A method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction

Abstract

The present invention discloses a method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction. The method comprises: subjecting salt lake brine to primary adsorption-desorption and secondary adsorption-desorption treatment in sequence to obtain a mixed desorption liquid; subjecting the mixed desorption liquid to forward osmosis primary concentration and electrodialysis secondary concentration treatment to obtain a secondary concentrated liquid; wherein the lithium ion content in the secondary concentrated liquid is 8.0-20.0 g / L, and the magnesium-lithium ratio is 0.01-0.8; the secondary concentrated liquid is mixed with aluminum salt and alkaline solution to coprecipitation reaction and boron removal treatment to obtain magnesium-based functional materials, boric acid and boron-removed lithium-rich solution; and, adjusting the pH value of the boron-removed lithium-rich solution, and then performing MVR evaporation crystallization to obtain battery-grade lithium dihydrogen phosphate. The method provided by the present invention realizes the co-production of lithium dihydrogen phosphate 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 invention belongs to the technical field of comprehensive utilization of salt lake resources and relates to a method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction. Background Art

[0002] Lithium (Li) is the lightest metal element in nature. It is silvery white and has unique physical and chemical properties such as high specific heat, high electrical conductivity and strong chemical activity. It 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, and the demand for lithium has also increased sharply. In nature, lithium resources are mainly found in solid ores and liquid brines. The important position of brine lithium resources in the development of lithium resources in the world has been established for nearly 40 years. 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 brine are precipitation, solvent extraction, adsorption, calcination, electrodialysis, nanofiltration and solar pool. The adsorption method has greater advantages than other methods from the perspective of environment and economy. The adsorption method uses an adsorbent that selectively adsorbs lithium ions to adsorb lithium ions, and then elutes the lithium ions, thereby achieving the purpose of separating lithium ions from other impurity ions. However, the existing process of extracting lithium from salt lakes by adsorption is mostly single-stage multi-column adsorption. The magnesium-lithium ratio in the desorption solution after adsorption is high. The subsequent process requires nanofiltration technology for secondary magnesium-lithium separation to further reduce the magnesium-lithium ratio. The process is complex and costly. The lithium concentration in the desorption is less than 500 mg / L. It needs to be concentrated several times before lithium salt can be prepared. The concentration multiple is large, the energy consumption is high, and the cost is high. After the secondary magnesium removal, the lithium-containing solution is concentrated by reverse osmosis, which has high energy consumption. At the same time, the existing production methods of lithium dihydrogen phosphate mostly use lithium carbonate, lithium hydroxide or lithium carbonate lithium mother liquor as raw materials, and add lithium phosphate, etc. to prepare it. The cost is high, the energy consumption is high, and the process is complex. 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 technology. Among them, patent CN201410813788.8 discloses a method for preparing battery-grade lithium dihydrogen phosphate, wherein phosphoric acid and ethanol are mixed, and then battery-grade lithium carbonate is slowly added to undergo double decomposition reaction, and lithium dihydrogen phosphate is crystallized and precipitated; after the double decomposition reaction is complete, the filter is filtered and the filter residue is retained, and the filter residue is washed and dried to obtain battery-grade lithium dihydrogen phosphate; patent CN200810044349.X uses phosphoric acid and lithium hydroxide double decomposition reaction, evaporation concentration, cooling crystallization, solid-liquid separation, and drying and packaging to prepare battery-grade lithium dihydrogen phosphate. Patent CN201110190405.2 discloses a method for preparing battery-grade lithium dihydrogen phosphate using high-purity lithium carbonate lithium precipitation mother liquor, including the following steps: using phosphoric acid and phosphate to perform preliminary lithium extraction and deep lithium extraction on lithium carbonate lithium precipitation mother liquor to obtain lithium phosphate and lithium dihydrogen phosphate solution, and then undergoing concentrated evaporation, cooling crystallization, centrifugal separation, saturated washing, drying, air flow crushing and packaging to obtain battery-grade lithium dihydrogen phosphate.Patent CN200910237019.7 discloses a method for preparing battery-grade lithium dihydrogen phosphate, the process steps of which are: (1) purification of industrial-grade lithium hydroxide monohydrate; (2) acid-base neutralization reaction; (3) product spray drying; (4) deep dehydration of the product; and obtaining a purity greater than 99.5% and a particle size D. 50 =3-15 micron battery-grade lithium dihydrogen phosphate products. However, the above patents use lithium carbonate and lithium hydroxide as raw materials to prepare lithium dihydrogen phosphate, which is costly, requires large amounts of acid and alkali, and has a complex process. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction, so as to overcome the shortcomings of the prior art.

[0004] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0005] The embodiment of the present invention provides a method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction, which comprises:

[0006] The salt lake brine is sequentially subjected to primary adsorption-desorption and secondary adsorption-desorption treatments to obtain a mixed desorption liquid;

[0007] The mixed desorption liquid is subjected to forward osmosis primary concentration and electrodialysis secondary concentration to obtain a secondary concentrated liquid; wherein the lithium ion content in the secondary concentrated liquid is 8.0 to 20.0 g / L, and the magnesium-lithium ratio is 0.01 to 0.8;

[0008] The secondary concentrated solution is mixed with aluminum salt and alkaline solution to carry out coprecipitation reaction and boron removal treatment to obtain magnesium-based functional materials, boric acid and boron-removed lithium-rich solution;

[0009] And, the pH value of the boron-removed lithium-enriched solution is adjusted, and then MVR evaporation and crystallization are performed to obtain battery-grade lithium dihydrogen phosphate.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention develops a multi-stage multi-column adsorption process coupling titanium, manganese and aluminum 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 from magnesium and lithium again, and forward osmosis is directly used for primary concentration, which shortens the process flow, reduces energy consumption, reduces costs, and improves 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, prepares battery-grade lithium dihydrogen phosphate in one step, and co-produces magnesium-based functional materials and boric acid, thereby realizing the comprehensive, green, efficient, and high-value development and utilization of salt lake resources and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 It is a schematic diagram of the process of preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction in a typical implementation scheme of the present invention. DETAILED DESCRIPTION

[0013] In view of the defects of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The main purpose is to develop a multi-stage multi-column adsorption process coupled with titanium, manganese and aluminum adsorbents, and adopt multi-stage multi-column adsorption-forward osmosis-co-precipitation magnesium removal-ion exchange method for boron removal-MVR evaporation crystallization technology to separate magnesium and lithium, concentrate lithium and prepare battery-grade lithium dihydrogen phosphate to co-produce magnesium-based functional materials and boric acid. It not only reduces the magnesium-to-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 from magnesium and lithium again, and forward osmosis is directly used for primary concentration, which shortens the process flow, comprehensively considers the synergistic extraction of lithium, magnesium and boron resources in the salt lake, and prepares battery-grade lithium dihydrogen phosphate in one step while co-producing magnesium-based functional materials and boric acid, realizing the comprehensive, green, efficient and high-value development and utilization of salt lake resources and reducing production costs.

[0014] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Specifically, as one aspect of the technical solution of the present invention, a method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and extraction of lithium involves:

[0016] The salt lake brine is sequentially subjected to primary adsorption-desorption and secondary adsorption-desorption treatments to obtain a mixed desorption liquid;

[0017] The mixed desorption liquid is subjected to forward osmosis primary concentration and electrodialysis secondary concentration to obtain a secondary concentrated liquid; wherein the lithium ion content in the secondary concentrated liquid is 8.0 to 20.0 g / L, and the magnesium-lithium ratio is 0.01 to 0.8;

[0018] The secondary concentrated solution is mixed with aluminum salt and alkaline solution to carry out coprecipitation reaction and boron removal treatment to obtain magnesium-based functional materials, boric acid and boron-removed lithium-rich solution;

[0019] And, the pH value of the boron-removed lithium-enriched solution is adjusted, and then MVR evaporation and crystallization are performed to obtain battery-grade lithium dihydrogen phosphate.

[0020] In some preferred embodiments, the schematic diagram of the process of preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and extraction of lithium in the present invention is as follows: Figure 1 shown.

[0021] Specifically, the method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and lithium extraction includes:

[0022] (1) Extraction of lithium by multi-stage multi-column coupling adsorption

[0023] After pretreatment to remove impurities such as silt and organic matter, the salt lake brine enters the primary adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water, and the primary adsorption washing liquid is returned to the primary adsorption to recover lithium. After washing, the saturated titanium adsorption column is desorbed with a primary desorbent to obtain a primary desorbent. 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. After adsorption, the tail liquid enters the secondary adsorption system for secondary adsorption after adjusting the pH. The adsorption tail liquid is discharged to the salt field. After the secondary adsorption, the saturated aluminum adsorption column is washed with water and desorbed with a secondary desorbent after washing to obtain a secondary desorbent. The secondary desorbent is mixed with the primary desorbent to obtain a mixed desorbent and enter the next process.

[0024] (2) Forward osmosis for primary concentration

[0025] The mixed desorption liquid obtained above enters the forward osmosis system for primary concentration to obtain the primary concentrated liquid and forward osmosis fresh water, which enter the next stage process and are returned for primary and secondary adsorption washing water respectively.

[0026] (3) Electrodialysis for secondary concentration

[0027] The primary concentrated solution obtained in the previous step enters the electrodialysis system for secondary concentration to obtain a secondary concentrated lithium-rich solution and ED fresh water (electrodialysis fresh water). The secondary concentrated solution enters the next stage of the process, and the ED fresh water is blended with the mixed desorption solution to achieve the recovery of residual lithium and the reuse of fresh water through the forward osmosis system.

[0028] Among them, the lithium concentration after electrodialysis concentration used in this application is higher, which can be as high as 20g / L. Lithium dihydrogen phosphate must continuously concentrate and enrich the lithium solution until saturated precipitation, and then continue to use MVR for evaporation concentration. If MVR concentration is directly used after the first-level concentration, the energy consumption will be very high and the cost will be very high.

[0029] (4) Deep removal of magnesium to prepare magnesium-based functional materials

[0030] A certain ratio of soluble aluminum salt is added to the secondary concentrated lithium-rich solution to prepare a mixed salt solution, and a mixed alkaline solution of sodium carbonate and sodium hydroxide is subjected to a coprecipitation reaction under certain conditions; after nucleation of the coprecipitation reaction, solid-liquid separation is performed to obtain a filter cake and a filtrate; after solid-liquid separation, the filter cake is washed and dried to obtain a white solid MgA1-LDH product; the filtrate is used for the next process of ion exchange method for boron removal.

[0031] Among them, the magnesium-based functional material in this application is a double metal hydroxide with a layered structure. The metal elements are arranged alternately on the layers, and anions can be inserted between the layers, forming a large class of important layered functional materials, which are widely used in highly dispersed catalysis, selective adsorption, functional additives (flame retardants, UV blockers, thermal stabilizers, etc.), biomedicine and other fields.

[0032] (5) Boron removal by ion exchange

[0033] The filtrate is passed through an ion exchange column filled with boron-specific resin to enrich boron in the ion exchange column, so that the boron content in the effluent is below 5 ppm, and a boron-free lithium-rich solution is obtained for the preparation of lithium dihydrogen phosphate for batteries in the next process, and the boron-saturated adsorption column is used for boric acid production.

[0034] (6) Preparation of battery-grade lithium dihydrogen phosphate

[0035] The pH value of the boron-removed lithium-rich solution is adjusted, and the solution after the pH adjustment is evaporated, concentrated and crystallized in the MVR system, and the crystallized product is dried to obtain a battery-grade lithium dihydrogen phosphate product.

[0036] In some preferred embodiments, the method specifically includes: adjusting the pH value of the boron-removed lithium-enriched solution to 0.5-4 using hydrochloric acid, then placing the obtained solution in an MVR system for evaporation, concentration and crystallization, and then drying to obtain battery-grade lithium dihydrogen phosphate.

[0037] Furthermore, the evaporation, concentration and crystallization process is carried out in vacuum or under the protection of an inert gas.

[0038] Furthermore, the temperature of the evaporation, concentration and crystallization is 70-120°C.

[0039] Furthermore, the drying process includes flash drying and / or tray drying.

[0040] Furthermore, the temperature of the drying process is 90-130°C.

[0041] In some preferred embodiments, the purity of the battery-grade lithium dihydrogen phosphate is above 99.5%.

[0042] In some preferred embodiments, the method specifically comprises:

[0043] The salt lake brine is placed in a primary adsorption system for primary adsorption treatment, and then the saturated adsorption column is washed with water, and then the saturated adsorption column is subjected to primary desorption treatment using a primary desorbent to obtain a primary desorption liquid and a primary tail liquid; wherein the primary adsorption system is an adsorption system filled with a titanium or manganese adsorbent; and the concentration of lithium ions in the primary tail liquid is 0.2-0.4 g / L;

[0044] The pH value of the primary tail liquid is adjusted to 3-6 and placed in a secondary adsorption system for secondary adsorption treatment, after which the saturated adsorption column is washed with water, and then the saturated adsorption column is subjected to secondary desorption treatment using a secondary desorbent to obtain a secondary desorption liquid and a secondary tail liquid; wherein the secondary adsorption system is an adsorption system filled with an aluminum-based adsorbent; and the concentration of lithium ions in the secondary tail liquid is less than 20 ppm;

[0045] and, mixing the primary desorption liquid with the secondary desorption liquid to obtain the mixed desorption liquid;

[0046] The mixed desorption liquid comprises a primary desorption liquid and a secondary desorption liquid, the brine obtained after potassium extraction from the salt lake brine has a magnesium-to-lithium ratio of 5 to 500 and a lithium ion concentration of 0.5 to 10 g / L; the lithium ion concentration in the mixed desorption liquid is 0.4 to 1.5 g / L, and the magnesium-to-lithium ratio is 0.1 to 0.4; the volume ratio of the primary desorption liquid to the secondary desorption liquid in the mixed desorption liquid is 1:1 to 5:1.

[0047] Furthermore, the primary adsorption treatment uses 3 to 10 multi-column adsorption.

[0048] Furthermore, the first-stage desorption treatment adopts 2 to 5 multi-column desorption.

[0049] Furthermore, the primary desorbent includes hydrochloric acid and / or sulfuric acid.

[0050] Furthermore, the concentration of the primary desorbent is 0.05-2.0 mol / L.

[0051] Furthermore, the secondary adsorption treatment uses 2 to 5 multi-column adsorption.

[0052] Furthermore, the secondary desorption treatment adopts 1 to 3 multi-column desorption.

[0053] Furthermore, the secondary desorbent includes water.

[0054] Furthermore, the temperature of the secondary desorption treatment is 35-70°C.

[0055] In some preferred embodiments, the method specifically includes: placing the mixed desorption liquid in a forward osmosis system for primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; wherein the concentration of lithium ions in the primary concentrated liquid is 1.5-3.0 g / L; the forward osmosis extraction liquid used in the forward osmosis system includes a saturated magnesium chloride solution or a saturated sodium chloride solution; the concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L; the volume ratio of the mixed desorption 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, but is not limited thereto.

[0056] In some preferred embodiments, the method specifically includes: placing the primary concentrated solution obtained by the primary concentration treatment of forward osmosis in an electrodialysis system for secondary concentration treatment to obtain a secondary concentrated solution and electrodialysis fresh water; wherein the lithium ion content in the secondary concentrated solution is 14.0 to 18.0 g / L; and the lithium ion content in the electrodialysis fresh water is 0.1 to 1.5 g / L.

[0057] Furthermore, the content of lithium ions in the electrodialysis fresh water is 0.4-1.0 g / L.

[0058] In some preferred embodiments, the method specifically comprises:

[0059] Aluminum salt is added to the secondary concentrated solution to form a mixed salt solution, and then a mixed alkali solution is added to perform a coprecipitation reaction under the conditions of pH 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 magnesium-removing lithium-rich solution; the content of magnesium ions in the magnesium-removing lithium-rich solution is less than 10 ppm;

[0060] And, the magnesium-removed lithium-rich solution is passed into an ion exchange column filled with boron-specific resin to obtain a boron-removed lithium-rich solution and a boron-saturated adsorption column; wherein the boron content in the boron-removed lithium-rich solution is below 5 ppm; the boron-saturated adsorption column is subjected to acid desorption, evaporation and crystallization to obtain boric acid.

[0061] Furthermore, the mixed salt solution contains Mg 2+ With Al 3+ The molar ratio is 2 to 4:1.

[0062] Furthermore, the aluminum salt includes any one of aluminum nitrate, aluminum sulfate, and aluminum chloride, or a combination of two or more thereof, but is not limited thereto.

[0063] Furthermore, the mixed alkaline solution is a mixed alkaline solution of sodium carbonate and sodium hydroxide; the volume of the mixed salt solution is the same as that of the alkaline solution.

[0064] Furthermore, the boron special effect resin includes any one of LSC-800, D403, D564, and XSC-700, or a combination of two or more thereof.

[0065] In some preferred embodiments, the method further comprises: pre-treating the salt lake brine at least to remove silt or organic matter; wherein the turbidity of the solution obtained after the pre-treatment is less than 3NTU.

[0066] Furthermore, the pretreatment is performed by any one of ultrafiltration, ceramic filtration and polyceramic membrane filtration.

[0067] In some more specific embodiments, the method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and extraction of lithium includes:

[0068] (1) Extraction of lithium by multi-stage multi-column coupling adsorption

[0069] After pretreatment to remove impurities such as silt and organic matter, the salt lake brine enters the primary adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water, and the primary adsorption washing liquid is returned to the primary adsorption to recover lithium. After washing, the saturated titanium or manganese adsorption column is desorbed with a primary desorbent to obtain a primary desorbent. The desorbed adsorption column is washed and enters the next cycle. The primary washing liquid after desorption is used to prepare the primary desorbent. After adsorption, the tail liquid enters the secondary adsorption system for secondary adsorption after adjusting the pH. The adsorption tail liquid is discharged to the salt field. After the secondary adsorption, the saturated aluminum adsorption column is washed with water, and after washing, it is desorbed with a secondary desorbent to obtain a secondary desorbent. The secondary desorbent is mixed with the primary desorbent to obtain a mixed desorbent and enters the next process. The salt lake brine is brine after potassium extraction, with a magnesium-lithium ratio of 5 to 500 and a lithium concentration of 0.5 to 10 / L; the pretreatment is one of ultrafiltration, ceramic filtration or polyceramic membrane filtration, and the turbidity in the brine after pretreatment is less than 3NTU; the primary adsorption system is an adsorption system filled with titanium or manganese adsorbents, the adsorption column for primary lithium adsorption is 2 to 10 multi-column adsorption, and the primary desorption column is 2 to 5 multi-column desorption; the primary desorbent is hydrochloric acid or sulfuric acid, and the concentration of hydrochloric acid or sulfuric acid is 0.05 to 2.0 mol / L; the tail liquid after adsorption is adjusted to pH 3 to 6 and enters the secondary The adsorption system has a lithium concentration of 0.2-0.4 g / L in the primary adsorption tail liquid; the secondary adsorption system is an adsorption system filled with an aluminum-based adsorbent, the secondary adsorption of lithium by the adsorption column is 2-5 multi-column adsorption, and the secondary desorption column is 1-3 multi-column desorption; the secondary desorbent contains pure water, and the secondary desorption temperature is 35-70°C; the mixed volume ratio of the primary desorption liquid to the secondary desorption liquid is 1:1-5:1, the lithium concentration in the desorption liquid is 0.4-1.5 g / L, and the magnesium-lithium ratio in the desorption liquid is 0.1-0.4; the lithium concentration of the secondary adsorption tail liquid is less than 20 ppm.

[0070] (2) Forward osmosis for primary concentration

[0071] The mixed desorption 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 primary and secondary adsorption washing respectively. The lithium concentration in the forward osmosis primary concentrated liquid is 1.5-3.0 g / L, the forward osmosis draw liquid is a saturated magnesium chloride or saturated sodium chloride solution prepared from salt lake magnesium chloride or sodium chloride, the forward osmosis fresh water returns to the secondary adsorption system for secondary washing, the lithium ion content in the forward osmosis fresh water is 0.005-0.10 g / L, the concentration volume ratio (mixed desorption liquid solution volume / primary concentrated liquid) is 2.0:1-4:1, and the forward osmosis membrane is one or both of a CTA membrane or a TFC membrane.

[0072] (3) Electrodialysis for secondary concentration

[0073] The primary concentrated solution obtained in the previous step enters the electrodialysis system for secondary concentration to obtain a secondary concentrated lithium-rich solution and ED fresh water. The secondary concentrated solution enters the next stage of the process, and the ED fresh water is mixed with the mixed desorption solution to achieve the recovery of residual lithium and the reuse of fresh water through the forward osmosis system. Among them, the lithium ion content in the secondary concentrated solution is 8.0-20.0 g / L, preferably 14.0-18.0 g / L; the magnesium-lithium ratio is 0.01-0.8 to control the lithium ion content in the ED fresh water to 0.1-1.5, preferably 0.4-1.0 g / L.

[0074] (4) Deep removal of magnesium to prepare magnesium-based functional materials

[0075] A certain proportion of soluble aluminum salt is added to the secondary concentrated lithium-rich solution to prepare a mixed salt solution, and the mixed salt solution is dripped into a mixed alkaline solution of sodium carbonate and sodium hydroxide under certain pH, temperature and flow rate conditions to perform a coprecipitation reaction; after the coprecipitation reaction is nucleated, the solution is aged under stirring and at a certain temperature and then solid-liquid separation is performed 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-rich solution does not exceed 10ppm, and the magnesium-rich solution is used for the next step of ion exchange resin boron removal. The mixed salt solution is a solution prepared by adding a certain proportion of soluble aluminum salt to the lithium-rich solution, wherein Mg 2+ With A1 3+ The molar ratio of is 2 to 4, the aluminum salt is one of aluminum nitrate, aluminum sulfate, and aluminum chloride; the volume of the mixed alkali solution is the same as the volume of the mixed salt solution, the reaction is a constant pH method, the pH is maintained at 8 to 13, and the reaction temperature is 25°C to 70°C.

[0076] (5) Boron removal by ion exchange

[0077] The filtrate is passed through an ion exchange column filled with a boron-specific resin to enrich boron in the ion exchange column, so that the boron content in the effluent is below 5 ppm, and a boron-free lithium-enriched solution is obtained for the preparation of lithium dihydrogen phosphate for batteries in the next process. The boron-specific resin is one of LSC-800, D403, D564 or XSC-700, and the boron saturated adsorption column is used for boric acid production.

[0078] (6) Preparation of battery-grade lithium dihydrogen phosphate

[0079] The pH value of the boron-removed lithium-rich solution is adjusted to 0.5-4, and the solution after the pH adjustment is evaporated, concentrated and crystallized 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, solid-liquid separation is performed, and the crystallized product is flash dried or disc dried to obtain a battery-grade lithium dihydrogen phosphate product. The drying temperature is 90-130°C, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%.

[0080] In view of the above shortcomings of the prior art, the present invention develops a multi-stage multi-column adsorption process coupling titanium, manganese and aluminum 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 from magnesium and lithium again, and forward osmosis is directly used for primary concentration, which shortens the process flow, reduces energy consumption, reduces costs, and improves the recovery rate of lithium resources in salt lakes.

[0081] The invention comprehensively considers the coordinated extraction of lithium, magnesium and boron resources in salt lakes, prepares battery-grade lithium dihydrogen phosphate in a one-step method, and simultaneously co-produces magnesium-based functional materials and boric acid, thereby realizing the comprehensive, green, efficient and high-value development and utilization of salt lake resources and reducing production costs. Meanwhile, the invention adopts multi-stage multi-column adsorption-forward osmosis-co-precipitation magnesium removal-ion exchange method boron removal-MVR evaporation crystallization technology to separate magnesium and lithium, concentrate and enrich lithium, and prepare battery-grade lithium dihydrogen phosphate and co-produce magnesium-based functional materials and boric acid, which has not been reported.

[0082] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0083] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0084] Example 1

[0085] The salt lake brine used in this example is old brine from a sulfate salt lake in Qinghai, where Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0086] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 2 columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L was adjusted to 4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 2 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by 1 column with pure water at 35°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 1:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.7 g / L and the magnesium-lithium ratio was 0.1. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution of sodium chloride prepared from a salt lake. The mixed desorbed liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 1.5 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 12 g / L, the magnesium-lithium ratio is 0.1, and the electrodialysis fresh water lithium concentration is 0.1 g / L. The secondary concentrated lithium-rich solution uses a reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain a MgAl-LDH product; the filtrate is passed through an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to below 5ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the lithium-rich boron-removing solution is used to prepare battery-grade lithium dihydrogen phosphate under certain conditions, the pH of the boron-removing lithium-rich solution is adjusted to 0.5, and then evaporated under vacuum evaporation conditions in an MVR system, the evaporation temperature is 70°C, and after solid-liquid separation, the solid is flash-dried at 90°C to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%.

[0087] Example 2

[0088] The salt lake brine used in this example is old brine from a sulfate salt lake in Qinghai, where Li + The concentration is 4g / L and the magnesium to lithium ratio is 12.

[0089] 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 for 5 columns with 1 mol / L sulfuric acid 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 5 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 for 2 columns with pure water at 45°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 enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 20 g / L, the magnesium-lithium ratio is 0.5, and the electrodialysis fresh water lithium concentration is 0.5 g / L. The secondary concentrated lithium-rich solution uses reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary 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 a MgAl-LDH product; the filtrate is passed through an adsorption column equipped with D403 boron-specific adsorption resin to reduce the boron in the filtrate to below 2ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; battery-grade lithium dihydrogen phosphate is prepared from the lithium-rich boron-removing solution under certain conditions, the pH of the boron-removing lithium-rich solution is adjusted to 4, and then evaporated under inert gas protection conditions in an MVR system, the evaporation temperature is 120°C, and after solid-liquid separation, the solid is dried on a 120°C disc to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%.

[0090] Example 3

[0091] The salt lake brine used in this example is old brine from a sulfate salt lake in Qinghai, where Li + The concentration is 2g / L and the magnesium-lithium ratio is 60.

[0092] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 1 and then entered the primary adsorption system equipped with titanium adsorbent. After 5 columns in series adsorption, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 4 columns with 0.5 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.3 g / L was adjusted to 4.4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 4 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 by 3 columns with pure water at 55°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 3:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 1.0 g / L and the magnesium-lithium ratio was 0.2. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from a salt lake. The mixed desorbed liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 2.0 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.02 g / L, and the concentration ratio is 3:1. The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 15 g / L, the magnesium-lithium ratio is 0.2, and the electrodialysis fresh water lithium concentration is 0.4 g / L. The secondary concentrated lithium-rich solution uses a reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary 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 10, the reaction temperature is 50°C, and after the reaction is complete, the material is aged and filtered to obtain a MgAl-LDH product; the filtrate is passed through an adsorption column equipped with D564 boron-specific adsorption resin to reduce the boron in the filtrate to below 4ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the lithium-rich boron-removing solution is used to prepare battery-grade lithium dihydrogen phosphate under certain conditions, the boron-removing lithium-rich solution is adjusted to a pH of 2 and then evaporated under vacuum evaporation conditions in an MVR system, the evaporation temperature is 90°C, and after solid-liquid separation, the solid is flash-dried at 100°C to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%.

[0093] Example 4

[0094] The salt lake brine used in this example is old brine from a sulfate salt lake in Qinghai, where Li + The concentration is 3g / L and the magnesium-lithium ratio is 40.

[0095] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with manganese adsorbent. After 8 columns in series adsorption, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 0.2 mol / L sulfuric acid for 3 columns to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.25 g / L was adjusted to 4.8 and entered the secondary adsorption system equipped with aluminum adsorbent. After 3 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by pure water for 1 column at 65°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 5:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.9 g / L and the magnesium-lithium ratio was 0.3. 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 2.5 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 18 g / L, the magnesium-lithium ratio is 0.4, and the electrodialysis fresh water lithium concentration is 0.3 g / L. The secondary concentrated lithium-rich solution uses reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2 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 9, the reaction temperature is 40°C, and after the reaction is complete, the MgAl-LDH product is obtained by aging and filtering; the filtrate is passed through an adsorption column equipped with XSC-700 boron-specific adsorption resin to reduce the boron in the filtrate to below 5ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; battery-grade lithium dihydrogen phosphate is prepared from the lithium-rich boron-removing solution under certain conditions, the pH of the boron-removing lithium-rich solution is adjusted to 3, and then evaporated under inert gas protection conditions in an MVR system, the evaporation temperature is 100°C, and after solid-liquid separation, the solid is flash-dried at 120°C to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%.

[0096] Comparative Example 1

[0097] The salt lake brine used in this comparative example is old brine from a sulfate salt lake in Qinghai, in which Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0098] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 2 columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L was adjusted to 4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 2 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by 1 column with pure water at 35°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 1:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.7 g / L and the magnesium-lithium ratio was 0.1. The mixed desorbed liquid enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrated solution is 12g / L, the magnesium-lithium ratio is 0.1, and the electrodialysis fresh water lithium concentration is 0.1g / L. The secondary concentrated lithium-rich solution adopts reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2, 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain a MgAl-LDH product; the filtrate is passed through an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to less than 5ppm to obtain a lithium-rich boron removal solution, and the boron saturated adsorption column is used for the preparation of boric acid byproducts; the lithium-rich boron removal solution is used to prepare battery-grade lithium dihydrogen phosphate under certain conditions, and the pH of the boron-removing lithium-rich solution is adjusted to 0.5 and then evaporated under vacuum evaporation conditions in an MVR system, the evaporation temperature is 70°C, and after solid-liquid separation, the solid is flash-dried at 90°C to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%. In this embodiment, the electrodialysis concentration multiple is increased by 1 times, the energy consumption is increased by 1 times, and the process cost is increased by a quarter.

[0099] Comparative Example 2

[0100] The salt lake brine used in this comparative example is old brine from a sulfate salt lake in Qinghai, in which Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0101] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After three columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by two columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The lithium concentration in the primary desorption liquid was 0.7 g / L, and the magnesium-lithium ratio was 0.1. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution of sodium chloride prepared from a salt lake. The mixed desorbed liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 1.5 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. The primary concentrate enters the electrodialysis secondary concentration system. The secondary concentrate has a lithium concentration of 12 g / L, carbonate 10 g / L, sulfate 11 g / L, boron trioxide 13 g / L, a magnesium-to-lithium ratio of 0.1, and an electrodialysis fresh water lithium concentration of 0.1 g / L. The secondary concentrated lithium-rich solution uses a reaction-separation technology to deeply remove magnesium to prepare a magnesium-based functional material. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the filtrate is passed through an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to less than 5ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the lithium-rich boron-removing solution is used to prepare battery-grade lithium dihydrogen phosphate under certain conditions, and the pH of the boron-removing lithium-rich solution is adjusted to 0.5 and then evaporated in a MVR system under vacuum evaporation conditions, the evaporation temperature is 70°C, and after solid-liquid separation, the solid is flash-dried at 90°C to obtain lithium dihydrogen phosphate, and the main content of lithium phosphate in the prepared battery-grade lithium phosphate is not less than 99.5%, the particle size of the battery-grade lithium phosphate is 6μm, and the lithium yield is only 80.5%.

[0102] Comparative Example 3

[0103] The salt lake brine used in this comparative example is old brine from a sulfate salt lake in Qinghai, in which Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0104] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 2 columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L was adjusted to 4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 2 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by 1 column with pure water at 35°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 1:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.7 g / L and the magnesium-lithium ratio was 0.1. The mixed desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from a salt lake. The mixed desorption liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 1.5 g / L to obtain a primary concentrated solution. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. 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 2, 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain a MgAl-LDH product; the filtrate is passed through an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to less than 5ppm to obtain a lithium-rich boron-removing solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the lithium-rich boron-removing solution is used to prepare battery-grade lithium dihydrogen phosphate under certain conditions, and the pH of the boron-removing lithium-rich solution is adjusted to 0.5 and then evaporated under vacuum evaporation conditions in an MVR system, the evaporation temperature is 70°C, and after solid-liquid separation, the solid is flash-dried at 90°C to obtain a battery-grade lithium dihydrogen phosphate product, and the main content of the lithium dihydrogen phosphate product is greater than 99.5%. At this time, the amount of water evaporated by the MVR system has increased by 4 times, and the energy consumption has increased by 4 times, resulting in a cost increase of about 2 times.

[0105] Comparative Example 4

[0106] The salt lake brine used in this comparative example is old brine from a sulfate salt lake in Qinghai, in which Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0107] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 2 columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L was adjusted to 4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 2 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by 1 column with pure water at 35°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 1:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.7 g / L and the magnesium-lithium ratio was 0.1. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution of sodium chloride prepared from a salt lake. The mixed desorbed liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 1.5 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 12 g / L, the magnesium-lithium ratio is 0.1, and the electrodialysis fresh water lithium concentration is 0.1 g / L. The secondary concentrated lithium-rich solution uses a reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain a MgAl-LDH product; after adjusting the pH of the lithium-rich solution to 0.5, it is evaporated under vacuum evaporation conditions in an MVR system, and the evaporation temperature is 70°C. After solid-liquid separation, the solid is flash-dried at 90°C to obtain a battery-grade lithium dihydrogen phosphate product. The main content of the lithium dihydrogen phosphate product is 98.7%, and the boron content is 1800ppm, which cannot meet the standard of battery-grade lithium dihydrogen phosphate.

[0108] Comparative Example 5

[0109] The salt lake brine used in this comparative example is old brine from a sulfate salt lake in Qinghai, in which Li + The concentration is 1.5g / L and the magnesium-lithium ratio is 100.

[0110] The old brine from a sulfate salt lake in Qinghai was ultrafiltrated to reduce the turbidity to below 3 and then entered the primary adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 2 columns with 0.1 mol / L hydrochloric acid to obtain a primary desorption liquid. The pH of the primary adsorption tail liquid with a lithium concentration of 0.2 g / L was adjusted to 4 and then entered the secondary adsorption system equipped with aluminum adsorbent. After 2 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 secondary adsorption saturated aluminum adsorption column was washed with water and then desorbed by 1 column with pure water at 35°C to obtain a secondary desorption liquid. The primary desorption liquid and the secondary desorption liquid were mixed at a ratio of 1:1 to obtain a mixed desorption liquid. The lithium concentration in the mixed desorption liquid was 0.7 g / L and the magnesium-lithium ratio was 0.1. The mixed desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution of sodium chloride prepared from a salt lake. The mixed desorbed liquid is forward osmotic through a CTA membrane to concentrate the lithium concentration to 1.5 g / L to obtain a primary concentrate. The lithium concentration in fresh water is controlled at 0.005 g / L, and the concentration ratio is 2:1. The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 12 g / L, the magnesium-lithium ratio is 0.1, and the electrodialysis fresh water lithium concentration is 0.1 g / L. The secondary concentrated lithium-rich solution uses a reaction-separation technology to deeply remove magnesium to prepare magnesium-based functional materials. Aluminum chloride hexahydrate is added to the secondary concentrated lithium-rich solution to prepare Mg 2+ With Al 3+ A mixed salt solution with a molar ratio of 2 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 8, the reaction temperature is 25°C, and after the reaction is complete, the material is aged and filtered to obtain the MgAl-LDH product; the filtrate is passed through an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to below 5ppm to obtain a lithium-rich boron removal solution, and the boron saturated adsorption column is used for the preparation of boric acid by-products; the lithium-rich boron removal solution is evaporated under vacuum evaporation conditions in the MVR system, and the evaporation temperature is 70°C. After solid-liquid separation, the solid is flash-dried at 90°C to obtain a mixture of lithium phosphate and lithium hydroxide, and the lithium dihydrogen phosphate product cannot be prepared, and the strong alkaline solution is very easy to corrode the MVR equipment, which greatly shortens the service life of the equipment.

[0111] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0112] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing lithium dihydrogen phosphate and magnesium-based functional materials by multi-stage adsorption and extraction of lithium, characterized in that include: The salt lake brine is sequentially subjected to primary adsorption-desorption and secondary adsorption-desorption treatments to obtain a mixed desorption liquid; The mixed desorption liquid is subjected to forward osmosis primary concentration and electrodialysis secondary concentration to obtain a secondary concentrated liquid; wherein the lithium ion content in the secondary concentrated liquid is 8.0-20.0 g / L, and the magnesium-lithium ratio is 0.01-0.8; The secondary concentrated solution is mixed with aluminum salt and alkaline solution to carry out coprecipitation reaction and boron removal treatment to obtain magnesium-based functional materials, boric acid and boron-removed lithium-rich solution; And, phosphoric acid is used to adjust the pH value of the boron-removed lithium-enriched solution, and then MVR evaporation and crystallization are carried out to obtain battery-grade lithium dihydrogen phosphate.

2. The method according to claim 1, characterized in that Specifically, the method comprises: adjusting the pH value of the boron-removed lithium-rich solution to 0.5-4 by using phosphoric acid, and then placing the obtained solution in an MVR system for evaporation, concentration and crystallization, and then drying the solution to obtain battery-grade lithium dihydrogen phosphate; The evaporation, concentration and crystallization process is carried out in a vacuum or under the protection of an inert gas; the temperature of the evaporation, concentration and crystallization is 70-120°C; the drying treatment is selected from flash drying and / or disc drying; the temperature of the drying treatment is 90-130°C.

3. The method according to claim 1, characterized in that: The purity of the battery-grade lithium dihydrogen phosphate is above 99.5%.

4. The method according to claim 1, characterized in that Specifically include: The salt lake brine is placed in a primary adsorption system for primary adsorption treatment, and then the saturated adsorption column is washed with water, and then the saturated adsorption column is subjected to primary desorption treatment using a primary desorbent to obtain a primary desorption liquid and a primary tail liquid; wherein the primary adsorption system is an adsorption system filled with a titanium or manganese adsorbent; and the concentration of lithium ions in the primary tail liquid is 0.2-0.4 g / L; The pH value of the primary tail liquid is adjusted to 3-6 and placed in a secondary adsorption system for secondary adsorption treatment, after which the saturated adsorption column is washed with water, and then the saturated adsorption column is subjected to secondary desorption treatment using a secondary desorbent to obtain a secondary desorption liquid and a secondary tail liquid; wherein the secondary adsorption system is an adsorption system filled with an aluminum-based adsorbent; and the concentration of lithium ions in the secondary tail liquid is less than 20 ppm; and, mixing the primary desorption liquid with the secondary desorption liquid to obtain the mixed desorption liquid; The mixed desorption liquid comprises a primary desorption liquid and a secondary desorption liquid, the salt lake brine is the brine after potassium extraction, 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 desorption liquid is 0.4-1.5 g / L, and the magnesium-lithium ratio is 0.1-0.4; the volume ratio of the primary desorption liquid to the secondary desorption liquid in the mixed desorption liquid is 1:1-5:

1.

5. The method according to claim 4, characterized in that: The first-level adsorption treatment uses 3 to 10 multi-columns for adsorption; the first-level desorption treatment uses 2 to 5 multi-columns for desorption; the first-level desorbent is selected from hydrochloric acid and / or sulfuric acid; the concentration of the first-level desorbent is 0.05 to 2.0 mol / L.

6. The method according to claim 4, characterized in that: The secondary adsorption treatment uses 2 to 5 multi-columns for adsorption; the secondary desorption treatment uses 1 to 3 multi-columns for desorption; the secondary desorbent is selected from water; the temperature of the secondary desorption treatment is 35 to 70°C.

7. The method according to claim 1, characterized in that Specifically include: The mixed desorption liquid is placed in a forward osmosis system for primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; wherein the concentration of lithium ions in the primary concentrated liquid is 1.5-3.0 g / L; the forward osmosis extraction liquid used in the forward osmosis system is selected from a saturated magnesium chloride solution or a saturated sodium chloride solution; the concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L; the volume ratio of the mixed desorption liquid to the primary concentrated liquid is 2.0:1-4:1; the forward osmosis membrane used in the forward osmosis system is selected from a CTA membrane and / or a TFC membrane.

8. The method according to claim 1, characterized in that Specifically include: The primary concentrated solution obtained by the primary concentration treatment of forward osmosis is placed in an electrodialysis system for secondary concentration treatment to obtain a secondary concentrated solution and electrodialysis fresh water; wherein the lithium ion content in the secondary concentrated solution is 14.0-18.0 g / L; and the lithium ion content in the electrodialysis fresh water is 0.1-1.5 g / L.

9. The method according to claim 8, characterized in that: The content of lithium ions in the electrodialysis fresh water is 0.4-1.0 g / L.

10. The method according to claim 1, characterized in that Specifically include: Aluminum salt is added to the secondary concentrated solution to form a mixed salt solution, and then a mixed alkali solution is added to perform a coprecipitation reaction under the conditions of pH 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 magnesium-removing lithium-rich solution; the content of magnesium ions in the magnesium-removing lithium-rich solution is less than 10 ppm; And, the magnesium-removed lithium-rich solution is passed into an ion exchange column filled with boron-specific resin to obtain a boron-removed lithium-rich solution and a boron-saturated adsorption column; wherein the boron content in the boron-removed lithium-rich solution is below 5 ppm; the boron-saturated adsorption column is subjected to acid desorption, evaporation and crystallization to obtain boric acid.

11. The method according to claim 10, characterized in that: The mixed salt solution contains Mg 2+ With Al 3+ The molar ratio is 2 to 4:1; the aluminum salt is selected from any one of aluminum nitrate, aluminum sulfate, and aluminum chloride, or a combination of two or more thereof; the mixed alkaline solution is a mixed alkaline solution of sodium carbonate and sodium hydroxide; and the volume of the mixed salt solution is the same as that of the alkaline solution.

12. The method according to claim 10, characterized in that: The boron special effect resin is selected from any one of LSC-800, D403, D564, and XSC-700, or a combination of two or more thereof.

13. The method according to claim 1, characterized in that Also includes: The salt lake brine is first pretreated to at least remove silt or organic matter; wherein the turbidity of the solution obtained after the pretreatment is less than 3NTU; the pretreatment is performed by any one of ultrafiltration, ceramic filtration, and polyceramic membrane filtration.

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