Process for the production of lithium hydroxide of battery grade from lithium carbonate

Abstract

The present application belongs to the technical field of lithium carbonate producing battery grade lithium hydroxide, and discloses a method for producing battery grade lithium hydroxide from lithium carbonate, which has low chemical reagent consumption, low energy consumption, high lithium resource recovery rate, full utilization of by-products, and low waste discharge. The method comprises an acidification process for outputting first acidified liquid after sulfuric acid treatment of lithium carbonate, and further comprises: impurity removal treatment of the first acidified liquid to obtain a clarified liquid; an electrolysis process comprising electrolysis treatment of the clarified liquid using a bipolar membrane electrolysis device to obtain an acid solution and an alkali solution; concentration treatment, crystallization treatment and solid-liquid separation treatment of the alkali solution in sequence to obtain battery grade lithium hydroxide and a first mother liquor; sulfuric acid treatment, lithium precipitation treatment and solid-liquid separation treatment of the first mother liquor in sequence to obtain lithium carbonate and a second mother liquor; and sulfuric acid treatment, pH adjustment treatment, crystallization treatment and solid-liquid separation treatment of the second mother liquor in sequence to obtain sodium sulfate and a third mother liquor.

Description

Technical Field

[0001] This invention relates to the technical field of producing battery-grade lithium hydroxide from lithium carbonate, and more specifically, to a method for producing battery-grade lithium hydroxide from lithium carbonate. Background Technology

[0002] As a core energy storage device in the new energy field, lithium batteries place extremely high demands on the quality of lithium hydroxide in the preparation of their cathode materials. Battery-grade lithium hydroxide has become an indispensable lithium source for high-nickel ternary cathode materials. Currently, the main industrial methods for producing lithium hydroxide from lithium carbonate are the causticization method and the freezing method.

[0003] The causticization method involves reacting lithium carbonate with calcium hydroxide in an aqueous solution to produce lithium hydroxide and calcium carbonate precipitates. After solid-liquid separation, a lithium hydroxide solution is obtained, which is then evaporated, concentrated, and crystallized to obtain the lithium hydroxide product. While this method has a simple process flow, it inevitably introduces impurities such as calcium ions during the reaction, making it difficult to achieve battery-grade purity. Furthermore, the calcium carbonate precipitate produced by the causticization reaction contains a large amount of lithium, resulting in a low lithium recovery rate. In addition, the disposal of large amounts of calcium carbonate waste increases environmental pressure.

[0004] The freezing method involves first reacting lithium carbonate with sulfuric acid to generate a lithium sulfate solution, then adding sodium hydroxide to the lithium sulfate solution to carry out a double decomposition reaction, generating a mixed solution of lithium hydroxide and sodium sulfate. Taking advantage of the characteristic that the solubility of sodium sulfate decreases sharply at low temperatures, sodium sulfate decahydrate (sodium sulfate) is precipitated by freezing crystallization. After removing sodium sulfate through solid-liquid separation, the mother liquor containing lithium hydroxide is evaporated, concentrated, and crystallized to finally obtain the lithium hydroxide product. While this method can yield high-purity lithium hydroxide, it has the following drawbacks: First, the process requires a large amount of sodium hydroxide, and the sodium sulfate precipitated by freezing has low economic value, resulting in high production costs. Second, the freezing crystallization process requires cooling a large amount of solution to a low temperature, which consumes a huge amount of cooling energy. Furthermore, the subsequent evaporation and concentration of lithium hydroxide requires a large amount of heat energy, and the alternation of heating and cooling leads to extremely high overall energy consumption. Third, a considerable concentration of lithium ions remains in the mother liquor after freezing and sodium precipitation, and the existing process lacks effective means to recover lithium resources from the mother liquor, resulting in a low overall lithium recovery rate. Fourth, sulfuric acid and sodium hydroxide are consumed only once throughout the entire process, making recycling impossible, resulting in low material utilization efficiency and poor economic performance.

[0005] In summary, existing methods for producing battery-grade lithium hydroxide from lithium carbonate generally suffer from problems such as high consumption of chemical reagents, high energy consumption, low lithium resource recovery rate, insufficient utilization of by-products, and large amounts of waste emissions. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method and system for producing battery-grade lithium hydroxide from lithium carbonate, which features low chemical reagent consumption, low energy consumption, high lithium resource recovery rate, full utilization of by-products, and low waste emissions. The technical solution is as follows: A method for producing battery-grade lithium hydroxide from lithium carbonate includes an acidification step of outputting a first acidification solution after sulfation treatment of lithium carbonate, and further includes the following steps: Impurity removal process: The first acidification solution is treated to remove impurities, resulting in a clarified solution; Electrolysis process: This includes electrolyzing the clarified liquid using bipolar membrane electrolysis equipment to obtain acid and alkaline solutions; Lithium hydroxide extraction process: The alkaline solution is sequentially concentrated, crystallized, and separated into solid and liquid components to obtain battery-grade lithium hydroxide and the first mother liquor; Lithium carbonate extraction process: The first mother liquor is subjected to sulfation treatment, lithium precipitation treatment and solid-liquid separation treatment in sequence to obtain lithium carbonate and second mother liquor; Sodium sulfate extraction process: The second mother liquor is subjected to sulfation treatment, pH adjustment treatment, crystallization treatment and solid-liquid separation treatment in sequence to obtain sodium sulfate and the third mother liquor.

[0007] The advantages of the method of the present invention are: (1) The lithium sulfate clarified solution is electrolyzed using a bipolar membrane electrolysis device, and directly converted into sulfuric acid and lithium hydroxide without the introduction of external chemical reagents. This fundamentally avoids the problems of introducing calcium ion impurities in the traditional causticization method and the large consumption of sodium hydroxide in the freezing method. The sulfuric acid produced by electrolysis can be recycled for sulfation treatment in other processes, realizing a closed-loop circulation of sulfuric acid in the process system, which significantly reduces the consumption of chemical reagents and production costs. (2) After the lithium hydroxide extraction process, the present invention further sets up a lithium carbonate extraction process to recover the residual lithium ions in the first mother liquor in the form of lithium carbonate, which effectively solves the problems of serious lithium loss and low overall recovery rate in the prior art. (3) After the lithium carbonate extraction process, the present invention also sets up a sodium sulfate extraction process to extract the sodium salt accumulated in the system in the form of sodium sulfate. Its economic value is significantly higher than that of the hydrous sodium sulfate by-product precipitated in the traditional freezing method, and no cold chain storage and transportation is required.

[0008] In summary, this invention constructs a closed-loop production system that integrates and couples acidification, impurity removal, electrolysis, lithium hydroxide extraction, lithium carbonate extraction, and sodium sulfate extraction processes. This system enables the recycling of sulfuric acid, multi-stage recovery of lithium resources, and high-value conversion of sodium salts. Intermediate materials generated in each process can be effectively utilized within the system, avoiding the high energy consumption caused by alternating hot and cold temperatures in the freezing method. The entire process generates no waste liquid discharge, achieving green, efficient, and economical production goals while ensuring that the product reaches battery-grade quality.

[0009] As a further improvement to the above method, the impurity removal process includes sequentially subjecting the first acidified solution to pH adjustment, solid-liquid separation, resin adsorption, and ultrafiltration. The pH adjustment is performed using sodium hydroxide to adjust the pH to 6-7. The resin adsorption process is used to adsorb polyvalent metal ions. Adjusting the pH to 6-7 allows some ferrous ions to precipitate and also facilitates resin adsorption. Thus, the synergistic effect of the multi-stage impurity removal process ensures that the purity of the clarified solution entering the bipolar membrane electrolysis equipment meets the requirements, effectively preventing membrane fouling and product quality degradation.

[0010] As a further improvement to the above method, the electrolysis process also includes concentrating the residual electrolyte discharged from the salt chamber outlet of the bipolar membrane electrolysis equipment and re-introducing the concentrated brine into the salt chamber. This concentration process utilizes a reverse osmosis membrane. This increases the lithium sulfate concentration and current efficiency within the salt chamber, thereby reducing the power consumption per unit product.

[0011] As a further improvement to the above method: in the lithium hydroxide extraction process, the concentration treatment adopts electrodialysis, the crystallization treatment adopts evaporation concentration and crystallization, and the solid-liquid separation treatment adopts centrifugation to output the battery-grade lithium hydroxide and the first mother liquor. Therefore, electrodialysis concentration consumes less energy than traditional evaporation concentration, and evaporation crystallization after electrodialysis concentration can significantly reduce the amount of water required for evaporation, thus significantly reducing energy consumption.

[0012] As a further improvement to the above method: in the lithium hydroxide extraction process, a portion of the first mother liquor enters the lithium carbonate extraction process, while the remaining first mother liquor is recycled to the lithium hydroxide extraction process for crystallization. This reduces the amount of lithium residue in the first mother liquor and further improves the overall lithium recovery rate.

[0013] As a further improvement to the above method: in the lithium carbonate extraction process, after sulfation treatment, a second acidified solution with a carbonate ion concentration ≤0.25 g / L is output; sodium carbonate is used as a precipitant for lithium precipitation; and centrifugation is used for solid-liquid separation, outputting the lithium carbonate and a second mother liquor. Thus, sulfation treatment can avoid carbonate ions interfering with the subsequent lithium precipitation reaction.

[0014] As a further improvement to the above method, the lithium carbonate extraction process also includes washing the lithium carbonate with the condensate generated during the crystallization process in the lithium hydroxide extraction and sodium sulfate extraction processes, reusing the cleaned lithium carbonate in the acidification process, and reusing the wash water to dilute the acid solution output from the bipolar membrane electrolysis equipment. This achieves dual recovery of water and lithium resources.

[0015] As a further improvement to the above method, a process is also included to prepare the acid solution output from the bipolar membrane electrolysis equipment to the required concentration using fresh sulfuric acid and wash water. This achieves unified recovery and utilization of lithium resources from the electrolytic acid production and wash water.

[0016] As a further improvement to the above method, the sulfuric acid used in the sulfation treatment of the acidification, lithium carbonate extraction, and sodium sulfate extraction processes all originates from the sulfuric acid preparation process. This achieves unified preparation and cyclical supply of electrolytically produced acid throughout the entire process, minimizing the need for fresh sulfuric acid replenishment and reducing acid consumption costs.

[0017] As a further improvement to the above method: In the sodium sulfate extraction process, the third acidified solution with a carbonate ion concentration ≤0.25 g / L is output after the sulfation treatment; the pH adjustment treatment uses sodium hydroxide to adjust the pH to 6-7; the crystallization treatment uses evaporation and concentration crystallization; the solid-liquid separation treatment uses centrifugation and outputs the sodium sulfate and the third mother liquor; the third mother liquor is refluxed to the lithium carbonate extraction process for lithium precipitation. Thus, the sulfation treatment removes residual carbonate ions, further pH adjustment facilitates sodium sulfate crystallization, and the reflux of the third mother liquor achieves deep lithium recovery.

[0018] A system for producing battery-grade lithium hydroxide from lithium carbonate includes an acidification unit for sulfating lithium carbonate and outputting a first acidified solution, the acidification unit including a first reaction tank, and further comprising: The impurity removal unit is used to remove impurities from the first acidification solution and output a clarified solution. An electrolysis unit, including a bipolar membrane electrolysis device for electrolyzing clarified liquid and outputting acid and alkaline solutions; The lithium hydroxide extraction unit is used to sequentially concentrate, crystallize, and separate an alkaline solution and output battery-grade lithium hydroxide and a first mother liquor. The lithium hydroxide extraction unit includes a first concentration device, a first crystallizer, and a first solid-liquid separation device connected in sequence. The inlet of the first concentration device is connected to the outlet of the alkaline chamber of the bipolar membrane electrolysis device. A lithium carbonate extraction unit is used to sequentially perform sulfation treatment, lithium precipitation treatment, and solid-liquid separation treatment on a first mother liquor and output lithium carbonate and a second mother liquor; the lithium carbonate extraction unit includes a second reaction tank, a lithium precipitation reactor, and a second solid-liquid separation device connected in sequence, and the inlet of the second reaction tank is connected to the outlet of the first solid-liquid separation device; The sodium sulfate extraction unit is used to sequentially perform sulfation treatment, pH adjustment treatment, crystallization treatment and solid-liquid separation treatment on the second mother liquor and output sodium sulfate and the third mother liquor; the sodium sulfate extraction unit includes a third reaction tank, a first adjustment tank, a second crystallizer and a third solid-liquid separation device connected in sequence, and the liquid inlet of the third reaction tank is connected to the liquid outlet of the second solid-liquid separation device.

[0019] The advantages of the system of the present invention are: (1) Under the action of an electric field, the bipolar membrane electrolysis equipment directly converts lithium sulfate into sulfuric acid and lithium hydroxide without the need for external chemical reagents such as sodium hydroxide or calcium hydroxide, thus eliminating the problems of the introduction of foreign impurity ions and the consumption of a large amount of chemical reagents in the traditional process. (2) The lithium hydroxide extraction unit realizes the continuous conversion of alkaline solution from dilute solution to battery-grade lithium hydroxide crystal product; the lithium carbonate extraction unit enables the residual lithium ions in the first mother liquor to be retained in the system in the form of lithium carbonate through sulfation treatment and lithium precipitation reaction; and the sodium sulfate extraction unit converts the sodium salt accumulated in the system into sodium sulfate product output. Thus, each unit constitutes a complete system of battery-grade lithium hydroxide extraction, lithium resource recycling and sodium salt high-value conversion, with no waste liquid discharge outlet and can operate with high efficiency.

[0020] As a further improvement to the above system: the impurity removal unit includes a second regulating tank, a fourth solid-liquid separation device, a resin adsorption device and an ultrafiltration device connected in sequence. The inlet of the second regulating tank is connected to the outlet of the first reaction tank. The fourth solid-liquid separation device adopts a precision filter. The product water outlet of the ultrafiltration device is connected to the salt chamber inlet of the bipolar membrane electrolysis device.

[0021] As a further improvement to the above system, the electrolysis unit also includes a second concentration device located on the reflux pipe between the salt chamber outlet and the salt chamber inlet of the bipolar membrane electrolysis device, wherein the second concentration device is a reverse osmosis device.

[0022] As a further improvement to the above system: in the lithium hydroxide extraction unit, the first concentration device is an electrodialysis device, the first crystallizer is an MVR evaporator, and the first solid-liquid separation device is a first centrifuge that outputs the battery-grade lithium hydroxide and the first mother liquor.

[0023] As a further improvement to the above system: the drain port of the first centrifuge is connected to the inlet of the first crystallizer and the second reaction tank through a diversion valve.

[0024] As a further improvement to the above system, the lithium carbonate extraction unit also includes a washing tank and a fourth solid-liquid separation device connected in sequence. The inlet of the washing tank is connected to the outlet of the second solid-liquid separation device, and the inlet is connected to the condensate outlet of the first crystallizer and the second crystallizer. The outlet of the fourth solid-liquid separation device is connected to the inlet of the first reaction tank. The second solid-liquid separation device is a second centrifuge. The fourth solid-liquid separation device is a fourth centrifuge.

[0025] As a further improvement to the above system, it also includes a sulfuric acid preparation unit for adjusting the acid solution output from the acid chamber of the bipolar membrane electrolysis equipment to the required concentration of sulfuric acid. The sulfuric acid preparation unit includes a preparation tank, the inlet of which is connected to the acid chamber outlet of the bipolar membrane electrolysis equipment, the drain outlet of the fourth centrifuge, and the fresh sulfuric acid delivery pipeline.

[0026] As a further improvement to the above system: the drain port of the mixing tank is connected to the inlet ports of the first reaction tank, the second reaction tank and the third reaction tank.

[0027] As a further improvement to the above system: in the sodium sulfate extraction unit, the second crystallizer is an MVR evaporator, and the third solid-liquid separation device is a third centrifuge.

[0028] As a further improvement to the above system: the drain port of the third centrifuge is connected to the inlet port of the lithium precipitation reactor.

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to aid in understanding the invention. The content provided in the drawings and their related descriptions can be used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the system for producing battery-grade lithium hydroxide from lithium carbonate according to the present invention. Detailed Implementation

[0031] The present invention will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that: The technical solutions and features provided in the various parts of this invention, including the following description, can be combined with each other without conflict.

[0032] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0033] Regarding the terminology and units used in this invention: The terms "comprising," "having," and any variations thereof in the specification, claims, and related parts of this invention are intended to cover non-exclusive inclusion.

[0034] The specific implementation of the method for producing battery-grade lithium hydroxide from lithium carbonate of the present invention includes the following steps: Acidification process: Lithium carbonate (industrial grade) is sulfated to convert lithium carbonate into lithium sulfate, resulting in a first acidification solution rich in lithium sulfate, with a pH of 2.4-2.6 and a carbonate ion concentration ≤0.25g / L; Impurity removal process: The first acidification solution is treated to remove impurities, resulting in a clarified solution; Preferably, the impurity removal process includes sequentially performing pH adjustment treatment, solid-liquid separation treatment, resin adsorption treatment, and ultrafiltration treatment on the first acidified liquid; the pH adjustment treatment uses sodium hydroxide to adjust the pH value to 6-7; the solid-liquid separation treatment is used to reduce acid-insoluble matter to below 5 mg / L; the resin adsorption treatment is used to adsorb polyvalent metal ions, using aminophosphonic acid chelating resin or imine diacetic acid (IDA) chelating resin; the ultrafiltration treatment is used to intercept large molecular particles and reduce turbidity to below 0.5 NTU.

[0035] Electrolysis process: This includes electrolyzing the clarified liquid using bipolar membrane electrolysis equipment to obtain acid and alkaline solutions; The bipolar membrane electrolysis device includes a salt chamber and acid and alkali chambers on both sides of the salt chamber. Both the acid and alkali chambers are equipped with bipolar membranes. The acid and salt chambers are separated by an anion membrane (for sulfate ions to pass through), and the alkali and salt chambers are separated by a cation membrane (for lithium ions to pass through). After being energized, water is electrolyzed on the bipolar membranes to generate hydrogen ions and hydroxide ions. Hydrogen ions enter the acid chamber, and hydroxide ions enter the alkali chamber. Sulfate ions in the salt chamber pass through the anion membrane and combine with hydrogen ions in the acid chamber to form sulfuric acid (i.e., an acidic solution). Lithium ions in the salt chamber pass through the cation membrane and combine with hydroxide ions in the alkali chamber to form lithium hydroxide (i.e., an alkali solution).

[0036] Meanwhile, the electrolysis process also includes concentrating the residual electrolyte discharged from the salt chamber outlet of the bipolar membrane electrolysis equipment and re-introducing the concentrated brine into the salt chamber. The concentration process is carried out using a reverse osmosis membrane.

[0037] Lithium hydroxide extraction process: The alkaline solution is sequentially concentrated, crystallized, and separated into solid and liquid components to obtain battery-grade lithium hydroxide and the first mother liquor; The concentration process employs electrodialysis, the crystallization process uses evaporation-concentration-crystallization, and the solid-liquid separation process uses centrifugation to output the battery-grade lithium hydroxide and the first mother liquor. Half of the first mother liquor enters the lithium carbonate extraction process, while the remaining first mother liquor is recycled to the lithium hydroxide extraction process for crystallization.

[0038] Lithium carbonate extraction process: The first mother liquor is subjected to sulfation treatment, lithium precipitation treatment and solid-liquid separation treatment in sequence to obtain lithium carbonate and second mother liquor; The process involves sulfation treatment followed by the output of a second acidified solution with a carbonate ion concentration ≤0.25g / L, lithium precipitation treatment using sodium carbonate as a precipitant, and solid-liquid separation treatment using centrifugation to output the lithium carbonate and a second mother liquor.

[0039] Preferably, the lithium carbonate extraction process further includes washing the lithium carbonate with the condensate generated during the crystallization process in the lithium hydroxide extraction process and the sodium sulfate extraction process, reusing the clean lithium carbonate in the acidification process, and reusing the wash water to dilute the acid solution output from the bipolar membrane electrolysis equipment.

[0040] Sodium sulfate extraction process: The second mother liquor is subjected to sulfation treatment, pH adjustment treatment, crystallization treatment and solid-liquid separation treatment in sequence to obtain sodium sulfate and the third mother liquor; The process involves the following steps: after sulfation treatment, a third acidified solution with a carbonate ion concentration ≤0.25 g / L is output; the pH adjustment treatment uses sodium hydroxide to adjust the pH value to 6-7; the crystallization treatment uses evaporation and concentration crystallization; the solid-liquid separation treatment uses centrifugation to output the sodium sulfate and the third mother liquor; and the third mother liquor is refluxed to the lithium carbonate extraction process for lithium precipitation treatment.

[0041] Sulfuric acid preparation process: Fresh sulfuric acid and washing water are used to prepare the acid solution output from the bipolar membrane electrolysis equipment to the required concentration. The sulfuric acid used in the sulfation treatment in the acidification process, lithium carbonate extraction process and sodium sulfate extraction process all come from the sulfuric acid preparation process.

[0042] To facilitate the implementation of the above-described method for producing battery-grade lithium hydroxide from lithium carbonate, the present invention also provides a system for producing battery-grade lithium hydroxide from lithium carbonate. Figure 1 This is a schematic diagram of the system for producing battery-grade lithium hydroxide from lithium carbonate according to the present invention. Figure 1 The system shown for producing battery-grade lithium hydroxide from lithium carbonate includes an acidification unit, a purification unit, an electrolysis unit, a lithium hydroxide extraction unit, a lithium carbonate extraction unit, a sodium sulfate extraction unit, and a sulfuric acid preparation unit.

[0043] The acidification unit is used to sulfate lithium carbonate and output a first acidified solution. The acidification unit includes a first reaction tank.

[0044] The impurity removal unit is used to remove impurities from the first acidified liquid and output a clarified liquid. The impurity removal unit includes a second regulating tank, a fourth solid-liquid separation device, a resin adsorption device, and an ultrafiltration device connected in sequence. The inlet of the second regulating tank is connected to the outlet of the first reaction tank. The fourth solid-liquid separation device uses a precision filter. The product water outlet of the ultrafiltration device is connected to the salt chamber inlet of the bipolar membrane electrolysis device. The precipitate intercepted by the precision filter is dewatered by a filter press and discharged from the system as solid waste.

[0045] The electrolysis unit includes a bipolar membrane electrolysis device that electrolyzes the clarified liquid and outputs acid and alkali solutions, and a second concentration device located on a reflux pipe between the salt chamber outlet and the salt chamber inlet of the bipolar membrane electrolysis device. The second concentration device is a reverse osmosis device (the reverse osmosis permeate can be used as makeup water for the acid and alkali chambers).

[0046] The lithium hydroxide extraction unit is used to sequentially concentrate, crystallize, and separate the alkaline solution, and output battery-grade lithium hydroxide and a first mother liquor. The lithium hydroxide extraction unit includes a first concentration device, a first crystallizer, and a first solid-liquid separation device connected in sequence. The inlet of the first concentration device is connected to the outlet of the alkaline chamber of the bipolar membrane electrolysis device. The first concentration device is an electrodialysis device (the electrodialysis permeate can be used as makeup water for the alkaline chamber of the bipolar membrane electrolysis device); the first crystallizer is an MVR evaporator; the first solid-liquid separation device is a first centrifuge and outputs the battery-grade lithium hydroxide and the first mother liquor. The outlet of the first centrifuge is connected to the inlet of the first crystallizer and the second reaction tank via a diversion valve.

[0047] The lithium carbonate extraction unit is used to sequentially perform sulfation treatment, lithium precipitation treatment, and solid-liquid separation treatment on the first mother liquor, and output lithium carbonate and a second mother liquor. The lithium carbonate extraction unit includes a second reaction tank, a lithium precipitation reactor, and a second solid-liquid separation device connected in sequence. The inlet of the second reaction tank is connected to the outlet of the first solid-liquid separation device. The lithium carbonate extraction unit also includes a washing tank and a fourth solid-liquid separation device connected in sequence. The inlet of the washing tank is connected to the outlet of the second solid-liquid separation device, and its water inlet is connected to the condensate outlet of the first and second crystallizers. The outlet of the fourth solid-liquid separation device is connected to the inlet of the first reaction tank. The second solid-liquid separation device uses a second centrifuge; the fourth solid-liquid separation device uses a fourth centrifuge.

[0048] The sodium sulfate extraction unit is used to sequentially perform sulfation treatment, pH adjustment treatment, crystallization treatment, and solid-liquid separation treatment on the second mother liquor, and output sodium sulfate and the third mother liquor. The sodium sulfate extraction unit includes a third reaction tank, a first adjustment tank, a second crystallizer, and a third solid-liquid separation device connected in sequence. The inlet of the third reaction tank is connected to the outlet of the second solid-liquid separation device. The second crystallizer is an MVR evaporator; the third solid-liquid separation device is a third centrifuge, and the outlet of the third centrifuge is connected to the inlet of the lithium precipitation reactor.

[0049] The sulfuric acid preparation unit is used to prepare the acid solution output from the acid chamber of the bipolar membrane electrolysis equipment to the required concentration. The sulfuric acid preparation unit includes a preparation tank. The inlet of the preparation tank is connected to the outlet of the acid chamber of the bipolar membrane electrolysis equipment, the drain outlet of the fourth centrifuge, and the fresh sulfuric acid delivery pipeline. The outlet of the preparation tank is connected to the inlets of the first reaction tank, the second reaction tank, and the third reaction tank.

[0050] The beneficial effects of the present invention will be illustrated below through specific embodiments.

[0051] Battery-grade lithium hydroxide was prepared using industrial-grade lithium carbonate with mass fractions of 79.86% carbonate and 18.64% lithium ions, as described above, through the aforementioned method and system. The process and results are as follows: Acidification process: Based on 1 ton of fresh industrial-grade lithium carbonate, approximately 0.036 tons of clean lithium carbonate extracted from the lithium carbonate extraction unit are added, along with approximately 14m³ of... 3 Lithium carbonate was sulfated using 1M prepared sulfuric acid (from the mixing tank) to obtain a first acidified solution with a pH of 2.4–2.6 and a carbonate ion concentration ≤0.2 g / L.

[0052] Impurity removal process: Add approximately 0.013 mg / L 3 The pH was adjusted to 6-7 with 30% sodium hydroxide; then, acid-insoluble matter was reduced to below 5 mg / L through precision filtration; finally, aminophosphonic acid chelating resin was used for adsorption to remove divalent metal ions (mainly Fe). 2+ Ca 2+ Mg 2+ The concentration was reduced to below 0.3 mg / L; then ultrafiltration was performed, controlling the product water recovery rate at 98%, yielding approximately 12.81 mg / L. 3 The ultrafiltration permeate is the clarified liquid.

[0053] Electrolysis process: The clarified solution flows into the salt chamber, and the bipolar membrane electrolysis water volume is 27.15 m³. 3 Pure water, producing approximately 13.58m³. 3 Acidic solutions (pH 0.1–0.5) and alkaline solutions (pH 13.5–14.0) produce approximately 21.84 m 3The residual electrolyte is concentrated to approximately 8.74 m³ using a reverse osmosis system. 3 It then flows back into the salt chamber.

[0054] Lithium hydroxide extraction process: The alkaline solution is concentrated to 8.15 mg / L using electrodialysis equipment. 3 The mixture underwent evaporation and crystallization followed by solid-liquid separation, producing approximately 7.13 m³ of condensate. 3 The first centrifuge yielded approximately 0.54 m. 3 The first mother liquor and approximately 1.13 tons of battery-grade lithium hydroxide (wet material, approximately 1.08 tons after drying). Half of the first mother liquor is recycled to the first crystallizer, and the other half is sent to the lithium carbonate extraction process.

[0055] Lithium carbonate extraction process: using approximately 0.26m 3 1M sulfuric acid was used to sulfate the first mother liquor (carbonate ion concentration ≤ 0.2 g / L), and then 0.24M sulfuric acid was added. 3 A lithium precipitation reaction was carried out with 20 wt.% sodium carbonate, and after centrifugation in a second centrifuge, approximately 0.84 mg of lithium was obtained. 3 The second mother liquor and approximately 0.036 tons of lithium carbonate were used to wash the lithium carbonate (the mass loss of wet material before and after washing is negligible) before being fed into the first reaction tank.

[0056] Sodium sulfate extraction process: using approximately 0.25m 3 The second mother liquor was sulfated with 1M sulfuric acid (carbonate ion concentration ≤0.2g / L). The pH was adjusted to 6-7 with a trace amount of 30% sodium hydroxide. Evaporation and crystallization processes followed by solid-liquid separation were then performed, producing approximately 0.95m³ of condensate. 3 After centrifugation in the third centrifuge, approximately 0.1 m was obtained. 3 The third mother liquor and approximately 0.09 tons of sodium sulfate.

[0057] Verification has shown that by utilizing a self-circulating 1M solution of sulfuric acid and clean lithium carbonate, an annual production of 5,000 tons of battery-grade lithium hydroxide requires only the purchase of approximately 64.8m³ of 30% sodium hydroxide. 3 Approximately 275 tons of 99% sodium carbonate and approximately 150 cubic meters of 98% sulfuric acid. 3 At the same time, it produces about 408 tons of sodium sulfate with a purity of 98.5% as a byproduct. Compared with the causticizing method and the freezing method, the cost of electricity and steam used is significantly reduced, and the overall operating cost per ton of product is significantly reduced, making it highly practical.

[0058] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the above description of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A method for producing battery-grade lithium hydroxide from lithium carbonate, comprising an acidification step of sulfatating lithium carbonate and outputting a first acidification solution, characterized in that: It also includes the following steps: Impurity removal process: The first acidification solution is treated to remove impurities, resulting in a clarified solution; Electrolysis process: This includes electrolyzing the clarified liquid using bipolar membrane electrolysis equipment to obtain acid and alkaline solutions; Lithium hydroxide extraction process: The alkaline solution is sequentially concentrated, crystallized, and separated into solid and liquid components to obtain battery-grade lithium hydroxide and the first mother liquor; Lithium carbonate extraction process: The first mother liquor is subjected to sulfation treatment, lithium precipitation treatment and solid-liquid separation treatment in sequence to obtain lithium carbonate and second mother liquor; Sodium sulfate extraction process: The second mother liquor is subjected to sulfation treatment, pH adjustment treatment, crystallization treatment and solid-liquid separation treatment in sequence to obtain sodium sulfate and the third mother liquor.

2. The method as described in claim 1, characterized in that: The impurity removal process includes sequentially performing pH adjustment treatment, solid-liquid separation treatment, resin adsorption treatment, and ultrafiltration treatment on the first acidified liquid. The pH adjustment treatment uses sodium hydroxide to adjust the pH value to 6-7, and the resin adsorption treatment is used to adsorb polyvalent metal ions.

3. The method as described in claim 1, characterized in that: The electrolysis process also includes concentrating the residual electrolyte discharged from the salt chamber outlet of the bipolar membrane electrolysis equipment and re-introducing the concentrated salt solution into the salt chamber. The concentration process is carried out using a reverse osmosis membrane.

4. The method as described in claim 1, characterized in that: In the lithium hydroxide extraction process, the concentration treatment is carried out by electrodialysis, the crystallization treatment is carried out by evaporation concentration and crystallization, and the solid-liquid separation treatment is carried out by centrifugation, and the battery-grade lithium hydroxide and the first mother liquor are output.

5. The method as described in claim 4, characterized in that: In the lithium hydroxide extraction process, part of the first mother liquor enters the lithium carbonate extraction process, while the remaining first mother liquor is recycled to the lithium hydroxide extraction process for crystallization treatment.

6. The method as described in claim 1, characterized in that: In the lithium carbonate extraction process, after sulfation treatment, a second acidified solution with a carbonate ion concentration ≤0.25g / L is output. Sodium carbonate is used as a precipitant for lithium precipitation treatment. The solid-liquid separation treatment is carried out by centrifugation, and the lithium carbonate and the second mother liquor are output.

7. The method as described in claim 6, characterized in that: The lithium carbonate extraction process also includes washing the lithium carbonate with the condensate generated from the crystallization process in the lithium hydroxide extraction process and the sodium sulfate extraction process, recycling the clean lithium carbonate back to the acidification process, and recycling the wash water back to dilute the acid solution output from the bipolar membrane electrolysis equipment.

8. The method as described in claim 7, characterized in that: It also includes a sulfuric acid preparation process that uses fresh sulfuric acid and washing water to adjust the acid solution output from the bipolar membrane electrolysis equipment to the required concentration.

9. The method as described in claim 8, characterized in that: The sulfuric acid used in the sulfation treatment of the acidification process, lithium carbonate extraction process, and sodium sulfate extraction process all comes from the sulfuric acid preparation process.

10. The method as described in claim 1, characterized in that: In the sodium sulfate extraction process, the third acidified solution with a carbonate ion concentration ≤0.25g / L is output after the sulfation treatment. The pH adjustment treatment uses sodium hydroxide to adjust the pH value to 6-7. The crystallization treatment uses evaporation concentration crystallization treatment. The solid-liquid separation treatment uses centrifugation treatment and outputs the sodium sulfate and the third mother liquor. The third mother liquor is refluxed to the lithium carbonate extraction process for lithium precipitation treatment.

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