Highly efficient and environmentally friendly method and device for extracting lithium from salt lakes

Abstract

The present invention relates to the technical field of lithium extraction from salt lakes, and is an efficient and environmentally friendly method and device for lithium extraction from salt lakes. The process of the former is as follows: the brine from the salt lake is successively passed through a pre-concentration unit, a pre-treatment nanofiltration unit, a primary concentration unit, a secondary nanofiltration unit, a secondary concentration unit, an electrolytic carbon lithium precipitation unit, an industrial carbon lithium precipitation unit and a tailings recovery unit to obtain battery-grade lithium carbonate products, industrial-grade lithium carbonate products and recyclable heavy metal mixed salts. By combining a production method integrating three-stage concentration, two-stage nanofiltration and two-stage lithium precipitation technologies, the present invention can meet the lithium extraction requirements of various different types of salt lakes, has low energy consumption, does not add external chemical agents, has good environmental affinity, meets the requirements of environmental protection production, and can effectively comprehensively utilize other resources in the salt lake while efficiently extracting lithium.

Description

Technical Field

[0001] The present invention relates to the technical field of extracting lithium from salt lakes, and is an efficient and environmentally friendly method and device for extracting lithium from salt lakes. Background Art

[0002] Lithium resources in China are mainly distributed in the plateau salt lakes in Qinghai and Tibet. They are characterized by rich resource types. Most of the salt lakes are special comprehensive salt lake deposits rich in lithium, sodium, potassium, rubidium, cesium, boron, with both solid and liquid coexisting; however, different salt lakes have their own brine characteristics, and the core difficulties in resource utilization are different; at the same time, most of the ore sources are located in remote areas, with poor supporting facilities such as water and electricity in the surrounding areas, weak environmental carrying capacity, and high environmental protection requirements.

[0003] The Chinese invention patent document with the publication number CN113336250A discloses a lithium carbonate solar pond and a lithium carbonate extraction method. By blending tail brine with incoming brine and feeding it into a lithium precipitation pond, it uses solar energy to stably raise the temperature to extract lithium carbonate products. This method can improve the yield of lithium carbonate compared with the traditional sun-dried salt field process, but the recovery rate and purity of lithium carbonate are very low and further refining treatment is required. Moreover, this technology can only be applied to carbonate-type salt lakes, cannot comprehensively recycle other resources, and at the same time, the solar pond process occupies too much land and has too high an investment.

[0004] The Chinese invention patent document with the publication number CN112624160A discloses a method for extracting lithium carbonate from carbonate-type salt lake brine. It uses the adsorption and desorption of a lithium adsorbent and processes such as denitrification treatment under a freezing condition to finally extract lithium carbonate products. This method can obtain high-quality lithium carbonate products well, but the adsorption process has high requirements for the composition of the front-end brine, the dissolution loss rate of the adsorbent is high, the mechanical properties are unstable, the water consumption during desorption is extremely large, and at the same time, the freezing process has high energy consumption. There is a large room for optimization in terms of general applicability and energy consumption for this process.

[0005] The Chinese utility model patent document with the publication number CN214060200U discloses a salt lake lithium extraction system based on membrane separation. It uses nanofiltration membranes, reverse osmosis, and electrodialysis to remove magnesium and boron from the raw brine and remove impurities, and then uses the brine after impurity removal to produce lithium carbonate products. The pollution degree of this system is low, but this method is only applicable to sulfate-type salt lakes with a low initial sodium ion content and does not have general applicability.

[0006] The Chinese invention patent document with the publication number CN108275703A discloses a process for producing lithium carbonate and potassium salt co-production using lithium-containing nanofiltration water. The process is aimed at potassium-rich magnesium sulfate subtype salt lakes. The nanofiltration water after nanofiltration separation of magnesium sulfate is first concentrated and impurities are removed in sections, and then industrial-grade potassium chloride and industrial-grade lithium carbonate products are obtained by low-temperature cooling crystallization and lithium precipitation crystallization. This process can be well used for comprehensive resource utilization of potassium-rich magnesium sulfate subtype salt lakes to obtain a variety of products. However, its process cannot meet the lithium extraction requirements of carbonate salt lakes. After evaporation, the concentrated divalent ions and other impurity ions are not processed, and only industrial-grade lithium carbonate products are obtained. At the same time, the lithium precipitation mother liquor is not processed after lithium precipitation, and the lithium ion recovery rate is low.

[0007] Therefore, providing a lithium extraction process with strong applicability, low comprehensive energy consumption, good environmental affinity, high lithium extraction efficiency and the ability to comprehensively utilize salt lake resources is a key problem that needs to be urgently solved in the development of plateau salt lakes. Summary of the invention

[0008] The present invention provides an efficient and environmentally friendly method and device for extracting lithium from salt lakes, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the existing problems of high production energy consumption, high cost, lack of universal applicability and low lithium ion recovery rate in the salt lake lithium extraction process.

[0009] One of the technical solutions of the present invention is achieved through the following measures: an efficient and environmentally friendly method for extracting lithium from a salt lake, which is carried out according to the following steps: in the first step, the brine from the salt lake is preliminarily concentrated in a pre-concentration unit to obtain concentrated brine; in the second step, the concentrated brine is sent to a pre-treatment nanofiltration unit, and the divalent magnesium ions, sulfate ions and carbonate ions present are removed by pre-treatment nanofiltration to obtain pre-treated product water; in the third step, the pre-treatment nanofiltration product water is sent to a primary concentration unit for primary concentration to increase the concentration of lithium ions and obtain primary concentrated brine; in the fourth step, the primary concentrated brine is sent to a secondary nanofiltration unit to further remove the impurity ions enriched by the primary concentration to obtain purified brine; in the fifth step, , the purified brine is concentrated again in the secondary concentration unit to obtain sodium chloride and potassium chloride as by-products, and high-lithium brine is obtained at the same time; the sixth step is to send the high-lithium brine to the carbon precipitation unit, add a lithium precipitation agent, and obtain carbon precipitation mother liquor and battery-grade lithium carbonate products after concentration, impurity removal, reaction, crystallization, washing, drying and crushing; the seventh step is to send the carbon precipitation mother liquor to the industrial carbon precipitation unit, and add sodium carbonate solution to the carbon precipitation mother liquor, and obtain industrial carbon precipitation mother liquor and industrial-grade lithium carbonate products after concentration, impurity removal, reaction, crystallization, washing, drying and crushing; the eighth step is to send the industrial carbon precipitation mother liquor to the tailings recovery unit, and obtain recyclable heavy metal mixed salt after evaporation and crystallization.

[0010] The following is a further optimization and / or improvement of one of the above-mentioned technical solutions:

[0011] In the first step above, the pre-concentration unit uses a salt pan process or an MVR evaporation process for preliminary concentration; or / and, in the second step, the pre-treatment nanofiltration unit uses high-pressure nanofiltration membrane elements resistant to alkali and boron for pre-treatment nanofiltration, where the operating pressure of the high-pressure nanofiltration membrane elements is 80 bar to 120 bar.

[0012] In the third step above, the first-stage concentration unit uses an MVR evaporation process for first-stage concentration; or / and, in the fourth step, the secondary nanofiltration unit uses high-pressure nanofiltration membrane elements resistant to alkali and boron for secondary nanofiltration, where the operating pressure of the high-pressure nanofiltration membrane elements is 40 bar to 80 bar.

[0013] In the fifth step above, the second-stage concentration unit uses an MVR evaporation process and a three-stage vacuum flashing process for second-stage concentration and vacuum potassium extraction, where in the MVR evaporation process, the evaporation end point is controlled at the sodium-potassium saturation point, and the final-stage vacuum degree in the three-stage vacuum flashing process is 2.5 KPaA to 3.5 KPaA.

[0014] In the sixth step above, the electrolytic carbon lithium precipitation unit includes an MVR evaporation process, a resin boron removal and purification process, a lithium precipitation reaction process, and a washing and drying process, where the lithium precipitating agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L.

[0015] In the seventh step above, the industrial carbon lithium precipitation unit includes a lithium precipitation nanofiltration process, an MVR evaporation process, and a lithium precipitation reaction process, where in the lithium precipitation nanofiltration process, high-pressure nanofiltration membrane elements resistant to alkali and boron are used for lithium precipitation nanofiltration, where the operating pressure of the high-pressure nanofiltration membrane elements is 40 bar to 80 bar, and the lithium precipitating agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L.

[0016] In the eighth step above, the evaporation crystallization of the tailings recovery unit uses an MVR evaporation crystallization process.

[0017] The second technical solution of the present invention is achieved by the following measures: A device for implementing an efficient and environmentally friendly method for extracting lithium from salt lakes, including a pre-concentration unit, a pre-treatment nanofiltration unit, a first-stage concentration unit, a secondary nanofiltration unit, a second-stage concentration unit, an electrolytic carbon lithium precipitation unit, an industrial carbon lithium precipitation unit, and a tailings recovery unit. The inlet of the pre-concentration unit is fixedly connected to a salt lake brine input pipeline. There is a first pipeline fixedly connected between the outlet of the pre-concentration unit and the inlet of the pre-treatment nanofiltration unit. There is a second pipeline fixedly connected between the outlet of the pre-treatment nanofiltration unit and the inlet of the first-stage concentration unit. There is a third pipeline fixedly connected between the outlet of the first-stage concentration unit and the inlet of the secondary nanofiltration unit. There is a fourth pipeline fixedly connected between the outlet of the secondary nanofiltration unit and the inlet of the second-stage concentration unit. There is a fifth pipeline fixedly connected between the first outlet of the second-stage concentration unit and the inlet of the electrolytic carbon lithium precipitation unit. There is a sixth pipeline fixedly connected between the first outlet of the electrolytic carbon lithium precipitation unit and the inlet of the industrial carbon lithium precipitation unit. There is a seventh pipeline fixedly connected between the first outlet of the industrial carbon lithium precipitation unit and the inlet of the tailings recovery unit. The outlet of the tailings recovery unit is fixedly connected to a heavy metal tail salt output pipeline. The second outlet of the second-stage concentration unit is fixedly connected to a sodium-potassium mixed salt output pipeline. The second outlet of the electrolytic carbon lithium precipitation unit is fixedly connected to a battery-grade lithium carbonate output pipeline. The second outlet of the industrial carbon lithium precipitation unit is fixedly connected to an industrial-grade lithium carbonate output pipeline.

[0018] The following is a further optimization or / and improvement of the above-mentioned second technical solution of the invention:

[0019] The above-mentioned electrolytic carbon lithium precipitation unit includes an evaporation concentration device, a resin impurity removal device, a precipitation crystallization device, a washing and separation device, and a drying and crushing device. There is a fifth pipeline fixedly connected between the first outlet of the second-stage concentration unit and the inlet of the evaporation concentration device. There is an eighth pipeline fixedly connected between the outlet of the evaporation concentration device and the inlet of the resin impurity removal device. There is a ninth pipeline fixedly connected between the outlet of the resin impurity removal device and the inlet of the precipitation crystallization device. There is a tenth pipeline fixedly connected between the outlet of the precipitation crystallization device and the inlet of the washing and separation device. There is an eleventh pipeline fixedly connected between the first outlet of the washing and separation device and the inlet of the drying and crushing device. The second outlet of the washing and separation device is fixedly connected to an electrolytic carbon lithium precipitation mother liquor pipeline.

[0020] The above-mentioned industrial carbon lithium precipitation unit includes a lithium precipitation nanofiltration device, a lithium precipitation evaporation device, and a continuous lithium precipitation device. There is an electrolytic carbon lithium precipitation mother liquor pipeline fixedly connected between the second outlet of the washing and separation device and the inlet of the lithium precipitation nanofiltration device. There is a thirteenth pipeline fixedly connected between the first outlet of the lithium precipitation nanofiltration device and the inlet of the lithium precipitation evaporation device. The second outlet of the lithium precipitation nanofiltration device is fixedly connected to a concentrated water discharge to salt lake pipeline. There is a fourteenth pipeline fixedly connected between the outlet of the lithium precipitation evaporation device and the inlet of the continuous lithium precipitation device. There is a seventh pipeline fixedly connected between the first outlet of the continuous lithium precipitation device and the inlet of the tailings recovery unit. The second outlet of the continuous lithium precipitation device is fixedly connected to an industrial-grade lithium carbonate output pipeline.

[0021] The production method of the present invention combines three - stage concentration, two - stage nanofiltration and two - stage lithium precipitation technologies, which can meet the lithium extraction requirements of various different types of salt lakes, has low energy consumption, does not add external chemical agents, has good environmental affinity, meets the requirements of environmental protection production, and while efficiently extracting lithium, can extract other resources in the salt lake for effective comprehensive utilization of the salt lake. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Appendix Figure 1 It is a process flow block diagram of Embodiment 8 of the present invention.

[0023] Appendix Figure 2 It is a process flow block diagram of Embodiment 9 of the present invention.

[0024] Appendix Figure 3 It is a process flow block diagram of Embodiment 10 of the present invention.

[0025] Appendix Figure 1 、 2 The encodings in 2 and 3 are respectively: 1 is the pre - concentration unit, 2 is the pre - treatment nanofiltration unit, 3 is the first - stage concentration unit, 4 is the secondary nanofiltration unit, 5 is the second - stage concentration unit, 6 is the electric - carbon lithium precipitation unit, 7 is the industrial - carbon lithium precipitation unit, 8 is the tailing recovery unit, 9 is the salt - lake brine input pipeline, 10 is the first pipeline, 11 is the second pipeline, 12 is the third pipeline, 13 is the fourth pipeline, 14 is the fifth pipeline, 15 is the sixth pipeline, 16 is the seventh pipeline, 17 is the heavy - metal tail salt output pipeline, 18 is the sodium - potassium mixed salt output pipeline, 19 is the battery - grade lithium carbonate output pipeline, 20 is the industrial - grade lithium carbonate output pipeline, 21 is the evaporation concentration device, 22 is the resin impurity removal device, 23 is the precipitation crystallization device, 24 is the washing and separation device, 25 is the drying and crushing device, 26 is the eighth pipeline, 27 is the ninth pipeline, 28 is the tenth pipeline, 29 is the eleventh pipeline, 30 is the electric - carbon lithium precipitation mother - liquid pipeline, 31 is the lithium - precipitation nanofiltration device, 32 is the lithium - precipitation evaporation device, 33 is the continuous lithium - precipitation device, 34 is the pipeline for discharging concentrated water to the salt lake, 35 is the thirteenth pipeline, 36 is the fourteenth pipeline. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solutions of the present invention and the actual situation. All chemical reagents and chemical supplies mentioned in the present invention are well - known and commonly used chemical reagents and chemical supplies in the prior art without special instructions.

[0027] The present invention will be further described below in conjunction with the embodiments:

[0028] Embodiment 1: As Figure 1As shown in the figure, the efficient and environmentally friendly method for extracting lithium from salt lakes is carried out according to the following steps: First step, the brine from the salt lake is preliminarily concentrated by the pre-concentration unit 1 to obtain concentrated brine; Second step, the concentrated brine is sent to the pre-treatment nanofiltration unit 2, and divalent magnesium ions, sulfate ions and carbonate ions present are removed by pre-treatment nanofiltration to obtain pre-treatment produced water; Third step, the pre-treatment nanofiltration produced water is sent to the first-stage concentration unit 3 for first-stage concentration to increase the concentration of lithium ions and obtain first-stage concentrated brine; Fourth step, the first-stage concentrated brine is sent to the secondary nanofiltration unit 4 to further remove the impurity ions enriched after the first-stage concentration to obtain purified brine; Fifth step, the purified brine is concentrated again in the second-stage concentration unit 5 to obtain by-products of sodium chloride and potassium chloride, and at the same time obtain high-lithium brine; Sixth step, the high-lithium brine is sent to the electro-chemical lithium precipitation unit 6, a lithium precipitation agent is added, and after concentration, impurity removal, reaction, crystallization, washing, drying and crushing, electro-chemical lithium precipitation mother liquor and battery-grade lithium carbonate products are obtained; Seventh step, the electro-chemical lithium precipitation mother liquor is sent to the industrial-chemical lithium precipitation unit 7, and sodium carbonate solution is added to the electro-chemical lithium precipitation mother liquor, and after concentration, impurity removal, reaction, crystallization, washing, drying and crushing again, industrial-chemical lithium precipitation mother liquor and industrial-grade lithium carbonate products are obtained; Eighth step, the industrial-chemical lithium precipitation mother liquor is sent to the tailings recovery unit 8, and after evaporation crystallization treatment, recoverable heavy metal mixed salts are obtained.

[0029] In the above embodiment, by adopting the principle of cross-setting of two-stage nanofiltration and three-stage concentration units, during the process of extracting lithium from salt lakes, the re-enrichment of impurity ions during the concentration process is avoided, which provides a guarantee for obtaining battery-grade lithium carbonate in one step; at the same time, through the technical method integrating two-stage lithium precipitation technology, it can meet the lithium extraction requirements of various different types of salt lakes. Compared with other existing lithium extraction technologies, the present invention has low energy consumption, does not add external chemical agents, has good environmental affinity, and while efficiently extracting lithium, can extract other resources in the salt lake for effective comprehensive utilization of the salt lake.

[0030] Example 2: As an optimization of the above embodiment, as Figure 1 shown, in the first step, the pre-concentration unit 1 adopts a salt field process or an MVR evaporation process for preliminary concentration; or / and, in the second step, the pre-treatment nanofiltration unit 2 adopts a high-pressure nanofiltration membrane element resistant to alkali and boron for pre-treatment nanofiltration, wherein the operating pressure of the high-pressure nanofiltration membrane element is 80 bar to 120 bar.

[0031] Example 3: As an optimization of the above embodiment, as Figure 1 shown, in the third step, the first-stage concentration unit 3 adopts an MVR evaporation process for first-stage concentration; or / and, in the fourth step, the secondary nanofiltration unit 4 adopts a high-pressure nanofiltration membrane element resistant to alkali and boron for secondary nanofiltration, wherein the operating pressure of the high-pressure nanofiltration membrane element is 40 bar to 80 bar.

[0032] Example 4: As an optimization of the above embodiments, as Figure 1 shown, in the fifth step, the secondary concentration unit 5 uses the MVR evaporation process and the three-stage vacuum flashing process for secondary concentration and vacuum potassium extraction. Among them, in the MVR evaporation process, the evaporation end point is controlled at the sodium-potassium saturation point, and the final-stage vacuum degree in the three-stage vacuum flashing process is 2.5 KPaA to 3.5 KPaA.

[0033] Example 5: As an optimization of the above embodiments, as Figure 1 shown, in the sixth step, the electro-chemical lithium precipitation unit 6 includes an electro-chemical lithium precipitation MVR evaporation process, a resin boron removal purification process, a lithium precipitation reaction process, and a washing and drying process. Among them, the lithium precipitating agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L.

[0034] As needed, the mass ratio of the added sodium carbonate solution to the high-lithium brine is generally about 1.1 to 1.5:1, and there will be fluctuations depending on the concentration.

[0035] In the above embodiments, during the electro-chemical lithium precipitation process of the electro-chemical lithium precipitation unit 6, the electro-chemical lithium precipitation MVR evaporation process uses the MVR evaporation process to increase the lithium ion content in the high-lithium brine to 20 g / L to 35 g / L; the boron content of the concentrated high-lithium brine is reduced to less than 10 ppm by using the resin boron removal purification process. At the same time, by setting a pipeline electromagnetic separator, possible iron impurities are removed, and then a sodium carbonate solution is introduced in the lithium precipitation reaction process. The carbonate ions react with the lithium ions in the high-lithium brine to form a lithium carbonate product precipitate. Among them, a continuous lithium precipitation reactor is used, and the lithium precipitation reaction temperature is controlled at 80 °C to 90 °C; then in the washing and drying process, a vertical filter press is used, and reverse cleaning with three-stage demineralized water is used to separate and wash the battery-grade lithium carbonate product; finally, an electric heating rotary kiln dryer is used, and the drying temperature is not less than 550 °C to ensure that the water content in the battery-grade lithium carbonate product ≤ 0.1%; airflow pulverization is used to crush the obtained battery-grade lithium carbonate product to ensure a particle size D90: 5 μm to 8 μm.

[0036] Example 6: As an optimization of the above embodiments, as Figure 1 shown, in the seventh step, the industrial carbon lithium precipitation unit 7 includes a lithium precipitation nanofiltration process, an industrial carbon lithium precipitation MVR evaporation process, and a lithium precipitation reaction process. Among them, in the lithium precipitation nanofiltration process, a high-pressure nanofiltration membrane element resistant to alkali and boron is used for lithium precipitation nanofiltration. Among them, the operating pressure of the high-pressure nanofiltration membrane element is 40 bar to 80 bar, and the lithium precipitating agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L.

[0037] In the above embodiments, during the industrial carbon lithium precipitation process of the industrial carbon lithium precipitation unit 7, carbonate in the electrolytic carbon mother liquor is removed by the lithium precipitation nanofiltration process. A certain amount of sodium chloride solution is added before nanofiltration. By utilizing the dialysis characteristics of the sodium chloride solution, the recovery rate of lithium ions during the nanofiltration process is increased. The MVR evaporation process is adopted in the MVR evaporation process of the industrial carbon lithium precipitation to increase the lithium ion content to 20 g / L to 35 g / L.

[0038] In traditional single-stage lithium precipitation, the lithium precipitation mother liquor in the first stage is not reused. The mother liquor usually still contains about 10 g / L of lithium carbonate residue, accounting for about 15% of the total lithium content. After two-stage lithium precipitation of electrolytic carbon lithium precipitation and industrial carbon lithium precipitation in the present invention, the residual lithium content in the final lithium precipitation mother liquor is only about 2% of the total lithium amount.

[0039] Example 7: As an optimization of the above embodiments, as Figure 1 shown, in the eighth step, MVR evaporation crystallization process is adopted for evaporation crystallization in the tailings recovery unit 8.

[0040] In the above embodiments, a set of MVR evaporation device is separately set up through the tailings recovery unit 8. The industrial carbon lithium precipitation mother liquor is directly evaporated to dryness by using the MVR evaporation crystallization process to crystallize out the miscellaneous salt containing rare heavy metals. Then, valuable metal elements in the salt lake brine, such as lithium, potassium, rubidium, and cesium, are all recovered. The finally obtained heavy metal mixed salt accounts for about 20% of all the mixed salts, realizing resource recycling.

[0041] Example 8: As Figure 1As shown in the figure, the device for implementing the efficient and environmentally friendly method for extracting lithium from salt lakes includes a pre-concentration unit 1, a pre-treatment nanofiltration unit 2, a primary concentration unit 3, a secondary nanofiltration unit 4, a secondary concentration unit 5, an electrolytic carbon lithium precipitation unit 6, an industrial carbon lithium precipitation unit 7, and a tailings recovery unit 8. The inlet of the pre-concentration unit 1 is fixedly connected to a salt lake brine input pipeline 9. There is a first pipeline 10 fixedly connected between the outlet of the pre-concentration unit 1 and the inlet of the pre-treatment nanofiltration unit 2. There is a second pipeline 11 fixedly connected between the outlet of the pre-treatment nanofiltration unit 2 and the inlet of the primary concentration unit 3. There is a third pipeline 12 fixedly connected between the outlet of the primary concentration unit 3 and the inlet of the secondary nanofiltration unit 4. There is a fourth pipeline 13 fixedly connected between the outlet of the secondary nanofiltration unit 4 and the inlet of the secondary concentration unit 5. There is a fifth pipeline 14 fixedly connected between the first outlet of the secondary concentration unit 5 and the inlet of the electrolytic carbon lithium precipitation unit 6. There is a sixth pipeline 15 fixedly connected between the first outlet of the electrolytic carbon lithium precipitation unit 6 and the inlet of the industrial carbon lithium precipitation unit 7. There is a seventh pipeline 16 fixedly connected between the first outlet of the industrial carbon lithium precipitation unit 7 and the inlet of the tailings recovery unit 8. The outlet of the tailings recovery unit 8 is fixedly connected to a heavy metal tail salt output pipeline 17. The second outlet of the secondary concentration unit 5 is fixedly connected to a sodium-potassium mixed salt output pipeline 18. The second outlet of the electrolytic carbon lithium precipitation unit 6 is fixedly connected to a battery-grade lithium carbonate output pipeline 19. The second outlet of the industrial carbon lithium precipitation unit 7 is fixedly connected to an industrial-grade lithium carbonate output pipeline 20.

[0042] Example 9: As an optimization of the above example, as Figure 2 shown in the figure, the electrolytic carbon lithium precipitation unit 6 includes an evaporation concentration device 21, a resin impurity removal device 22, a precipitation crystallization device 23, a washing and separation device 24, and a drying and crushing device 25. There is a fifth pipeline 14 fixedly connected between the first outlet of the secondary concentration unit 5 and the inlet of the evaporation concentration device 21. There is an eighth pipeline 26 fixedly connected between the outlet of the evaporation concentration device 21 and the inlet of the resin impurity removal device 22. There is a ninth pipeline 27 fixedly connected between the outlet of the resin impurity removal device 22 and the inlet of the precipitation crystallization device 23. There is a tenth pipeline 28 fixedly connected between the outlet of the precipitation crystallization device 23 and the inlet of the washing and separation device 24. There is an eleventh pipeline 29 fixedly connected between the first outlet of the washing and separation device 24 and the inlet of the drying and crushing device 25. The second outlet of the washing and separation device 24 is fixedly connected to an electrolytic carbon lithium precipitation mother liquor pipeline 30.

[0043] Example 10: As an optimization of the above example, as Figure 3As shown in the figure, the industrial carbon lithium precipitation unit 7 includes a lithium precipitation nanofiltration device 31, a lithium precipitation evaporation device 32, and a continuous lithium precipitation device 33. There is a fixed connection between the second outlet of the washing and separation device 24 and the inlet of the lithium precipitation nanofiltration device 31 through an electrocarbon lithium precipitation mother liquor pipeline 30. There is a fixed connection between the first outlet of the lithium precipitation nanofiltration device 31 and the inlet of the lithium precipitation evaporation device 32 through a thirteenth pipeline 35. The second outlet of the lithium precipitation nanofiltration device 31 is fixedly connected to a concentrated water discharge to salt lake pipeline 34. There is a fixed connection between the outlet of the lithium precipitation evaporation device 32 and the inlet of the continuous lithium precipitation device 33 through a fourteenth pipeline 36. There is a fixed connection between the first outlet of the continuous lithium precipitation device 33 and the inlet of the tailings recovery unit 8 through a seventh pipeline 16. The second outlet of the continuous lithium precipitation device 33 is fixedly connected to an industrial grade lithium carbonate output pipeline 20.

[0044] Example 11: The brine in this example is a potassium-rich carbonate-type salt lake brine in a certain place in Tibet, China.

[0045] The main component composition of the salt lake brine is: Li + Concentration: 0.7 g / L, Na + Concentration: 90.0 g / L, K + Concentration: 24.5 g / L, SO 4 2- Concentration: 21.0 g / L, CO 3 2- Concentration: 24.5 g / L;

[0046] In the first step, the brine from the salt lake is preliminarily concentrated by the salt field process in the pre-concentration unit 1 to obtain concentrated brine, and the concentration of Li + in the concentrated brine can reach 1.0 g / L;

[0047] In the second step, after intercepting divalent ions in the pretreatment nanofiltration unit 2, the content of Mg 2+ is < 5 mg / L, and the concentration of SO 4 2- is about 22 mg / L, and the concentration of CO 3 2- is about 260 mg / L;

[0048] In the third step, using the MVR evaporation process, after primary concentration in the primary concentration unit 3, the concentration of Li+ in the primary concentrated brine reaches 1.37 g / L, and sodium chloride is by-produced at the same time;

[0049] In the fourth step, in the purified brine obtained by secondary nanofiltration in the secondary nanofiltration unit 4, the concentration of Li+ is about 1.1 g / L, and the concentrations of SO 4 2- and CO 3 2- are almost negligible;

[0050] Step 5: The purified brine undergoes the MVR evaporation process in the secondary concentration unit 5 to adjust the concentration ratio of Na + to K + to about 2:3. Then, through the tertiary vacuum flashing process, with the final-stage vacuum degree set at about 3 KPaA, sodium chloride salt, industrial-grade potassium chloride, and high-lithium brine are obtained;

[0051] Step 6: The high-lithium brine is concentrated in the MVR evaporation process of the electro-chemical lithium precipitation unit 6 to obtain concentrated brine with a Li + concentration of about 25 g / L to 30 g / L. Sodium carbonate solution is added to the concentrated brine. The sodium carbonate solution is required to have a carbonate content of not less than 150 g / L, and the added amount is about 10% in excess of the theoretically calculated value. The reactants are filtered under pressure, washed three times, dried, and crushed to finally obtain battery-grade lithium carbonate products and electro-chemical lithium precipitation mother liquor;

[0052] Step 7: Using the electro-chemical lithium precipitation mother liquor in Step 6 as raw material, sodium carbonate solution is added to the electro-chemical lithium precipitation mother liquor. After lithium precipitation nanofiltration, evaporation and concentration, and continuous lithium precipitation, industrial-grade lithium carbonate products and industrial-carbon lithium precipitation mother liquor are obtained;

[0053] Step 8: Using the industrial-carbon lithium precipitation mother liquor in Step 7 as raw material, after evaporation and crystallization in the tailings recovery unit 8, a mixed salt containing heavy metals such as rubidium and cesium is finally obtained and recovered.

[0054] In Example 11, the content of the obtained sodium chloride salt is 99.5 wt%, the potassium chloride content in the obtained industrial-grade potassium chloride is 98.7%, the pre-concentrated nanofiltration concentrated water is returned to the salt field without considering the recovery rate, and the lithium recovery rate after pre-treatment nanofiltration is 99%. The recovered rubidium and cesium heavy metal mixed salt accounts for 20% of all the mixed salts.

[0055] Example 12: The brine in this example is a sodium sulfate subtype salt lake brine from a certain place in Tibet, China.

[0056] The main component composition of the salt lake brine is: Li + concentration: 0.78 g / L, Na + concentration: 32.00 g / L, K + concentration: 6.00 g / L, SO 4 2- concentration: 13.00 g / L, CO 3 2- concentration: 3.60 g / L;

[0057] Step 1: The brine from the salt lake is preliminarily concentrated by the salt field process in the pre-concentration unit 1 to obtain concentrated brine, and the Li + concentration in the concentrated brine can reach 1.25 g / L;

[0058] Step 2: After the divalent ions are intercepted by the pre-treatment nanofiltration unit 2, the content of Mg 2+ is < 60 mg / L, the concentration of SO 4 2- is about 50 mg / L, and the concentration of Li + is 1.2 g / L;

[0059] Step 3: Using the MVR evaporation process, after the first-stage concentration by the first-stage concentration unit 3, the total salt TDS can reach about 380 g / L, and sodium chloride salt is produced as a by-product; the content of Mg 2+ ions and the concentration of SO 4 2- can both reach 150 mg / L to 500 mg / L, and the concentration of Li+ is 3.0 g / L to 3.5 g / L;

[0060] Step 4: After the secondary nanofiltration by the secondary nanofiltration unit 4, the concentrations of Mg 2+ and SO 4 2- are almost negligible;

[0061] Step 5: The purified brine undergoes the MVR evaporation process in the second-stage concentration unit 5. After adjusting the concentration ratio of Na+ and K+ to the co-saturation point, through the three-stage vacuum flashing process, with the final-stage vacuum degree set at about 3 KPaA, sodium chloride salt, industrial-grade potassium chloride, and high-lithium brine are obtained;

[0062] Step 6: In the electro-chemical lithium precipitation unit 6, the high-lithium brine is concentrated in the electro-chemical lithium precipitation MVR evaporation process to obtain concentrated brine with a Li + concentration of about 25 g / L to 30 g / L. Sodium carbonate solution is added to the concentrated brine. The sodium carbonate solution is required to have a carbonate content of not less than 150 g / L, and the added amount is about 10% more than the theoretically calculated value; the reactants are filtered under pressure, washed three times, dried, and crushed to finally obtain battery-grade lithium carbonate products and electro-chemical lithium precipitation mother liquor;

[0063] Step 7: Using the electro-chemical lithium precipitation mother liquor in Step 6 as raw material, sodium carbonate solution is added to the electro-chemical lithium precipitation mother liquor. After lithium precipitation nanofiltration, evaporation concentration, and continuous lithium precipitation, industrial-grade lithium carbonate products and industrial-carbon lithium precipitation mother liquor are obtained;

[0064] Step 8: Using the industrial-carbon lithium precipitation mother liquor in Step 7 as raw material, through evaporation crystallization in the tailings recovery unit 8, a mixed salt containing heavy metals such as rubidium and cesium is finally obtained and recovered.

[0065] In Example 12, the obtained sodium chloride salt content was 99.6 wt%, the potassium chloride content in the obtained industrial-grade potassium chloride was 99.0%, the pre-concentrated nanofiltration concentrated water was returned to the salt field without considering the recovery rate, the lithium recovery rate after pretreatment nanofiltration was 99.4%, and the recovered rubidium and cesium heavy metal mixed salts accounted for 20% of all the mixed salts.

[0066] In summary, the production method of the present invention combines three-stage concentration, two-stage nanofiltration and two-stage lithium precipitation technologies, which can meet the lithium extraction requirements of various different types of salt lakes, has low energy consumption, does not add external chemical agents, has good environmental affinity, meets the requirements of environmental protection production, and while efficiently extracting lithium, can extract other resources in the salt lake for effective comprehensive utilization of the salt lake.

[0067] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effects. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. An efficient and environmentally friendly method for extracting lithium from salt lakes, characterized in that it is carried out according to the following steps: First step, the brine from the salt lake is preliminarily concentrated by a pre-concentration unit to obtain concentrated brine; Second step, the concentrated brine is sent to a pre-treatment nanofiltration unit, and divalent magnesium ions, sulfate ions and carbonate ions present are removed by pre-treatment nanofiltration to obtain pre-treatment product water. The pre-treatment nanofiltration unit uses a high-pressure nanofiltration membrane element resistant to alkali and boron for pre-treatment nanofiltration. Among them, the operating pressure of the high-pressure nanofiltration membrane element is 80 bar to 120 bar; Third step, the pre-treatment product water is sent to a primary concentration unit for primary concentration to increase the concentration of lithium ions and obtain primary concentrated brine; Fourth step, the primary concentrated brine is sent to a secondary nanofiltration unit to further remove the impurity ions enriched after primary concentration to obtain purified brine. The secondary nanofiltration unit uses a high-pressure nanofiltration membrane element resistant to alkali and boron for secondary nanofiltration. Among them, the operating pressure of the high-pressure nanofiltration membrane element is 40 bar to 80 bar; Fifth step, the purified brine is concentrated again in a secondary concentration unit to obtain by-products of sodium chloride and potassium chloride, and at the same time obtain high-lithium brine. The secondary concentration unit uses an MVR evaporation process and a three-stage vacuum flashing process for secondary concentration and vacuum potassium extraction. Among them, the evaporation end point is controlled at the sodium-potassium saturation point in the MVR evaporation process, and the final-stage vacuum degree is 2.5 KPaA to 3.5 KPaA in the three-stage vacuum flashing process; Sixth step, the high-lithium brine is sent to an electro-chemical lithium precipitation unit, a lithium precipitation agent is added, and after concentration, impurity removal, reaction, crystallization, washing, drying and crushing, an electro-chemical lithium precipitation mother liquor and a battery-grade lithium carbonate product are obtained. The electro-chemical lithium precipitation unit includes an electro-chemical lithium precipitation MVR evaporation process, a resin boron removal purification process, a lithium precipitation reaction process and a washing and drying process. Among them, the lithium precipitation agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L; Seventh step, the electro-chemical lithium precipitation mother liquor is sent to an industrial-grade lithium precipitation unit, and a sodium carbonate solution is added to the electro-chemical lithium precipitation mother liquor. After concentration, impurity removal, reaction, crystallization, washing, drying and crushing again, an industrial-grade lithium precipitation mother liquor and an industrial-grade lithium carbonate product are obtained. The industrial-grade lithium precipitation unit includes a lithium precipitation nanofiltration process, an industrial-grade lithium precipitation MVR evaporation process and a lithium precipitation reaction process. In the lithium precipitation nanofiltration process, a high-pressure nanofiltration membrane element resistant to alkali and boron is used for lithium precipitation nanofiltration. Among them, the operating pressure of the high-pressure nanofiltration membrane element is 40 bar to 80 bar, and the lithium precipitation agent is a sodium carbonate solution with a concentration of 200 g / L to 350 g / L; Eighth step, the industrial-grade lithium precipitation mother liquor is sent to a tailings recovery unit, and after evaporation crystallization treatment, a recoverable heavy metal mixed salt is obtained.

2. The efficient and environmentally friendly method for extracting lithium from salt lakes according to claim 1, characterized in that in the first step, the pre-concentration unit uses a salt field process or an MVR evaporation process for preliminary concentration.

3. The efficient and environmentally friendly method for extracting lithium from salt lakes according to claim 1 or 2, characterized in that in the third step, the primary concentration unit uses an MVR evaporation process for primary concentration.

4. The efficient and environmentally friendly method for extracting lithium from salt lakes according to any one of claims 1 to 3, characterized in that In the eighth step, MVR evaporation crystallization process is adopted for evaporation crystallization in the tailings recovery unit.

5. An apparatus for implementing the highly efficient and environmentally friendly method for extracting lithium from salt lakes according to any one of claims 1 to 4, characterized in that it includes a pre-concentration unit, a pre-treatment nanofiltration unit, a primary concentration unit, a secondary nanofiltration unit, a secondary concentration unit, an electrolytic carbon lithium precipitation unit, an industrial carbon lithium precipitation unit and a tailings recovery unit. The inlet of the pre-concentration unit is fixedly connected to a salt lake brine input pipeline. There is a first pipeline fixedly connected between the outlet of the pre-concentration unit and the inlet of the pre-treatment nanofiltration unit. There is a second pipeline fixedly connected between the outlet of the pre-treatment nanofiltration unit and the inlet of the primary concentration unit. There is a third pipeline fixedly connected between the outlet of the primary concentration unit and the inlet of the secondary nanofiltration unit. There is a fourth pipeline fixedly connected between the outlet of the secondary nanofiltration unit and the inlet of the secondary concentration unit. There is a fifth pipeline fixedly connected between the first outlet of the secondary concentration unit and the inlet of the electrolytic carbon lithium precipitation unit. There is a sixth pipeline fixedly connected between the first outlet of the electrolytic carbon lithium precipitation unit and the inlet of the industrial carbon lithium precipitation unit. There is a seventh pipeline fixedly connected between the first outlet of the industrial carbon lithium precipitation unit and the inlet of the tailings recovery unit. The outlet of the tailings recovery unit is fixedly connected to a heavy metal tail salt output pipeline. The second outlet of the secondary concentration unit is fixedly connected to a sodium-potassium mixed salt output pipeline. The second outlet of the electrolytic carbon lithium precipitation unit is fixedly connected to a battery-grade lithium carbonate output pipeline. The second outlet of the industrial carbon lithium precipitation unit is fixedly connected to an industrial-grade lithium carbonate output pipeline.

6. The apparatus according to claim 5, characterized in that the electrolytic carbon lithium precipitation unit includes an evaporation concentration device, a resin impurity removal device, a precipitation crystallization device, a washing and separation device and a drying and crushing device. There is a fifth pipeline fixedly connected between the first outlet of the secondary concentration unit and the inlet of the evaporation concentration device. There is an eighth pipeline fixedly connected between the outlet of the evaporation concentration device and the inlet of the resin impurity removal device. There is a ninth pipeline fixedly connected between the outlet of the resin impurity removal device and the inlet of the precipitation crystallization device. There is a tenth pipeline fixedly connected between the outlet of the precipitation crystallization device and the inlet of the washing and separation device. There is an eleventh pipeline fixedly connected between the first outlet of the washing and separation device and the inlet of the drying and crushing device. The second outlet of the washing and separation device is fixedly connected to an electrolytic carbon lithium precipitation mother liquor pipeline.

7. The apparatus according to claim 6, characterized in that the industrial carbon lithium precipitation unit includes a lithium precipitation nanofiltration device, a lithium precipitation evaporation device and a continuous lithium precipitation device. There is an electrolytic carbon lithium precipitation mother liquor pipeline fixedly connected between the second outlet of the washing and separation device and the inlet of the lithium precipitation nanofiltration device. There is a thirteenth pipeline fixedly connected between the first outlet of the lithium precipitation nanofiltration device and the inlet of the lithium precipitation evaporation device. The second outlet of the lithium precipitation nanofiltration device is fixedly connected to a pipeline for discharging concentrated water to the salt lake. There is a fourteenth pipeline fixedly connected between the outlet of the lithium precipitation evaporation device and the inlet of the continuous lithium precipitation device. There is a seventh pipeline fixedly connected between the first outlet of the continuous lithium precipitation device and the inlet of the tailings recovery unit. The second outlet of the continuous lithium precipitation device is fixedly connected to an industrial-grade lithium carbonate output pipeline.

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