A preparation method of battery-grade lithium dihydrogen phosphate and boric acid

Abstract

The present invention discloses a method for preparing battery-grade lithium dihydrogen phosphate and boric acid. The preparation method comprises: subjecting carbonate-type salt lake halogen or lithium carbonate lithium precipitation mother liquor to adsorption-desorption treatment to obtain a desorption liquid; subjecting the desorption liquid to forward osmosis primary concentration, nanofiltration separation, and electrodialysis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution; wherein the content of lithium ions in the secondary concentrated lithium-rich solution is 8.0-20.0 g / L; subjecting the secondary concentrated lithium-rich solution to boron removal treatment to obtain a deborated lithium-rich solution and boric acid; and, adjusting the pH value of the deborated lithium-rich solution to 0.5-4, and then performing MVR evaporation crystallization to obtain battery-grade lithium dihydrogen phosphate. The present invention provides the co-production of boric acid while preparing battery-grade lithium dihydrogen phosphate, realizing the comprehensive, green, efficient, and high-value development and utilization of salt lake resources, and reducing production costs.

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 battery-grade lithium dihydrogen phosphate and boric acid, and specifically to a method for co-producing battery-grade lithium dihydrogen phosphate and boric acid by utilizing carbonate salt lake or lithium carbonate precipitation mother liquor. 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 dramatically. 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. Among them, carbonate salt lakes and lithium carbonate mother liquor in brine lithium resources are important lithium resources containing a large amount of carbonate. At present, the main processes for extracting lithium from carbonate salt lakes and lithium carbonate mother liquor are precipitation method and adsorption method. However, the precipitation method has a long process flow and is completely dependent on local climatic conditions to produce lithium carbonate, which is dependent on the weather, has a low degree of automation, and a low yield. The current adsorption method mostly produces lithium hydroxide products, and there are still impurity ions such as carbonate, sulfate, and boron in the desorption solution after adsorption. If lithium is directly concentrated, the increased carbonate concentration will form lithium carbonate precipitate with lithium, which will directly lead to membrane contamination and failure, and cannot effectively concentrate and enrich lithium efficiently. Impurity ions such as sulfate and boron will cause a high content of impurity ions in the product and a low product purity. 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 battery-grade lithium dihydrogen phosphate having a purity greater than 99.5% and a particle size D 50 =3-15 micron battery-grade lithium dihydrogen phosphate product. However, the above patent uses 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 complicated process. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for preparing battery-grade lithium dihydrogen phosphate and boric acid 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] An embodiment of the present invention provides a method for preparing battery-grade lithium dihydrogen phosphate and boric acid, which comprises:

[0006] Carrying out adsorption-desorption treatment on carbonate salt lake raw brine or lithium carbonate precipitation mother liquor to obtain desorption liquid;

[0007] The desorption liquid is subjected to forward osmosis primary concentration, nanofiltration separation, and electrodialysis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution; wherein the content of lithium ions in the secondary concentrated lithium-rich solution is 8.0 to 20.0 g / L;

[0008] Performing a boron removal treatment on the secondary concentrated lithium-rich solution to obtain a boron-removed lithium-rich solution and boric acid;

[0009] And, the pH value of the boron-removed lithium-enriched solution is adjusted to 0.5-4, and then MVR evaporation and crystallization are performed to obtain battery-grade lithium dihydrogen phosphate.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] (1) The present invention develops a process of separation of lithium by adsorption-forward osmosis primary concentration-nanofiltration deep separation-electroosmosis secondary concentration-ion exchange method for boron removal-MVR evaporation crystallization-drying technology, lithium concentration enrichment and preparation of battery-grade lithium dihydrogen phosphate and co-production of boric acid, thereby increasing the concentration of lithium in the desorption solution, and the desorption solution is further subjected to deep carbonate and lithium separation, and boron is removed by ion exchange method, thereby increasing the product purity and lithium resource recovery rate;

[0012] (2) The present invention comprehensively considers the synergistic extraction of lithium and boron resources in salt lakes, prepares battery-grade lithium dihydrogen phosphate in one step and simultaneously produces boric acid, thereby achieving comprehensive, green, efficient and high-value development and utilization of salt lake resources and reducing production costs;

[0013] (3) The present invention uses adsorption-forward osmosis primary concentration-nanofiltration deep separation-electro-osmosis secondary concentration-ion exchange method for boron removal-MVR evaporation crystallization-drying reaction crystallization technology to separate lithium, concentrate lithium and prepare battery-grade lithium dihydrogen phosphate and co-produce boric acid, which has not been reported. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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.

[0015] Figure 1 It is a schematic diagram of the process of preparing battery-grade lithium dihydrogen phosphate and boric acid in a typical embodiment of the present invention. DETAILED DESCRIPTION

[0016] 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. It mainly develops adsorption and desorption-forward osmosis primary concentration-nanofiltration deep separation-electroosmosis secondary concentration-ion exchange method for boron removal-MVR evaporation crystallization-drying technology to separate lithium, concentrate lithium and prepare battery-grade lithium dihydrogen phosphate and co-produce boric acid, increase the concentration of lithium in the desorption solution, and deeply separate carbonate and lithium in the desorption solution again, remove boron by ion exchange, and improve product purity and lithium resource recovery rate.

[0017] 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.

[0018] Specifically, as one aspect of the technical solution of the present invention, a method for preparing battery-grade lithium dihydrogen phosphate and boric acid includes:

[0019] Carrying out adsorption-desorption treatment on carbonate salt lake raw brine or lithium carbonate precipitation mother liquor to obtain desorption liquid;

[0020] The desorption liquid is subjected to forward osmosis primary concentration, nanofiltration separation, and electrodialysis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution; wherein the content of lithium ions in the secondary concentrated lithium-rich solution is 8.0 to 20.0 g / L;

[0021] Performing a boron removal treatment on the secondary concentrated lithium-rich solution to obtain a boron-removed lithium-rich solution and boric acid;

[0022] And, the pH value of the boron-removed lithium-enriched solution is adjusted to 0.5-4, and then MVR evaporation and crystallization are performed to obtain battery-grade lithium dihydrogen phosphate.

[0023] In some preferred embodiments, the process diagram of the present invention for co-producing battery-grade lithium dihydrogen phosphate and boric acid from carbonate salt lake or lithium carbonate precipitation mother liquor is as follows: Figure 1 shown.

[0024] The present invention develops a process of separating lithium by adsorption-forward osmosis primary concentration-nanofiltration deep separation-electrodialysis secondary concentration-ion exchange method for boron removal-reaction crystallization technology, and concentrates and enriches lithium to prepare battery-grade lithium dihydrogen phosphate and co-produce boric acid, thereby increasing the concentration of lithium in the desorption solution, and the desorption solution is again subjected to deep separation of divalent ions such as carbonate and sulfate from lithium, and then the ion exchange method is used to remove boron, thereby achieving regulation of impurity ions in the solution, and improving product purity and lithium resource recovery rate. The forward osmosis-nanofiltration-electrodialysis coupling method is used for lithium enrichment, thereby reducing energy consumption, increasing lithium yield, and reducing production costs. The present invention comprehensively considers the coordinated extraction of lithium and boron resources in salt lakes, and prepares battery-grade lithium dihydrogen phosphate in one step while co-producing boric acid, thereby achieving comprehensive, green, efficient, and high-value development and utilization of salt lake resources, and reducing production costs.

[0025] Specifically, the preparation method of the battery-grade lithium dihydrogen phosphate and boric acid comprises:

[0026] (1) After pretreatment to remove impurities such as silt and organic matter, the carbonate salt lake brine or lithium carbonate mother liquor enters the adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water, and the adsorption washing liquid is returned to the first-level adsorption to recover lithium. After washing, the saturated adsorption column is desorbed by a desorbent to obtain a desorbent. After desorption, the adsorption column is washed with water and enters the next cycle. The desorption washing liquid is used to wash the saturated adsorption column. After adsorption, the tail liquid is discharged to the salt field, and the desorbent liquid enters the next process.

[0027] (2) Forward osmosis for primary concentration

[0028] The 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 adsorption washing water respectively.

[0029] (3) Nanofiltration deep separation

[0030] The primary concentrated liquid obtained above enters the nanofiltration deep separation system for deep separation of carbonate, sulfate and lithium, the obtained lithium-containing solution enters the next stage of the process, and the low-lithium solution enters the adsorption system to recover lithium.

[0031] (4) Electrodialysis for secondary concentration

[0032] The lithium-containing 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 desorption solution to achieve the recovery of residual lithium and the reuse of fresh water through the forward osmosis system.

[0033] The lithium concentration after electrodialysis concentration in this application is higher, which can be as high as 20g / L. Lithium dihydrogen phosphate must be continuously concentrated and enriched to saturated precipitation of lithium solution. After electrodialysis concentration to 20g / L, MVR is continued to be used for evaporation concentration.

[0034] (5) Boron removal by ion exchange

[0035] The above-mentioned secondary concentrated liquid is passed through an ion exchange column filled with boron special effect resin to enrich boron in the ion exchange column filled with boron special effect resin, so that the boron content in the effluent is below 5ppm, and a boron-free lithium-enriched solution is obtained for the preparation of battery-grade lithium dihydrogen phosphate in the next process. The boron saturated adsorption column is used for boric acid production.

[0036] (6) Preparation of battery-grade lithium dihydrogen phosphate

[0037] 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.

[0038] In some preferred embodiments, the preparation method specifically includes: using hydrochloric acid to adjust the pH value of the boron-removed lithium-enriched solution to 0.5-4, then placing the obtained solution in an MVR system for evaporation, concentration and crystallization, and then drying to obtain battery-grade lithium dihydrogen phosphate.

[0039] Furthermore, the evaporation, concentration and crystallization process is carried out in vacuum or under the protection of an inert gas.

[0040] Furthermore, the temperature of the evaporation, concentration and crystallization is 70-120°C.

[0041] Furthermore, the drying process includes flash drying and / or tray drying.

[0042] Furthermore, the temperature of the drying process is 90-130°C.

[0043] In some preferred embodiments, the purity of the battery-grade lithium dihydrogen phosphate is above 99.5%.

[0044] In some preferred embodiments, the preparation method specifically includes: placing the carbonate salt lake raw brine or lithium carbonate lithium precipitation mother liquor in an adsorption system for adsorption treatment, then washing the saturated adsorption column with water, and then using a desorbent to desorb the saturated adsorption column to obtain a desorption liquid; wherein the carbonate salt lake raw brine includes the following components: lithium ions 0.01-2.5 g / L, carbonate 30-40 g / L, sulfate 7-10 g / L, boron trioxide 8-10 g / L; the lithium carbonate lithium precipitation mother liquor includes the following components: lithium ions 0.3-3.0 g / L, carbonate 15-25 g / L, boron trioxide 1-2 g / L; the content of carbonate in the desorption liquid is 1-3 g / L, the content of sulfate is 0.5-1 g / L, and the content of boron trioxide is 0.5-1 g / L.

[0045] Furthermore, the water washing liquid produced by the water washing saturated adsorption column is used for lithium recovery.

[0046] Furthermore, the adsorption system is an adsorption system filled with titanium-based or manganese-based adsorbent.

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

[0048] Furthermore, the desorption process adopts 2 to 5 multi-column desorption.

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

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

[0051] Furthermore, the lithium concentration in the adsorption tail liquid generated after the adsorption treatment is less than 20 ppm.

[0052] In some preferred embodiments, the preparation method specifically comprises:

[0053] Placing the desorbed liquid in a forward osmosis system for primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; wherein the primary concentrated liquid has a lithium ion content of 0.5 to 5.0 g / L, a carbonate content of 2 to 12 g / L, a sulfate content of 2 to 4 g / L, and a boron trioxide content of 2 to 4 g / L;

[0054] The primary concentrated solution is placed in a nanofiltration deep separation system for deep separation of carbonate, sulfate and lithium to obtain a lithium-containing solution and a low-lithium solution; wherein the concentrations of carbonate and sulfate in the lithium-containing solution are both below 0.1 g / L; and the lithium ion content in the lithium-containing solution is 0.5 to 5.0 g / L;

[0055] And, placing the lithium-containing solution in an electrodialysis system for secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and electrodialysis fresh water; wherein the content of lithium ions in the electrodialysis fresh water is 0.1 to 1.5 g / L.

[0056] In some preferred embodiments, the forward osmosis draw solution used in the forward osmosis system includes saturated magnesium chloride or saturated sodium chloride solution.

[0057] In some preferred embodiments, the concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L.

[0058] In some preferred embodiments, the volume ratio of the desorption liquid to the primary concentrated liquid is 2.0:1 to 4:1.

[0059] In some preferred embodiments, the forward osmosis membrane used in the forward osmosis system includes a CTA membrane and / or a TFC membrane.

[0060] In some preferred embodiments, the nanofiltration depth separation unit in the nanofiltration depth separation system is a multi-stage nanofiltration, and the nanofiltration depth separation unit is in the form of multi-stage and multi-section series connection; the ratio range of nanofiltration membranes between different sections in the nanofiltration depth separation unit is 1:1 to 7:1, preferably 2:1 to 5:1; the operating pressure of the nanofiltration depth separation unit is 0.5 to 5.0 MPa, preferably 3.0 to 4.0 MPa.

[0061] In some preferred embodiments, the nanofiltration membrane used in the nanofiltration depth separation system includes any one of a DK membrane, a DL membrane, and a NF membrane, or a combination of two or more thereof.

[0062] In some preferred embodiments, the content of lithium ions in the secondary concentrated lithium-rich solution is 14.0 to 18.0 g / L.

[0063] In some preferred embodiments, the content of lithium ions in the electrodialysis fresh water is 0.4-1.0 g / L.

[0064] In some preferred embodiments, the electrodialysis fresh water is mixed with the desorption solution to achieve the recovery of residual lithium and the reuse of fresh water through a forward osmosis system.

[0065] In some preferred embodiments, the preparation method specifically includes: passing the secondary concentrated lithium-rich solution into an ion exchange column filled with a boron-specific resin to obtain a deborated lithium-rich solution and a boron-saturated adsorption column; wherein the boron content in the deborated lithium-rich solution is below 5 ppm; after acid desorption from the boron-saturated adsorption column, a boric acid solution is obtained, and the boric acid solution is evaporated and crystallized to prepare boric acid.

[0066] 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.

[0067] In some preferred embodiments, the preparation method further comprises: first pre-treating the carbonate salt lake brine or lithium carbonate precipitation mother liquor, at least for removing silt or organic matter; wherein the turbidity of the solution obtained after the pre-treatment is less than 3NTU.

[0068] Furthermore, the pretreatment is performed by any one of ultrafiltration, ceramic filtration and polyceramic membrane filtration.

[0069] In some more specific embodiments, the method for preparing battery-grade lithium dihydrogen phosphate and boric acid comprises:

[0070] (1) The carbonate salt lake brine or lithium carbonate mother liquor is pre-treated to remove impurities such as silt and organic matter, and then enters the adsorption system for adsorption. After adsorption, the saturated adsorption column is washed with water, and the adsorption washing liquid is returned to the adsorption system to recover lithium. After washing, the saturated adsorption column is desorbed by a desorbent to obtain a desorbent, and the desorbent enters the next process. The desorption adsorption column is washed with water and enters the next cycle. The washing liquid after desorption is used to prepare the desorbent, and the adsorption tail liquid is discharged to the salt field. The lithium ion concentration in the carbonate salt lake raw brine is 0.01-2.5 g / L, carbonate is 30-40 g / L, sulfate is 7-10 g / L, and boron trioxide is 8-10 g / L; the lithium ion concentration in the lithium carbonate precipitation mother liquor is 0.3-3.0 / L, carbonate is 15-25 g / L, and boron trioxide is 1-2 g / L; the pretreatment is one of ultrafiltration, ceramic filtration or polyceramic membrane filtration, and the turbidity in the brine after pretreatment is less than 3 NTU; the adsorption system The invention relates to an adsorption system filled with titanium or manganese adsorbents, wherein the adsorption columns for lithium adsorption are 3 to 10 columns, and the desorption columns are 2 to 5 columns. The desorbent is hydrochloric acid or sulfuric acid, and the concentration of the hydrochloric acid or sulfuric acid is 0.05 to 2.0 mol / L. The lithium concentration in the desorption liquid is 1.0 to 1.5 g / L, the carbonate in the desorption liquid is 1 to 3 g / L, the sulfate is 0.5 to 1 g / L, and the boron trioxide is 0.5 to 1 g / L. The lithium concentration in the adsorption tail liquid is less than 20 ppm.

[0071] (2) Forward osmosis for primary concentration

[0072] The desorbent obtained above enters the forward osmosis system for primary concentration to obtain a primary concentrated solution and forward osmosis fresh water, which enter the next stage process and are returned for adsorption washing water respectively. The lithium concentration in the forward osmosis primary concentrated solution is 0.5-5.0 g / L, the carbonate concentration is 2-12 g / L, the sulfate concentration is 2-4 g / L, and the boron trioxide concentration is 2-4 g / L. The forward osmosis drawn 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 adsorption system for washing water. The lithium ion content in the forward osmosis fresh water is 0.005-0.10 g / L. The concentration volume ratio (volume of desorbent solution / primary concentrated solution) is 2.0:1-4:1. The forward osmosis membrane is one or both of a CTA membrane or a TFC membrane.

[0073] (3) Nanofiltration deep separation

[0074] The first-level concentrated solution obtained above enters the nanofiltration deep separation system for deep separation of carbonate, sulfate and lithium, and the obtained lithium-containing solution enters the next stage of the process, and the low-lithium solution enters the adsorption system to recover lithium. The nanofiltration deep separation unit is a multi-stage nanofiltration. After the lithium-containing solution is separated by the first-level nanofiltration, the permeate enters the second-level nanofiltration process to further reduce the ratio of secondary ions such as carbonate to monovalent ions in the permeate, thereby increasing its lithium ion concentration; after the second-level nanofiltration, the permeate continues to enter the next-level nanofiltration process to further increase the lithium ion concentration, and so on, until the concentrations of lithium carbonate and sulfate in the solution are reduced to below 0.1g / L, respectively. Each level of nanofiltration key equipment is divided into two sections, that is, the separation unit adopts a multi-stage and multi-section series form. The obtained lithium-containing solution enters the next stage of the process, and the low-lithium solution returns to the adsorption system of step (1) to recover lithium. The ratio of nanofiltration membranes between different sections of the separation unit is in the range of 1:1 to 7:1, preferably 2:1 to 5:1; the operating pressure of the separation unit is 0.5 to 5.0 MPa, preferably 3.0 to 4.0; the lithium ion content in the nanofiltration lithium-containing solution is 0.5 to 5.0 g / L; the nanofiltration membrane used is one or two of DK membrane, DL membrane and NF membrane.

[0075] (4) Electrodialysis for secondary concentration

[0076] The lithium-containing 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 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 8.0-20.0g / L, preferably 14.0-18.0g / L; the lithium ion content in the ED fresh water is controlled to be 0.1-1.5g / L, preferably 0.4-1.0g / L.

[0077] (5) Boron removal by ion exchange

[0078] The above-mentioned secondary concentrated lithium-rich solution is passed through an ion exchange column filled with a boron special effect resin to enrich boron in the ion exchange column filled with the boron special effect resin, 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 battery-grade lithium dihydrogen phosphate in the next process. The boron special effect resin is one of LSC-800, D403, D564 or XSC-700, and the boron saturated adsorption column is used for boric acid production.

[0079] (6) Preparation of battery-grade lithium dihydrogen phosphate

[0080] 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%.

[0081] The invention comprehensively considers the coordinated extraction of lithium and boron resources in salt lakes, prepares battery-grade lithium dihydrogen phosphate and co-produces boric acid in one step, realizes the comprehensive, green, efficient and high-value development and utilization of salt lake resources, and reduces production costs; at the same time, the invention adopts adsorption-forward osmosis primary concentration-nanofiltration deep separation-electroosmosis secondary concentration-ion exchange method boron removal-MVR evaporation crystallization-drying reaction crystallization technology to separate lithium, concentrate and enrich lithium, and prepare battery-grade lithium dihydrogen phosphate and co-produce boric acid, which has never 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 embodiment is raw brine of a carbonate salt lake, wherein the concentration of lithium in the raw brine of the carbonate salt lake is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0086] The raw brine from a carbonate salt lake is ultrafiltrated to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from the salt lake. The desorption liquid is forward osmosis through a CTA membrane to concentrate the lithium concentration to 2g / L to obtain a primary concentrate. The primary concentrate contains 2g / L carbonate, 2g / L sulfate, and 2g / L boron trioxide. The lithium concentration in fresh water is controlled at 0.005g / L, and the concentration ratio is 2:1 (volume ratio of desorption liquid to primary concentrate). The primary concentrated solution enters the DK nanofiltration membrane separation system for deep separation of divalent ions such as carbonate and lithium, and obtains nanofiltration lithium-containing desalinated water solution and nanofiltration low-lithium concentrated solution. The operating pressure is 0.5MPa, and the nanofiltration membrane ratio range between different stages is 1:1. The lithium ion content in the lithium-containing desalinated water solution is 2.5g / L, and the carbonate and sulfate concentrations are reduced to below 0.08g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing desalinated water enters the electrodialysis secondary concentration system, and the lithium concentration of the secondary concentrate is 12g / L, and the lithium concentration of the electrodialysis desalinated water is 0.1g / L. The secondary concentrated lithium-rich solution enters an adsorption column equipped with LSC-800 boron-specific adsorption resin to reduce the boron in the filtrate to below 5 ppm to obtain a lithium-rich boron-removed solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the pH of the boron-removed lithium-rich solution is adjusted to 0.5 and then evaporated under vacuum evaporation conditions in an MVR system at an evaporation temperature of 70°C. 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 lithium precipitation mother liquor used in this embodiment is a lithium carbonate lithium precipitation mother liquor from a salt lake in Qinghai, wherein the Li+ concentration is 1 g / L, the carbonate concentration is 15 g / L, and the boron trioxide concentration is 1 g / L.

[0089] The lithium carbonate mother liquor from a salt lake in Qinghai was passed through a ceramic membrane to reduce the turbidity to below 3 and then entered into a primary adsorption system equipped with a manganese adsorbent. After 10 columns were adsorbed in series, the saturated adsorption column was washed with water. After washing, the saturated lithium saturated adsorption column was desorbed by 5 columns with 1 mol / L sulfuric acid to obtain a desorbed liquid with a lithium concentration of 1.5 g / L, a carbonate concentration of 2 g / L, and a boron trioxide concentration of 0.6 g / L. The lithium concentration of the adsorption tail liquid was reduced to below 20 ppm and discharged to the salt field. The desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with magnesium chloride from a salt lake. The desorbed liquid is forward osmotic through a TFC membrane to concentrate the lithium concentration to 4 g / L to obtain a primary concentrated liquid. The carbonate concentration is 10 g / L, the boron trioxide concentration is 3 g / L, the lithium concentration in the fresh water is controlled at 0.1 g / L, and the concentration ratio is 4:1 (volume ratio of the desorbed liquid to the primary concentrated liquid); the primary concentrated liquid enters the DL nanofiltration membrane separation system for a deep separation system of divalent ions such as carbonate and lithium to obtain a nanofiltration lithium-containing freshwater solution and a nanofiltration low-lithium concentrated solution. The operating pressure is 5 MPa, and the nanofiltration membrane ratio range between different sections is 7:1. The lithium ion content in the lithium-containing freshwater solution is 4.5 g / L, and the carbonate and sulfate concentrations are reduced to below 0.05 g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing solution enters the electrodialysis secondary concentration system, the lithium concentration of the secondary concentrate is 20g / L, and the lithium concentration of the electrodialysis fresh water is 0.5g / L; the secondary concentrated lithium-rich solution 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-removed solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the boron-removed lithium-rich solution is adjusted to pH 4 and then evaporated under inert gas protection conditions in an MVR system at an evaporation temperature of 120°C. After solid-liquid separation, the solid is disk-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%.

[0090] Example 3

[0091] The salt lake brine used in this embodiment is raw brine of a carbonate salt lake, wherein the concentration of lithium in the raw brine of the carbonate salt lake is 1.2 g / L, the concentration of carbonate is 40 g / L, the concentration of sulfate is 10 g / L, and the concentration of boron trioxide is 10 g / L.

[0092] The old brine from a sulfate salt lake in Qinghai was reduced to below 1 by a polyceramic membrane and then entered an adsorption system equipped with a titanium adsorbent. After 5 columns of adsorption in series, the saturated adsorption column was washed with water. After washing, 0.5 mol / L hydrochloric acid was used to desorb the saturated lithium saturated adsorption column by 4 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid was 1.2 g / L, the carbonate was 3 g / L, the sulfate was 0.8 g / L, and the boron trioxide was 1 g / L. The lithium concentration of the adsorption tail liquid was reduced to below 20 ppm and discharged to the salt field. The desorption liquid entered the forward osmosis primary concentration system. The forward osmosis draw liquid was a saturated solution prepared with sodium chloride from the salt lake. The mixed desorption liquid was forward osmosis through a CTA membrane to concentrate the lithium concentration to 3 g / L to obtain a primary concentrate. The primary concentrate contained 10 g / L carbonate, 4 g / L sulfate, and 4 g / L boron trioxide. The lithium concentration in fresh water was controlled at 0.08 g / L, and the concentration ratio was 3:1 (volume ratio of the desorption liquid to the primary concentrate). The primary concentrated liquid enters the NF nanofiltration membrane separation system for deep separation of divalent ions such as carbonate and lithium, and obtains nanofiltration lithium-containing freshwater solution and nanofiltration low-lithium concentrated solution. The operating pressure is 4MPa, and the nanofiltration membrane ratio range between different sections is 2:1. The lithium ion content in the lithium-containing freshwater solution is 3.5g / L, and the concentrations of carbonate and sulfate are reduced to below 0.08g / L, respectively. The lithium-containing solution enters the electrodialysis secondary concentration system, the lithium concentration of the secondary concentrate is 18g / L, and the lithium concentration of the electrodialysis fresh water is 1.0g / L; the secondary concentrated lithium-rich solution 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-removed solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the boron-removed lithium-rich solution is adjusted to pH 2 and then evaporated under vacuum evaporation conditions in an MVR system at an evaporation temperature of 90°C. 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 lithium precipitation mother liquor used in this embodiment is a lithium carbonate lithium precipitation mother liquor from a salt lake in Qinghai, wherein the Li+ concentration is 2.5 g / L, the carbonate concentration is 25 g / L, and the boron trioxide concentration is 2 g / L.

[0095] The lithium carbonate mother liquor from a 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, 0.2 mol / L sulfuric acid was used to desorb the saturated lithium saturated adsorption column for 3 columns to obtain the desorption liquid. The lithium concentration in the desorption liquid was 1.4 g / L, the carbonate concentration was 2.5 g / L, and the boron trioxide concentration was 0.8 g / L. The lithium concentration of the adsorption tail liquid was reduced to below 20 ppm and discharged to the salt field. The desorbed liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with magnesium chloride from a salt lake. The mixed desorbed liquid is forward osmotic through a TFC membrane to concentrate the lithium concentration to 2 g / L to obtain a primary concentrated liquid. The carbonate is 6 g / L, the boron trioxide is 2.5 g / L, the lithium concentration in the fresh water is controlled at 0.01 g / L, and the concentration ratio is 2:1 (the volume ratio of the desorbed liquid to the primary concentrated liquid); the primary concentrated liquid enters the DL nanofiltration membrane separation system for a deep separation system of divalent ions such as carbonate and lithium to obtain a nanofiltration lithium-containing freshwater solution and a nanofiltration low-lithium concentrated solution. The operating pressure is 3 MPa, and the nanofiltration membrane ratio range between different sections is 5:1. The lithium ion content in the lithium-containing freshwater solution is 3 g / L, and the carbonate and sulfate concentrations are reduced to below 0.09 g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing solution enters the electrodialysis secondary concentration system, the lithium concentration of the secondary concentrate is 14g / L, and the lithium concentration of the electrodialysis fresh water is 0.8g / L; the secondary concentrated lithium-rich solution 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-removed solution, and the boron-saturated adsorption column is used for the preparation of boric acid by-products; the boron-removed lithium-rich solution is adjusted to pH 3 and then evaporated under inert gas protection conditions in an MVR system at an evaporation temperature of 100°C. 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 raw brine from a carbonate salt lake, wherein the concentration of lithium in the raw brine is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0098] The raw brine from a carbonate salt lake is ultrafiltered to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain the desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the DK nanofiltration membrane separation system for the deep separation of carbonate and other divalent ions and lithium, and obtains nanofiltration lithium-containing freshwater solution and nanofiltration low-lithium concentrated solution. The operating pressure is 0.5MPa, and the nanofiltration membrane ratio between different sections is 1:1. The lithium ion content in the lithium-containing freshwater solution is 1.2g / L, and the carbonate and sulfate concentrations are reduced to below 0.08g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing desalted water solution enters the electrodialysis secondary concentration system, the lithium concentration of the secondary concentrated solution is 8g / L, and the lithium concentration of the electrodialysis desalted water is 0.1g / L. The secondary concentrated lithium-rich solution enters the 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-removed solution, and the boron-saturated adsorption column is used for the preparation of boric acid byproducts; the boron-removed lithium-rich solution is adjusted to pH 3 and then evaporated under vacuum evaporation conditions in the MVR system at an evaporation temperature of 70°C. 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 one quarter.

[0099] Comparative Example 2

[0100] The salt lake brine used in this comparative example is raw brine from a carbonate salt lake, wherein the concentration of lithium in the raw brine is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0101] The raw brine from a carbonate salt lake is ultrafiltrated to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from the salt lake. The desorption liquid is forward osmosis through a CTA membrane to concentrate the lithium concentration to 2g / L to obtain a primary concentrate. The primary concentrate contains 2g / L carbonate, 2g / L sulfate, and 2g / L boron trioxide. The lithium concentration in fresh water is controlled at 0.005g / L, and the concentration ratio is 2:1 (volume ratio of desorption liquid to primary concentrate). The primary concentrate enters the electrodialysis secondary concentration system. The lithium concentration of the secondary concentrate is 12g / L, carbonate 10g / L, sulfate 11g / L, boron trioxide 13g / L, and the electrodialysis fresh water lithium concentration is 0.1g / L. The secondary concentrated lithium-rich solution enters the 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. The boron-saturated adsorption column is used for the preparation of boric acid byproducts; the boron-removing lithium-rich solution is adjusted to pH 1.5 and then evaporated under vacuum evaporation conditions in the MVR system at an evaporation temperature of 70°C. After solid-liquid separation, the solid is flash-dried at 90°C to obtain a mixture of lithium dihydrogen phosphate and lithium carbonate, with a lithium phosphate content of only 60.5%.

[0102] Comparative Example 3

[0103] The salt lake brine used in this comparative example is raw brine from a carbonate salt lake, wherein the concentration of lithium in the raw brine is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0104] The raw brine from a carbonate salt lake is ultrafiltrated to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from the salt lake. The desorption liquid is forward osmosis through a CTA membrane to concentrate the lithium concentration to 2g / L to obtain a primary concentrate. The primary concentrate contains 2g / L carbonate, 2g / L sulfate, and 2g / L boron trioxide. The lithium concentration in fresh water is controlled at 0.005g / L, and the concentration ratio is 2:1 (volume ratio of desorption liquid to primary concentrate). The primary concentrated solution enters the DK nanofiltration membrane separation system for deep separation of carbonate and other divalent ions from lithium, and obtains nanofiltration lithium-containing desalted water solution and nanofiltration low-lithium concentrated solution. The operating pressure is 0.5MPa, and the nanofiltration membrane ratio range between different sections is 1:1. The lithium ion content in the lithium-containing desalted water solution is 2.5g / L, and the concentrations of carbonate and sulfate are reduced to below 0.08g / L respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing solution enters the 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. The boron-saturated adsorption column is used for the preparation of boric acid byproducts; the pH of the boron-removing lithium-rich solution is adjusted to 0.5 and then evaporated under vacuum evaporation conditions in the MVR system. 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. 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 raw brine from a carbonate salt lake, wherein the concentration of lithium in the raw brine is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0107] The raw brine from a carbonate salt lake is ultrafiltrated to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from the salt lake. The desorption liquid is forward osmosis through a CTA membrane to concentrate the lithium concentration to 2g / L to obtain a primary concentrate. The primary concentrate contains 2g / L carbonate, 2g / L sulfate, and 2g / L boron trioxide. The lithium concentration in fresh water is controlled at 0.005g / L, and the concentration ratio is 2:1 (volume ratio of desorption liquid to primary concentrate). The primary concentrated solution enters the DK nanofiltration membrane separation system for deep separation of divalent ions such as carbonate and lithium, and obtains nanofiltration lithium-containing desalted water solution and nanofiltration low-lithium concentrated solution. The operating pressure is 0.5MPa, and the nanofiltration membrane ratio range between different sections is 1:1. The lithium ion content in the lithium-containing desalted water solution is 2.5g / L, and the carbonate and sulfate concentrations are reduced to below 0.08g / L respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing desalted water solution enters the electrodialysis secondary concentration system, and the lithium concentration of the secondary concentrated solution is 12g / L, and the lithium concentration of the electrodialysis desalted water is 0.1g / L. After the pH of the secondary concentrated lithium-rich solution is adjusted to 4, it 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 battery-grade lithium dihydrogen phosphate product. The main content of the lithium dihydrogen phosphate product is 99.0%, and the boron content is 1500ppm, which cannot meet the requirements of battery-grade lithium dihydrogen phosphate.

[0108] Comparative Example 5

[0109] The salt lake brine used in this comparative example is raw brine from a carbonate salt lake, wherein the concentration of lithium in the raw brine is 0.7 g / L, the concentration of carbonate is 30 g / L, the concentration of sulfate is 7 g / L, and the concentration of boron trioxide is 8 g / L.

[0110] The raw brine from a carbonate salt lake is ultrafiltrated to reduce the turbidity to below 3 and then enters the adsorption system equipped with titanium adsorbent. After 3 columns of adsorption in series, the saturated adsorption column is washed with water. After washing, 0.1mol / L hydrochloric acid is used to desorb the saturated lithium saturated adsorption column by 2 columns to obtain a desorption liquid. The lithium concentration in the desorption liquid is 1.0g / L, the carbonate is 1g / L, the sulfate is 0.5g / L, and the boron trioxide is 0.5g / L. The lithium concentration of the adsorption tail liquid is reduced to below 20ppm and discharged to the salt field. The desorption liquid enters the forward osmosis primary concentration system. The forward osmosis draw liquid is a saturated solution prepared with sodium chloride from the salt lake. The desorption liquid is forward osmosis through a CTA membrane to concentrate the lithium concentration to 2g / L to obtain a primary concentrate. The primary concentrate contains 2g / L carbonate, 2g / L sulfate, and 2g / L boron trioxide. The lithium concentration in fresh water is controlled at 0.005g / L, and the concentration ratio is 2:1 (volume ratio of desorption liquid to primary concentrate). The primary concentrated solution enters the DK nanofiltration membrane separation system for deep separation of divalent ions such as carbonate and lithium, and obtains nanofiltration lithium-containing desalinated water solution and nanofiltration low-lithium concentrated solution. The operating pressure is 0.5MPa, and the nanofiltration membrane ratio range between different stages is 1:1. The lithium ion content in the lithium-containing desalinated water solution is 2.5g / L, and the carbonate and sulfate concentrations are reduced to below 0.08g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing desalinated water enters the electrodialysis secondary concentration system, and the lithium concentration of the secondary concentrate is 12g / L, and the lithium concentration of the electrodialysis desalinated water is 0.1g / L. The secondary concentrated lithium-rich solution enters the 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 and deboronized solution. The boron-saturated adsorption column is used to prepare boric acid by-products; the deborated lithium-rich solution enters the MVR system and evaporates under vacuum evaporation conditions at a temperature of 70°C. After solid-liquid separation, the solid is flash-dried at 90°C to obtain a mixture of lithium phosphate and lithium hydroxide. It is impossible to prepare lithium dihydrogen phosphate products, 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 battery-grade lithium dihydrogen phosphate and boric acid, characterized in that include: Carrying out adsorption-desorption treatment on carbonate salt lake raw brine or lithium carbonate precipitation mother liquor to obtain desorption liquid; The desorption liquid is subjected to forward osmosis primary concentration, nanofiltration separation, and electrodialysis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution; wherein the content of lithium ions in the secondary concentrated lithium-rich solution is 8.0-20.0 g / L; Performing a boron removal treatment on the secondary concentrated lithium-rich solution to obtain a boron-removed lithium-rich solution and boric acid; And, phosphoric acid is used to adjust the pH value of the boron-removed lithium-rich solution to 0.5-4, and then MVR evaporation and crystallization are performed to obtain battery-grade lithium dihydrogen phosphate.

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

4. The preparation method according to claim 1, characterized in that Specifically include: Placing carbonate salt lake raw brine or lithium carbonate lithium precipitation mother liquor in an adsorption system for adsorption treatment, then washing a saturated adsorption column with water, and then using a desorbent to desorb the saturated adsorption column to obtain a desorption liquid; wherein the carbonate salt lake raw brine includes the following components: lithium ion 0.01-2.5 g / L, carbonate 30-40 g / L, sulfate 7-10 g / L, and boron trioxide 8-10 g / L; the lithium carbonate lithium precipitation mother liquor includes the following components: lithium ion 0.3-3.0 g / L, carbonate 15-25 g / L, and boron trioxide 1-2 g / L; the content of carbonate in the desorption liquid is 1-3 g / L, the content of sulfate is 0.5-1 g / L, and the content of boron trioxide is 0.5-1 g / L; Among them, the water washing liquid generated by the water-washed saturated adsorption column is used for lithium recovery; the adsorption system is an adsorption system filled with titanium-based or manganese-based adsorbents; 3 to 10 multi-column adsorption is adopted during the adsorption treatment; 2 to 5 multi-column desorption is adopted for the desorption treatment; the desorbent is selected from hydrochloric acid and / or sulfuric acid; the concentration of the desorbent is 0.05 to 2.0 mol / L; the lithium concentration in the adsorption tail liquid generated after the adsorption treatment is less than 20 ppm.

5. The preparation method according to claim 1, characterized in that Specifically include: Placing the desorbed liquid in a forward osmosis system for primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; wherein the primary concentrated liquid has a lithium ion content of 0.5-5.0 g / L, a carbonate content of 2-12 g / L, a sulfate content of 2-4 g / L, and a boron trioxide content of 2-4 g / L; The primary concentrated solution is placed in a nanofiltration deep separation system for deep separation of carbonate, sulfate and lithium to obtain a lithium-containing solution and a low-lithium solution; wherein the concentrations of carbonate and sulfate in the lithium-containing solution are both below 0.1 g / L; and the lithium ion content in the lithium-containing solution is 0.5-5.0 g / L; And, placing the lithium-containing solution in an electrodialysis system for secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and electrodialysis fresh water; wherein the content of lithium ions in the electrodialysis fresh water is 0.1-1.5 g / L.

6. The preparation method according to claim 5, characterized in that: The forward osmosis draw solution used in the forward osmosis system is selected from saturated magnesium chloride solution or saturated sodium chloride solution.

7. The preparation method according to claim 5, characterized in that: The concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L.

8. The preparation method according to claim 5, characterized in that: The volume ratio of the desorption liquid to the primary concentrated liquid is 2.0:1-4:

1.

9. The preparation method according to claim 5, characterized in that: 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 5, characterized in that: The nanofiltration depth separation unit in the nanofiltration depth separation system is a multi-stage nanofiltration, and the nanofiltration depth separation unit adopts a multi-stage and multi-segment series connection form; the ratio range of nanofiltration membranes between different numbers of segments in the nanofiltration depth separation unit is 1:1~7:1, and the operating pressure of the nanofiltration depth separation unit is 0.5~5.0MPa.

11. The preparation method according to claim 5, characterized in that: The nanofiltration membrane used in the nanofiltration depth separation system is selected from any one of DK membrane, DL membrane and NF membrane or a combination of two or more thereof.

12. The preparation method according to claim 5, characterized in that: The content of lithium ions in the secondary concentrated lithium-rich solution is 14.0-18.0 g / L.

13. The preparation method according to claim 5, characterized in that: The content of lithium ions in the electrodialysis fresh water is 0.4-1.0 g / L.

14. The preparation method according to claim 5, characterized in that: The electrodialysis fresh water is mixed with the desorption liquid and the residual lithium is recovered and the fresh water is reused through a forward osmosis system.

15. The preparation method according to claim 1, characterized in that Specifically include: The secondary concentrated lithium-rich solution is passed through an ion exchange column filled with a boron-specific resin to obtain a deborated lithium-rich solution and a boron-saturated adsorption column; wherein the boron content in the deborated lithium-rich solution is below 5 ppm; and the boron-saturated adsorption column is used to prepare boric acid.

16. The preparation method according to claim 1, characterized in that Also includes: The carbonate salt lake raw brine or lithium carbonate precipitation mother liquor is first pretreated to at least remove sediment or organic matter; wherein the turbidity of the solution obtained after the pretreatment is less than 3NTU.

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