A method for extracting lithium from salt lakes

Abstract

The present application provides a method for extracting lithium from salt lakes. The method comprises the following steps: (1) subjecting concentrated brine to ammonia vapor magnesium precipitation treatment to obtain a magnesium-removed filtrate and filter residue; (2) mixing the filter residue with hydrobromic acid, adjusting the pH to precipitate boric acid, and performing solid-liquid separation to obtain a filtrate and boric acid; (3) evaporating and concentrating the filtrate obtained in step (2), performing aeration treatment after drying treatment, and performing water immersion separation treatment to obtain a lithium-rich solution and magnesium oxide; (4) mixing the lithium-rich solution and lithium carbonate to perform a solid-phase transformation reaction, and filtering to obtain a purified lithium salt solution and calcium carbonate. The method of the present application can separate boron, magnesium, and calcium-lithium in one step, and further calcium removal can separate calcium and lithium, which is beneficial to obtaining high-purity lithium carbonate and reducing lithium loss caused by the adsorption of lithium by magnesium hydroxide colloid.

Description

Technical Field

[0001] This application belongs to the technical field of lithium extraction from salt lakes, such as a method for extracting lithium from salt lakes. Background Art

[0002] Lithium, as the lightest and smallest-radius alkaline earth metal in nature, has active chemical properties. Lithium and its compounds have many special properties, making them widely used in the fields of aviation, medicine, chemical engineering, and new energy. Therefore, the development and utilization of lithium resources have received extensive attention. Although China has large reserves of lithium salts in salt lakes, the magnesium-lithium ratio is relatively high, and how to comprehensively recycle and utilize them remains a difficult problem.

[0003] The main methods for lithium extraction include extraction method, adsorption method, ion exchange method, membrane separation method, precipitation method, etc. Except for the precipitation method, the above methods have not yet achieved true industrial production.

[0004] The precipitation method generally directly uses sodium carbonate to precipitate lithium ions in the salt lake to produce lithium carbonate, but this method is not applicable in brines with a high magnesium-lithium ratio. The improvement of the precipitation method is generally to first generate magnesium hydroxide precipitation to remove magnesium, and then obtain lithium carbonate. However, magnesium hydroxide is in a gel state, difficult to filter, and the gel-like precipitate is extremely likely to adsorb lithium ions, resulting in a significant reduction in the lithium ion recovery rate.

[0005] CN112850758A discloses a lithium extraction system and method for salt lake brine. The lithium extraction system includes: a continuous magnesium removal device, a continuous lithium precipitation device, and a continuous washing device; the continuous magnesium removal device is used to continuously remove magnesium from lithium-rich brine with sodium hydroxide solution to obtain magnesium-removed liquid and magnesium slag; the continuous lithium precipitation device is connected to the continuous magnesium removal device and is used to continuously precipitate lithium from the magnesium-removed liquid to obtain crude lithium carbonate and lithium precipitation mother liquor; and the continuous washing device is connected to the continuous lithium precipitation device and is used to continuously wash the crude lithium carbonate to obtain lithium carbonate solid.

[0006] CN112661321A discloses a salt lake lithium extraction system and method based on membrane separation. The method includes the steps of: 1) deep magnesium removal; 2) deep boron removal; 3) preparation of lithium carbonate; 4) recycling of lithium precipitation mother liquor.

[0007] The above-mentioned salt lake lithium extraction methods have the problem of low lithium ion recovery rate. How to overcome the above defects and improve the lithium recovery rate is a difficult problem. Summary of the Invention

[0008] The following is an overview of the subject matter described in detail in this article. This overview is not intended to limit the scope of protection of the claims.

[0009] This application provides a method for extracting lithium from salt lakes. The method of this application can separate boron, magnesium, and calcium-lithium in one step, and further calcium removal can separate calcium and lithium, which is beneficial to obtaining high-purity lithium carbonate and reducing lithium loss caused by the adsorption of lithium by magnesium hydroxide colloid.

[0010] To achieve the purpose of this application, the following technical solutions are adopted in this application:

[0011] The embodiment of this application provides a method for extracting lithium from salt lakes, and the method includes the following steps:

[0012] (1) Perform ammonia vapor magnesium precipitation treatment on the concentrated brine to obtain a magnesium-removed filtrate and filter residue;

[0013] (2) Mix the filter residue with hydrobromic acid, adjust the pH to precipitate boric acid crystals, and perform solid-liquid separation to obtain a filtrate and boric acid;

[0014] (3) Evaporate and concentrate the filtrate obtained in step (2), perform ventilation treatment after drying, and perform water immersion separation treatment to obtain a lithium-rich solution and magnesium oxide;

[0015] (4) Mix the lithium-rich solution and lithium carbonate for a solid-phase conversion reaction, and filter to obtain a purified lithium salt solution and calcium carbonate.

[0016] Due to the presence of boron elements, it will affect the high-temperature performance of magnesium oxide. Magnesium hydroxide is a colloid, and boron elements and lithium elements are easily co-precipitated by being adsorbed by Mg(OH) 2 colloid, which will cause about 15% lithium loss and the presence of boron impurities, and it is difficult to remove lithium by washing with water. The embodiment of this application can remove boron before preparing magnesium hydroxide, and can prepare high-purity magnesium oxide using brine. And using the properties of magnesium bromide, magnesium oxide can be prepared without high-temperature calcination, which can save energy and reduce carbon emissions.

[0017] In one embodiment, the Baumé degree of the concentrated brine in step (1) is 18-24 °Bé, for example: 18 °Bé, 19 °Bé, 20 °Bé, 22 °Bé or 24 °Bé, etc.

[0018] In one embodiment, the feeding rate of the concentrated brine in step (1) is 100-120 m 3 / h, for example: 100 m 3 / h, 105 m 3 / h, 110 m 3 / h, 115 m 3 / h or 120 m 3 / h, etc.

[0019] In one embodiment, the flow rate of the ammonia vapor is 20 to 30 t / h, for example: 20 t / h, 22 t / h, 25 t / h, 28 t / h, or 30 t / h, etc.

[0020] In one embodiment, the temperature of the ammonia vapor for magnesium precipitation treatment is 80 to 100 °C, for example: 80 °C, 85 °C, 90 °C, 95 °C, or 100 °C, etc.

[0021] In one embodiment, the pH of the ammonia vapor for magnesium precipitation treatment is 11 to 12, for example: 11, 11.2, 11.5, 11.8, or 12, etc.

[0022] In one embodiment, the molar amount of hydrobromic acid added in step (2) is 1.05 to 1.2 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue, for example: 1.05 times, 1.08 times, 1.1 times, 1.15 times, or 1.2 times, etc.

[0023] Magnesium bromide reacts with oxygen to form magnesium oxide and bromine gas. Lithium bromide is not easily deteriorated or decomposed in the atmosphere, and boric acid precipitates, which can be directly separated.

[0024] In one embodiment, the pH in step (2) is 1 to 4, for example: 1, 2, 3, or 4, etc.

[0025] In one embodiment, the drying treatment in step (3) is carried out under vacuum conditions.

[0026] In one embodiment, the temperature of the drying treatment is 100 to 120 °C, for example: 100 °C, 105 °C, 110 °C, 115 °C, or 120 °C, etc.

[0027] In one embodiment, the time of the drying treatment is 3 to 5 h, for example: 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc.

[0028] In one embodiment, the gas for the ventilation treatment in step (3) includes air and / or oxygen.

[0029] In one embodiment, the gas flow rate of the ventilation treatment is 100 to 1000 mL / min, for example: 100 mL / min, 200 mL / min, 500 mL / min, 800 mL / min, or 1000 mL / min, etc.

[0030] In one embodiment, the time of the ventilation treatment is 8 to 24 h, for example: 8 h, 10 h, 12 h, 16 h, 20 h, or 24 h, etc.

[0031] In one embodiment, the molar ratio of the lithium carbonate to the calcium ions in the lithium-rich solution in step (3) is (1.05 - 1.2):1, for example: 1.05:1, 1.08:1, 1.1:1, 1.15:1, or 1.2:1, etc.

[0032] In one embodiment, the temperature of the solid-phase transformation reaction in step (3) is 30 - 80 °C, for example: 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, or 80 °C, etc.

[0033] As an alternative solution of the present application, the method includes the following steps:

[0034] (1) Perform ammonia vapor magnesium precipitation treatment on the concentrated brine with a Baume degree of 18 - 24 °Bé at 80 - 100 °C and a pH of 11 - 12 at a feeding rate of the concentrated brine of 100 - 120 m 3 / h and a flow rate of ammonia vapor of 20 - 30 t / h to obtain a magnesium-removed filtrate and filter residue;

[0035] (2) Mix the filter residue with hydrobromic acid. The molar amount of the added hydrobromic acid is 1.05 - 1.2 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue. Adjust the pH to 1 - 4 until boric acid crystallizes out, and perform solid-liquid separation to obtain a filtrate and boric acid;

[0036] (3) Evaporate and concentrate the filtrate obtained in step (2), perform drying treatment at 100 - 120 °C, and then ventilate at a flow rate of 100 - 1000 mL / min for 8 - 24 h, and perform water immersion separation treatment to obtain a lithium-rich solution and magnesium oxide;

[0037] (4) Mix the lithium-rich solution and lithium carbonate according to a molar ratio of the lithium carbonate to the calcium ions in the lithium-rich solution of (1.05 - 1.2):1 to perform a solid-phase transformation reaction, and filter to obtain a purified lithium salt solution and calcium carbonate.

[0038] Compared with the related art, the present application has the following beneficial effects:

[0039] (1) The method for extracting lithium from salt lakes in the present application can remove boron before preparing magnesium hydroxide, and can use brine to prepare high-purity magnesium oxide. And by utilizing the properties of magnesium bromide, magnesium oxide can be prepared without high-temperature calcination, which can save energy and reduce carbon emissions.

[0040] (2) The lithium loss rate of the method for extracting lithium from salt lakes in the present application can reach below 2.31%.

[0041] Other aspects can be understood after reading and understanding the drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the technical solutions herein, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions herein, and do not constitute a limitation to the technical solutions herein.

[0043] Figure 1 It is a flowchart of the method for extracting lithium from salt lakes described in Embodiment 1 of the present application. Specific Embodiments

[0044] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present application and should not be regarded as specific limitations to the present application.

[0045] Embodiment 1

[0046] This embodiment provides a method for extracting lithium from salt lakes. The flowchart of the method is as Figure 1 shown. The method includes the following steps:

[0047] (1) Filter and purify the raw brine to remove sediment and other insoluble impurities, obtaining preliminarily purified brine. Evaporate the obtained brine to obtain concentrated brine in a nearly saturated state (20°Bé). Pass ammonia vapor through a continuous reaction system to carry out a magnesium precipitation reaction. Among them, the concentrated brine and ammonia vapor are fed at flow rates of 110 m3 / h and 25 t / h respectively. Control the reaction temperature between 80 and 90 °C, and the pH is 11 - 12. Filter the product to obtain magnesium-removed filtrate and filter residue;

[0048] (2) Add hydrobromic acid to the filter residue to adjust the pH of the brine to 2 until boric acid crystallizes out. Separate the solid and liquid to obtain filtrate and boric acid. Among them, the molar amount of hydrobromic acid added is 1.1 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue;

[0049] (3) After evaporating and concentrating the filtrate under vacuum conditions, dry it at 120 °C for 5 h. Subsequently, maintain the temperature and continuously introduce at least one of dry air and oxygen. The gas flow rate is 500 ml / min, and the ventilation time is 10 h. Separate magnesium and lithium calcium by water immersion to obtain a lithium-rich solution and magnesium oxide;

[0050] (4) Add lithium carbonate to the lithium-rich solution to carry out a solid-phase transformation reaction at 60 °C. Through the solid-phase transformation reaction of lithium carbonate to calcium carbonate, filter and separate calcium carbonate to obtain a purified lithium salt solution and calcium carbonate. Among them, the molar ratio of lithium carbonate added satisfies Li 2 CO 3 :Ca 2+ = 1.1:1.

[0051] Embodiment 2

[0052] This embodiment provides a method for extracting lithium from salt lakes. The flow chart of the method is as shown in Figure 1 and the method includes the following steps:

[0053] (1) Filter and purify the raw brine to remove sediment and other insoluble impurities, obtaining preliminarily purified brine. Evaporate the obtained brine to obtain concentrated brine close to the saturated state (19°Bé). Pass ammonia vapor through a continuous reaction system to carry out the magnesium precipitation reaction. Among them, the concentrated brine and ammonia vapor are fed at flow rates of 115 m3 / h and 27 t / h respectively. Control the reaction temperature between 85 and 95 °C, with a pH of 11 to 12. Filter the product to obtain magnesium-removed filtrate and filter residue;

[0054] (2) Add hydrobromic acid to the filter residue, adjust the pH of the brine to 1.5 until boric acid crystallizes out, and perform solid-liquid separation to obtain filtrate and boric acid. Among them, the molar amount of hydrobromic acid added is 1.12 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue;

[0055] (3) After evaporating and concentrating the filtrate under vacuum conditions, dry it at 120 °C for 5 h. Subsequently, maintain the temperature and continuously introduce at least one of dry air and oxygen. The gas flow rate is 400 ml / min, and the gas introduction time is 12 h. Perform water immersion to separate magnesium and lithium-calcium, obtaining a lithium-rich solution and magnesium oxide;

[0056] (4) Add lithium carbonate to the lithium-rich solution and carry out a solid-phase transformation reaction at 50 °C. Through the solid-phase transformation reaction of lithium carbonate to calcium carbonate, filter and separate calcium carbonate to obtain a purified lithium salt solution and calcium carbonate. Among them, the molar ratio of lithium carbonate added satisfies Li 2 CO 3 :Ca 2+ = 1.12:1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is only that hydrobromic acid is replaced with sulfuric acid, and other conditions and parameters are exactly the same as those in Example 1.

[0059] Comparative Example 2

[0060] This comparative example provides a method for extracting lithium from salt lakes. The method includes the following steps:

[0061] S1: Filter and purify the raw brine to remove sediment and other insoluble impurities, obtaining preliminarily purified brine.

[0062] S2: Evaporate the brine obtained in S1 to obtain concentrated brine close to the saturated state (20°Bé).

[0063] S3: Magnesium precipitation by ammonia method: Pass ammonia vapor through a continuous reaction system for magnesium precipitation reaction. Among them, concentrated brine and ammonia vapor are fed at flow rates of 110 m3 / h and 25 t / h respectively, control the reaction temperature between 80 and 90 °C, and the pH is 11 - 12.

[0064] S4: Filter the product of S3 to obtain magnesium-removed filtrate and filter residue.

[0065] S5: Add hydrochloric acid to the filter residue, adjust the pH of the brine to 2 until boric acid crystallizes out, and perform solid-liquid separation to obtain filtrate and boric acid. Among them, the molar amount of hydrochloric acid added is 1.1 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue.

[0066] S6: Evaporate and concentrate the filtrate, and dry it at 120 °C for 5 h under an air atmosphere. Subsequently, heat it to 400 °C at a heating rate of 5 °C / min and react for 3 h, continuously introduce at least one of air and oxygen, and the gas flow rate is 500 ml / min.

[0067] S7: Leach and separate magnesium from lithium and calcium to obtain a lithium-rich solution and magnesium oxide.

[0068] S8: Add lithium carbonate to the lithium-rich solution for solid-phase transformation reaction. Through the solid-phase transformation reaction of lithium carbonate to calcium carbonate, filter and separate calcium carbonate to obtain a purified lithium salt solution and calcium carbonate. The reaction temperature is 60 °C, and the molar ratio of lithium carbonate added satisfies Li 2 CO 3 : Ca 2+ = 1.1:1.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is only that hydrobromic acid is not added, and directly leach with water to obtain filter residue, and separate the washed filter residue and lithium-containing filtrate.

[0071] Performance test:

[0072] Use ICP test to measure the lithium ion concentration in the concentrated brine and calculate the lithium loss rate. The test results are shown in Table 1:

[0073] Table 1

[0074] Lithium ion concentration in concentrated brine (g / L) Lithium loss rate (%) Example 1 2.436 2.31 Example 2 2.437 2.28 Comparative Example 1 2.432 12.85 Comparative Example 2 2.434 5.34 Comparative Example 3 2.427 10.62

[0075] It can be seen from Table 1 that from Examples 1 - 2, the lithium loss rate of the lithium extraction method from salt lakes described in this application can reach below 2.31%.

[0076] It can be obtained by comparing Example 1 and Comparative Example 1 that the type of acid used in the lithium extraction method from salt lakes described in this application will affect the efficiency of lithium extraction from salt lakes. Replacing hydrobromic acid with common sulfuric acid can remove boron element, but magnesium and lithium elements cannot be further separated at this temperature.

[0077] It can be obtained by comparing Example 1 and Comparative Example 2 that when hydrobromic acid is replaced by hydrochloric acid, hydrolysis reaction occurs during the drying process to generate magnesium hydroxide, and then high-temperature treatment is carried out to obtain magnesium oxide, thereby separating magnesium and lithium elements. Replacing with hydrochloric acid can remove boron elements, but high temperature is required to separate magnesium and lithium, resulting in high energy consumption and high cost.

[0078] It can be obtained by comparing Example 1 and Comparative Example 3 that water immersion can wash away part of the lithium ions adsorbed by magnesium hydroxide colloid, but not all of the lithium ions.

Claims

1. A method for extracting lithium from salt lakes, the method comprises the following steps: (1) Carry out ammonia vapor magnesium precipitation treatment on concentrated brine to obtain magnesium-removed filtrate and filter residue; (2) Mix the filter residue with hydrobromic acid, adjust the pH to precipitate boric acid, and perform solid-liquid separation to obtain filtrate and boric acid; (3) Evaporate and concentrate the filtrate obtained in step (2), carry out ventilation treatment after drying treatment, and carry out water immersion separation treatment to obtain a lithium-rich solution and magnesium oxide; (4) Mix the lithium-rich solution and lithium carbonate for solid-phase conversion reaction, and filter to obtain a purified lithium salt solution and calcium carbonate.

2. The method according to claim 1, wherein, the Baume degree of the concentrated brine in step (1) is 18 - 24 °Bé.

3. The method according to claim 1, wherein, The feeding rate of the concentrated brine in step (1) is 100 - 120 m 3 / h.

4. The method according to claim 1, wherein, the flow rate of the ammonia vapor is 20 - 30 t / h.

5. The method according to claim 1, wherein, the temperature of the ammonia vapor magnesium precipitation treatment is 80 - 100 °C.

6. The method according to claim 1, wherein, the pH of the ammonia vapor magnesium precipitation treatment is 11 - 12.

7. The method according to claim 1, wherein, the molar amount of hydrobromic acid added in step (2) is 1.05 - 1.2 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue.

8. The method according to claim 1, wherein, the pH in step (2) is 1 - 4.

9. The method according to claim 1, wherein, the drying treatment in step (3) is carried out under vacuum conditions.

10. The method according to claim 1, wherein, the temperature of the drying treatment is 100 - 120 °C.

11. The method according to claim 1, wherein, the time of the drying treatment is 3 - 5 h.

12. The method according to claim 1, wherein, the gas for the ventilation treatment in step (3) includes air and / or oxygen.

13. The method according to claim 12, wherein, the gas flow rate for the ventilation treatment is 100 - 1000 mL / min.

14. The method according to claim 12, wherein, the time of the ventilation treatment is 8 - 24 h.

15. The method according to claim 1, wherein, the molar ratio of lithium carbonate to calcium ions in the lithium-rich solution in step (4) is (1.05 - 1.2):

1.

16. The method according to claim 1, wherein, the temperature of the solid-phase conversion reaction in step (4) is 30 - 80 °C.

17. The method according to claim 1, wherein, the method comprises the following steps: (1) The concentrated brine with a Baumé degree of 18 - 24°Bé is subjected to magnesium precipitation treatment with ammonia vapor at 80 - 100 °C and a pH of 11 - 12 at a feed rate of the concentrated brine of 100 - 120 m 3 / h and an ammonia vapor flow rate of 20 - 30 t / h to obtain a magnesium-removed filtrate and filter residue; (2) Mix the filter residue with hydrobromic acid, the molar amount of hydrobromic acid added is 1.05 - 1.2 times the total molar amount of boron, lithium, magnesium, and calcium ions in the filter residue, adjust the pH to 1 - 4 until boric acid crystallizes out, and perform solid-liquid separation to obtain filtrate and boric acid; (3) Evaporate and concentrate the filtrate obtained in step (2), carry out drying treatment at 100 - 120 °C, then ventilate at a flow rate of 100 - 1000 mL / min for 8 - 24 h, and carry out water immersion separation treatment to obtain a lithium-rich solution and magnesium oxide; (4) Mix the lithium-rich solution and lithium carbonate at a molar ratio of lithium carbonate to calcium ions in the lithium-rich solution of (1.05 - 1.2):1 to carry out a solid-phase transformation reaction. After filtration, a purified lithium salt solution and calcium carbonate are obtained.

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