A preparation method of battery-grade lithium hydroxide and magnesium-based functional materials

Abstract

The present invention discloses a preparation method of battery-grade lithium hydroxide and magnesium-based functional materials. The preparation method includes: sequentially performing primary adsorption-desorption and secondary adsorption-desorption on the salt lake brine to obtain a mixed desorption solution; performing forward osmosis primary concentration treatment on the mixed desorption solution to obtain a primary concentrated solution; mixing the primary concentrated solution with an aluminum salt and an alkali solution for coprecipitation reaction to prepare a magnesium-based functional material and a lithium-rich magnesium-removing solution; performing bipolar membrane electrodialysis treatment on the lithium-rich magnesium-removing solution to obtain a lithium hydroxide enrichment solution and a boric acid enrichment solution; performing MVR evaporation crystallization on the lithium hydroxide enrichment solution to prepare monohydrate battery-grade lithium hydroxide. The method provided by the present invention realizes the co-production of battery-grade lithium hydroxide and magnesium-based functional materials, and at the same time realizes the comprehensive, green, efficient and high-value development and utilization of salt lake resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of salt lake resources, and relates to a preparation method of battery-grade lithium hydroxide and magnesium-based functional materials. Background Art

[0002] Lithium (Li) is the lightest metallic element in nature, silver-white, with unique physical and chemical properties such as high specific heat, high electrical conductivity, and strong chemical activity, and has a wide range of uses. In recent years, with the rapid development of new energy vehicles, the demand for lithium batteries and lithium power batteries has increased day by day, thus the demand for lithium has also increased sharply. In nature, lithium resources are mainly stored in solid ores and liquid brines. The important position of brine lithium resources in the development of world lithium resources has been established for nearly 40 years, and it has attracted the attention of the lithium resource development industry in terms of application and extraction of lithium compounds. At present, the main processes for extracting lithium from salt lake brines are precipitation method, solvent extraction method, adsorption method, calcination method, electrodialysis method, nanofiltration method, and solar pond method. The adsorption method has greater advantages than other methods from the perspectives of environment and economy. The adsorption method uses an adsorbent with selective adsorption for lithium ions to adsorb lithium ions, and then elutes the lithium ions, so as to achieve the separation of lithium ions from other impurity ions. However, the existing processes for extracting lithium from salt lakes using the adsorption method are mostly single-stage multi-column adsorption. The magnesium-lithium ratio in the desorbed solution after adsorption is high, and the subsequent process requires nanofiltration technology for secondary magnesium-lithium separation to further reduce the magnesium-lithium ratio. The process is complex, costly, and the lithium concentration in the desorption is less than 500 mg / L. Multiple concentration steps are required later to prepare lithium salts. The concentration multiple is large, the energy consumption is high, and the cost is high. After secondary magnesium removal, the lithium-containing solution is concentrated in one stage by reverse osmosis, and the energy consumption is high. Therefore, from the perspective of comprehensive, green, efficient, and high-value development of salt lake resources, it is urgent to solve the problems of complex processes and high costs in the existing technologies. Among them, in Patent CN106011917A, the crystallization mother liquor wastewater after producing potassium chloride from salt lake brine is adsorbed by an ion sieve and eluted to obtain a qualified eluate. The qualified solution is ultrafiltered, nanofiltrated, and then high-purity lithium hydroxide products are prepared by in vitro regeneration continuous ion exchange technology, reverse osmosis, ion membrane electrolysis technology, and crystallization evaporation technology; in Patent CN114836621A, during the process of extracting lithium from brine by the adsorption method, the adsorption process is divided into two stages. In the first stage, the adsorbent adsorbs the brine, and in the second stage, the adsorbent adsorbs the bipolar membrane alkali liquor concentrated mother liquor in the subsequent section. The desorbed solution is treated by bipolar membrane electrolysis to obtain acid solution and alkali solution. After the alkali solution is concentrated and crystallized, LiOH is obtained; in Patent CN108660476A, using lithium chloride solution after lithium extraction from brine (adsorption method or membrane method), magnesium removal, and reverse osmosis pre-concentration as raw materials, electrodialysis technology, reverse osmosis technology, resin adsorption technology, ion membrane electrolysis technology, and evaporation crystallization technology are used to produce high-purity lithium hydroxide products. However, the above-mentioned patent processes have long flow paths, high energy consumption, and high costs. Summary of the Invention

[0003] The main object of the present invention is to provide a preparation method of battery-grade lithium hydroxide and magnesium-based functional materials to overcome the deficiencies of the prior art.

[0004] To achieve the aforementioned invention object, the technical solutions adopted by the present invention include:

[0005] An embodiment of the present invention provides a preparation method of battery-grade lithium hydroxide and magnesium-based functional materials, which includes:

[0006] Subjecting the salt lake brine to primary adsorption-desorption and secondary adsorption-desorption treatments in sequence to obtain a mixed desorption solution;

[0007] Performing forward osmosis primary concentration treatment on the mixed desorption solution to obtain a primary concentrated solution; wherein, the concentration of lithium ions in the primary concentrated solution is 1.5 - 3.0 g / L;

[0008] Mixing the primary concentrated solution with an aluminum salt and an alkali solution for coprecipitation reaction to prepare a magnesium-based functional material and a lithium-rich magnesium-removing solution;

[0009] Performing bipolar membrane electrodialysis treatment on the lithium-rich magnesium-removing solution to obtain a lithium hydroxide enrichment solution and a boric acid enrichment solution; wherein, the content of lithium ions in the lithium hydroxide enrichment solution is 10 - 20 g / L;

[0010] And, performing MVR evaporation crystallization on the lithium hydroxide enrichment solution to prepare monohydrate battery-grade lithium hydroxide.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention develops a coupling multi-stage multi-column adsorption process of titanium-based, manganese-based and aluminum-based adsorbents, which not only reduces the magnesium-lithium ratio in the desorption solution, but also increases the lithium concentration in the desorption solution. The desorption solution does not need to be separated again for magnesium and lithium, and directly uses forward osmosis for primary concentration, shortening the process flow, reducing energy consumption, reducing costs, and increasing the recovery rate of salt lake lithium resources; at the same time, the present invention comprehensively considers the synergistic extraction of salt lake lithium, magnesium and boron resources, co-produces magnesium-based functional materials and boric acid while preparing battery-grade lithium hydroxide by a one-step method, realizing the comprehensive, green, efficient and high-value development and utilization of salt lake resources, and reducing production costs. Description of the Drawings

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0013] Figure 1It is a schematic flow chart of preparing battery-grade lithium hydroxide and magnesium-based functional materials in a typical embodiment of the present invention. Detailed implementation manners

[0014] In view of the defects of the prior art, the inventors of this case have, through long-term research and a large number of practices, been able to propose the technical solution of the present invention. It mainly develops adsorbents of titanium-based, manganese-based and aluminum-based coupled with a multi-stage and multi-column adsorption process, which not only reduces the magnesium-lithium ratio in the desorbing solution, but also increases the lithium concentration in the desorbing solution. The desorbing solution does not need to be separated again for magnesium and lithium, and direct osmosis is directly used for primary concentration, shortening the process flow, reducing energy consumption, reducing costs, and increasing the recovery rate of lithium resources in salt lakes.

[0015] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] Specifically, as an aspect of the technical solution of the present invention, a preparation method of battery-grade lithium hydroxide and magnesium-based functional materials includes:

[0017] Subjecting the salt lake brine to primary adsorption-desorption and secondary adsorption-desorption treatments in sequence to obtain a mixed desorbing solution;

[0018] Performing direct osmosis primary concentration treatment on the mixed desorbing solution to obtain a primary concentrated solution; wherein, the concentration of lithium ions in the primary concentrated solution is 1.5 - 3.0 g / L;

[0019] Mixing the primary concentrated solution with an aluminum salt and an alkali solution for coprecipitation reaction to prepare a magnesium-based functional material and a lithium-rich magnesium-removing solution;

[0020] Performing bipolar membrane electrodialysis treatment on the lithium-rich magnesium-removing solution to obtain a lithium hydroxide enriched solution and a boric acid enriched solution; wherein, the content of lithium ions in the lithium hydroxide enriched solution is 10 - 20 g / L;

[0021] And, performing MVR evaporation crystallization on the lithium hydroxide enriched solution to prepare monohydrate battery-grade lithium hydroxide.

[0022] In some preferred embodiments, the schematic flow chart of preparing battery-grade lithium hydroxide and magnesium-based functional materials in the present invention is as Figure 1 shown.

[0023] Specifically, the preparation method of the battery-grade lithium hydroxide and magnesium-based functional materials includes:

[0024] (1) After the brine from the salt lake is pretreated to remove impurities such as sediment and organic matter, it enters the primary adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water. The primary adsorption washing liquid is returned to the primary adsorption for lithium recovery. After washing, a primary desorbent is used to desorb the saturated titanium-based or manganese-based adsorption column to obtain a primary desorbed liquid. After desorption, the adsorption column is washed with water and enters the next cycle. The primary washing liquid after desorption is used to wash the saturated adsorption column. The tail liquid after adsorption enters the secondary adsorption system for secondary adsorption after adjusting the pH. The adsorption tail liquid is discharged to the salt field. After secondary adsorption, the saturated aluminum-based adsorption column is washed with water and then desorbed with a secondary desorbent to obtain a secondary desorbed liquid. The secondary desorbed liquid is mixed with the primary desorbed liquid to obtain a mixed desorbed liquid, which enters the next process.

[0025] (2) Forward osmosis for primary concentration

[0026] The above-mentioned mixed desorbed liquid enters the forward osmosis system for primary concentration to obtain a primary concentrated liquid and forward osmosis fresh water, which enter the next-stage process and are returned for use in the primary and secondary adsorption washing water respectively.

[0027] (3) Deep magnesium removal to prepare magnesium-based functional materials

[0028] A soluble aluminum salt in a certain ratio is added to the primary concentrated liquid to form a mixed salt solution. A mixed alkali solution of sodium carbonate and sodium hydroxide undergoes a coprecipitation reaction under certain conditions; after the coprecipitation reaction nucleates, solid-liquid separation is carried out to obtain a filter cake and a filtrate; after solid-liquid separation, the filter cake is washed and dried to obtain a white solid MgAl-LDH product; the filtrate is used for the preparation of battery-grade lithium hydroxide in the next process.

[0029] Among them, the magnesium-based functional material is a layered double metal hydroxide. The metal elements are alternately arranged on the layer board, and anions can be inserted between the layers, forming a large class of important layered functional materials, which have wide applications in fields such as highly dispersed catalysis, selective adsorption, functional additives (flame retardants, ultraviolet blockers, heat stabilizers, etc.), and biomedicine.

[0030] (4) Preparation of battery-grade lithium hydroxide

[0031] The lithium-rich magnesium-removed solution obtained above is treated by a bipolar membrane electrodialysis system. The bipolar membrane electrodialysis system is a two-chamber bipolar membrane electrodialysis, and its membrane stack is composed of bipolar membranes, cation exchange membranes, and chamber partitions. Water electrolyzes to produce H + and OH - , under the action of a direct current electric field and the catalysis of the bipolar membrane. Under the action of the direct current electric field, OH - enters the alkali chamber, while H + enters the feed liquid chamber; Li + and Na + in the feed liquid chamber enter the alkali chamber. Under the continuous electrodialysis process, Li + and OH- Enrichment in the alkali chamber. Finally, a lithium hydroxide enriched solution and a boric acid enriched solution are obtained; the main component of the lithium hydroxide enriched solution is lithium hydroxide and contains a small amount of sodium hydroxide. Since the solubility of lithium hydroxide and sodium hydroxide in water varies greatly, battery-grade lithium hydroxide monohydrate crude product can be obtained by evaporation and crystallization. After recrystallization of the battery-grade lithium hydroxide monohydrate crude product, high-purity battery-grade lithium hydroxide monohydrate product is obtained by drying. The boric acid enriched solution is used for the preparation of boric acid products.

[0032] In some preferred embodiments, the preparation method specifically includes: subjecting the lithium-rich magnesium-removed solution to bipolar membrane electrodialysis treatment in a bipolar membrane electrodialysis system to obtain a lithium hydroxide enriched solution and a boric acid enriched solution; wherein, the content of lithium ions in the lithium-rich magnesium-removed solution is 1.5 - 3.0 g / L; the boric acid enriched solution is used for the preparation of boric acid;

[0033] And, subjecting the lithium hydroxide enriched solution to evaporation, concentration and crystallization in an MVR system, and then through drying treatment, battery-grade lithium hydroxide is prepared.

[0034] Further, the bipolar membrane electrodialysis system is a two-chamber bipolar membrane electrodialysis system, and the membrane stack of the bipolar membrane electrodialysis system is composed of a bipolar membrane, a cation exchange membrane and a chamber partition; the bipolar membrane electrodialysis system includes a pole chamber, an alkali chamber and a feed liquid chamber, the pole chamber is externally connected with a pole liquid tank, the alkali chamber is externally connected with an alkali liquid tank, and the feed liquid chamber is externally connected with a feed liquid tank; the circulation time of the bipolar membrane electrodialysis system is 20 - 40 min, and the bipolar membrane electrodialysis voltage of the bipolar membrane electrodialysis system is 20 - 35 V.

[0035] Further, the process of evaporation, concentration and crystallization is carried out under vacuum or under the protection of an inert gas.

[0036] Further, the temperature of evaporation, concentration and crystallization is 70 - 120 °C.

[0037] Further, the temperature of the drying treatment is 90 - 130 °C.

[0038] Further, the purity of the battery-grade lithium hydroxide monohydrate is above 99%.

[0039] In some preferred embodiments, the preparation method specifically includes:

[0040] Subjecting the salt lake brine to primary adsorption treatment in a primary adsorption system, then washing the saturated adsorption column with water, and then subjecting the saturated adsorption column to primary desorption treatment with a primary desorbent to obtain a primary desorbed solution and a primary tail liquid; wherein, the primary adsorption system is an adsorption system filled with a titanium-based or manganese-based adsorbent; the concentration of lithium ions in the primary tail liquid is 0.2 - 0.4 g / L;

[0041] Adjust the pH value of the primary tail liquid to 3 - 6 and place it in a secondary adsorption system for secondary adsorption treatment. Then, wash the saturated adsorption column with water, and then perform secondary desorption treatment on the saturated adsorption column with a secondary desorbent to obtain a secondary desorbed liquid and a secondary tail liquid. Among them, the secondary adsorption system is an adsorption system filled with an aluminum-based adsorbent; the concentration of lithium ions in the secondary tail liquid is less than 20 ppm;

[0042] And, mix the primary desorbed liquid and the secondary desorbed liquid to obtain the mixed desorbed liquid.

[0043] Furthermore, the mixed desorbed liquid includes the primary desorbed liquid and the secondary desorbed liquid. The salt lake brine is the brine after potassium extraction, and the magnesium-lithium ratio in the brine after potassium extraction is 5 - 500, and the lithium ion concentration is 0.5 - 10 g / L; the lithium ion concentration in the mixed desorbed liquid is 0.4 - 1.5 g / L, and the magnesium-lithium ratio is 0.1 - 0.4; the volume ratio of the primary desorbed liquid to the secondary desorbed liquid in the mixed desorbed liquid is 1:1 - 5:1.

[0044] Furthermore, during the primary adsorption treatment, 3 - 10 multi-column adsorptions are used.

[0045] Furthermore, during the primary desorption treatment, 2 - 5 multi-column desorptions are used.

[0046] Furthermore, the primary desorbent includes hydrochloric acid and / or sulfuric acid, and is not limited thereto.

[0047] Furthermore, the concentration of the primary desorbent is 0.05 - 2.0 mol / L.

[0048] Furthermore, during the secondary adsorption treatment, 2 - 5 multi-column adsorptions are used.

[0049] Furthermore, during the secondary desorption treatment, 1 - 3 multi-column desorptions are used.

[0050] Furthermore, the secondary desorbent includes water; and / or, the temperature of the secondary desorption treatment is 35 - 70 °C.

[0051] In some preferred embodiments, the preparation method specifically includes: placing the mixed desorbed liquid in a forward osmosis system for primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; among them, the forward osmosis draw solution used in the forward osmosis system includes a saturated magnesium chloride solution or a saturated sodium chloride solution; the lithium ion concentration in the forward osmosis fresh water is 0.005 - 0.10 g / L; the volume ratio of the mixed desorbed liquid to the primary concentrated liquid is 2.0:1 - 4:1; the forward osmosis membrane used in the forward osmosis system includes a CTA membrane and / or a TFC membrane.

[0052] In some preferred embodiments, the preparation method specifically includes: adding an aluminum salt to the first-stage concentrated solution to form a mixed salt solution, then adding a mixed alkali solution and carrying out a coprecipitation reaction under the conditions of a pH of 8-13, a stirring rate of 50-200 rpm, and a temperature of 25-70 °C, followed by aging, separation, washing, and drying to obtain a magnesium-based functional material and a lithium-rich solution with reduced magnesium content; the content of magnesium ions in the lithium-rich solution with reduced magnesium content is below 10 ppm.

[0053] Further, the molar ratio of Mg 2+ to Al 3+ in the mixed salt solution is 2-4:1.

[0054] Further, the aluminum salt includes any one or a combination of two or more of aluminum nitrate, aluminum sulfate, and aluminum chloride, and is not limited thereto.

[0055] Further, the mixed alkali solution is a mixed alkali solution of sodium carbonate and sodium hydroxide; the volumes of the mixed salt solution and the alkali solution are the same.

[0056] In some preferred embodiments, the preparation method further includes: first pre-treating the salt lake brine, at least for removing sediment or organic matter; wherein, the turbidity of the solution obtained after the pre-treatment is less than 3 NTU.

[0057] Further, any one of ultrafiltration, ceramic filtration, and poly-ceramic membrane filtration is used for the pre-treatment.

[0058] In some more specific embodiments, the preparation method of the battery-grade lithium hydroxide and the magnesium-based functional material includes:

[0059] (1) After the salt lake brine is pretreated to remove impurities such as sediment and organic matter, it enters the primary adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water. The primary adsorption washing liquid is returned to the primary adsorption to recover lithium. After washing, a primary desorbent is used to desorb the saturated titanium-based or manganese-based adsorption column to obtain a primary desorbed liquid. After the adsorption column is washed, it enters the next cycle. The primary washing liquid after desorption is used for preparing the primary desorbent. The tail liquid after adsorption is adjusted to a pH of 3-6 and then enters the secondary adsorption system for secondary adsorption. The adsorption tail liquid is discharged to the salt field. After secondary adsorption, the saturated aluminum-based adsorption column is washed with water and then desorbed with a secondary desorbent to obtain a secondary desorbed liquid. The secondary desorbed liquid is mixed with the primary desorbed liquid to obtain a mixed desorbed liquid, which enters the next process. The salt lake brine is the brine after potassium extraction, with a magnesium-lithium ratio of 5-500 and a lithium concentration of 0.5-10 g / L; the pretreatment is one of ultrafiltration, ceramic filtration or polyceramic membrane filtration, and the turbidity of the brine after pretreatment is less than 3 NTU; the primary adsorption system is an adsorption system filled with titanium-based or manganese-based adsorbents. The primary adsorption of lithium by the adsorption column is multi-column adsorption with 2-10 columns, and the primary desorption column is multi-column desorption with 2-5 columns; the primary desorbent is hydrochloric acid or sulfuric acid, and the concentration of hydrochloric acid or sulfuric acid is 0.05-2.0 mol / L; the pH of the tail liquid after adsorption is adjusted to 3-6 and then enters the secondary adsorption system. The lithium concentration in the primary adsorption tail liquid is 0.2-0.4 g / L; the secondary adsorption system is an adsorption system filled with aluminum-based adsorbents. The secondary adsorption of lithium by the adsorption column is multi-column adsorption with 2-5 columns, and the secondary desorption column is multi-column desorption with 1-3 columns; the secondary desorbent contains pure water, and the secondary desorption temperature is 35-70 °C; the mixing volume ratio of the primary desorbed liquid to the secondary desorbed liquid is 1:1-5:1, the lithium concentration in the desorbed liquid is 0.4-1.5 g / L, and the magnesium-lithium ratio in the desorbed liquid is 0.05-0.5. The lithium concentration in the secondary adsorption tail liquid is less than 20 ppm.

[0060] (2) Forward osmosis for primary concentration

[0061] The mixed desorbed liquid obtained above enters the forward osmosis system for primary concentration to obtain a primary concentrated liquid and forward osmosis fresh water, which enter the next stage process and are returned for use in the primary and secondary adsorption washing water respectively. The lithium concentration in the forward osmosis primary concentrated liquid is 1.5-3.0 g / L. The forward osmosis draw solution is a saturated magnesium chloride or saturated sodium chloride solution prepared from salt lake magnesium chloride or sodium chloride. The forward osmosis fresh water is returned to the secondary adsorption system for secondary washing water. The lithium ion content in the forward osmosis fresh water is 0.005-0.10 g / L. The concentration volume ratio (mixed desorbed liquid solution volume / primary concentrated liquid) is 2.0:1-4:1. The forward osmosis membrane is one or two of CTA membrane or TFC membrane.

[0062] (3) Deep magnesium removal to prepare magnesium-based functional materials

[0063] A soluble aluminum salt is added to the primary concentrated solution to prepare a mixed salt solution. A mixed alkali solution of sodium carbonate and sodium hydroxide is added dropwise to the mixed salt solution under certain pH, temperature, and flow rate conditions for a coprecipitation reaction; after the coprecipitation reaction nucleates, it is aged under stirring and at a certain temperature and then solid-liquid separated to obtain a filter cake and a filtrate; after solid-liquid separation, the filter cake is washed and dried to obtain a white solid MgAl-LDH product; the content of magnesium ions in the magnesium-removed and lithium-enriched solution does not exceed 10 ppm, and the magnesium-removed and lithium-enriched solution is used for boron removal by ion exchange resin in the next process. The mixed salt solution is prepared by adding a certain soluble aluminum salt to the lithium-enriched solution, where the molar ratio of Mg 2+ to Al 3+ is 2 to 4, and the aluminum salt is one of aluminum nitrate, aluminum sulfate, and aluminum chloride; the volume of the mixed alkali solution is the same as that of the mixed salt solution, and the reaction is the constant pH method, maintaining the pH at 8 to 13, the reaction temperature is 25°C to 70°C, and the lithium-enriched and magnesium-removed solution is used for the preparation of battery-grade lithium hydroxide.

[0064] (4) Preparation of battery-grade lithium hydroxide

[0065] The obtained lithium-enriched and magnesium-removed solution is treated by a bipolar membrane electrodialysis system. The bipolar membrane electrodialysis system is a two-chamber bipolar membrane electrodialysis, and its membrane stack is composed of bipolar membranes, cation exchange membranes, and chamber partitions. These bipolar membranes separate to form a number of alternating alkali chambers and feed solution chambers, and each chamber (i.e., the alkali chamber and the feed solution chamber) has a chamber partition. The outer part of the electrode chamber is connected to an electrode solution tank, the outer part of the alkali chamber is connected to an alkali solution tank, and the outer part of the feed solution chamber is connected to a feed solution tank; the electrode solution tank stores the initial electrode solution (originally the magnesium-removed and lithium-enriched solution), and the alkali solution tank stores the initial battery-grade lithium hydroxide solution. Water electrolyzes to produce H + and OH - under the catalytic action of a direct current electric field and a bipolar membrane. Under the action of the direct current electric field, OH - enters the alkali chamber, while H + enters the feed solution chamber; Li + in the feed solution chamber enters the alkali chamber. Under the continuous electrodialysis process, Li + and OH - are enriched in the alkali chamber. Finally, a secondary concentrated lithium-enriched solution (lithium hydroxide enriched solution) is obtained in the alkali chamber; the main component of this secondary concentrated lithium-enriched solution is battery-grade lithium hydroxide. The concentration of lithium in the feed solution tank is 1.5 to 3.0 g / L, and the content of Li + ions in the initial battery-grade lithium hydroxide solution added to the alkali solution tank is 0.7 to 1.5 g / L; the content of Na + ions in the sodium chloride electrode solution added to the electrode solution tank is 6.5 to 15 g / L; the content of Li +The ionic content is 10 - 20 g / L, which can be directly used for the preparation of battery-grade lithium hydroxide products. The concentrated lithium-rich solution is subjected to evaporation concentration and crystallization in an MVR system. The evaporation process is vacuum evaporation or evaporation under the protection of inert gas, and the evaporation temperature is 70°C - 120°C. After evaporation concentration and crystallization, the crystalline product can be dried at 70°C - 110°C to obtain battery-grade lithium hydroxide products; the obtained boric acid-enriched solution is used for the preparation of boric acid products. The cycle time is 20 - 40 min, and the bipolar membrane electrodialysis voltage is 20 - 35 V.

[0066] In view of the above-mentioned disadvantages of the prior art, the present invention has developed a coupling multi-stage multi-column adsorption process of titanium-based, manganese-based and aluminum-based adsorbents, which not only reduces the magnesium-lithium ratio in the desorbing solution, but also increases the lithium concentration in the desorbing solution. The desorbing solution does not need to be separated again for magnesium and lithium, and direct osmosis is directly used for primary concentration, shortening the process flow, reducing energy consumption, reducing costs, and increasing the recovery rate of lithium resources in salt lakes.

[0067] The present invention comprehensively considers the co-extraction of lithium, magnesium and boron resources in salt lakes, and simultaneously produces magnesium-based functional materials and boric acid while preparing battery-grade lithium hydroxide by a one-step method, realizing the comprehensive, green, efficient and high-value development and utilization of salt lake resources and reducing production costs; at the same time, the present invention uses a multi-stage multi-column adsorption - direct osmosis - co-precipitation for magnesium removal - bipolar membrane coupling technology to separate magnesium and lithium, concentrate and enrich lithium, and prepare battery-grade lithium hydroxide while producing magnesium-based functional materials and boric acid, which has not been reported.

[0068] The technical solutions of the present invention will be further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. These embodiments are implemented on the premise of the technical solutions of the invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0069] The experimental materials used in the following embodiments can be purchased from conventional biochemical reagent companies without special instructions.

[0070] Example 1

[0071] The salt lake brine used in this example is the old brine of a certain sulfate-type salt lake in Qinghai, where the concentration of Li + is 0.5 g / L and the magnesium-lithium ratio is 500.

[0072] The old brine from a sulfate-type salt lake in Qinghai is ultrafiltered to reduce the turbidity to below 3 and then enters the primary adsorption system equipped with a titanium-based adsorbent. After 2-column series adsorption, the saturated adsorption column is washed with water. After washing, 0.05 mol / L hydrochloric acid is used to desorb 2 columns of the saturated lithium-saturated adsorption column to obtain a primary desorbed solution; the pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L is adjusted to 3 and then enters the secondary adsorption system equipped with an aluminum-based adsorbent. After 2-column adsorption, the lithium concentration of the secondary adsorption tail liquid is reduced to below 20 ppm and discharged to the salt field; after washing the aluminum-based adsorption column saturated in the secondary adsorption, it is desorbed with pure water at 35 °C for 1 column to obtain a secondary desorbed solution. The primary desorbed solution and the secondary desorbed solution are mixed in a ratio of 1:1 to obtain a mixed desorbed solution. The lithium concentration in the mixed desorbed solution is 0.7 g / L, and the magnesium-lithium ratio is 0.1. The mixed desorbed solution enters the forward osmosis primary concentration system. The forward osmosis draw solution is a saturated solution prepared with sodium chloride from the salt lake. The mixed desorbed solution is concentrated by forward osmosis through a CTA membrane to a lithium concentration of 1.5 g / L to obtain a primary concentrated solution. The lithium concentration in the fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1; the lithium-rich solution concentrated at one stage is deeply desulfurized by a reaction-separation technology to prepare a magnesium-based functional material. Aluminum chloride hexahydrate is added to the lithium-rich solution concentrated at one stage to prepare a mixed salt solution with a molar ratio of Mg 2+ to Al 3+ of 2. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared. The mixed salt solution is dropped into the mixed alkali solution at a certain speed for a coprecipitation reaction. The reaction pH is 8, the reaction temperature is 25 °C. After the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the lithium + -rich solution with a concentration of 1.5 g / L after desulfurization is added to the feed liquid tank, and lithium + -rich solution with a concentration of 0.7 g / L of the initial battery-grade lithium hydroxide solution is added to the alkali liquid tank, and sodium + -rich solution with a concentration of 6.5 g / L is added to the electrode liquid tank. The lithium-rich solution concentrated at one stage is circulated between the feed liquid tank and the feed liquid chamber, the initial battery-grade lithium hydroxide solution is circulated between the alkali liquid tank and the alkali chamber, and the electrode liquid is circulated between the electrode liquid tank and the two electrode chambers through the feed liquid pump, alkali liquid pump, and electrode liquid pump respectively. After circulating for 20 min, the bipolar membrane electrodialysis voltage is set to 20 V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid-enriched solution is obtained in the feed liquid tank for the preparation of boric acid products. At the same time, a lithium + -rich solution with a concentration of 10 g / L is obtained in the alkali liquid tank. The lithium-rich solution is evaporated, concentrated, and crystallized in an MVR system under the protection of inert gas at a temperature of 70 °C. The crystalline product is dried at 70 °C to obtain battery-grade lithium hydroxide. In the obtained battery-grade lithium hydroxide, the content of lithium hydroxide monohydrate is as high as over 99.0%.

[0073] Example 2

[0074] The salt lake brine used in this example is old brine from a sulfate salt lake in Qinghai, where Li + The concentration is 10g / L and the magnesium-lithium ratio is 5.

[0075] The old brine from a sulfate salt lake in Qinghai was passed through a ceramic membrane to reduce the turbidity to below 3 and then entered a primary adsorption system equipped with a manganese adsorbent. After 10 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed with 2 mol / L sulfuric acid for 5 columns to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.4 g / L was adjusted to 6 and then entered a secondary adsorption system equipped with an aluminum adsorbent. After 5 columns of adsorption, the lithium concentration of the secondary adsorption tail liquid was reduced to below 20 ppm and discharged to the salt field. The saturated aluminum adsorption column of the secondary adsorption was washed with water and then desorbed with pure water for 2 columns at 70°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 2:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 1.3 g / L and the magnesium-lithium ratio was 0.4. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with magnesium chloride from salt lakes. The mixed desorbed liquid is forward osmotic through a TFC membrane to concentrate the lithium concentration to 3 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.1 g / L, and the concentration ratio is 4:1. The primary concentrate is subjected to deep magnesium removal using reaction-separation technology to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the primary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 3 is prepared, and then a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared, and the mixed salt solution is added dropwise to the mixed alkali solution at a certain speed for co-precipitation reaction, the reaction pH is 13, the reaction temperature is 70°C, and after the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the Li + Add 3.0g / L magnesium-removed lithium-rich solution into the liquid tank, and add Li + The initial lithium hydroxide solution with a concentration of 1.5 g / L was added with Na + The pole liquid with a concentration of 15g / L is circulated between the feed liquid tank and the feed liquid chamber, the initial lithium hydroxide solution is circulated between the alkali liquid tank and the alkali chamber, and the pole liquid is circulated between the pole liquid tank and the two pole chambers through the feed liquid pump, the alkali liquid pump and the pole liquid pump. After 40 minutes of circulation, the bipolar membrane electrodialysis voltage is set to 25V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid-enriched solution is obtained in the feed liquid tank for the preparation of boric acid products. At the same time, Li + The concentration of the concentrated lithium-rich liquid is 20 g / L. The concentrated lithium-rich liquid is evaporated, concentrated and crystallized in a MVR system under vacuum at a temperature of 120° C. The crystallized product is dried at 110° C. to obtain battery-grade lithium hydroxide. The content of lithium hydroxide monohydrate in the obtained battery-grade lithium hydroxide is as high as over 99.0%.

[0076] Example 3

[0077] The salt lake brine used in this example is the old brine of a sulfate-type salt lake in Qinghai, where the Li + concentration is 2 g / L and the magnesium-lithium ratio is 60.

[0078] The old brine from a sulfate-type salt lake in Qinghai is ultrafiltered to reduce the turbidity to less than 1 and then enters the primary adsorption system equipped with a titanium-based adsorbent. After 5-column series adsorption, the saturated adsorption column is washed with water. After washing, 0.5 mol / L hydrochloric acid is used to desorb 4 columns of the saturated lithium-saturated adsorption column to obtain a primary desorbed solution; the pH of the primary adsorption tail solution with a lithium concentration of 0.3 g / L is adjusted to 4.4 and then enters the secondary adsorption system equipped with an aluminum-based adsorbent. After 4-column adsorption, the lithium concentration of the secondary adsorption tail solution is reduced to less than 20 ppm and discharged to the salt pan; after washing the aluminum-based adsorption column saturated by secondary adsorption, 3 columns are desorbed with pure water at 55 °C to obtain a secondary desorbed solution. The primary desorbed solution and the secondary desorbed solution are mixed in a ratio of 3:1 to obtain a mixed desorbed solution. The lithium concentration in the mixed desorbed solution is 1.0 g / L and the magnesium-lithium ratio is 0.2. The mixed desorbed solution enters the forward osmosis primary concentration system. The forward osmosis draw solution is a saturated solution prepared with sodium chloride from the salt lake. The mixed desorbed solution is concentrated to a lithium concentration of 2.0 g / L by CTA membrane forward osmosis to obtain a primary concentrated solution. The lithium concentration in the fresh water is controlled at 0.02 g / L and the concentration ratio is 3:1; the primary concentrated solution uses a reaction-separation technology for deep magnesium removal to prepare a magnesium-based functional material. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare a mixed salt solution with a molar ratio of Mg 2+ to Al 3+ of 3. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared. The mixed salt solution is added dropwise to the mixed alkali solution at a certain speed for coprecipitation reaction. The reaction pH is 10, the reaction temperature is 50 °C. After the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the magnesium-removed lithium-rich solution with a Li + concentration of 2.5 g / L obtained by filtration is added to the feed liquid tank, the initial lithium hydroxide solution with a Li + concentration of 1.0 g / L is added to the alkali liquid tank, and the polar liquid with a Na + concentration of 10 g / L is added to the polar liquid tank. The primary concentrated lithium-rich solution is circulated between the feed liquid tank and the feed liquid chamber, the initial lithium hydroxide solution is circulated between the alkali liquid tank and the alkali chamber, and the polar liquid is circulated between the polar liquid tank and the two polar chambers through the feed liquid pump, alkali liquid pump, and polar liquid pump respectively. After circulating for 30 min, the bipolar membrane electrodialysis voltage is set to 30 V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid enrichment solution is obtained in the feed liquid tank for the preparation of boric acid products. At the same time, a solution with Li +A concentrated lithium-rich solution with a concentration of 15 g / L. The concentrated lithium-rich solution is evaporated, concentrated and crystallized in an MVR system under the protection of inert gas at a temperature of 100 °C. The crystalline product is dried at 80 °C to obtain battery-grade lithium hydroxide. In the obtained battery-grade lithium hydroxide, the content of lithium hydroxide monohydrate is as high as over 99.0%.

[0079] Example 4

[0080] The salt lake brine used in this example is the old brine of a sulfate-type salt lake in Qinghai, where the Li + concentration is 3 g / L and the magnesium-lithium ratio is 40.

[0081] The old brine from a sulfate-type salt lake in Qinghai enters the first-stage adsorption system equipped with a manganese-based adsorbent after the turbidity is reduced to less than 3 by ultrafiltration. After 8-column series adsorption, the saturated adsorption column is washed with water. After washing, 0.2 mol / L sulfuric acid is used to desorb the saturated lithium-saturated adsorption column for 3 columns to obtain a primary desorbed solution; the pH of the primary adsorption tail solution with a lithium concentration of 0.25 g / L is adjusted to 4.8 and then enters the second-stage adsorption system equipped with an aluminum-based adsorbent. After 3-column adsorption, the lithium concentration of the secondary adsorption tail solution is reduced to less than 20 ppm and discharged to the salt field; after the aluminum-based adsorption column saturated in the second stage is washed with water, it is desorbed with pure water for 1 column at 65 °C to obtain a secondary desorbed solution. The primary desorbed solution and the secondary desorbed solution are mixed in a ratio of 5:1 to obtain a mixed desorbed solution. The lithium concentration in the mixed desorbed solution is 0.9 g / L and the magnesium-lithium ratio is 0.3. The mixed desorbed solution enters the forward osmosis first-stage concentration system. The forward osmosis draw solution is a saturated solution prepared from magnesium chloride in the salt lake. The mixed desorbed solution is concentrated to a lithium concentration of 2.5 g / L through TFC membrane forward osmosis to obtain a first-stage concentrated solution. The lithium concentration in the fresh water is controlled at 0.005 g / L and the concentration ratio is 2:1; the first-stage concentrated solution is deeply de-magnesiumized by a reaction-separation technology to prepare a magnesium-based functional material. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare a mixed salt solution with a molar ratio of Mg 2+ to Al 3+ of 2. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared. The mixed salt solution is added dropwise to the mixed alkali solution at a certain speed for co-precipitation reaction. The reaction pH is 9, the reaction temperature is 40 °C. After the reaction is complete, it is aged and filtered to obtain the MgAl-LDH product; the lithium-rich solution with a lithium concentration of 2 g / L after de-magnesiumization obtained by filtration is added to the feed liquid tank, and lithium hydroxide solution with an initial lithium concentration of 1.2 g / L is added to the alkali liquid tank. Sodium + is added to the electrode liquid tank + with a concentration of 1.2 g / L +The extremely concentrated solution with a concentration of 8.5 g / L circulates the primary lithium-rich concentrated solution between the feed liquid tank and the feed liquid chamber, the initial lithium hydroxide solution between the lye tank and the lye chamber, and the extremely concentrated solution between the extremely concentrated solution tank and the two electrode chambers through the feed liquid pump, the lye pump, and the extremely concentrated solution pump respectively. After circulating for 35 minutes, the bipolar membrane electrodialysis voltage is set to 35 V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid-enriched solution is obtained in the feed liquid tank for the preparation of boric acid products, and at the same time, Li + The concentrated lithium-rich solution with a concentration of 18 g / L is evaporated, concentrated, and crystallized in an MVR system under vacuum at a temperature of 110 °C. The crystallization product is dried at 100 °C to obtain battery-grade lithium hydroxide. In the obtained battery-grade lithium hydroxide, the content of lithium hydroxide monohydrate is as high as over 99.0%.

[0082] Comparative Example 1

[0083] The salt lake brine used in this comparative example is the old brine of a sulfate-type salt lake in Qinghai, where Li + has a concentration of 0.5 g / L and a magnesium-lithium ratio of 500.

[0084] The old brine from a sulfate-type salt lake in Qinghai enters the first-stage adsorption system equipped with a titanium-based adsorbent after the turbidity is reduced to less than 3 by ultrafiltration. After two-column series adsorption, the saturated adsorption column is washed with water. After washing, 0.05 mol / L hydrochloric acid is used to desorb two columns of the saturated lithium-saturated adsorption column to obtain the primary desorbed solution; the pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L is adjusted to 3 and then enters the second-stage adsorption system equipped with an aluminum-based adsorbent. After two-column adsorption, the lithium concentration of the second-stage adsorption tail liquid is reduced to less than 20 ppm and discharged to the salt field; after washing the aluminum-based adsorption column saturated in the second stage, it is desorbed with pure water at 35 °C to obtain the secondary desorbed solution. The primary desorbed solution and the secondary desorbed solution are mixed in a ratio of 1:1 to obtain the mixed desorbed solution. The lithium concentration in the mixed desorbed solution is 0.7 g / L, and the magnesium-lithium ratio is 0.1. The mixed desorbed solution is deeply de-magnesiumized by a reaction-separation technology to prepare a magnesium-based functional material. Aluminum chloride hexahydrate is added to the mixed desorbed solution to prepare a mixed salt solution with a molar ratio of Mg 2+ to Al 3+ of 2. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared. The mixed salt solution is added dropwise to the mixed alkali solution at a certain speed for co-precipitation reaction. The reaction pH is 8, and the reaction temperature is 25 °C. After the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the lithium-rich solution with a lithium concentration of 0.7 g / L after de-magnesiumization obtained by filtration is added to the feed liquid tank, and lithium hydroxide solution with a lithium concentration of 0.7 g / L is added to the lye tank. Sodium hydroxide solution with a certain concentration is added to the extremely concentrated solution tank. + The lithium-rich solution with a lithium concentration of 0.7 g / L after de-magnesiumization is added to the feed liquid tank, and lithium hydroxide solution with a lithium concentration of 0.7 g / L is added to the lye tank. + The initial battery-grade lithium hydroxide solution with a lithium concentration of 0.7 g / L is added to the lye tank, and sodium hydroxide solution with a certain concentration is added to the extremely concentrated solution tank. +The extreme liquid with a concentration of 6.5 g / L circulates the primary concentrated lithium-rich liquid between the feed liquid tank and the feed liquid chamber, the initial battery-grade lithium hydroxide liquid between the alkali liquid tank and the alkali chamber, and the extreme liquid between the extreme liquid tank and the two extreme chambers through the feed liquid pump, alkali liquid pump, and extreme liquid pump respectively. After circulating for 20 minutes, the bipolar membrane electrodialysis voltage is set to 20 V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid enrichment liquid is obtained in the feed liquid tank for the preparation of boric acid products, and at the same time, Li + The concentrated lithium-rich liquid with a concentration of 10 g / L is evaporated, concentrated, and crystallized in the MVR system under the protection of inert gas at a temperature of 70 °C. The crystallization product is dried at 70 °C to obtain battery-grade lithium hydroxide. In the obtained battery-grade lithium hydroxide, the content of lithium hydroxide monohydrate is as high as over 99.0%. In the example, the concentration multiple of bipolar membrane electrodialysis increases by 1 time, the energy consumption increases by 1 time, and the process cost increases by one-fourth.

[0085] Comparative Example 2

[0086] The salt lake brine used in this comparative example is the old brine of a sulfate-type salt lake in Qinghai, where Li + has a concentration of 0.5 g / L and a magnesium-lithium ratio of 500.

[0087] The old brine from a sulfate-type salt lake in Qinghai enters the first-stage adsorption system equipped with a titanium-based adsorbent after the turbidity is reduced to less than 3 through ultrafiltration. After series adsorption of 2 columns, the saturated adsorption column is washed with water. After washing, 0.05 mol / L hydrochloric acid is used to desorb 2 columns of the saturated lithium-saturated adsorption column to obtain the primary desorbed liquid; the primary desorbed liquid enters the forward osmosis first-stage concentration system. The forward osmosis draw solution is a saturated solution prepared with salt lake sodium chloride. The primary draw solution is concentrated to 1.5 g / L in lithium concentration through CTA membrane forward osmosis to obtain the first-stage concentrated liquid, and the lithium concentration in the fresh water is controlled at 0.005 g / L, with a concentration ratio of 2:1; the first-stage concentrated lithium-rich solution is deeply desulfurized to prepare a magnesium-based functional material using a reaction-separation technology. Aluminum chloride hexahydrate is added to the first-stage concentrated lithium-rich solution to prepare a mixed salt solution with a molar ratio of Mg 2+ to Al 3+ of 2. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared, and the mixed salt solution is dropped into the mixed alkali solution at a certain speed for coprecipitation reaction. The reaction pH is 8, the reaction temperature is 25 °C. After the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the magnesium-removed lithium-rich liquid with a lithium concentration of 1.5 g / L obtained by filtration is added to the feed liquid tank, and lithium hydroxide solution with a lithium concentration of 0.7 g / L is added to the alkali liquid tank. Sodium + is added to the extreme liquid tank + with a concentration of 0.7 g / L of the initial battery-grade lithium hydroxide liquid, and Na +The extreme liquid with a concentration of 6.5 g / L circulates the primary concentrated lithium-rich solution between the feed liquid tank and the feed liquid chamber, the initial battery-grade lithium hydroxide solution between the alkali liquid tank and the alkali chamber, and the extreme liquid between the extreme liquid tank and the two extreme chambers through the feed liquid pump, alkali liquid pump, and extreme liquid pump respectively. After circulating for 20 minutes, the bipolar membrane electrodialysis voltage is set to 20 V for bipolar membrane electrodialysis. After bipolar membrane electrodialysis, a boric acid-enriched solution is obtained in the feed liquid tank for the preparation of boric acid products, and at the same time, Li + The concentrated lithium-rich solution with a concentration of 10 g / L is evaporated, concentrated, and crystallized in an MVR system under the protection of an inert gas at a temperature of 70 °C. The crystallization product is dried at 70 °C to obtain battery-grade lithium hydroxide. In the obtained battery-grade lithium hydroxide, the content of lithium hydroxide monohydrate is as high as over 99.0%, and the lithium recovery rate is only 81.2%.

[0088] Comparative Example 3

[0089] The salt lake brine used in this comparative example is the old brine of a certain sulfate-type salt lake in Qinghai, where Li + has a concentration of 0.5 g / L and a magnesium-lithium ratio of 500.

[0090] The old brine from a certain sulfate-type salt lake in Qinghai enters the first-stage adsorption system equipped with a titanium-based adsorbent after the turbidity is reduced to less than 3 through ultrafiltration. After 2-column series adsorption, the saturated adsorption column is washed with water. After washing, 0.05 mol / L hydrochloric acid is used to desorb 2 columns of the saturated lithium-saturated adsorption column to obtain a primary desorbed solution; the pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L is adjusted to 3 and then enters the second-stage adsorption system equipped with an aluminum-based adsorbent. After 2-column adsorption, the lithium concentration of the second-stage adsorption tail liquid is reduced to less than 20 ppm and discharged to the salt field; after washing the aluminum-based adsorption column saturated in the second stage, it is desorbed with pure water at 35 °C for 1 column to obtain a secondary desorbed solution. The primary desorbed solution and the secondary desorbed solution are mixed in a ratio of 1:1 to obtain a mixed desorbed solution. The lithium concentration in the mixed desorbed solution is 0.7 g / L, and the magnesium-lithium ratio is 0.1. The mixed desorbed solution enters the forward osmosis first-stage concentration system. The forward osmosis draw solution is a saturated solution prepared with sodium chloride from the salt lake. The mixed desorbed solution is concentrated to a lithium concentration of 1.5 g / L through CTA membrane forward osmosis to obtain a first-stage concentrated solution. The lithium concentration in the fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1; the first-stage concentrated lithium-rich solution is deeply de-magnesiated by a reaction-separation technology to prepare a magnesium-based functional material. Aluminum trichloride hexahydrate is added to the first-stage concentrated lithium-rich solution to prepare a mixed salt solution of Mg 2+ and Al 3+ with a molar ratio of 2. Then, a mixed alkali solution of sodium hydroxide and sodium carbonate is prepared. The mixed salt solution is added dropwise to the mixed alkali solution at a certain speed for coprecipitation reaction. The reaction pH is 8, the reaction temperature is 25 °C. After the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the Li +The lithium-rich solution with magnesium removed at a concentration of 1.5 g / L is evaporated, concentrated and crystallized in an MVR system under the protection of inert gas at a temperature of 70 °C, and the crystallization product is dried at 70 °C. In this example, lithium hydroxide monohydrate product cannot be obtained.

[0091] In addition, the inventors of this case also referred to the foregoing examples, and conducted tests with other raw materials, process operations, and process conditions described in this specification, and all obtained relatively ideal results.

[0092] It should be understood that the technical solution of the present invention is not limited to the limitations of the above specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the purpose of the present invention and the scope protected by the claims falls within the protection scope of the present invention.

Claims

1. A preparation method of battery-grade lithium hydroxide and magnesium-based functional materials, characterized in that Including: Placing the salt lake brine in a primary adsorption system for primary adsorption treatment, then washing the saturated adsorption column with water, and then performing primary desorption treatment on the saturated adsorption column with a primary desorbent to obtain a primary desorbed solution and a primary tail solution; wherein, the primary adsorption system is an adsorption system filled with a titanium-based or manganese-based adsorbent; the concentration of lithium ions in the primary tail solution is 0.2 - 0.4 g / L; the salt lake brine is the brine after potassium extraction, and the magnesium-lithium ratio in the brine after potassium extraction is 5 - 500, and the lithium ion concentration is 0.5 - 10 g / L; Adjusting the pH value of the primary tail solution to 3 - 6 and placing it in a secondary adsorption system for secondary adsorption treatment, then washing the saturated adsorption column with water, and then performing secondary desorption treatment on the saturated adsorption column with a secondary desorbent to obtain a secondary desorbed solution and a secondary tail solution; wherein, the secondary adsorption system is an adsorption system filled with an aluminum-based adsorbent; the concentration of lithium ions in the secondary tail solution is less than 20 ppm; Mixing the primary desorbed solution and the secondary desorbed solution to obtain a mixed desorbed solution; wherein, the lithium ion concentration in the mixed desorbed solution is 0.4 - 1.5 g / L, and the magnesium-lithium ratio is 0.1 - 0.4; the volume ratio of the primary desorbed solution to the secondary desorbed solution in the mixed desorbed solution is 1:1 - 5:1; Performing forward osmosis primary concentration treatment on the mixed desorbed solution to obtain a primary concentrated solution; wherein, the lithium ion concentration in the primary concentrated solution is 1.5 - 3.0 g / L; Mixing the primary concentrated solution with an aluminum salt and an alkali solution to carry out a coprecipitation reaction to prepare a magnesium-based functional material and a lithium-rich magnesium-removing solution; Placing the lithium-rich magnesium-removing solution in a bipolar membrane electrodialysis system for bipolar membrane electrodialysis treatment to obtain a lithium hydroxide enrichment solution and a boric acid enrichment solution; wherein, the lithium ion content in the lithium hydroxide enrichment solution is 10 - 20 g / L; the lithium ion content in the lithium-rich magnesium-removing solution is 1.5 - 3.0 g / L; the boric acid enrichment solution is used for preparing boric acid; And, placing the lithium hydroxide enrichment solution in an MVR system for evaporation concentration and crystallization, and then performing drying treatment to prepare battery-grade lithium hydroxide monohydrate.

2. The preparation method according to claim 1, characterized in that: The bipolar membrane electrodialysis system is a two-chamber bipolar membrane electrodialysis system, and the membrane stack of the bipolar membrane electrodialysis system is composed of a bipolar membrane, a cation exchange membrane, and a chamber partition; the bipolar membrane electrodialysis system includes a pole chamber, an alkali chamber, and a feed solution chamber, the pole chamber is externally connected with a pole liquid tank, the alkali chamber is externally connected with an alkali liquid tank, and the feed solution chamber is externally connected with a feed solution tank; the circulation time of the bipolar membrane electrodialysis system is 20 - 40 min, and the bipolar membrane electrodialysis voltage of the bipolar membrane electrodialysis system is 20 - 35 V.

3. The preparation method according to claim 1, characterized in that: The process of evaporation concentration and crystallization is carried out under vacuum or under the protection of an inert gas.

4. The preparation method according to claim 1, characterized in that: The temperature of the evaporation concentration and crystallization is 70 - 120 °C.

5. The preparation method according to claim 1, characterized in that: The temperature of the drying treatment is 90 - 130 °C.

6. The preparation method according to claim 1, characterized in that: The purity of the battery-grade lithium hydroxide monohydrate is above 99%.

7. The preparation method according to claim 1, characterized in that: During the primary adsorption treatment, 3 - 10 multi-column adsorptions are adopted; the primary desorbent is selected from hydrochloric acid and / or sulfuric acid; the concentration of the primary desorbent is 0.05 - 2.0 mol / L.

8. The preparation method according to claim 1, characterized in that: During the secondary adsorption treatment, 2 to 5 multi-column adsorptions are adopted; the secondary desorbent is selected from water; the temperature of the secondary desorption treatment is 35 to 70 °C.

9. The preparation method according to claim 1, characterized in that Specifically, it includes: Placing the mixed desorption solution in a forward osmosis system for primary concentration treatment to obtain a primary concentrated solution and forward osmosis fresh water; wherein, the forward osmosis draw solution used in the forward osmosis system is selected from saturated magnesium chloride solution or saturated sodium chloride solution; the concentration of lithium ions in the forward osmosis fresh water is 0.005 to 0.10 g / L; the volume ratio of the mixed desorption solution to the primary concentrated solution is 2.0:1 to 4:1; the forward osmosis membrane used in the forward osmosis system is selected from CTA membrane and / or TFC membrane.

10. The preparation method according to claim 1, characterized in that Specifically, it includes: Adding an aluminum salt to the primary concentrated solution to form a mixed salt solution, then adding a mixed alkali solution and carrying out a coprecipitation reaction under the conditions of pH 8 to 13, stirring rate of 50 to 200 rpm, and temperature of 25 to 70 °C, followed by aging, separation, washing, and drying to obtain a magnesium-based functional material and a lithium-rich solution with magnesium removed; the content of magnesium ions in the lithium-rich solution with magnesium removed is below 10 ppm.

11. The preparation method according to claim 10, characterized in that: The molar ratio of Mg 2+ to Al 3+ in the mixed salt solution is 2 to 4:

1.

12. The preparation method according to claim 10, characterized in that: The aluminum salt is selected from any one or a combination of two or more of aluminum nitrate, aluminum sulfate, and aluminum chloride.

13. The preparation method according to claim 10, characterized in that: The mixed alkali solution is a mixed alkali solution of sodium carbonate and sodium hydroxide; the volumes of the mixed salt solution and the alkali solution are the same.

14. The preparation method according to claim 1, characterized in that It also includes: First, pretreating the salt lake brine, at least for removing sediment or organic matter; wherein, the turbidity of the solution obtained after the pretreatment is less than 3 NTU.

15. The preparation method according to claim 14, characterized in that: The pretreatment is carried out by any one of ultrafiltration, ceramic filtration, and poly-ceramic membrane filtration.

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