Method and system for preparing lithium hydroxide from salt lake lithium-containing solution

Abstract

The invention provides a method and a system for preparing lithium hydroxide from a salt lake lithium-containing solution. The method comprises the following steps: concentrating a lithium-containing solution from salt lake brine to obtain a lithium-rich solution; performing calcium and magnesium removal treatment on the lithium-rich solution to remove at least part of calcium ions and magnesium ions in the lithium-rich solution to obtain a first feed liquid; performing bipolar membrane electrodialysis treatment on the first feed liquid to obtain second feed liquid containing lithium hydroxide and sodium hydroxide; and carrying out multi-stage evaporative crystallization on the second feed liquid so as to at least separate a lithium hydroxide product from the second feed liquid. According to the method provided by the invention, lithium and sodium separation can be effectively realized to prepare a battery-grade lithium hydroxide product, and the problems that an ion exchange membrane is easy to scale and pollute, the content of impurity ions in the product is high, the current efficiency is low, a byproduct acid solution is difficult to effectively utilize and the like when lithium hydroxide is prepared by a bipolar membrane electrodialysis method in the prior art can be solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction technology from salt lake brine, specifically relating to a method and system for preparing lithium hydroxide from salt lake brine. Background Technology

[0002] Currently, salt lake brine has become the main raw material for the production of basic lithium salts in my country, but the direct production of battery-grade lithium hydroxide from lithium-containing salt lake brine still faces significant challenges. Although some breakthroughs have been made in related technological development, no technology for the direct production of lithium hydroxide from salt lake brine has yet been applied on a large scale.

[0003] Existing methods for preparing lithium hydroxide from salt lake brine mainly include causticization, calcination, ion-exchange membrane electrolysis, and bipolar membrane electrodialysis. Among these, the causticization method requires first preparing lithium carbonate from the salt lake brine, followed by a metathesis reaction to obtain lithium hydroxide, resulting in a long process flow and low product purity and yield. The calcination, ion-exchange membrane electrolysis, and bipolar membrane electrodialysis methods can directly prepare lithium hydroxide from lithium-rich brine; however, the calcination method consumes a large amount of fresh water, leading to high energy consumption. While the ion-exchange membrane electrolysis method eliminates the need for chemicals and produces high-purity products, it requires addressing the recovery of byproduct gases and its relatively low current efficiency. In contrast, bipolar membrane electrodialysis achieves efficient water dissociation and the production of acids and bases through the combined effect of a locally enhanced electric field and catalytic hydrolysis in the intermediate layer, offering significant advantages in product purity, process energy consumption, and material recycling.

[0004] However, the practical application of bipolar membrane electrodialysis technology in salt lake brine systems currently faces several limitations, mainly including (1) the coexistence of monovalent cations and Li + (2) Effective separation of Mg by bipolar membrane electrodialysis process 2+ Ca 2+ (2) Stringent requirements for the content of polyvalent cations; (3) Comprehensive utilization of acidic by-products from bipolar membrane electrodialysis. Lithium-containing brine in salt lakes reacts with Li + A large amount of Na coexist + The presence of monovalent cations as the primary component presents a significant challenge for effective separation, leading to high impurity ion content in lithium hydroxide products prepared via bipolar membrane electrodialysis. Furthermore, the competitive mass transfer between monovalent cations during electrodialysis results in decreased current efficiency and increased power consumption in lithium hydroxide preparation. Additionally, residual Mg in the bipolar membrane electrodialysis feed solution... 2+ Ca 2+Plasma readily produces precipitation, leading to membrane fouling. However, the abundant magnesium resources in salt lake brines and the similarity in physicochemical properties between magnesium and lithium hydrates make magnesium-lithium separation extremely difficult. Although extensive basic research and industrial integration work on the separation of multivalent ions has been carried out, and breakthroughs in large-scale applications have been achieved, the lithium-rich feed solution obtained after the magnesium-lithium separation process, suitable for preparing lithium carbonate products, cannot be directly used for the bipolar membrane electrodialysis method to prepare lithium hydroxide because of the residual magnesium... 2+ Ca 2+ The content still cannot meet the requirements of bipolar membrane electrodialysis. Furthermore, the preparation of lithium hydroxide by bipolar membrane electrodialysis produces a certain amount of acid solution, and the acid solution yield matches the alkali solution yield. Therefore, the effective comprehensive utilization of the by-product acid solution is also a factor restricting the practical application of bipolar membrane electrodialysis technology.

[0005] Existing technology ZL 201410124047.9 discloses a method for extracting lithium hydroxide from salt lake brine. First, sodium carbonate is added to remove calcium and magnesium ions from the brine to obtain a low magnesium-to-lithium ratio brine. Then, ordinary electrodialysis is used to enrich and concentrate the low magnesium-to-lithium ratio brine to obtain concentrated brine. Next, an appropriate amount of sodium carbonate is added again for further magnesium removal, followed by the addition of more sodium carbonate to obtain lithium carbonate. The obtained lithium carbonate is dissolved and then processed using an electrolysis-bipolar membrane electrodialysis system to obtain the lithium hydroxide product. This method, by adding sodium carbonate to reduce the magnesium-to-lithium ratio in the brine, requires a large amount of soda ash, increasing process costs, and the large amount of carbonate byproducts generated is difficult to utilize effectively. In addition, this technology requires the first preparation of an intermediate product, lithium carbonate, from salt lake brine, followed by the preparation of lithium hydroxide using an electrolysis-bipolar membrane electrodialysis system. Therefore, lithium ions in the brine must undergo at least two evaporation and crystallization processes (the first being the crystallization of lithium carbonate and the second being the crystallization of lithium hydroxide), resulting in a long process flow and making it difficult to guarantee the lithium ion yield during the preparation of high-purity lithium hydroxide. This also increases the energy consumption of the product preparation process.

[0006] Existing technology CN 201710972445.X discloses a method for preparing LiOH using a membrane coupling process. Using actual salt lake brine as raw material, it proposes a brine-to-LiOH process based on a fully membrane coupling procedure. The process flow includes nanofiltration → reverse osmosis-conventional electrodialysis → deep calcium and magnesium removal → bipolar membrane electrodialysis → evaporation and crystallization. This method mainly uses chemical precipitation for deep calcium and magnesium removal, resulting in a lithium-rich solution with reduced Mg content. 2+ Ca 2+ The content is high and cannot solve the scaling and fouling problem after long-term operation of bipolar membrane electrodialysis.

[0007] The prior art CN201910238356.1 discloses a method for preparing lithium hydroxide from salt lake brine by integrating selective electrodialysis and selective bipolar membrane electrodialysis. First, selective electrodialysis is used for primary magnesium-lithium separation. Then, acetic acid precipitation and ion exchange resin treatment are used to remove divalent cation impurities in the low magnesium solution in multiple steps. After replacing the cation exchange membrane in the conventional three-chamber BMED membrane stack with a monovalent ion selective membrane with divalent cation retention capacity, the scaling problem on the membrane surface can be solved to a certain extent. However, this electrodialysis process needs to be controlled at a low current density to avoid calcium and magnesium scaling on the surface of the monovalent ion selective membrane. Therefore, the final alkaline solution has a low Li+ concentration and the product treatment efficiency is difficult to meet the needs of practical applications.

[0008] Prior art CN116964247A discloses a system and method for the direct production of lithium hydroxide, which uses an ion-selective membrane with high lithium-ion selectivity (such as LiTAS) TM Introduced into a three-compartment bipolar membrane electrodialysis stack, because this membrane is sensitive to Li + The selectivity is better than Mg 2+ Ca 2+ Isovalent cations and Na + K + The presence of monovalent cations in the feed solution suggests that this method could potentially solve both the scaling and fouling issues on the bipolar membrane electrodialysis surface and the effective separation of coexisting monovalent cations and Li+. However, this method is problematic for the Mg content of the feed solution. 2+ Ca 2+ The content is limited to below 25 and 50 ppm respectively, and the ion-selective membrane used must contain metal-organic framework (MOF) functional materials. Its high preparation cost will limit its practical application.

[0009] Existing technology CN108385128A uses resin adsorption technology to remove Mg from lithium-containing solutions. 2+ Ca 2+ The method for removing sodium chloride (Na₂O₃) involves mixing hydrochloric acid, a byproduct of bipolar membrane electrodialysis, into the feed solution and utilizing the common ion effect to precipitate sodium chloride. + and Li + The separation of lithium and the utilization of by-product hydrochloric acid are issues. However, the actual process control of salting out due to the common ion effect is complex, and the sodium chloride crystallization process is prone to carrying a large amount of Li+, resulting in the loss of lithium.

[0010] It is evident that existing bipolar membrane electrodialysis technology for the direct preparation of lithium hydroxide from salt lake brine still suffers from problems such as easy scaling and fouling of ion exchange membranes, high content of impurity ions in the product, low current efficiency, and low utilization rate of by-product acid. Overcoming one or more of these defects is of great significance for promoting the industrialization of the technology for the direct preparation of lithium hydroxide from salt lake brine. Summary of the Invention

[0011] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0012] One objective of this invention is to provide a method for preparing lithium hydroxide from a lithium-containing solution in a salt lake, comprising:

[0013] A lithium-containing solution derived from salt lake brine is concentrated to obtain a lithium-rich solution.

[0014] The lithium-rich solution is subjected to a calcium and magnesium removal treatment to remove at least some of the calcium and magnesium ions from the lithium-rich solution to obtain a first feed solution;

[0015] The first feed solution is subjected to bipolar membrane electrodialysis to obtain a second feed solution containing lithium hydroxide and sodium hydroxide;

[0016] The second feed solution is subjected to multi-stage evaporation and crystallization to separate lithium hydroxide product from at least the second feed solution.

[0017] The method provided by this invention places the lithium-sodium separation process after bipolar membrane electrodialysis. Utilizing the solubility difference between lithium hydroxide and sodium hydroxide in a lithium / sodium mixed alkaline solution, a multi-stage evaporation crystallization process is proposed to achieve effective separation of lithium and sodium. The method proposed in this invention can ensure deep removal of sodium ions during lithium hydroxide crystallization, thereby producing lithium hydroxide products that meet battery-grade application requirements. Compared to existing technologies that typically use high-cost separation materials before bipolar membrane electrodialysis, the method provided by this invention has advantages such as high maturity of separation equipment technology, convenient operation, and low cost.

[0018] In some embodiments, the lithium-containing solution may be obtained from salt lake brine through magnesium-lithium separation, such as multi-stage nanofiltration magnesium-lithium separation.

[0019] In some embodiments, the lithium ion concentration in the lithium-containing solution is 1–5 g / L, the sodium ion concentration is 0.1–5 g / L, the magnesium ion concentration is 0.1–2 g / L, and the calcium ion concentration is 0.1–2 g / L.

[0020] In some embodiments, the pH of the lithium-containing solution is adjusted to 2-6, and then it is concentrated to a concentration factor of 2-10 times.

[0021] In some embodiments, the concentration treatment includes a coupling of one or more methods such as reverse osmosis and electrodialysis, for example, high-pressure reverse osmosis or reverse osmosis-conventional electrodialysis coupling. The reverse osmosis permeate can be stored and used for pure water consumption in subsequent processes. Of course, the concentration treatment can also employ conventional enrichment and concentration methods used in the prior art for salt lake brine or brine-derived feed solutions.

[0022] In some embodiments, the lithium-rich solution obtained by the concentration treatment has a lithium ion concentration of 2-20 g / L, a sodium ion concentration of 0.2-20 g / L, a magnesium ion concentration of 0.2-20 g / L, and a calcium ion concentration of 0.2-20 g / L.

[0023] In some embodiments, the calcium and magnesium removal treatment specifically includes:

[0024] The lithium-rich solution is mixed with a precipitant to allow at least some of the calcium and magnesium ions in the lithium-rich solution to react with the precipitant to form a precipitate, and a low-calcium-magnesium solution is obtained by solid-liquid separation.

[0025] At least one resin adsorption method is used to deeply remove calcium and magnesium ions from the low-calcium-magnesium solution to obtain the first feed solution.

[0026] In some preferred embodiments, the lithium-rich solution is first mixed with a precipitant to chemically precipitate calcium and magnesium, and then the low-calcium-magnesium solution obtained by chemical precipitation is subjected to resin adsorption to remove calcium and magnesium.

[0027] The two-stage treatment method for calcium and magnesium removal provided by this invention, combining chemical precipitation and resin adsorption, effectively removes calcium and magnesium ions, thereby reducing or avoiding the risk of scaling and fouling of the bipolar membrane electrodialysis system. The chemical precipitation process partially removes calcium and magnesium ions, which reduces the amount of resin used in subsequent calcium and magnesium removal processes, lowering overall technical costs. Furthermore, the high-sodium mother liquor obtained from the subsequent multi-stage evaporation and crystallization coupled with mother liquor recycling can be used as the precipitant for chemical precipitation, further reducing overall process losses. Placing the calcium and magnesium removal resin after the chemical precipitation process fully leverages the resin's selectivity, facilitating deep removal of calcium and magnesium from lithium-rich solutions and ensuring the smooth operation of the subsequent bipolar membrane electrodialysis process.

[0028] In some embodiments, the precipitant includes an alkaline precipitant, such as lithium hydroxide, sodium hydroxide, etc.

[0029] In some embodiments, the low-calcium-magnesium solution obtained by chemical precipitation to remove calcium and magnesium has a lithium ion concentration of 2–20 g / L, a sodium ion concentration of 0.2–20 g / L, a magnesium ion concentration of 0.01–1 g / L, and a calcium ion concentration of 0.01–1 g / L. The high-magnesium slag obtained from solid-liquid separation is collected in a storage tank.

[0030] In some embodiments, the first feed solution obtained by using resin adsorption to deeply remove calcium and magnesium ions from the low calcium and magnesium solution is the magnesium removal solution. The lithium ion concentration in the first feed solution is 2-20 g / L, the sodium ion concentration is 0.2-20 g / L, the magnesium ion concentration is 0.1-10 ppm, and the calcium ion concentration is 0.1-10 ppm.

[0031] In some embodiments, the calcium and magnesium removal resin used in the resin adsorption method includes chelating resin, strong acid cation resin, and weak acid cation resin, but is not limited to these. It can also be other resins that have selective adsorption function for calcium and magnesium ions, or it can be mixed with other non-resin adsorbents. After the resin adsorption is saturated, the adsorption function can be restored by acid and alkali regeneration.

[0032] In some embodiments, the method further includes adjusting the pH of the first feed solution to 2-6 before performing the bipolar membrane electrodialysis treatment.

[0033] In some embodiments, the lithium ion concentration in the second feed solution obtained by the bipolar membrane electrodialysis treatment is 2-20 g / L, the sodium ion concentration is 0.2-20 g / L, the hydroxide ion concentration is 15-40 g / L, the magnesium ion concentration is 0.1-10 ppm, and the calcium ion concentration is 0.1-10 ppm.

[0034] In addition to obtaining the second feed solution in the alkali chamber of the bipolar membrane electrodialysis device and the alkali tank connected to the alkali chamber, electrodialysis also obtains desalination solution and acid solution.

[0035] In some embodiments, the method further includes: mixing the desalination solution obtained from the bipolar membrane electrodialysis treatment with the lithium-containing solution and then performing the concentration treatment to achieve recycling of the desalination solution. In some embodiments, the lithium ion concentration of the obtained desalination solution is 0.5–5 g / L, the sodium ion concentration is 0.05–5 g / L, the magnesium ion concentration is 0.1–10 ppm, and the calcium ion concentration is 0.1–10 ppm.

[0036] In some embodiments, the method further includes using the acid solution obtained from the bipolar membrane electrodialysis treatment for acid regeneration of the resin used for adsorbing calcium and magnesium. The acid solution, a byproduct of bipolar membrane electrodialysis, can be directly used for resin regeneration without dilution or concentration, making this comprehensive utilization method convenient and effective, thus solving the problem of low comprehensive utilization rate of bipolar membrane electrodialysis byproduct acid solution in the prior art. In some embodiments, the obtained acid solution is a hydrochloric acid solution, wherein the hydrogen ion concentration is 0.8–2.5 g / L, and the lithium ion concentration is 0.01–0.5 g / L.

[0037] In some embodiments, the multi-stage evaporation crystallization specifically includes:

[0038] a: The second liquid is subjected to the first-stage evaporation and crystallization, and the first slurry obtained by the first-stage evaporation and crystallization is subjected to the first-stage solid-liquid separation to obtain first-stage crude lithium hydroxide and first-stage mother liquor;

[0039] b: After dissolving the primary crude lithium hydroxide, perform the secondary evaporation and crystallization, and perform a second solid-liquid separation on the second slurry obtained from the secondary evaporation and crystallization to obtain secondary crude lithium hydroxide and secondary mother liquor;

[0040] c: The secondary crude lithium hydroxide is further processed to obtain a lithium hydroxide product, or the secondary crude lithium hydroxide is subjected to one or more evaporation and crystallization processes to obtain a crude lithium hydroxide product, and then further processed to obtain a lithium hydroxide product, wherein the further processing includes drying.

[0041] It should be noted that the crude secondary lithium hydroxide obtained through two-stage evaporation crystallization can be dried to obtain battery-grade lithium hydroxide product. However, in some embodiments with higher requirements for lithium hydroxide product quality, the crude secondary lithium hydroxide can be subjected to one or more further evaporation crystallization processes to obtain lithium hydroxide product with higher purity. Considering production cost, energy consumption, and product quality, two-stage evaporation crystallization can ensure the production of battery-grade lithium hydroxide product that meets most industrial and commercial requirements under conditions of lower cost and lower energy consumption.

[0042] In some embodiments, in step a, when the solid content of the first slurry is 10-20 wt%, the first solid-liquid separation is performed at a temperature of 50-90°C; in step b, when the solid content of the second slurry is 10-20 wt%, the second solid-liquid separation is performed at a temperature of 50-90°C.

[0043] In some embodiments, the lithium ion concentration in the primary mother liquor is 10–40 g / L, the sodium ion concentration is 20–150 g / L, and the hydroxide ion concentration is 40–200 g / L.

[0044] In some embodiments, the lithium ion concentration in the secondary mother liquor is 10–40 g / L, the sodium ion concentration is 10–120 g / L, and the hydroxide ion concentration is 30–160 g / L.

[0045] In some embodiments, the method further includes:

[0046] d: Return the primary mother liquor and / or secondary mother liquor to step a and mix with the second feed liquid for reuse, so that the primary mother liquor and / or secondary mother liquor are recycled at least once to obtain the first high-sodium mother liquor;

[0047] e: The first high-sodium mother liquor is evaporated and crystallized to obtain a third slurry, and the third slurry is subjected to a third solid-liquid separation to obtain a high-sodium crude product and a second high-sodium mother liquor. The high-sodium crude product is mixed with the first-stage lithium hydroxide crude product and then subjected to the second-stage evaporation and crystallization.

[0048] In some embodiments, when the Na / Li mass ratio in the first high-sodium mother liquor reaches 1 to 3, 10 wt% to 30 wt% of the total amount of the first high-sodium mother liquor is fed into step e for the aforementioned evaporation and crystallization.

[0049] In some embodiments, when the solid content of the third slurry is 20-40 wt%, the third solid-liquid separation is carried out at a temperature of 50-90°C.

[0050] The method provided by this invention allows for the recycling of the mother liquor obtained from evaporation and crystallization, which enables effective separation of sodium and magnesium, improves the overall lithium yield, and also enhances the utilization rate of sodium.

[0051] In some embodiments, the method further includes: using the second high-sodium mother liquor obtained in step e as a precipitant in the chemical precipitation process for removing calcium and magnesium, and / or using the second high-sodium mother liquor for the alkali regeneration of the resin in the resin adsorption process for removing calcium and magnesium.

[0052] The range of key ion contents such as lithium, sodium, calcium, and magnesium in the lithium-containing solution, lithium-rich solution, first feed solution, and second feed solution mentioned above are the optimal parameters obtained by the present invention through systematic research. By reasonably controlling the composition and concentration of the feed solution obtained in the relevant processes, the mass transfer characteristics of the separation process in each process can be fully utilized to improve the separation efficiency of the overall process and reduce the overall process energy consumption.

[0053] Furthermore, the preferred process coupling sequence proposed in this invention is: lithium solution concentration - chemical precipitation to remove calcium and magnesium - resin adsorption to remove calcium and magnesium - bipolar membrane electrodialysis - multi-stage evaporation crystallization - recycling of mother liquor. This coupling sequence and the connection method between the feed and liquid can ensure full utilization of the process characteristics of different processes, and achieve effective separation of lithium and sodium in lithium-rich solutions, efficient preparation of lithium hydroxide products, and effective comprehensive utilization of by-products.

[0054] In some embodiments, the method further includes drying and packaging steps, wherein the lithium hydroxide obtained by multi-stage evaporation crystallization is dried and packaged to obtain lithium hydroxide product. The lithium hydroxide product produced based on the process of the present invention can reach battery grade.

[0055] A second objective of this invention is to provide a system for preparing lithium hydroxide from a lithium-containing solution in a salt lake. This system can be used to implement a method for preparing lithium hydroxide from a lithium-containing solution in a salt lake, comprising:

[0056] The concentration unit is used to enrich and concentrate the lithium-containing solution from salt lake brine to obtain a lithium-rich solution.

[0057] The calcium and magnesium removal unit is used to remove at least some of the calcium and magnesium ions from the lithium-rich solution to obtain a first feed solution.

[0058] A bipolar membrane electrodialysis unit is used to electrodialyze the first feed solution to obtain a second feed solution consisting of a mixture of lithium hydroxide and sodium hydroxide;

[0059] A multi-stage evaporation and crystallization unit is used to perform multi-stage evaporation of the second feed liquid to separate lithium hydroxide and sodium hydroxide, thereby obtaining lithium hydroxide product.

[0060] In some embodiments, the concentration unit includes a reverse osmosis mechanism or a reverse osmosis-electrodialysis coupling mechanism.

[0061] In some embodiments, the calcium and magnesium removal unit includes a mechanism for chemical precipitation to remove calcium and magnesium and a resin adsorption mechanism.

[0062] In some embodiments, the bipolar membrane electrodialysis unit includes a three-chamber membrane stack bipolar membrane electrodialysis device. The three-chamber membrane stack bipolar membrane electrodialysis device can adopt a conventional structure in the prior art, for example, including an anode chamber, a cathode chamber, and one or more repeating membrane units disposed between the anode and cathode chambers; wherein, one membrane unit includes an alkali chamber, a feed chamber, and an acid chamber arranged sequentially from the cathode chamber to the anode chamber; the alkali chamber and the feed chamber are separated by a cation exchange membrane, the feed chamber and the acid chamber are separated by an anion exchange membrane, and the cathode chamber and the alkali chamber, and the anode chamber and the acid chamber are separated by bipolar membranes. The alkali chamber, the feed chamber, and the acid chamber are respectively connected to an alkali tank, a feed liquid tank, and an acid tank, and the cathode chamber and the anode chamber are connected to an electrode liquid tank. The bipolar membrane electrodialysis device is also equipped with a feed liquid circulation pump, an alkali liquid circulation pump, an acid liquid circulation pump, and an electrode liquid circulation pump, which are used to circulate the feed liquid, alkali liquid, acid liquid, and electrode liquid between their respective storage tanks and chambers.

[0063] In some embodiments, the multi-stage evaporation crystallization unit includes a primary evaporation crystallization mechanism and a secondary evaporation crystallization mechanism. The evaporation crystallization mechanism can employ conventional structures used in evaporation crystallization in the prior art, such as MVR devices or other devices capable of achieving essentially the same effect; this invention does not impose any particular limitation on this. Of course, depending on actual needs, in addition to the primary and secondary evaporation crystallization mechanisms, more stages of evaporation crystallization mechanisms can also be configured.

[0064] In some embodiments, the system further includes a brine pretreatment unit, which includes a nanofiltration mechanism for separating magnesium and lithium in the brine or a liquid derived from the brine to obtain the lithium-containing solution. The nanofiltration mechanism can employ conventional structures already used for treating brine to separate magnesium and lithium, and this invention does not impose any particular limitation on it.

[0065] In some embodiments, the system further includes a lithium hydroxide post-processing unit for post-processing the lithium hydroxide obtained in the multi-stage evaporation and crystallization unit to obtain commercially and industrially usable lithium hydroxide products. The lithium hydroxide post-processing unit includes a drying mechanism and may also include a crushing, demagnetizing, and packaging mechanism.

[0066] Compared with the prior art, the present invention has at least the following beneficial effects:

[0067] (1) To address the problem of the difficulty in effectively separating lithium and sodium in lithium-rich brine, the method provided by this invention places the lithium-sodium separation process after bipolar membrane electrodialysis treatment. By utilizing the solubility difference between lithium hydroxide and sodium hydroxide in the lithium / sodium mixed alkaline solution, multi-stage evaporation crystallization is used to ensure the deep removal of sodium ions in lithium hydroxide crystals, so as to achieve the preparation of battery-grade lithium hydroxide products. Furthermore, the mother liquor recycling process is coupled to optimize the effective separation of lithium and sodium and improve the utilization rate of sodium resources. Compared with the existing technology that uses high-cost processes to separate sodium and lithium before bipolar membrane electrodialysis treatment, the method of this invention has the advantages of high maturity of separation equipment technology, convenient operation, and low cost.

[0068] (2) Furthermore, in view of the problem that residual calcium and magnesium in the lithium-rich solution of salt lake causes a high risk of scaling and fouling of bipolar membrane electrodialysis membrane, the method provided by the present invention uses chemical precipitation-resin adsorption to deeply remove calcium and magnesium. The chemical precipitation process can partially remove calcium and magnesium ions, which on the one hand helps to reduce the amount of calcium and magnesium removal resin used in the subsequent process and reduce the overall technical cost. On the other hand, the high-sodium mother liquor obtained by the subsequent multi-stage evaporation crystallization coupled mother liquor recycling process can be used as the precipitant for chemical precipitation to remove calcium and magnesium, which helps to reduce the overall process loss. Placing the calcium and magnesium removal resin after the chemical calcium and magnesium removal process can give full play to the resin's selectivity advantage, which is conducive to achieving deep removal in the lithium-rich solution and ensuring the subsequent bipolar membrane electrodialysis process.

[0069] (3) Furthermore, in view of the comprehensive utilization of the by-product acid liquid of bipolar membrane electrodialysis, the present invention utilizes the overall process characteristics to use the by-product acid liquid of bipolar membrane electrodialysis for the regeneration of resin in the process of deep calcium and magnesium removal by resin adsorption, so as to improve the comprehensive utilization rate of the by-product acid liquid.

[0070] (4) After systematic research, the present invention proposes a reasonable and effective combined process scheme, and optimizes the process control parameters and material handling methods for each process. The overall process has a high lithium yield, low preparation cost, and the product can reach battery grade. In addition, the process of the present invention can also solve the problems of lithium and sodium being difficult to separate effectively, calcium and magnesium causing scaling and pollution of bipolar membrane electrodialysis membrane, and low comprehensive utilization rate of bipolar membrane electrodialysis by-product acid liquid in the prior art. Attached Figure Description

[0071] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0072] Figure 1This is a schematic diagram of the process for preparing lithium hydroxide from a lithium-containing solution in one embodiment of the present invention;

[0073] Figure 2 This is a schematic diagram of the structure of a bipolar membrane electrodialysis device used in one embodiment of the present invention. Detailed Implementation

[0074] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be construed as limiting, but are merely intended to form the basis of the claims and to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0075] Figure 1 The process flow of some typical embodiments of the present invention is shown, specifically including:

[0076] (1) Concentration of lithium-containing solution: The lithium-containing solution in the salt lake is concentrated by passing it into a high-pressure reverse osmosis or reverse osmosis-conventional electrodialysis coupling device to obtain a lithium-rich solution;

[0077] (2) Chemical precipitation to remove calcium and magnesium: Add an alkaline precipitant to the lithium-rich solution to react and precipitate, and then obtain a low calcium and magnesium solution through solid-liquid separation.

[0078] (3) Removal of calcium and magnesium by resin adsorption: The residual calcium and magnesium ions in the low calcium and magnesium brine are removed by resin adsorption to obtain a magnesium removal solution (i.e., the first feed solution).

[0079] (4) Bipolar membrane electrodialysis: The magnesium removal solution enters the bipolar membrane electrodialysis device to obtain lithium / sodium mixed alkaline solution (i.e., the second feed solution), hydrochloric acid solution, and desalting solution respectively; wherein, the lithium / sodium mixed alkaline solution enters the subsequent process; the hydrochloric acid solution is returned to step (3) for resin acid regeneration; the desalting solution is returned to step (1) and mixed with the lithium-containing solution of the salt lake for reuse.

[0080] (5) Multi-stage evaporation crystallization: The lithium / sodium mixed alkaline solution is evaporated in the first stage to obtain the first-stage crude product and the first-stage mother liquor. The first-stage crude product is dissolved in pure water and then evaporated in the second stage to obtain the second-stage crude product and the second-stage mother liquor. The second-stage crude product enters the subsequent drying process. The first-stage mother liquor and the second-stage mother liquor are mixed and returned to the front end to be combined with the lithium / sodium mixed alkaline solution for reuse. After the mother liquor is recycled for a certain period of time, the recycled mother liquor is obtained and sent to the next process.

[0081] (6) Recycling mother liquor reuse: The recycled mother liquor is evaporated in a single stage to obtain high sodium crude product and high sodium mother liquor. The high sodium crude product is mixed with the first-stage crude product and then dissolved in pure water for reuse. Part of the high sodium mother liquor is returned to step (2) as a precipitant and part is returned to step (3) for resin alkali regeneration.

[0082] (7) Drying and packaging: The secondary crude product obtained in step (5) is dried and packaged to obtain battery-grade lithium hydroxide product.

[0083] The technical solution of the present invention will be further described below with reference to several embodiments. Unless otherwise specified, the raw materials, equipment, etc. used in the following embodiments can be purchased from the market, and the corresponding testing methods are also commonly used in the art; unless otherwise specified, the percentage content (%) described in the following embodiments is a mass percentage.

[0084] Example 1

[0085] The raw material solution in this embodiment is a lithium-containing solution obtained from brine of a salt lake in Qinghai Province after multi-stage nanofiltration magnesium-lithium separation. The lithium-containing solution contains lithium ions at a concentration of 3.1 g / L, sodium ions at a concentration of 1.5 g / L, magnesium ions at a concentration of 1.5 g / L, and calcium ions at a concentration of 2.0 g / L. Figure 1 This is a schematic diagram of the process for preparing lithium hydroxide from the lithium-containing solution in this embodiment. The specific process flow is as follows:

[0086] (1) The pH of the lithium-containing solution in the salt lake was adjusted to 5.0 using 10wt% hydrochloric acid, and then sent to a membrane concentration device (high-pressure reverse osmosis device) for concentration. The concentration factor was 4 times to obtain a lithium-rich solution with a lithium ion concentration of 11.8 g / L, a sodium ion concentration of 5.9 g / L, a magnesium ion concentration of 6.2 g / L, and a calcium ion concentration of 7.6 g / L. The reverse osmosis permeate obtained was stored for pure water reuse.

[0087] (2) The lithium-rich solution was added to a stirred reactor, and a saturated sodium hydroxide solution was added at 70-80°C to carry out a precipitation reaction. After 1 hour of reaction, the slurry was filtered through a plate and frame filter to obtain a low-calcium magnesium solution and a high-magnesium slag. The low-calcium magnesium solution had a lithium ion concentration of 11.5 g / L, a sodium ion concentration of 6.5 g / L, a magnesium ion concentration of 0.2 g / L, and a calcium ion concentration of 0.5 g / L. The low-calcium magnesium solution was introduced into a calcium-magnesium resin raw material tank, and the high-magnesium slag was stored in a storage tank.

[0088] (3) The low calcium and magnesium solution in the raw material tank of the calcium and magnesium removal resin is pumped into the calcium and magnesium removal resin (chelating resin) adsorption tower for adsorption. The effluent is the magnesium removal solution. The magnesium removal solution has a lithium ion concentration of 11.3 g / L, a sodium ion concentration of 6.4 g / L, a magnesium ion concentration of 0.5 ppm, and a calcium ion concentration of 1.2 ppm. The magnesium removal solution is introduced into the raw material tank of the bipolar membrane electrodialysis device. The calcium and magnesium removal resin used is a calcium and magnesium removal chelating resin. After the resin is saturated with adsorption, it is first regenerated with 7 wt% hydrochloric acid solution and washed with water, and then regenerated with 5% sodium hydroxide solution and washed with water.

[0089] (4) Use 10wt% hydrochloric acid to adjust the pH of the magnesium removal solution in the bipolar membrane electrodialysis feed tank to 4.5. Add 0.1mol / L lithium hydroxide to the alkali tank and 0.1mol / L hydrochloric acid to the acid tank as start-up solution. Add 3wt% lithium hydroxide solution to the electrode tank. After starting the material circulation pump and circulating for 20 minutes, turn on the DC power supply of the electrodialysis device. After running for 4 hours, lithium / sodium mixed alkali solution, hydrochloric acid solution and desalting solution are obtained.

[0090] Among them, the lithium / sodium mixed alkaline solution had a lithium ion concentration of 12.5 g / L, a sodium ion concentration of 8.1 g / L, a hydroxide ion concentration of 36.5 g / L, and no magnesium or calcium ions were detected.

[0091] The desalination solution has a lithium ion concentration of 3.2 g / L, a sodium ion concentration of 2.2 g / L, a magnesium ion concentration of 0.4 ppm, and a calcium ion concentration of 1.5 ppm.

[0092] The hydrochloric acid solution has a hydrogen ion concentration of 2.1 g / L, a lithium ion concentration of 0.1 g / L, and a sodium ion concentration of 0.05 g / L.

[0093] (5) The lithium / sodium mixed alkaline solution obtained by electrodialysis is fed into a first-stage MVR unit for first-stage evaporation and crystallization. When the solid content of the mother liquor slurry obtained by first-stage evaporation and crystallization reaches 15wt%, the slurry at a temperature of 80℃ is fed into a scraper centrifuge for solid-liquid separation to obtain a first-stage crude product and a first-stage mother liquor. The lithium ion concentration of the first-stage mother liquor is 18.2g / L, the sodium ion concentration is 40.8g / L, and the hydroxide ion concentration is 68.9g / L.

[0094] The primary crude product is dissolved in pure water and then fed into a secondary MVR unit for secondary evaporation and crystallization. When the solid content of the mother liquor slurry obtained from the secondary evaporation and crystallization is 12wt%, the slurry at a temperature of 80℃ is fed into a scraper centrifuge for solid-liquid separation to obtain the secondary crude product and the secondary mother liquor. The secondary mother liquor has a lithium ion concentration of 22.6g / L, a sodium ion concentration of 32.4g / L, and a hydroxide concentration of 78.4g / L. The secondary crude product is then sent to the subsequent drying process.

[0095] After mixing the secondary mother liquor with the primary mother liquor, it is returned to the front end and combined with the lithium / sodium mixed alkaline solution. Then, they are all fed into the primary MVR unit for evaporation and crystallization. When the Na / Li mass ratio in the primary mother liquor is 3.0, 20% of the primary mother liquor is sent to the next process.

[0096] (6) The above 20% of the primary mother liquor is subjected to single-stage evaporation and crystallization in an evaporation kettle. When the solid content of the mother liquor slurry reaches 25wt%, solid-liquid separation is performed to obtain high sodium crude product and high sodium mother liquor. The high sodium mother liquor has a lithium ion concentration of 8.2g / L, a sodium ion concentration of 129.8g / L, and a hydroxide ion concentration of 115.9g / L. It is sent to step (2) as a precipitant in the precipitation reaction device for reuse. The high sodium crude product is mixed with the primary crude product and then dissolved in pure water for reuse in the secondary evaporation and crystallization device.

[0097] (7) Drying and packaging: The secondary crude product obtained in step (5) is sent to a drying and packaging device for drying and packaging to obtain battery-grade lithium hydroxide product.

[0098] In this embodiment, the total lithium-ion yield is 92.8%, and the power consumption of the lithium hydroxide product is 4.5 kWh / kg.

[0099] The structure of the bipolar membrane electrodialysis device used in step (4) of this embodiment is as follows: Figure 2 As shown, it is a conventional three-chamber membrane stack (excluding the electrode chamber) bipolar membrane electrodialysis device, including a cathode chamber, an anode chamber, and a repeating membrane unit, which is located between the cathode chamber and the anode chamber. Each membrane unit includes an alkali chamber, a feed chamber, and an acid chamber arranged sequentially from the cathode chamber to the anode chamber. The alkali chamber and the feed chamber are separated by a cation exchange membrane, the feed chamber and the acid chamber are separated by an anion exchange membrane, and the cathode chamber and the alkali chamber, as well as the anode chamber and the acid chamber, are separated by bipolar membranes. The alkali chamber is connected to the alkali solution tank, the feed chamber is connected to the desalination solution tank, the acid chamber is connected to the acid solution tank, and the cathode chamber and the anode chamber are connected to the electrode solution tank. In step (4) above, the magnesium removal solution after pH adjustment is added to the desalination solution tank, and a lithium / sodium mixed alkali solution is obtained in the alkali solution tank after electrodialysis.

[0100] In summary, the method for preparing lithium hydroxide from lithium-containing solutions in salt lakes provided by this invention solves the problems of easy scaling and contamination of ion exchange membranes, high content of impurity ions in the product, low current efficiency, and difficulty in effectively utilizing by-product acid liquid in the process of preparing lithium hydroxide by bipolar membrane electrodialysis. This method has outstanding prospects for large-scale application after solving the relevant technical bottlenecks.

[0101] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0102] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0103] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing lithium hydroxide from a lithium-containing solution in a salt lake, characterized in that, include: A lithium-containing solution derived from salt lake brine is concentrated to obtain a lithium-rich solution. The lithium-rich solution is subjected to a calcium and magnesium removal treatment to remove at least some of the calcium and magnesium ions from the lithium-rich solution to obtain a first feed solution; The first feed solution is subjected to bipolar membrane electrodialysis to obtain a second feed solution containing lithium hydroxide and sodium hydroxide. The second feed solution is subjected to multi-stage evaporation and crystallization to separate lithium hydroxide product from at least the second feed solution.

2. The method according to claim 1, characterized in that, The calcium and magnesium removal treatment specifically includes: The lithium-rich solution is mixed with a precipitant to allow at least some of the calcium and magnesium ions in the lithium-rich solution to react with the precipitant to form a precipitate, and a low-calcium-magnesium solution is obtained by solid-liquid separation. At least one resin adsorption method is used to deeply remove calcium and magnesium ions from the low-calcium-magnesium solution to obtain the first feed solution.

3. The method according to claim 1, characterized in that, The multi-stage evaporation crystallization specifically includes: a: The second liquid is subjected to the first-stage evaporation and crystallization, and the first slurry obtained by the first-stage evaporation and crystallization is subjected to the first-stage solid-liquid separation to obtain first-stage crude lithium hydroxide and first-stage mother liquor; b: After dissolving the primary crude lithium hydroxide, perform the secondary evaporation and crystallization, and perform a second solid-liquid separation on the second slurry obtained from the secondary evaporation and crystallization to obtain secondary crude lithium hydroxide and secondary mother liquor; c: The secondary crude lithium hydroxide is post-processed to obtain a lithium hydroxide product, or the secondary crude lithium hydroxide is subjected to one or more evaporation and crystallization processes to obtain a crude lithium hydroxide product, and the crude lithium hydroxide is then post-processed to obtain a lithium hydroxide product, wherein the post-processing includes drying; Preferably, in step a, when the solid content of the first slurry is 10-20 wt%, the first solid-liquid separation is carried out at a temperature of 50-90°C; in step b, when the solid content of the second slurry is 10-20 wt%, the second solid-liquid separation is carried out at a temperature of 50-90°C. Preferably, the lithium ion concentration in the primary mother liquor is 10-40 g / L, the sodium ion concentration is 20-150 g / L, and the hydroxide ion concentration is 40-200 g / L. Preferably, the lithium ion concentration in the secondary mother liquor is 10–40 g / L, the sodium ion concentration is 10–120 g / L, and the hydroxide ion concentration is 30–160 g / L.

4. The method according to claim 3, characterized in that, Also includes: d: Return the primary mother liquor and / or secondary mother liquor to step a and mix with the second feed liquid for reuse, so that the primary mother liquor and / or secondary mother liquor are recycled at least once to obtain the first high-sodium mother liquor; e: The first high-sodium mother liquor is evaporated and crystallized to obtain a third slurry, and the third slurry is subjected to a third solid-liquid separation to obtain a high-sodium crude product and a second high-sodium mother liquor. The high-sodium crude product is mixed with the first-stage lithium hydroxide crude product and then subjected to the second-stage evaporation and crystallization. Preferably, when the Na / Li mass ratio in the first high-sodium mother liquor reaches 1 to 3, 10 wt% to 30 wt% of the total amount of the first high-sodium mother liquor is fed into step e for the evaporation and crystallization. Preferably, when the solid content of the third slurry is 20-40 wt%, the third solid-liquid separation is carried out at a temperature of 50-90°C.

5. The method according to claim 4, characterized in that: The second high-sodium mother liquor obtained in step e is used as a precipitant in the chemical precipitation process for removing calcium and magnesium, and / or the second high-sodium mother liquor is used for the alkali regeneration of the resin in the resin adsorption process for removing calcium and magnesium.

6. The method according to claim 2, characterized in that, Also includes: The acid solution obtained from the bipolar membrane electrodialysis treatment is used for acid regeneration of the resin used for adsorption of calcium and magnesium; and / or, the desalination solution obtained from the bipolar membrane electrodialysis treatment is mixed with the lithium-containing solution and then subjected to the concentration treatment.

7. The method according to claim 1, characterized in that: The concentration process includes a combination of one or more methods such as reverse osmosis and electrodialysis.

8. The method according to any one of claims 1-7, characterized in that: The lithium-containing solution has a lithium ion concentration of 1–5 g / L, a sodium ion concentration of 0.1–5 g / L, a magnesium ion concentration of 0.1–2 g / L, and a calcium ion concentration of 0.1–2 g / L. And / or, the lithium-rich solution contains lithium ion concentrations of 2–20 g / L, sodium ion concentrations of 0.2–20 g / L, magnesium ion concentrations of 0.2–20 g / L, and calcium ion concentrations of 0.2–20 g / L. And / or, the lithium ion concentration in the first feed solution is 2-20 g / L, the sodium ion concentration is 0.2-20 g / L, the magnesium ion concentration is 0.1-10 ppm, and the calcium ion concentration is 0.1-10 ppm; And / or, the lithium ion concentration in the second feed solution is 2-20 g / L, the sodium ion concentration is 0.2-20 g / L, the hydroxide ion concentration is 15-40 g / L, the magnesium ion concentration is 0.1-10 ppm, and the calcium ion concentration is 0.1-10 ppm.

9. A system for preparing lithium hydroxide from a lithium-containing solution in a salt lake, characterized in that, include: The concentration unit is used to enrich and concentrate the lithium-containing solution from salt lake brine to obtain a lithium-rich solution. The calcium and magnesium removal unit is used to remove at least some of the calcium and magnesium ions from the lithium-rich solution to obtain a first feed solution. A bipolar membrane electrodialysis unit is used to electrodialyze the first feed solution to obtain a second feed solution consisting of a mixture of lithium hydroxide and sodium hydroxide; A multi-stage evaporation and crystallization unit is used to perform multi-stage evaporation of the second feed liquid to separate lithium hydroxide and sodium hydroxide, thereby obtaining lithium hydroxide product.

10. The system according to claim 9, characterized in that: The concentration unit includes a reverse osmosis mechanism or a reverse osmosis-electrodialysis coupling mechanism; And / or, the calcium and magnesium removal unit includes a mechanism for chemical precipitation to remove calcium and magnesium and a resin adsorption mechanism; And / or, the bipolar membrane electrodialysis unit includes a three-chamber membrane stack bipolar membrane electrodialysis device; And / or, the multi-stage evaporation crystallization unit includes a primary evaporation crystallization mechanism and a secondary evaporation crystallization mechanism; And / or, the system further includes a brine pretreatment unit, the pretreatment unit including a nanofiltration mechanism for separating magnesium and lithium from the brine or the liquid derived from the brine to obtain the lithium-containing solution; And / or, the system further includes a post-processing unit for post-processing the lithium hydroxide obtained in the multi-stage evaporation and crystallization unit to obtain a lithium hydroxide product, the lithium hydroxide post-processing unit including a drying mechanism.

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