A process for the recovery of industrial and battery grade lithium carbonate from sodium aluminate liquor

Abstract

The application provides a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor, and belongs to the technical field of high-value recovery of waste. The method can effectively utilize waste slag generated in the production process of the aluminum industry, convert the waste slag into valuable lithium resources, and realizes the resource utilization and recycling of waste; the raw materials used in the recovery process do not have the risk of corrosion and explosion, and the technical safety and reliability are high; the obtained industrial-grade lithium carbonate meets the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate"; the battery-grade lithium carbonate meets the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate", and the quality of the recovered lithium carbonate is excellent.

Description

Technical Field

[0001] This invention relates to the field of high-value waste recycling technology, and in particular to a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor. Background Technology

[0002] The Bayer process is currently the most important and economical industrial method for producing alumina, accounting for over 95% of global production. Its core principle utilizes the amphoteric nature of alumina, dissolving it under high-temperature, high-alkali conditions and decomposing it under low-temperature, diluted, and seeded conditions. The entire system is a closed-loop cycle, during which sodium aluminate mother liquor is continuously recycled. However, with the continuous utilization of the sodium aluminate mother liquor, its lithium content accumulates.

[0003] Lithium is one of the most strategically significant and talked-about elements of our time, hailed as "white oil" and "the metal driving the energy revolution." Currently, the raw materials used to produce industrial-grade and battery-grade lithium carbonate are mainly salt lake brine and spodumene, both of which are non-renewable resources. With the development of technology, high-quality salt lake brine and spodumene are being continuously consumed, leading to a year-on-year increase in production costs. Therefore, providing a new method for the recycling and preparation of industrial-grade and battery-grade lithium carbonate is of great importance.

[0004] Therefore, how to utilize the sodium aluminate mother liquor obtained from the Bayer process alumina system to recover industrial-grade and battery-grade lithium carbonate, thereby realizing its resource utilization and high-value application, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor. The industrial-grade lithium carbonate separated and recovered by the method of this invention conforms to the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate", and the battery-grade lithium carbonate conforms to the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate", thus realizing the resource utilization and high-value utilization of sodium aluminate mother liquor.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor, comprising the following steps: (1) After mixing the sodium aluminate mother liquor and the acid solution, a precipitation treatment is carried out to obtain a mixture of material liquid and aluminum hydroxide mud water; (2) Filter the liquid obtained in step (1) to obtain ultrafiltration permeate; (3) The ultrafiltration permeate obtained in step (2) is concentrated in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate; (4) Perform tertiary electrodialysis on the primary reverse osmosis concentrate obtained in step (3) to obtain tertiary electrodialysis desalinated water and primary electrodialysis concentrate; (5) The primary electrodialysis concentrate obtained in step (4) is treated with boron removal resin to obtain boron removal resin permeate; (6) The boron removal resin permeate obtained in step (5) is evaporated and concentrated to obtain concentrated evaporated water and condensate; (7) After mixing the concentrated water obtained in step (6) with the sodium carbonate solution, lithium is precipitated to obtain solid lithium carbonate and lithium precipitation mother liquor; (8) The lithium carbonate solid obtained in step (7) is washed with water, centrifuged and dried in sequence to obtain industrial grade lithium carbonate; (9) Extract and back-extract the lithium precipitation mother liquor obtained in step (7) in sequence to obtain battery-grade lithium carbonate.

[0007] Preferably, the sodium aluminate mother liquor in step (1) comprises: lithium element concentration of 1.2~1.8 g / L, aluminum element concentration of 0.15~0.2 g / L, and carbonate ion concentration of 5~6.5 g / L.

[0008] Preferably, the precipitant used in step (1) is a PAC solution and / or a PAM solution, the mass concentration of the PAC solution and the PAM solution is independently 40-60%, the amount of precipitant is 0.01-0.05% of the mass of the sodium aluminate mother liquor, and the pH value of the precipitation treatment is 5-7.

[0009] Preferably, the operating pressure of the first-stage reverse osmosis system in step (3) is ≤7MPa.

[0010] Preferably, the parameters for the three-stage electrodialysis in step (4) include: first-stage membrane voltage 0.6~0.8V, and electrical density 350~450A / m. 2 A total of 2400 pairs; secondary pair membrane voltage 0.6~0.8V, electrical density 250~350A / m 2 A total of 1200 pairs; three-stage pair membrane voltage 0.8~1.0V, electrical density 80~120A / m 2 A total of 1000 pairs.

[0011] Preferably, in step (5), the boron removal resin treatment is performed using a complex ion exchange resin with N-methylglucosamine groups, the volumetric flow rate of the boron removal resin treatment is 4~8 BV / h, and the temperature of the boron removal resin treatment is 30~40℃.

[0012] Preferably, in step (7), the mass concentration of sodium carbonate solution is 20-30%, and the molar ratio of lithium element in the evaporated concentrate to sodium carbonate in the sodium carbonate solution is 1:(1.4-1.8).

[0013] Preferably, in step (7), the lithium precipitation temperature is 90~95℃ and the lithium precipitation time is 30~60min.

[0014] Preferably, the extraction method in step (9) is as follows: the lithium precipitation mother liquor and the alkaline solution are mixed to obtain the extract to be extracted, and then the extract to be extracted and the organic phase are mixed in reverse to extract the lithium-loaded organic phase and the raffinate. Then the lithium-loaded organic phase and pure water are mixed in reverse to wash the lithium-loaded organic phase.

[0015] Preferably, the back-extraction method in step (9) is as follows: carbon dioxide, the loaded organic phase obtained by extraction and solvent are mixed for back-extraction to obtain a water-oil mixture. Then the water-oil mixture is separated into phases to obtain back-extraction liquid and raffinate. Next, the back-extraction liquid is treated with an oil removal adsorption column and a calcium and magnesium removal resin column in sequence. Then, pyrolysis and solid-liquid separation are performed to obtain a solid and a liquid phase. Finally, the solid and pure water are mixed and then centrifuged and dried in sequence to obtain battery-grade lithium carbonate.

[0016] This invention provides a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor, comprising the following steps: mixing sodium aluminate mother liquor and an acid solution and then performing precipitation treatment to obtain a feed solution and an aluminum hydroxide mud-water mixture; filtering the feed solution to obtain ultrafiltration permeate; concentrating the ultrafiltration permeate in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate; subjecting the primary reverse osmosis concentrate to tertiary electrodialysis to obtain tertiary electrodialysis desalination and primary electrodialysis concentrate; treating the primary electrodialysis concentrate with boron removal resin to obtain boron removal resin permeate; evaporating and concentrating the boron removal resin permeate to obtain evaporated concentrate and condensate; mixing the evaporated concentrate with a sodium carbonate solution and then performing lithium precipitation to obtain lithium carbonate solid and lithium precipitation mother liquor; sequentially washing, centrifuging, and drying the lithium carbonate solid to obtain industrial-grade lithium carbonate; and sequentially extracting and back-extracting the lithium precipitation mother liquor to obtain battery-grade lithium carbonate. The method provided by this invention can effectively utilize sodium aluminate mother liquor generated during aluminum industry production, converting it into valuable lithium resources, thus realizing the resource utilization and reuse of waste. The raw materials used in the recycling process do not pose any risk of corrosion or explosion, ensuring high technical safety and reliability. The obtained industrial-grade lithium carbonate meets the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate"; the battery-grade lithium carbonate also meets the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate," and the quality of the recycled lithium carbonate is excellent. The results of the embodiments show that the industrial-grade lithium carbonate recovered by the method provided by this invention has a purity ≥99%, sodium content <350ppm, and moisture ≤0.15%, meeting the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate"; the recovered battery-grade lithium carbonate has a lithium carbonate mass concentration ≥99.5%, sodium content ≤250ppm, iron content ≤10ppm, and boron content ≤50ppm, meeting the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate." Detailed Implementation

[0017] This invention provides a method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor, comprising the following steps: (1) After mixing the sodium aluminate mother liquor and the acid solution, a precipitation treatment is carried out to obtain a mixture of material liquid and aluminum hydroxide mud water; (2) Filter the liquid obtained in step (1) to obtain ultrafiltration permeate; (3) The ultrafiltration permeate obtained in step (2) is concentrated in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate; (4) Perform tertiary electrodialysis on the primary reverse osmosis concentrate obtained in step (3) to obtain tertiary electrodialysis desalinated water and primary electrodialysis concentrate; (5) The primary electrodialysis concentrate obtained in step (4) is treated with boron removal resin to obtain boron removal resin permeate; (6) The boron removal resin permeate obtained in step (5) is evaporated and concentrated to obtain concentrated evaporated water and condensate; (7) After mixing the concentrated water obtained in step (6) with the sodium carbonate solution, lithium is precipitated to obtain solid lithium carbonate and lithium precipitation mother liquor; (8) The lithium carbonate solid obtained in step (7) is washed with water, centrifuged and dried in sequence to obtain industrial grade lithium carbonate; (9) Extract and back-extract the lithium precipitation mother liquor obtained in step (7) in sequence to obtain battery-grade lithium carbonate.

[0018] In this invention, unless otherwise specified, all raw materials used are commercially available products and equipment (systems) well known to those skilled in the art.

[0019] This invention involves mixing sodium aluminate mother liquor and acid solution, followed by precipitation treatment to obtain a mixture of feed liquid and aluminum hydroxide mud water.

[0020] In this invention, the sodium aluminate mother liquor is preferably obtained from the Bayer process alumina system; the composition of the sodium aluminate mother liquor preferably includes: lithium concentration 1.2~1.8 g / L, aluminum concentration 0.15~0.2 g / L, carbonate ion concentration 5~6.5 g / L, more preferably: lithium concentration 1.5 g / L, aluminum concentration 0.18 g / L, carbonate ion concentration 6 g / L. In this invention, the pH value of the sodium aluminate mother liquor is preferably 12~13, more preferably 12.67; the temperature of the sodium aluminate mother liquor is preferably 70~80℃. This invention, by using the above-mentioned sodium aluminate mother liquor as a raw material to recover industrial-grade lithium carbonate and battery-grade lithium carbonate, can achieve full utilization of resources.

[0021] In this invention, the sodium aluminate mother liquor is preferably subjected to heat exchange before being mixed with an acid solution; the heat exchange is preferably carried out in a heat exchanger; the temperature of the sodium aluminate mother liquor after heat exchange is preferably 30~40℃, more preferably 35℃. This invention allows the temperature of the sodium aluminate mother liquor to drop rapidly through heat exchange.

[0022] In this invention, the acid solution is preferably a nitric acid solution; the mass concentration of the acid solution is preferably 50-70%, more preferably 55-65%, and even more preferably 60%. This invention does not impose any special limitation on the specific amount of the acid solution used, as long as it ensures that the pH value during subsequent precipitation treatment is 5-7.

[0023] In this invention, the precipitant used in the precipitation treatment is preferably a PAC solution (polyaluminum chloride solution) and / or a PAM solution (polyacrylamide solution), more preferably an aqueous PAC solution and / or an aqueous PAM solution; the mass concentration of the PAC solution and the PAM solution is preferably 40-60% independently; the amount of the precipitant is preferably 0.01-0.05% of the mass of the sodium aluminate mother liquor. As one embodiment of this invention, the mass concentration of the PAC solution and the PAM solution can be independently 40%, 45%, 50%, 55%, or 60%; the amount of the precipitant can be 0.01%, 0.02%, 0.03%, 0.04%, or 0.05% of the mass of the sodium aluminate mother liquor. This invention, by adding a precipitant for precipitation treatment, can convert aluminum into precipitates such as aluminum hydroxide, facilitating the removal of aluminum impurities.

[0024] In this invention, the pH value of the precipitation treatment is preferably 5-7. By controlling the pH value of the precipitation treatment, this invention allows aluminum to precipitate, such as aluminum hydroxide precipitate.

[0025] In this invention, the preferred method of sedimentation treatment is to first stir for 10-20 minutes, and then settle in an integrated sedimentation tank for 60-240 minutes, more preferably to first stir for 15 minutes, and then settle in an integrated sedimentation tank for 120-180 minutes; the preferred inclination angle of the inclined plate in the integrated sedimentation tank is 50-70°, more preferably 55-65°, and even more preferably 60°. This invention utilizes an inclined plate sedimentation tank for sedimentation treatment. Based on the theory of shallow sedimentation, it increases the sedimentation area and shortens the particle settling distance by setting parallel inclined plates at a certain angle within the sedimentation tank, thereby improving sedimentation efficiency. The specific working process of the inclined plate sedimentation tank is as follows: 1. Wastewater enters from one end of the sedimentation tank and is evenly distributed between the inclined plates through a water distribution system; 2. Suspended particles in the wastewater slide along the surface of the inclined plates under the action of gravity and gradually settle to the bottom of the tank. The presence of the inclined plates greatly increases the effective sedimentation area and shortens the distance for particles to reach the bottom of the tank, thus accelerating the sedimentation speed; 3. The settled sludge will concentrate at the bottom of the tank to form a relatively thick sludge layer, which is periodically discharged through a sludge removal device; 4. The treated clean water overflows from above the inclined plates, is collected in a water collection tank, and flows out of the sedimentation tank.

[0026] The present invention does not impose any special limitations on the separation method of the liquid material and the aluminum hydroxide mud-water mixture; conventional separation methods can be used.

[0027] In this invention, the suspended solids (SS) of the feed solution (solid particles suspended in the feed solution that cannot be removed by filtration or filter membrane) is preferably 15-25 mg / L, more preferably 18-22 mg / L, and even more preferably 20 mg / L; the water content of the aluminum hydroxide mud-water mixture is preferably ≥97%, more preferably ≥98%. This invention, through precipitation treatment, can significantly reduce the concentration of suspended solids.

[0028] The present invention preferably further includes pressure filtration of the aluminum hydroxide mud-water mixture to obtain filtrate and mud cake; the filtrate is preferably refluxed for desorption and analysis; the mud cake is preferably returned to the alumina production process of the Bayer process alumina system; the pressure filtration is preferably carried out using a plate and frame filter press; the pressure of the pressure filtration is preferably 0.2~0.4MPa, more preferably 0.3MPa; the pressure filtration time is preferably 4~6h. In this invention, the aluminum hydroxide mud-water mixture still contains approximately 95% to 97% water content and has a large volume. Direct disposal would waste resources and cause environmental pollution. Therefore, filtration using a plate and frame filter press can further remove pore water and capillary water from the aluminum hydroxide mud-water mixture, reducing its volume. After filtration, the water content of the filter cake can be reduced to 70% to 80%, and its volume is 1 / 10 to 1 / 4 of the original volume, which is beneficial for subsequent transportation and processing. The plate and frame filter press uses the pressure difference between the two sides of the filter medium as the driving force to force the water in the aluminum hydroxide mud-water mixture through. The filter medium forms a filtrate, while solid particles are trapped on the medium to form a filter cake, thereby achieving the purpose of sludge dewatering. In a plate and frame filter press, plates and frames are arranged alternately, and filter cloth is covered on both sides of the filter plates. The plates and frames are pressed together by a pressing device, forming a filter press chamber between the plates and frames. Small holes are opened at the same position at the upper middle of the plates and frames, which become a channel after pressing. The sludge cake pressurized to 0.2~0.4MPa enters the filter press chamber through this channel. The surface of the filter plate is engraved with grooves, and the lower end is drilled with holes for the filtrate to be discharged. Under pressure, the filtrate passes through the filter cloth and is discharged from the filter press along the grooves and holes, thus dewatering the aluminum hydroxide sludge-water mixture.

[0029] After obtaining the feed liquid, the present invention filters the feed liquid to obtain ultrafiltration permeate.

[0030] This invention preferably adjusts the pH of the feed solution to 4.0 before filtration; the preferred method for pH adjustment is the addition of nitric acid solution. This invention does not have specific limitations on the concentration and amount of the added nitric acid solution, as long as the pH of the feed solution is 4.0. In one embodiment of this invention, the mass concentration of the nitric acid solution can be 60%. By adjusting the pH of the feed solution to 4.0, this invention can remove alkalinity (i.e., the total amount of alkaline substances that can react with strong acids, such as carbonate or bicarbonate ions) from the feed solution, thus preventing the formation of lithium carbonate precipitation in the subsequent concentration stage.

[0031] In this invention, the filtration method is preferably a combination of primary sand filtration, secondary sand filtration, and ultrafiltration; the filters used for the primary and secondary sand filtration are preferably prepared using quartz sand and anthracite of four particle sizes as packing materials; the ultrafiltration is preferably carried out in an ultrafiltration system; the membrane pore size of the ultrafiltration is preferably 0.002~0.1μm; the operating pressure of the ultrafiltration is preferably 0.2~0.4MPa; the molecular weight cutoff of the ultrafiltration is preferably 1000~100000 Daltons; and the flux of the ultrafiltration is preferably 30~50 L / (m³). 2 ·h). As one embodiment of the present invention, the pore size of the ultrafiltration membrane can be 0.002 μm, 0.005 μm, 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, or 0.1 μm; the operating pressure of the ultrafiltration can be 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, or 0.4 MPa; the molecular weight cutoff of the ultrafiltration can be 1000 Daltons, 5000 Daltons, 10000 Daltons, 20000 Daltons, 50000 Daltons, 80000 Daltons, or 100000 Daltons; and the flux of the ultrafiltration can be 30 L / (m²). 2 ·h), 32L / (m 2 ·h), 35L / (m 2 ·h), 38L / (m 2 ·h), 40L / (m 2 ·h), 42L / (m 2 ·h), 45L / (m 2 ·h), 48L / (m 2 ·h) or 50L / (m 2 (h). This invention uses two-stage sand filtration to reduce the turbidity of the filtrate to 5 NTU. Then, an ultrafiltration system is used to treat the pre-treated product water, protecting the downstream membrane equipment. This process removes impurities such as bacteria, microorganisms, and suspended solids, resulting in clear, transparent water with near-zero turbidity. This can improve the turbidity of the ultrafiltration product water to <0.1 NTU, thus enhancing water quality and protecting the downstream membrane system.

[0032] After obtaining the ultrafiltration permeate, the present invention concentrates the ultrafiltration permeate in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate.

[0033] In this invention, the operating pressure of the primary reverse osmosis system is preferably ≤7MPa, more preferably 6MPa. This invention increases the lithium concentration in the primary reverse osmosis concentrate by concentrating the ultrafiltration permeate in the primary reverse osmosis system, while simultaneously obtaining high-quality primary reverse osmosis permeate.

[0034] In this invention, the concentration of lithium in the primary reverse osmosis concentrate is preferably 3.5~4.5 g / L, more preferably 4.0 g / L.

[0035] In this invention, the TDS of the primary reverse osmosis permeate is preferably 0.6~1 g / L, more preferably 0.8 g / L; the primary reverse osmosis permeate is preferably used for alumina production using the Bayer process. This invention reduces wastewater discharge by recovering the primary reverse osmosis permeate.

[0036] After obtaining the primary reverse osmosis concentrate, the present invention performs tertiary electrodialysis on the primary reverse osmosis concentrate to obtain tertiary electrodialysis desalinated water and primary electrodialysis concentrate.

[0037] In this invention, the tertiary electrodialysis is preferably performed in a tertiary electrodialysis system; the parameters of the tertiary electrodialysis preferably include: first-stage membrane voltage 0.6~0.8V, and electrical density 350~450A / m. 2 A total of 2400 pairs; secondary pair membrane voltage 0.6~0.8V, electrical density 250~350A / m 2 A total of 1200 pairs; three-stage pair membrane voltage 0.8~1.0V, electrical density 80~120A / m 2 A total of 1000 pairs, preferably: first-stage pair membrane voltage 0.7V, electrical density 400A / m 2 A total of 2400 pairs (2 sets of equipment); secondary pair membrane voltage 0.7V, electrical density 300A / m 2 A total of 1200 pairs (1 set of equipment); three-stage membrane voltage 1.0V, electrical density 100A / m 2 A total of 1000 pairs. In this invention, tertiary electrodialysis uses potential difference as the driving force and utilizes the selective permeability of anion and cation exchange membranes to allow lithium ions to migrate from one part of the water to another, thereby further increasing the concentration of lithium.

[0038] In this invention, the lithium concentration in the primary electrodialysis concentrate is preferably 15-20 g / L, more preferably 18 g / L; the lithium concentration in the tertiary electrodialysis desalination water is preferably 0.3-0.5 g / L, more preferably 0.4 g / L.

[0039] The present invention preferably introduces the tertiary electrodialysis desalination water into the secondary reverse osmosis system for further desalination to obtain secondary reverse osmosis permeate and secondary reverse osmosis concentrate. The secondary reverse osmosis permeate is then used for the Bayer process to produce alumina, and the secondary reverse osmosis concentrate is returned to the primary reverse osmosis system.

[0040] In this invention, the pressure of the secondary reverse osmosis system is preferably ≤2.4 MPa, more preferably 1.8 MPa. By desalinating the secondary reverse osmosis system, this invention yields secondary reverse osmosis concentrate with a high lithium concentration (approximately 1.7 g / L), which can be used for further lithium recovery. Meanwhile, the secondary reverse osmosis permeate (TDS approximately 0.5 g / L) has fewer impurities and can be used for alumina production via the Bayer process.

[0041] After obtaining the primary electrodialysis concentrate, the present invention treats the primary electrodialysis concentrate with boron removal resin to obtain boron removal resin permeate.

[0042] In this invention, the boron removal resin treatment is preferably carried out in a boron removal resin system; the boron removal resin treatment method is preferably using a complex ion exchange resin with N-methylglucamine groups; the volumetric flow rate of the primary electrodialysis concentrate during the boron removal resin treatment is preferably 4~8 BV / h, more preferably 5~7 BV / h, and even more preferably 6 BV / h; the temperature of the boron removal resin treatment is preferably 30~40℃, more preferably 35℃. The specific process of the boron removal resin treatment in this invention is as follows: 1. Ion exchange: The boron removal resin contains specific functional groups, which can react with borate ions (B(OH)4) in the water. - 1. **Reversible ion exchange reaction:** Boron-containing water undergoes a reversible ion exchange reaction with boric acid molecules (H3BO3). When boron-containing water passes through the resin bed, boron ions combine with functional groups on the resin and are adsorbed onto the resin, thereby achieving the purpose of boron removal. 2. **Selective adsorption:** The boron-removing resin has high selectivity and can preferentially adsorb boron ions, effectively removing boron even in the presence of other competing anions. 3. **Regenerable:** After the active sites on the boron-removing resin become saturated with boron, their adsorption capacity can be restored through regeneration, reducing production costs. This invention reduces the boron content in the boron-removing resin-treated water.

[0043] The present invention preferably further includes regenerating the complexed ion exchange resin after the boron removal resin treatment; the regeneration treatment is preferably performed sequentially as follows: washing, elution, first washing, transformation, and second washing; the first washing and second washing are preferably performed by rinsing with clean water; the elution is preferably performed using a 2 mol / L nitric acid solution; the transformation is preferably performed using a 2 mol / L NaOH solution; the waste liquid after regeneration is preferably neutralized before discharge. The present invention can remove boron from the complexed ion exchange resin through elution; and can regenerate the complexed ion exchange resin through transformation, enabling the complexed ion exchange resin to be reused and reducing costs.

[0044] After obtaining the boron removal resin permeate, the present invention evaporates and concentrates the boron removal resin permeate to obtain concentrated evaporated water and condensate.

[0045] In this invention, the evaporation and concentration are preferably carried out in a falling film evaporator; the evaporation and concentration temperature is preferably 100~110℃; and the compressor outlet pressure during evaporation and concentration is preferably 0.4~0.5MPa. This invention does not have a specific limitation on the model and source of the falling film evaporator; commercially available falling film evaporators well-known to those skilled in the art can be used. This invention does not have a specific limitation on the evaporation and concentration time, as long as the lithium concentration in the concentrated water meets the requirements. This invention utilizes the secondary steam generated in the evaporator, which is compressed by a compressor to increase its pressure and temperature, thus increasing its enthalpy. This steam is then sent to the heating chamber of the evaporator as heating steam, maintaining the processed liquid in a boiling state, while the heating steam itself condenses into water. The steam that would otherwise be wasted is fully utilized, latent heat is recovered, thermal efficiency is improved, and production costs are reduced.

[0046] In this invention, the concentration of lithium in the evaporated concentrate is preferably 24~25 g / L.

[0047] In this invention, the condensate is preferably used in the Bayer process for the production of alumina.

[0048] After obtaining the concentrated evaporated water, the present invention mixes the concentrated evaporated water with a sodium carbonate solution and then performs lithium precipitation to obtain lithium carbonate solid and lithium precipitation mother liquor.

[0049] In this invention, the preferred mass concentration of the sodium carbonate solution is 20-30%; the preferred molar ratio of lithium in the concentrated evaporated water to sodium carbonate in the sodium carbonate solution is 1:(1.4-1.8). As one embodiment of this invention, the mass concentration of the sodium carbonate solution can be 20%, 22%, 24%, 25%, 26%, 27%, 28%, or 30%; the molar ratio of lithium in the concentrated evaporated water to sodium carbonate in the sodium carbonate solution can be 1:1.4, 1:1.45, 1:1.5, 1:1.55, 1:1.6, 1:1.65, 1:1.7, 1:1.75, or 1:1.8. By adding the sodium carbonate solution, this invention facilitates the formation of solid lithium carbonate during subsequent lithium precipitation.

[0050] In this invention, the preferred temperature for lithium precipitation is 90-95°C; the preferred precipitation time is 30-60 minutes, more preferably 45 minutes; the preferred method of lithium precipitation is stirred lithium precipitation; and the lithium precipitation is preferably carried out in a lithium precipitation reactor. This invention does not impose any specific limitations on the model or source of the lithium precipitation reactor; commercially available lithium precipitation reactors well-known to those skilled in the art can be used. This invention does not impose any specific limitations on the stirring rate for stirred lithium precipitation; it can be determined based on the technical knowledge of those skilled in the art. By controlling the temperature and time of lithium precipitation, this invention can further improve the efficiency of lithium precipitation.

[0051] The present invention does not impose any special limitation on the specific method of separating the lithium carbonate solid and the lithium precipitation mother liquor. Conventional separation methods, such as filtration or centrifugation, can be used.

[0052] After obtaining solid lithium carbonate, the present invention sequentially washes the solid lithium carbonate with water, centrifuges and dries it to obtain industrial-grade lithium carbonate.

[0053] In this invention, the liquid-to-solid ratio of the water wash is preferably 30:1; the number of water washes is preferably 2-3 times; the water wash is preferably carried out under stirring conditions; the stirring time is preferably 30-60 minutes, more preferably 45 minutes. This invention does not have a specific limitation on the stirring rate; it can be determined based on the technical knowledge of those skilled in the art, as long as it removes impurities as much as possible. This invention, through water washing, can dissolve impurities attached to solid lithium carbonate into the water, thereby helping to further improve the purity of solid lithium carbonate.

[0054] This invention does not impose specific limitations on the centrifugal separation and drying operations; the goal is to separate the lithium carbonate solid from water and then dry it until the moisture content in industrial-grade lithium carbonate is ≤0.15%. As one embodiment of this invention, the centrifugal separation rate can be 2800~3000 r / min, or even 2900 r / min; the heating medium for drying can be 0.6 MPa saturated steam. This invention, through centrifugal separation, separates lithium carbonate solid from water containing impurities, and through drying, removes residual water, thereby obtaining high-purity lithium carbonate.

[0055] The lithium precipitation process of this invention is mainly as follows: 1. Lithium precipitation process: Addition of precipitant: Sodium carbonate is added to the pretreated lithium-containing solution, and under certain temperature and pH conditions, lithium is precipitated in the form of lithium carbonate; 2. Solid-liquid separation: The generated lithium carbonate is separated from the liquid by filtration, centrifugation, etc., to obtain wet lithium carbonate; 3. Washing and drying: In order to further remove residual impurities and moisture, the lithium carbonate is washed, and finally the washed lithium carbonate is dried to obtain a pure industrial-grade lithium carbonate product; 4. Recycling and reuse: The mother liquor generated during the lithium precipitation process can be recycled or further processed to recover the remaining lithium and other valuable components, reduce waste and lower costs.

[0056] In this invention, the purity of the industrial-grade lithium carbonate is preferably ≥99%; the sodium content of the industrial-grade lithium carbonate is preferably <350ppm. The industrial-grade lithium carbonate provided by this invention conforms to the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate".

[0057] After obtaining the lithium precipitation mother liquor, the present invention extracts and back-extracts the lithium precipitation mother liquor sequentially to obtain battery-grade lithium carbonate.

[0058] This invention preferably involves heat exchange before extraction; the heat exchange is preferably performed using a plate heat exchanger; the temperature after heat exchange is preferably 40-50°C, more preferably 45°C. This invention does not have specific limitations on the model or source of the plate heat exchanger; commercially available plate heat exchangers well-known to those skilled in the art can be used. This invention can rapidly reduce the temperature of the lithium precipitation mother liquor through heat exchange, facilitating subsequent extraction.

[0059] In this invention, the preferred extraction method is as follows: the mother liquor of lithium precipitation after heat exchange is mixed with an alkaline solution to obtain an extractant; then the extractant and an organic phase are counter-currently mixed and extracted to obtain a lithium-loaded organic phase and a raffinate; subsequently, the lithium-loaded organic phase is counter-currently mixed and washed with pure water to obtain a loaded organic phase. In this invention, the alkaline solution is preferably a sodium hydroxide solution; the mass concentration of the alkaline solution is preferably 30-40%, more preferably 32-35%; the pH value of the extractant is preferably ≥13; the organic phase is preferably tributyl phosphate and / or dimethylheptyl methylphosphonate; and the flow rate of the extractant during counter-current mixing extraction is preferably 10-11 m³ / s. 3 / h, more preferably 10.5m 3 / h; the preferred flow rate of the organic phase during the reverse mixing extraction is 10~20m³. 3 / h, more preferably 15m 3 / h; The reverse mixing extraction is preferably carried out in an extraction tank; the extraction tank preferably includes a primary extraction tank, a secondary extraction tank, a tertiary extraction tank, and a quaternary extraction tank; during the reverse mixing extraction, the extractant enters the tertiary extraction tank and the secondary extraction tank sequentially from the quaternary extraction tank, while the organic phase enters the tertiary extraction tank and the quaternary extraction tank sequentially from the secondary extraction tank, thus completing the reverse mixing extraction; The reverse mixing washing is preferably carried out in a washing tank; the washing tank preferably includes a primary washing tank, a secondary washing tank, a tertiary washing tank, and a quaternary washing tank; during the reverse mixing washing, the lithium-loaded organic phase enters the primary washing tank via the quaternary extraction tank, and then sequentially enters the secondary and tertiary washing tanks, while pure water enters the secondary washing tank and the primary washing tank sequentially from the tertiary washing tank, thus completing the reverse mixing washing; the flow rate of the lithium-loaded organic phase is preferably 10~20m³. 3 / h, more preferably 15m 3 / h; the preferred flow rate of the pure water is 2.5~3m³ / h. 3 / h, more preferably 2.72m 3 / h. This invention can extract lithium from lithium precipitation mother liquor through extraction.

[0060] In this invention, the raffinate is preferably mixed with a nitric acid solution before oil-water separation. More preferably, the raffinate enters the first stage of the extraction tank from the second stage of the extraction tank, mixes with the nitric acid solution, and then enters the raffinate oil separator for oil-water separation to obtain an aqueous phase and an oil phase. This invention does not impose any special limitations on the concentration and amount of the nitric acid solution; it is sufficient to separate the aqueous and oil phases based on the technical knowledge of those skilled in the art. As one embodiment of this invention, the mass concentration of the nitric acid solution can be 5%.

[0061] In this invention, the wash water obtained from the reverse mixing wash preferably enters the first stage of the washing tank, then mixes with the nitric acid solution, then enters the fourth stage of the extraction tank, and finally flows into the raffinate. This invention does not have specific limitations on the concentration and amount of the nitric acid solution; based on the technical knowledge of those skilled in the art, it is sufficient that it has the same pH value as the raffinate. As one embodiment of this invention, the mass concentration of the nitric acid solution can be 5%.

[0062] In this invention, the preferred method of back-extraction is as follows: Carbon dioxide, the extracted supported organic phase, and a solvent are mixed for back-extraction to obtain a water-oil mixture. This mixture is then separated into back-extraction solution and raffinate. The back-extraction solution is then treated sequentially using an oil removal adsorption column and a calcium-magnesium removal resin column. Following this, pyrolysis and solid-liquid separation are performed to obtain a solid and a liquid phase. Finally, the solid is mixed with pure water and then subjected to centrifugation and drying to obtain battery-grade lithium carbonate. In this invention, the solvent is preferably pure water; when the carbon dioxide, supported organic phase, and solvent are mixed, the flow rate of the supported organic phase is preferably 10-20 m³ / h. 3 / h, more preferably 15m 3 / h; the preferred flow rate of the solvent is 2.5~3m³ / h. 3 / h, more preferably 2.72m 3 / h; the preferred CO2 flow rate is 70~75 Nm³. 3 / h, more preferably 74Nm 3 / h; the carbon dioxide is vented after back-extraction; the venting flow rate is preferably 20~25 Nm. 3 / h, more preferably 22Nm 3 / h. In this invention, the phase separation is preferably carried out in a phase separation tank. After phase separation, the raffinate enters a blank organic tank, and the back-extraction liquid enters an aqueous phase tank. In this invention, the oil removal adsorption column preferably consists of three adsorption columns; the three adsorption columns are preferably connected in series; two of the three adsorption columns are preferably in use and one is on standby; the calcium and magnesium resin removal column preferably consists of two adsorption columns; one of the two adsorption columns is preferably in use and one is on standby. In this invention, the pyrolysis is preferably carried out in a pyrolysis kettle; the pyrolysis temperature is preferably 90~95℃; the carbon dioxide after pyrolysis is emitted into the atmosphere, and the condensate from the pyrolysis steam enters a condensate tank. This invention does not have a special limitation on the ratio of the solid to pure water; it can be determined based on the technical knowledge of those skilled in the art. In this invention, the solid-liquid separation and centrifugal separation are preferably carried out independently in a centrifuge; the drying method is preferably to dry the material by heat exchange with steam in a disc dryer. In this invention, the liquid phase preferably enters a hot mother liquor tank. In this invention, the raffinate is preferably treated with an oil removal adsorption column for oil removal. This invention can recover solid lithium carbonate through back-extraction, and after separation and drying, battery-grade lithium carbonate can be obtained.

[0063] The main process for obtaining battery-grade lithium carbonate in this invention is as follows: 1. Mixing: The pretreated lithium-containing aqueous phase and organic phase are thoroughly mixed to ensure sufficient contact between the two phases. Under appropriate temperature and stirring conditions, the extractant selectively forms a complex with lithium ions in the aqueous phase and transfers to the organic phase; 2. Separation: The two mixed phases enter a clarifier and gradually separate into layers under gravity. The upper layer is the lithium-rich organic phase, and the lower layer is the depleted aqueous phase; 3. Back-extraction: In order to recover the lithium extracted into the organic phase, carbon dioxide is usually used to back-extract the organic phase, so that the lithium is released back into the aqueous phase, forming a high-concentration lithium bicarbonate solution; 4. Washing and drying: The generated lithium compound precipitate is subjected to pyrolysis, washing, and drying to finally obtain pure battery-grade lithium carbonate.

[0064] The present invention preferably further includes passing battery-grade lithium carbonate sequentially through a vibrating screen, an air jet mill, a buffer silo, a mixer, an electromagnetic separator, and a packaging machine. The present invention does not impose any special limitations on the specific operations described above, which can be understood based on the technical knowledge of those skilled in the art.

[0065] In this invention, the lithium carbonate mass concentration in the battery-grade lithium carbonate is preferably ≥99.5%; the sodium content in the battery-grade lithium carbonate is preferably ≤250ppm; the iron content in the battery-grade lithium carbonate is preferably ≤10ppm; and the boron content in the battery-grade lithium carbonate is preferably ≤50ppm. The battery-grade lithium carbonate provided by this invention conforms to the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate".

[0066] The recycling method provided by this invention has the following advantages: (1) It can effectively utilize the sodium aluminate mother liquor generated during the aluminum industry production process and convert it into valuable lithium resources, thereby realizing the resource utilization and reuse of waste; (2) The entire process of recovering industrial-grade lithium carbonate and battery-grade lithium carbonate from sodium aluminate mother liquor is free of wastewater discharge, making it an economical and environmentally friendly production process. (3) The raw materials used in the recycling process do not pose any risk of corrosion or explosion, and the technology is highly safe and reliable; (4) The recovered industrial-grade lithium carbonate meets the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate"; the battery-grade lithium carbonate meets the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate" and the quality of the recovered lithium carbonate is excellent.

[0067] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0068] Example 1 A method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor comprises the following steps: (1) The sodium aluminate mother liquor obtained from the Bayer process alumina system was heated to 35°C in a heat exchanger, then mixed with an acid solution to adjust the pH to 6, followed by the addition of a 50% PAC aqueous solution and stirring for 15 min. Finally, it was precipitated in an integrated sedimentation tank for 180 min. After separation, a mixture of feed liquid and aluminum hydroxide sludge was obtained. The aluminum hydroxide sludge mixture was filtered using a plate and frame filter press at a pressure of 0.03 MPa for 6 h to obtain filtrate and sludge cake (70% water content). The filtrate was recycled for desorption and analysis, and the sludge cake was returned to the Bayer process alumina system. The process involves a conventional alumina production procedure. The sodium aluminate mother liquor has the following composition: lithium concentration 1.5 g / L, aluminum concentration 0.18 g / L, and carbonate ion concentration 6 g / L. The pH value of the sodium aluminate mother liquor is 12.67. The temperature of the sodium aluminate mother liquor is 80°C. The acid solution is a 60% (w / w) nitric acid solution. The amount of PAC aqueous solution used is 0.02% of the mass of the sodium aluminate mother liquor. The inclined plate in the integrated sedimentation tank has an inclination angle of 60°. The suspended solids (SS) of the feed solution is 20 mg / L, and the water content of the aluminum hydroxide sludge-water mixture is 98%. (2) Add a 60% nitric acid solution to the feed solution obtained in step (1) to adjust the pH value to 4.0, and then filter to obtain ultrafiltration permeate; the filtration method is primary sand filtration, secondary sand filtration and ultrafiltration; the filters used for primary sand filtration and secondary sand filtration are prepared by using quartz sand and anthracite of four particle sizes as packing materials; the ultrafiltration is carried out in an ultrafiltration system with an ultrafiltration membrane pore size of 0.03 μm, an ultrafiltration operating pressure of 0.23 MPa, an ultrafiltration molecular weight cutoff of 100,000 Daltons, and an ultrafiltration flux of 40 L / (m 2 ·h); (3) The ultrafiltration permeate obtained in step (2) is concentrated in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate; the operating pressure of the primary reverse osmosis system is 6 MPa; the lithium concentration in the primary reverse osmosis concentrate is 4.0 g / L; the TDS of the primary reverse osmosis permeate is 0.8 g / L; the primary reverse osmosis permeate is used for alumina production in the Bayer process; (4) The primary reverse osmosis concentrate obtained in step (3) is subjected to tertiary electrodialysis to obtain tertiary electrodialysis desalination and primary electrodialysis concentrate; the tertiary electrodialysis is carried out in a tertiary electrodialysis system; the parameters of the tertiary electrodialysis are: primary membrane voltage 0.7V, electrical density 400A / m 2 A total of 2400 pairs (2 sets of equipment); secondary pair membrane voltage 0.7V, electrical density 300A / m 2 A total of 1200 pairs (1 set of equipment); three-stage membrane voltage 1.0V, electrical density 100A / m 2 A total of 1000 pairs are used; the lithium concentration in the first-stage electrodialysis concentrate is 17 g / L; the lithium concentration in the third-stage electrodialysis desalination water is 0.4 g / L; the third-stage electrodialysis desalination water is further desalinated into the second-stage reverse osmosis system to obtain second-stage reverse osmosis permeate (TDS approximately 0.5 g / L) and second-stage reverse osmosis concentrate. The second-stage reverse osmosis permeate is then used for alumina production using the Bayer process, and the second-stage reverse osmosis concentrate is returned to the first-stage reverse osmosis system; the pressure of the second-stage reverse osmosis system is 1.8 MPa. (5) The primary electrodialysis concentrate obtained in step (4) is subjected to boron removal resin treatment in a boron removal resin system using a complex ion exchange resin with N-methylglucamine. The volumetric flow rate of the primary electrodialysis concentrate during boron removal resin treatment is 6 BV / h and the temperature is 35°C to obtain boron removal resin permeate. The complex ion exchange resin after boron removal resin treatment is then regenerated. The waste liquid generated during regeneration is neutralized and then discharged. The regeneration process consists of sequential water rinsing, 2 mol / L nitric acid solution elution, water rinsing, 2 mol / L NaOH solution conversion, and water rinsing. (6) The boron removal resin permeate obtained in step (5) is evaporated and concentrated in a falling film evaporator to obtain concentrated evaporate and condensate; the evaporation and concentration temperature is 110°C, and the compressor outlet pressure is 0.4 MPa during evaporation and concentration; the lithium concentration in the concentrated evaporate is 25 g / L; the condensate is used for the Bayer process to produce alumina; (7) The concentrated water obtained in step (6) and the sodium carbonate solution are mixed and stirred in a lithium precipitation vessel to precipitate lithium. After separation, solid lithium carbonate and lithium precipitation mother liquor are obtained. The mass concentration of the sodium carbonate solution is 27%, and the molar ratio of lithium element in the concentrated water to sodium carbonate in the sodium carbonate solution is 1:1.43. The lithium precipitation temperature is 95℃ and the lithium precipitation time is 45min. (8) The lithium carbonate solid obtained in step (7) is sequentially washed with water, centrifuged and dried to obtain industrial grade lithium carbonate; the liquid-to-solid ratio of the water washing is 30:1, the number of water washings is 2, the water washing is carried out under stirring conditions, and the stirring time is 45 min; the centrifugation rate is 2900 r / min; the heating medium for drying is 0.6 MPa saturated steam; (9) The lithium precipitation mother liquor obtained in step (7) is heat-exchanged through a plate heat exchanger. The temperature of the lithium precipitation mother liquor after heat exchange is 45°C. Then, extraction and back-extraction are performed in sequence to obtain battery-grade lithium carbonate. The extraction method is as follows: The heated lithium precipitation mother liquor is mixed with a 32% sodium hydroxide solution to obtain an extractable solution with a pH of 13. Then, the extractable solution and the organic phase (dimethylheptyl methylphosphonate) are subjected to counter-current mixing extraction in an extraction tank (containing four stages). During counter-current mixing extraction, the extractable solution enters the third and second stages of the extraction tank sequentially from the fourth stage, while the organic phase enters the third and fourth stages sequentially from the second stage. The flow rate of the extractable solution during counter-current mixing extraction is 10.5 m³ / s. 3 / h, the flow rate of the organic phase is 15m³ / h. 3 The reverse mixing extraction process is completed at a flow rate of 15 m³ / h, yielding a lithium-loaded organic phase and raffinate. The lithium-loaded organic phase and pure water are then reverse-mixed and washed in a washing tank (containing washing tank stages 1, 2, 3, and 4). During the reverse mixing and washing, the lithium-loaded organic phase enters washing tank stage 1 via extraction tank stage 4, then sequentially enters washing tank stages 2 and 3. Pure water enters washing tank stages 2 and 1 sequentially from washing tank stage 3. The flow rate of the lithium-loaded organic phase is 15 m³ / h. 3 / h, the flow rate of pure water is 2.72m³ / h. 3 / h, complete the reverse mixing and washing to obtain the loaded organic phase and washing water; the raffinate enters the first stage of the extraction tank from the second stage of the extraction tank, mixes with a 5% nitric acid solution, and then enters the raffinate oil separator for oil-water separation to obtain the aqueous phase and oil phase; the washing water enters the first stage of the washing tank, then mixes with a 5% nitric acid solution, then enters the fourth stage of the extraction tank, and finally flows into the raffinate. The back-extraction method is as follows: carbon dioxide (flow rate 74 Nm³) is added... 3 / h), the extracted loaded organic phase (flow rate of 15m³ / h), 3 / h) and pure water (flow rate of 2.72m) 3 ( / h) Mix and back-extract, then vent carbon dioxide 22Nm 3 The process involves obtaining a water-oil mixture at a rate of / h, followed by phase separation in a phase separation tank to obtain a back-extraction liquid and a raffinate. The raffinate is then transferred to a blank organic tank for oil removal using an oil removal adsorption column. The back-extraction liquid is transferred to an aqueous phase tank and subsequently treated with an oil removal adsorption column and a calcium-magnesium resin column. Pyrolysis is then performed in a pyrolysis reactor at 95°C, with carbon dioxide emitted at high altitude. The condensate from the pyrolysis steam enters a condensate tank and undergoes solid-liquid separation in a centrifuge to obtain a solid and a liquid phase. The solid is mixed with pure water and then centrifuged. Finally, the material is dried in a disc dryer by heat exchange with steam to obtain battery-grade lithium carbonate. The oil removal adsorption column consists of three columns connected in series, with two columns in operation and one on standby. The calcium-magnesium resin column consists of two columns, with one in operation and one on standby.

[0069] The industrial-grade and battery-grade lithium carbonate obtained in Example 1 of this invention were tested, and the results were as follows: the purity of the industrial-grade lithium carbonate was ≥99%, the sodium content was <350ppm, and the moisture content was ≤0.15%, which meets the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate"; the mass concentration of lithium carbonate in the battery-grade lithium carbonate was ≥99.5%, the sodium content was ≤250ppm, the iron content was ≤10ppm, and the boron content was ≤50ppm, which also meets the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate". It can be seen that the method provided by this invention can recover industrial-grade and battery-grade lithium carbonate from the sodium aluminate mother liquor obtained from the Bayer process alumina system, realizing the resource utilization and reuse of waste. Furthermore, the wastewater and waste generated in this process are recycled and reused, with no wastewater discharge throughout the entire process, making it an economical and environmentally friendly production process.

[0070] Comparative Example 1 In step (4), the tertiary electrodialysis is replaced with a secondary electrodialysis. The parameters for the secondary electrodialysis are: primary membrane voltage 1.0V, electrical density 400A / m. 2A total of 2400 pairs (2 sets of equipment), secondary pair membrane voltage 1.0V, electrical density 100A / m 2 A total of 1000 pairs; Other conditions are the same as in Example 1.

[0071] The industrial-grade lithium carbonate obtained in Comparative Example 1 conforms to the industrial-grade standard in GB / T 11075-2013 "Lithium Carbonate", and the battery-grade lithium carbonate conforms to the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate".

[0072] Compared to Example 1, although the process of Comparative Example 1 was not affected, when using sodium aluminate mother liquor from the same source and in the same amount for recovery, Comparative Example 1 obtained less industrial-grade lithium carbonate and battery-grade lithium carbonate, indicating a higher lithium loss rate.

[0073] Comparative Example 2 Step (5) is omitted, and the other conditions are the same as in Example 1.

[0074] The purity of the battery-grade lithium carbonate obtained in Comparative Example 2 decreased significantly, failing to meet the battery-grade standard in GB / T 11075-2013 "Lithium Carbonate".

[0075] Comparative Example 3 In step (7), the mass concentration of the sodium carbonate solution is 35%, and other conditions are the same as in Example 1.

[0076] The purity of industrial-grade and battery-grade lithium carbonate obtained in Comparative Example 3 decreased because the concentration of sodium carbonate solution was too high, which caused impurities such as magnesium and calcium to co-precipitate, leading to sodium ion adsorption or encapsulation, resulting in excessive sodium content and alkalinity in industrial-grade and battery-grade lithium carbonate. At the same time, the high concentration of sodium carbonate solution led to "explosive nucleation", resulting in small crystal particle size, irregular crystal shape, and easy agglomeration, which made separation difficult, greatly increased the washing water volume, and the large specific surface area of ​​the small crystals increased the dissolution loss of lithium carbonate during the washing process.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering industrial-grade and battery-grade lithium carbonate from sodium aluminate mother liquor, characterized in that, Includes the following steps: (1) After mixing the sodium aluminate mother liquor and the acid solution, a precipitation treatment is carried out to obtain a mixture of material liquid and aluminum hydroxide mud water; (2) Filter the liquid obtained in step (1) to obtain ultrafiltration permeate; (3) The ultrafiltration permeate obtained in step (2) is concentrated in a primary reverse osmosis system to obtain primary reverse osmosis concentrate and primary reverse osmosis permeate; (4) Perform tertiary electrodialysis on the primary reverse osmosis concentrate obtained in step (3) to obtain tertiary electrodialysis desalinated water and primary electrodialysis concentrate; (5) The primary electrodialysis concentrate obtained in step (4) is treated with boron removal resin to obtain boron removal resin permeate; (6) The boron removal resin permeate obtained in step (5) is evaporated and concentrated to obtain concentrated evaporated water and condensate; (7) After mixing the concentrated water obtained in step (6) with the sodium carbonate solution, lithium is precipitated to obtain solid lithium carbonate and lithium precipitation mother liquor; (8) The lithium carbonate solid obtained in step (7) is washed with water, centrifuged and dried in sequence to obtain industrial grade lithium carbonate; (9) Extract and back-extract the lithium precipitation mother liquor obtained in step (7) in sequence to obtain battery-grade lithium carbonate.

2. The method according to claim 1, characterized in that, The sodium aluminate mother liquor in step (1) comprises: lithium element concentration of 1.2~1.8 g / L, aluminum element concentration of 0.15~0.2 g / L, and carbonate ion concentration of 5~6.5 g / L.

3. The method according to claim 1, characterized in that, In step (1), the precipitant used for precipitation treatment is PAC solution and / or PAM solution. The mass concentration of PAC solution and PAM solution is 40-60% independently. The amount of precipitant used is 0.01-0.05% of the mass of sodium aluminate mother liquor. The pH value of precipitation treatment is 5-7.

4. The method according to claim 1, characterized in that, In step (3), the operating pressure of the first-stage reverse osmosis system is ≤7MPa.

5. The method according to claim 1, characterized in that, The parameters for the three-stage electrodialysis in step (4) include: first-stage membrane voltage 0.6~0.8V, electrical density 350~450A / m 2 A total of 2400 pairs; secondary pair membrane voltage 0.6~0.8V, electrical density 250~350A / m 2 A total of 1200 pairs; three-stage pair membrane voltage 0.8~1.0V, electrical density 80~120A / m 2 A total of 1000 pairs.

6. The method according to claim 1, characterized in that, In step (5), the boron removal resin treatment is performed using a complex ion exchange resin with N-methylglucosamine groups. The volumetric flow rate of the boron removal resin treatment is 4~8 BV / h, and the temperature of the boron removal resin treatment is 30~40℃.

7. The method according to claim 1, characterized in that, In step (7), the mass concentration of sodium carbonate solution is 20-30%, and the molar ratio of lithium element in the evaporated concentrated water to sodium carbonate in the sodium carbonate solution is 1:(1.4-1.8).

8. The method according to claim 1, characterized in that, In step (7), the lithium precipitation temperature is 90~95℃ and the precipitation time is 30~60min.

9. The method according to claim 1, characterized in that, The extraction method in step (9) is as follows: the lithium precipitation mother liquor and the alkaline solution are mixed to obtain the extract to be extracted, and then the extract to be extracted and the organic phase are mixed in reverse to extract the lithium-loaded organic phase and the raffinate. Then the lithium-loaded organic phase and pure water are mixed in reverse to wash the lithium-loaded organic phase.

10. The method according to claim 1, characterized in that, The back-extraction method in step (9) is as follows: carbon dioxide, the loaded organic phase obtained by extraction and solvent are mixed for back-extraction to obtain a water-oil mixture. Then the water-oil mixture is separated into phases to obtain back-extraction liquid and raffinate. Next, the back-extraction liquid is treated with an oil removal adsorption column and a calcium and magnesium removal resin column in sequence. Then, pyrolysis and solid-liquid separation are performed to obtain a solid and a liquid phase. Finally, the solid and pure water are mixed and then centrifuged and dried in sequence to obtain battery-grade lithium carbonate.