnesium boron-containing brine is a magnesium saturated solution containing lithium, wherein the concentration of boron ions is preferably 3 g / L-15 g / L.

[0035] The features and performance of the present invention are further described in detail below in conjunction with the accompanying drawings, examples and comparative examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0036] Example 1 This embodiment provides a method for pretreating high-magnesium boron-containing brine, comprising the following steps: S1: Take 400L of high-magnesium boron-containing brine from the Laolu Salt Field of Dongtai Lithium Resources and mix it with water in a volume ratio of 1:1 to obtain diluted high-magnesium boron-containing brine.

[0037] S2: After adding 100 g of schistite to the diluted high-magnesium boron-containing brine, slowly stir at 15° C. for 4 hours, then let it stand for 15 days, and take the supernatant for ultrafiltration to obtain the first pretreated high-magnesium boron-containing brine.

[0038] S3: adding hydrochloric acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 6.22 to obtain a second pretreated high-magnesium boron-containing brine.

[0039] The boron precipitation rate is 18.6%.

[0040] Instructions attached Figure 2 This is a graph showing the current density change during the electrodialysis process of lithium extraction at a constant voltage for 256 hours in the second pretreated high-magnesium boron-containing brine obtained in this embodiment. It can be seen that the current density changes relatively steadily, which means that the electrodialysis lithium extraction process is running stably. At the same time, the mold stack is dismantled to check that there is no magnesium borate salt precipitation in the membrane, pipeline, circulation tank, etc.

[0041] Example 2 This embodiment provides a method for pretreating high-magnesium boron-containing brine, comprising the following steps: S1: Take 20L of high-magnesium boron-containing brine from the Uyuni Salt Lake in Bolivia and mix it with water in a volume ratio of 1:1 to obtain diluted high-magnesium boron-containing brine.

[0042] S2: After adding 5g of Zhang's boraxite and 5g of boraxite to the diluted high-magnesium boron-containing brine, slowly stir for 6h at 5°C, then let it stand for 25d, take the supernatant and perform ultrafiltration treatment to obtain the first pretreated high-magnesium boron-containing brine.

[0043] S3: adding nitric acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 6.07 to obtain a second pretreated high-magnesium boron-containing brine.

[0044] The boron precipitation rate is 41.5%.

[0045] Example 3 This embodiment provides a method for pretreating high-magnesium boron-containing brine, comprising the following steps: S1: Take 400L of high-magnesium boron-containing brine from the Uyuni Salt Lake in Bolivia and mix it with water in a volume ratio of 1:2 to obtain diluted high-magnesium boron-containing brine.

[0046] S2: After adding 1360 g of schistite to the diluted high-magnesium boron-containing brine, slowly stir at -15°C for 48 hours, then let it stand for 60 days, take the supernatant and perform ultrafiltration treatment to obtain the first pretreated high-magnesium boron-containing brine.

[0047] S3: adding hydrochloric acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 6.5 to obtain a second pretreated high-magnesium boron-containing brine.

[0048] The boron precipitation rate is 15.11%.

[0049] Example 4 This embodiment provides a method for pretreating high-magnesium boron-containing brine, comprising the following steps: S1: Take 400L of high-magnesium boron-containing brine from the Laolu Salt Field of Dongtai Lithium Resources and mix it with water in a volume ratio of 1:0.1 to obtain diluted high-magnesium boron-containing brine.

[0050] S2: After adding 18.2 g of Zhang's boron magnesium stone to the diluted high-magnesium boron-containing brine, slowly stir at 25°C for 1 hour, then let it stand and settle for 7 days, take the supernatant and perform ultrafiltration treatment to obtain the first pretreated high-magnesium boron-containing brine.

[0051] S3: adding hydrochloric acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 5.0 to obtain a second pretreated high-magnesium boron-containing brine.

[0052] The boron precipitation rate is 11.10%.

[0053] Comparative Example 1 In this embodiment, no pretreatment is performed on the high-magnesium boron-containing brine.

[0054] Instructions attached Figure 3 This is the current density change diagram of the high-magnesium boron-containing brine in Comparative Example 1 during the constant voltage and continuous 256h electrodialysis lithium extraction process in Experiment 3. It can be seen that as the electrodialysis lithium extraction process proceeds, the current density shows a downward trend, and at the same time, the mold stack is dismantled to check that the membrane, pipeline, circulation tank, etc. all have magnesium borate salt precipitation.

[0055] Test Example 1: Ion Concentration Test Inductively coupled plasma atomic emission spectrometry (ICP-OES) was used to determine the ion concentration in the solution. The test results are shown in Tables 1 to 4.

[0056] Test Example 2: Calculation of Boron Separation Rate

[0057] The above formula is used to calculate the boron precipitation rate ω(B) , where is the mass of precipitated solid (g), is the content of B in the precipitated solid (%), is the mass of seed added (g), is the content of B in the seed crystal (%), is the B content of the feed brine (g / L), is the volume of feed brine (L).

[0058] Test Example 3 The effective area of ​​a single membrane is 0.02m 2 The electrodialysis lithium extraction device containing 40 pairs of electrodialysis membrane stacks was used to continuously perform electrodialysis lithium extraction for 256 hours on the brine obtained in the above-mentioned embodiment and comparative example at a constant voltage. The membrane pair voltage for electrodialysis lithium extraction was 0.5V, and the lithium extraction temperature was 33°C.

[0059] Table 1

[0060] Table 2

[0061] Table 3

[0062] Table 4

[0063] It can be seen from Tables 1 to 4 that the high-magnesium boron-containing brine of the embodiments will have varying degrees of crystallization and precipitate magnesium borate when seed crystals are added after dilution. The boron ion concentration in the first pretreated high-magnesium boron-containing brine obtained after ultrafiltration is significantly reduced, which is beneficial to reduce the precipitation of magnesium borate salt during the electrodialysis process.

[0064] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for pretreating high-magnesium boron-containing brine, characterized in that: The pretreatment method comprises the following steps: S1: diluting the high-magnesium boron-containing brine with water to obtain diluted high-magnesium boron-containing brine; S2: adding seed crystals to the diluted high-magnesium boron-containing brine, stirring and then standing to settle, taking the supernatant to obtain the first pretreated high-magnesium boron-containing brine; S3: adding acid to the first pretreated high-magnesium boron-containing brine to adjust its pH to 5.0-6.5 to obtain a second pretreated high-magnesium boron-containing brine.

2. The method for pretreating high-magnesium boron-containing brine according to claim 1, characterized in that: The volume ratio of the high-magnesium boron-containing brine to water dilution is 1:(0.1-2).

3. The pretreatment method of high-magnesium boron-containing brine according to claim 1-2, characterized in that: The seed crystal is a magnesium borate salt, including at least one of boraxite, boraxite, magnesium hexaborate, boraxite, boraxite and boraxite.

4. The pretreatment method of high-magnesium boron-containing brine according to claims 1-3, characterized in that: The mass ratio of the boron in the seed crystal to the boron in the diluted high-magnesium boron-containing brine is (0.001-0.05):

1.

5. The pretreatment method of high-magnesium boron-containing brine according to claims 1-4, characterized in that: Step S2 satisfies at least one of the following conditions ①-②: ① The stirring time is 1h-48h, and the stirring temperature is -15°C to 25°C; ② The static sedimentation time is 7d-60d, and the static sedimentation temperature is -15℃ to 25℃.

6. The method for pretreating high-magnesium boron-containing brine according to claim 1, characterized in that: The step S2 comprises: adding seed crystals to the diluted high-magnesium boron-containing brine, stirring and then standing to settle, taking the supernatant for ultrafiltration treatment to obtain the first pretreated high-magnesium boron-containing brine.

7. The method for pretreating high-magnesium boron-containing brine according to claim 1, characterized in that: The acid includes at least one of hydrochloric acid, sulfuric acid and nitric acid.

8. An application of the method for pretreating high-magnesium boron-containing brine according to claim 1, characterized in that: The pretreatment method of the high-magnesium boron-containing brine is used in the technical field of electrodialysis lithium extraction, and the high-magnesium boron-containing brine is a magnesium saturated solution containing lithium.

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