Method for co-producing lithium phosphate and boric acid from carbonate salt lake or lithium carbonate precipitation mother liquor

Abstract

The present invention discloses a method for co-producing lithium phosphate and boric acid from carbonate salt lake or lithium carbonate lithium precipitation mother liquor. The method comprises: adsorbing and desorbing carbonate salt lake halogen or lithium carbonate lithium precipitation mother liquor to obtain desorption liquid; performing forward osmosis primary concentration treatment on the desorption liquid to obtain primary concentrated liquid and forward osmosis fresh water; performing nanofiltration deep separation treatment on the primary concentrated liquid to obtain lithium-containing solution and low-lithium solution; performing high-pressure reverse osmosis secondary concentration treatment on the lithium-containing solution to obtain secondary concentrated lithium-rich solution and reverse osmosis fresh water; performing ion exchange method on the secondary concentrated lithium-rich solution to remove boron to obtain a deborated lithium-rich solution and boric acid; performing ultrasonic precipitation-ultrasonic coupling method on the deborated lithium-rich solution to precipitate lithium to obtain battery-grade lithium phosphate. The method provided by the present invention realizes the co-production of battery-grade lithium phosphate and boric acid; 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 co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate precipitation mother liquor, and specifically relates to a method for co-producing lithium phosphate and boric acid from a 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 completely relies on local climatic conditions to achieve the preparation of lithium carbonate, which is dependent on the weather, has a low degree of automation, and a low yield; the current adsorption method mostly prepares 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 precipitation with lithium, and the lithium carbonate precipitation will directly lead to membrane pollution and failure, and it is impossible to effectively concentrate and enrich lithium efficiently. Impurity ions such as sulfate and boron will cause high impurity ion content in the product and low product purity. At present, there is no relevant report on the preparation of lithium phosphate from lithium in carbonate salt lakes or lithium carbonate lithium precipitation mother liquor. Therefore, from the perspective of comprehensive, green, efficient, and high-value development of salt lake resources, it is an urgent problem to provide a method for co-producing lithium phosphate and boric acid from carbonate salt lakes or lithium carbonate lithium precipitation mother liquor. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate lithium precipitation mother liquor, 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 co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate lithium precipitation mother liquor, which comprises:

[0006] Provide carbonate salt lake raw brine or lithium carbonate precipitation mother liquor;

[0007] The carbonate salt lake raw brine or lithium carbonate lithium precipitation mother liquor is subjected to adsorption and desorption treatment to obtain a desorption liquid; wherein the concentration of lithium ions in the carbonate salt lake raw brine is 0.01-2.5 g / L, the concentration of carbonate is 30-40 g / L, the concentration of sulfate is 7-10 g / L, and the concentration of boron trioxide is 8-10 g / L; the concentration of lithium ions in the lithium carbonate lithium precipitation mother liquor is 0.3-3.0 g / L, the concentration of carbonate is 15-25 g / L, and the concentration of boron trioxide is 1-2 g / L; the concentration of carbonate in the desorption liquid is 1-3 g / L, the concentration of sulfate is 0.5-1 g / L, and the concentration of boron trioxide is 0.5-1 g / L;

[0008] The desorbed liquid is subjected to a forward osmosis primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water;

[0009] The primary concentrated solution is subjected to a nanofiltration deep separation treatment to obtain a lithium-containing solution and a low-lithium solution; wherein the nanofiltration deep separation treatment at least achieves a deep separation of carbonate, sulfate and lithium ions;

[0010] The lithium-containing solution is subjected to a high-pressure reverse osmosis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water;

[0011] The secondary concentrated lithium-rich solution is subjected to a boron removal treatment by an ion exchange method to obtain a boron-removed lithium-rich solution and boric acid;

[0012] Furthermore, the boron-removed lithium-rich solution is subjected to lithium precipitation treatment by ultrasonic precipitation-ultrasonic coupling method to obtain battery-grade lithium phosphate.

[0013] In some more specific embodiments, the purity of the battery-grade lithium phosphate is above 99.5%, and the particle size of the battery-grade lithium phosphate is below 8 μm.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention develops a process of adsorption-desorption-forward osmosis primary concentration-nanofiltration deep separation-high-pressure reverse osmosis secondary concentration-ion exchange method for boron removal-precipitation-ultrasonic coupled reaction crystallization technology to separate lithium, concentrate lithium and prepare battery-grade lithium phosphate and co-produce 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 the ion exchange method is used to remove boron, thereby increasing the product purity and lithium resource recovery rate;

[0016] (2) The present invention comprehensively considers the synergistic extraction of lithium and boron resources in salt lakes, prepares battery-grade lithium 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;

[0017] (3) The present invention uses adsorption-desorption-forward osmosis primary concentration-nanofiltration deep separation-high-pressure reverse osmosis secondary concentration-ion exchange method for boron removal-precipitation-ultrasonic coupled reaction crystallization technology to separate lithium, concentrate lithium and prepare battery-grade lithium phosphate and co-produce boric acid, which has not been reported. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 It is a schematic diagram of the process of co-producing lithium phosphate and boric acid in a typical implementation scheme of the present invention. DETAILED DESCRIPTION

[0020] 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-high-pressure reverse osmosis secondary concentration-ion exchange method for boron removal-precipitation-ultrasonic coupled reaction crystallization technology to separate lithium, concentrate lithium and prepare battery-grade lithium 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 method, and improve product purity and lithium resource recovery rate.

[0021] 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.

[0022] Specifically, as one aspect of the technical solution of the present invention, a method for co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate precipitation mother liquor comprises:

[0023] Provide carbonate salt lake raw brine or lithium carbonate precipitation mother liquor;

[0024] The carbonate salt lake raw brine or lithium carbonate lithium precipitation mother liquor is subjected to adsorption and desorption treatment to obtain a desorption liquid; wherein the concentration of lithium ions in the carbonate salt lake raw brine is 0.01-2.5 g / L, the concentration of carbonate is 30-40 g / L, the concentration of sulfate is 7-10 g / L, and the concentration of boron trioxide is 8-10 g / L; the concentration of lithium ions in the lithium carbonate lithium precipitation mother liquor is 0.3-3.0 g / L, the concentration of carbonate is 15-25 g / L, and the concentration of boron trioxide is 1-2 g / L; the concentration of carbonate in the desorption liquid is 1-3 g / L, the concentration of sulfate is 0.5-1 g / L, and the concentration of boron trioxide is 0.5-1 g / L;

[0025] The desorbed liquid is subjected to a forward osmosis primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water;

[0026] The primary concentrated solution is subjected to a nanofiltration deep separation treatment to obtain a lithium-containing solution and a low-lithium solution; wherein the nanofiltration deep separation treatment at least achieves a deep separation of carbonate, sulfate and lithium ions;

[0027] The lithium-containing solution is subjected to a high-pressure reverse osmosis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water;

[0028] The secondary concentrated lithium-rich solution is subjected to a boron removal treatment by an ion exchange method to obtain a boron-removed lithium-rich solution and boric acid;

[0029] Furthermore, the boron-removed lithium-rich solution is subjected to lithium precipitation treatment by ultrasonic precipitation-ultrasonic coupling method to obtain battery-grade lithium phosphate.

[0030] In some preferred embodiments, the process diagram of the present invention for co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate lithium precipitation mother liquor is as follows: Figure 1 shown.

[0031] Specifically, the method for co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate precipitation mother liquor comprises:

[0032] (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 adsorption system 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 enters the next process.

[0033] (2) Forward osmosis for primary concentration

[0034] 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.

[0035] (3) Nanofiltration deep separation

[0036] 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.

[0037] (4) High-pressure reverse osmosis for secondary concentration

[0038] The lithium-containing solution obtained in the previous step enters a high-pressure reverse osmosis system for secondary concentration to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water. The secondary concentrated solution enters the next stage of the process, and the reverse osmosis fresh water is blended with the desorption solution to achieve the recovery of residual lithium and the reuse of fresh water through the forward osmosis system.

[0039] (5) Boron removal by ion exchange

[0040] 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 lithium phosphate for batteries in the next process, and the boron saturated adsorption column is used for boric acid production.

[0041] (6) Preparation of battery-grade lithium phosphate by precipitation-ultrasonic coupling

[0042] A sodium phosphate solution is added to the boron-removed lithium-rich solution at a certain flow rate, and a co-precipitation reaction is carried out under certain pH, ultrasonic and temperature conditions. A solid lithium phosphate product is obtained through the steps of nucleation, aging, filtration, washing and drying.

[0043] In some preferred embodiments, the method specifically includes: placing the carbonate salt lake brine or lithium carbonate 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 desorbed liquid.

[0044] Furthermore, the water washing liquid produced by the water washing saturated adsorption column is used for lithium recovery.

[0045] Furthermore, the adsorption system is an adsorption system filled with titanium-based or manganese-based adsorbent.

[0046] Furthermore, the adsorption treatment adopts 3 to 10 multi-column adsorption.

[0047] Furthermore, the desorption process adopts 2 to 5 multi-column desorption.

[0048] Furthermore, the desorbent includes hydrochloric acid and / or sulfuric acid.

[0049] Furthermore, the concentration of the desorbent is 0.05-2.0 mol / L.

[0050] Furthermore, the lithium concentration in the adsorption tail liquid generated after the adsorption treatment is less than 20 ppm.

[0051] In some preferred embodiments, the method specifically comprises: placing the 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 0.5 to 5.0 g / L, the concentration of carbonate is 2 to 12 g / L, the concentration of sulfate is 2 to 4 g / L, and the concentration of boron trioxide is 2 to 4 g / L.

[0052] Furthermore, the forward osmosis draw solution used in the forward osmosis system includes saturated magnesium chloride or saturated sodium chloride solution.

[0053] Furthermore, the concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L.

[0054] Furthermore, the volume ratio of the desorption liquid to the primary concentrated liquid is 2.0:1 to 4:1.

[0055] Furthermore, the forward osmosis membrane used in the forward osmosis system includes a CTA membrane and / or a TFC membrane.

[0056] In some preferred embodiments, the method specifically includes: placing the primary concentrated solution 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.

[0057] Furthermore, the concentration of lithium ions in the lithium-containing solution is 2.5 to 4.5 g / L.

[0058] Furthermore, the nanofiltration depth separation unit in the nanofiltration depth separation system is a multi-stage nanofiltration, and the nanofiltration depth separation unit adopts 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, and is particularly preferably 2:1 to 5:1; the operating pressure of the nanofiltration depth separation unit is 0.5 to 5.0 MPa, and is particularly preferably 3.0 to 4.0 MPa.

[0059] Furthermore, the nanofiltration membrane used in the nanofiltration deep separation system includes any one of a DK membrane, a DL membrane, and a NF membrane, or a combination of two or more thereof.

[0060] In some preferred embodiments, the method specifically includes: placing the lithium-containing solution in a high-pressure reverse osmosis system for secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water; wherein the high-pressure reverse osmosis system adopts a multi-stage reverse osmosis device; the concentration of lithium ions in the secondary concentrated lithium-rich solution is 5 to 10 g / L.

[0061] Furthermore, the volume ratio of the lithium-containing solution to the secondary concentrated lithium-rich solution is 1:1 to 4:1.

[0062] Furthermore, the concentration of lithium ions in the reverse osmosis fresh water is 0.005-0.10 g / L.

[0063] Furthermore, the mass ratio of Mg to Li in the reverse osmosis fresh water is 0.1-0.4:1.

[0064] Furthermore, the secondary concentration unit in the high-pressure reverse osmosis system adopts a two-stage series connection.

[0065] Furthermore, the operating pressure of the secondary concentration unit in the high-pressure reverse osmosis system is 1.0-10.0 MPa.

[0066] Furthermore, the reverse osmosis membrane used in the high-pressure reverse osmosis system includes Dow BW membrane and / or SW membrane.

[0067] In some preferred embodiments, the method specifically includes: passing the secondary concentrated lithium-rich solution into an ion exchange column filled with a 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 concentration of lithium ions in the boron-removed lithium-rich solution is 5 to 10 g / L; and the boron-saturated adsorption column is used to prepare boric acid.

[0068] Furthermore, the boron saturated adsorption column is subjected to acid desorption and evaporation crystallization treatment to obtain boric acid.

[0069] 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.

[0070] In some preferred embodiments, the method specifically includes: adding sodium phosphate solution to the boron-removed lithium-rich solution, and carrying out a co-precipitation reaction under the conditions of an ultrasonic frequency of 10 to 50 kHz, an ultrasonic power of 100 to 1000 W, a pH of 8 to 12, a stirring rate of 50 to 200 rpm, and a temperature of 80 to 110°C, followed by nucleation, aging, filtering, washing, and drying to obtain battery-grade lithium phosphate.

[0071] Furthermore, the ultrasonic wave frequency is 20-40 kHz.

[0072] Furthermore, the ultrasonic power is 300-800W.

[0073] Furthermore, the stirring rate is 100-150 rpm.

[0074] Furthermore, the temperature is 90-100°C.

[0075] Furthermore, the ultrasonic time during the coprecipitation reaction is 10 to 60 minutes.

[0076] Furthermore, the mass concentration of the sodium phosphate solution is 10-30%, preferably 18-25%.

[0077] Furthermore, the washing liquid used in the washing treatment includes water and a dispersant, and the dispersant includes polyethylene glycol and / or ethanol dispersant.

[0078] In some preferred embodiments, the purity of the battery-grade lithium phosphate is above 99.5%, and the particle size of the battery-grade lithium phosphate is below 8 μm.

[0079] In some preferred embodiments, the method further comprises: pre-treating the carbonate salt lake raw brine or lithium carbonate precipitation mother liquor to at least remove silt or organic matter;

[0080] Furthermore, the turbidity of the solution obtained after the pretreatment is less than 3NTU.

[0081] Furthermore, the pretreatment is performed by any one of ultrafiltration, ceramic filtration and polyceramic membrane filtration.

[0082] In some preferred embodiments, the method for co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate precipitation mother liquor comprises:

[0083] (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. The adsorption washing liquid returns to the adsorption system to recover lithium. After washing, the saturated adsorption column is desorbed by a desorbent to obtain a desorbent. 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 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 carbonate precipitation mother liquor has a concentration of 0.3-3.0 g / 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 is filled The adsorption system is equipped 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 for desorption; 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 of the adsorption tail liquid is less than 20 ppm.

[0084] (2) Forward osmosis for primary concentration

[0085] The stripping solution 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 primary and adsorption washing water respectively. The lithium concentration in the forward osmosis primary concentrated solution is 0.5-5.0 g / L, the carbonate radical is 2-12 g / L, the sulfate radical is 2-4 g / L, and the boron trioxide 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 (stripping solution volume / 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.

[0086] (3) Nanofiltration deep separation

[0087] The primary 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 primary nanofiltration, the permeate enters the secondary nanofiltration process to further reduce the wallpaper of secondary ions such as carbonate and monovalent ions in the permeate, thereby increasing its lithium ion concentration; after the secondary nanofiltration, the permeate continues to enter the next nanofiltration process to further increase the lithium ion concentration, and so on, until the carbonate and sulfate concentrations in the solution are reduced to below 0.1g / L, respectively. Each stage 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 to recover lithium. The nanofiltration membrane ratio range between different sections of the separation unit is 1:1-7:1, preferably 2:1-5:1; the operating pressure of the separation unit is 0.5-5.0, preferably 3.0-4.0; the lithium ion content in the nanofiltration lithium-containing solution is 2.5-4.5 g / L; the nanofiltration membrane used is one or two of DK membrane, DL membrane and NF membrane.

[0088] (4) High-pressure reverse osmosis for secondary concentration

[0089] The lithium-containing solution obtained above enters the high-pressure reverse osmosis system for secondary concentration. The lithium-containing solution is secondary concentrated by a multi-stage reverse osmosis device to further increase the lithium ion concentration and produce fresh water. The reverse osmosis fresh water is mixed with the mixed desorption liquid, and the residual lithium is recovered and the fresh water is reused through the forward osmosis system. The high-pressure reverse osmosis concentrated liquid enters the deep magnesium removal unit. The secondary concentration unit adopts the form of two sections in series, each section contains a different number of reverse osmosis membranes, and the ratio of reverse osmosis membranes between different sections is 1:1 to 7:1. After secondary concentration by high-pressure reverse osmosis, the lithium ion content in the reverse osmosis concentrated liquid is 5 to 10 g / L; the lithium ion content in the reverse osmosis fresh water is 0.005 to 0.10 g / L; the Mg / Li mass ratio is 0.1-0.4; the concentration volume ratio (lithium-containing solution volume / secondary concentrated liquid) is 1:1 to 4:1; the operating pressure during the secondary concentration unit is 1.0 to 10.0 MPa; the reverse osmosis membrane is one or both of Dow BW membrane or SW membrane.

[0090] (5) Boron removal by ion exchange

[0091] The above-mentioned secondary concentrated liquid 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 5ppm, and a boron-free lithium-enriched solution is obtained for the preparation of battery lithium carbonate 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.

[0092] (6) Preparation of battery-grade lithium phosphate by precipitation-ultrasonic coupling

[0093] Add sodium phosphate solution to the deborated lithium-rich solution at a certain flow rate, and perform a coprecipitation reaction under certain pH, ultrasonic and temperature conditions. After nucleation, aging, filtration, washing, drying and other steps, a solid lithium phosphate product is obtained. Add sodium phosphate solution to the deborated lithium-rich solution at a certain flow rate to perform a coprecipitation reaction to form lithium phosphate nuclei, i.e., the lithium phosphate nucleation process. The lithium-rich solution has a Li++ concentration of 5-10g / L; ultrasonic waves are introduced during the reaction stage, and the ultrasonic frequency is 10-50kHZ, preferably 20-40kHZ; the ultrasonic power is 100-1000W, preferably 300-800W, and the ultrasonic time is 10-60min; the reaction pH value is controlled between 8 and 12; the mass concentration of sodium phosphate is 10-30%, preferably 18-25%; the amount of sodium phosphate is 10-30% in excess, preferably 10-30% in excess. The stirring rate is 50-200 rpm, preferably 100-150 rpm; the reaction temperature is 80-110° C., preferably 90-100° C.; after aging, the slurry is solid-liquid separated, and after solid-liquid separation, the filter cake is washed and dried to obtain a white solid battery-grade lithium phosphate product, wherein the washing is 2 slurry washings, the washing liquid is deionized water, and a small amount of polyethylene glycol or ethanol dispersant is added, and the main content of the prepared lithium phosphate is ≥99.5%, and the particle size is ≤8 μm.

[0094] The present invention comprehensively considers the synergistic extraction of lithium and boron resources in salt lakes, prepares battery-grade lithium 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. There are no reports on the separation of lithium, lithium concentration and enrichment, and preparation of battery-grade lithium phosphate and co-production of boric acid using adsorption-forward osmosis primary concentration-nanofiltration deep separation-high-pressure reverse osmosis secondary concentration-ion exchange method boron removal-precipitation-ultrasonic coupled reaction crystallization technology.

[0095] 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.

[0096] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0097] Example 1

[0098] 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.

[0099] 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. The volume ratio of the desorption liquid to the primary concentrate is 2:1. The primary concentrated liquid enters the DK nanofiltration membrane separation system for deep separation of carbonate and other divalent ions from 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 liquid enters the high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrated liquid is 5g / L; the lithium ion content in the secondary desalted water is 0.10g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW series, and the first and second stage membranes are configured at 1:1. The membrane inlet pressure is controlled to be 1MPa, and the concentration volume ratio (nanofiltration lithium-containing solution / secondary concentrated liquid) is 1. The obtained high-pressure reverse osmosis desalted water is directly mixed with the desorption liquid. The secondary concentrated lithium-rich solution 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 deboronized solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the deboronized lithium-rich solution is heated to 80°C, wherein the lithium in the lithium-rich solution is 5g / L, and an excess of 10% (based on the mass converted into a reaction formula ratio) of a sodium phosphate solution with a mass fraction of 30% is added thereto, the reaction pH value is 8, the stirring speed is 50rpm for precipitation reaction, and an ultrasonic wave of 10kHZ and a power of 100W is turned on in the feeding nucleation stage, and the ultrasonic time is 10min; after the reaction, the battery-grade lithium phosphate is obtained by filtering, washing and drying, and the main lithium phosphate content of the battery-grade lithium phosphate prepared by washing twice and adding a small amount of polyethylene glycol dispersant is not less than 99.5%, the particle size of the battery-grade lithium phosphate is 6μm, and the lithium yield is 95%.

[0100] Example 2

[0101] The lithium precipitation mother liquor used in this embodiment is a lithium carbonate lithium precipitation mother liquor from a salt lake in Qinghai, wherein Li + The concentration is 1g / L, carbonate 15g / L, boron trioxide 1g / L.

[0102] 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 volume ratio of the desorbed liquid to the primary concentrated liquid is 4:1. 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 high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrated solution is 10g / L, and the lithium ion content in the secondary fresh water is 0.005g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow SW series, and the ratio of the first and second stage membranes is 7:1. The membrane inlet pressure is controlled at 10MPa and the concentration volume ratio (lithium-containing solution / secondary concentrated solution) is 4. The obtained high-pressure reverse osmosis fresh water is directly mixed with the desorption liquid. 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 deboronized solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the deboronized lithium-rich solution is heated to 110°C, wherein the lithium in the lithium-rich solution is 10g / L, and an excess of 30% (based on the mass converted into a reaction formula ratio) of a sodium carbonate solution with a mass fraction of 10% is added thereto, the reaction pH value is 12, the stirring speed is 200rpm for precipitation reaction, and an ultrasonic wave of 50kHZ and a power of 1000W is turned on in the feeding nucleation stage, and the ultrasonic time is 10min; after the reaction, the battery-grade lithium phosphate is obtained by filtering, washing and drying, and the washing adopts two pulp washings and a small amount of polyethanol dispersant is added. The main content of lithium phosphate in the prepared battery-grade lithium phosphate is not less than 99.5%, and the particle size of the battery-grade lithium phosphate is 5μm.

[0103] Example 3

[0104] 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.

[0105] 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. The volume ratio of the desorption liquid to the primary concentrate was 3:1. The primary concentrate enters the NF nanofiltration membrane separation system for deep separation of carbonate and other divalent ions from lithium, and obtains nanofiltration lithium-containing desalinated water and nanofiltration low-lithium concentrated solution. The operating pressure is 4MPa, and the nanofiltration membrane ratio range between different stages is 2:1. The lithium ion content in the lithium-containing desalinated water is 3.5g / L, and the carbonate and sulfate concentrations are reduced to below 0.08g / L. The secondary concentrate enters the high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrate is 7g / L, and the magnesium-lithium ratio is 0.3; the lithium ion content in the secondary fresh water is 0.02g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW+SW series, the ratio of the first and second stage membranes is 4:1, the membrane inlet pressure is controlled to be 5MPa, and the concentration volume ratio (lithium-containing solution / primary concentrated liquid) is 2.0. The obtained high-pressure reverse osmosis fresh water is directly mixed with the desorption liquid. The secondary concentrated lithium-rich solution is passed through an adsorption column filled with D564 boron-specific adsorption resin to reduce the boron in the filtrate to below 4 ppm to obtain a lithium-rich deboronized solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the deboronized lithium-rich solution is heated to 90°C, wherein the lithium in the lithium-rich solution is 6 g / L, and an excess of 15% (based on the mass converted to the reaction formula ratio) of a sodium phosphate solution with a mass fraction of 20% is added thereto, the reaction pH value is 9, the stirring speed is 100 rpm for precipitation reaction 9, and an ultrasonic wave of 20 kHz and a power of 300 W is turned on in the feeding nucleation stage, the ultrasonic wave time is 10 minutes, and after the reaction, it is filtered, washed, and dried to obtain a battery-grade lithium phosphate. The washing adopts two pulp washings and a small amount of polyethylene glycol dispersant to prepare the battery-grade lithium phosphate. The main lithium phosphate content in the prepared battery-grade lithium phosphate is not less than 99.5%, and the particle size of the battery-grade lithium phosphate is 7 μm.

[0106] Example 4

[0107] The lithium precipitation mother liquor used in this embodiment is a lithium carbonate lithium precipitation mother liquor from a salt lake in Qinghai, wherein Li +The concentration is 2.5g / L, carbonate 25g / L, and boron trioxide 2g / L.

[0108] 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, where 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 2g / L to obtain a primary concentrated liquid, with a carbonate concentration of 6g / L and a boron trioxide concentration of 2.5g / L. The lithium concentration in the fresh water is controlled at 0.01g / L, and the volume ratio of the desorbed liquid to the primary concentrated liquid is 2:1; 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, with an operating pressure of 3MPa, a nanofiltration membrane ratio range of 5:1 between different sections, a lithium ion content of 3g / L in the lithium-containing freshwater solution, and lithium carbonate and sulfate concentrations are reduced to below 0.09g / L, respectively. The low-lithium solution returns to the adsorption system to recover lithium. The lithium-containing solution enters the high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrated solution is 8g / L, and the magnesium-lithium ratio is 0.2; the lithium ion content in the secondary fresh water is 0.08g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW series, and the ratio of the first and second stage membranes is 5:1. The membrane inlet pressure is controlled to be 8MPa, and the concentration volume ratio (lithium-containing solution / primary concentrated solution) is 3.0. The obtained high-pressure reverse osmosis fresh water is directly mixed with the mixed desorption liquid. 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 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 byproducts. The boron-removed lithium-rich solution is heated to 100° C., wherein the lithium content of the lithium-rich solution is 8 g / L, and an excess of 25% (based on the mass converted into the reaction formula ratio) of a 25% mass fraction of a sodium carbonate solution is added thereto, the reaction pH value is 10, the stirring speed is 150 rpm for precipitation reaction, and an ultrasonic wave of 40 kHz and a power of 800 W is turned on during the feeding nucleation stage, the ultrasonic time is 10 minutes, and after the reaction, the battery-grade lithium phosphate is obtained by filtering, washing and drying. The main lithium phosphate content of the battery-grade lithium phosphate prepared by washing twice and adding a small amount of polyethylene glycol dispersant is not less than 99.5%, and the particle size of the battery-grade lithium phosphate is 8 μm.

[0109] Comparative Example 1

[0110] 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.

[0111] 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 from 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 0.6g / 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 liquid enters the high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrated liquid is 1.2g / L; the lithium ion content in the secondary fresh water is 0.10g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW series, and the first and second stage membranes are configured at 1:1. The membrane inlet pressure is controlled at 1MPa and the concentration volume ratio (nanofiltration lithium-containing solution / secondary concentrated liquid) is 1. The obtained high-pressure reverse osmosis fresh water is directly mixed with the desorption liquid. The secondary concentrated lithium-rich solution 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 deboronized solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the deboronized lithium-rich solution is heated to 80°C, wherein the lithium in the lithium-rich solution is 1.2g / L, and an excess of 10% (based on the mass converted into a reaction formula ratio) of a sodium phosphate solution with a mass fraction of 30% is added thereto, the reaction pH value is 8, the stirring speed is 50rpm for precipitation reaction, and an ultrasonic wave of 10kHZ and a power of 100W is turned on in the feeding nucleation stage, and the ultrasonic time is 10min; after the reaction, the battery-grade lithium phosphate is obtained by filtering, washing and drying, and the main lithium phosphate content of the battery-grade lithium phosphate prepared by washing twice and adding a small amount of polyethylene glycol dispersant is not less than 99.5%, the particle size of the battery-grade lithium phosphate is 6μm, and the lithium yield is only 75%.

[0112] Comparative Example 2

[0113] 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.

[0114] 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. The volume ratio of the desorption liquid to the primary concentrate is 2:1. The primary concentrate enters the high-pressure reverse osmosis system for secondary concentration, and the secondary concentrate has a lithium ion content of 5g / L, carbonate 5.2g / L, sulfate 4.8g / L, and boron trioxide 5.1g / L; the lithium ion content in the secondary fresh water is 0.10g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW series, and the first and second stage membranes are configured at 1:1. The membrane inlet pressure is controlled at 1MPa and the concentration volume ratio (nanofiltration lithium-containing solution / secondary concentrated liquid) is 1. The obtained high-pressure reverse osmosis fresh water is directly mixed with the desorption liquid. The secondary concentrated lithium-rich solution is passed through 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 deboronized solution, and the boron-saturated adsorption column is used to prepare a boric acid byproduct; the deboronized lithium-rich solution is heated to 80°C, wherein the lithium in the lithium-rich solution is 5 g / L, and an excess of 10% (based on the mass converted to the reaction formula ratio) of a sodium phosphate solution with a mass fraction of 30% is added thereto, the reaction pH value is 8, the stirring speed is 50 rpm for precipitation reaction, and an ultrasonic wave of 10 kHz and a power of 100 W is turned on in the feeding nucleation stage, and the ultrasonic time is 10 minutes; after the reaction, it is filtered, washed, and dried to obtain battery-grade lithium phosphate, and the product prepared by washing with two pulp washings and adding a small amount of polyethylene glycol dispersant is a mixture of lithium phosphate and lithium carbonate, and the lithium phosphate content is only 67.5%.

[0115] Comparative Example 3

[0116] 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.

[0117] 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. The volume ratio of the desorption liquid to the primary concentrate is 2:1. The primary concentrated liquid enters the DK 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 0.5MPa, and the nanofiltration membrane ratio range between different stages is 1:1. The lithium ion content in the lithium-containing freshwater 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 freshwater solution is passed through 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 deboronized solution, and the boron-saturated adsorption column is used for the preparation of boric acid byproducts; the deboronized lithium-rich solution is heated to 80°C, wherein the lithium in the lithium-rich solution is 2.5 g / L, and an excess of 10% (based on the mass converted into a reaction formula ratio) of a sodium phosphate solution with a mass fraction of 30% is added thereto, the reaction pH value is 8, the stirring speed is 50 rpm for precipitation reaction, and an ultrasonic wave of 10 kHz and a power of 100 W is turned on in the feeding nucleation stage, and the ultrasonic time is 10 minutes; after the reaction, the battery-grade lithium phosphate is obtained by filtering, washing and drying, and the main lithium phosphate content of the battery-grade lithium phosphate prepared by washing twice and adding a small amount of polyethylene glycol dispersant is not less than 99.5%, the particle size of the battery-grade lithium phosphate is 6 μm, and the lithium yield is 89%.

[0118] Comparative Example 4

[0119] 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.

[0120] 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. The volume ratio of the desorption liquid to the primary concentrate is 2:1. The primary concentrated liquid enters the DK nanofiltration membrane separation system for deep separation of carbonate and other divalent ions from 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 liquid enters the high-pressure reverse osmosis system for secondary concentration, and the lithium ion content in the secondary concentrated liquid is 5g / L; the lithium ion content in the secondary desalted water is 0.10g / L. The reverse osmosis membrane used in the reverse osmosis system is the Dow BW series, and the first and second stage membranes are configured at 1:1. The membrane inlet pressure is controlled to be 1MPa, and the concentration volume ratio (nanofiltration lithium-containing solution / secondary concentrated liquid) is 1. The obtained high-pressure reverse osmosis desalted water is directly mixed with the desorption liquid. The secondary concentrated lithium-rich solution is heated to 80° C., wherein the lithium content in the lithium-rich solution is 5 g / L, and an excess of 10% (based on the mass converted into the reaction formula ratio) of a sodium phosphate solution with a mass fraction of 30% is added thereto, the reaction pH value is 8, the stirring speed is 50 rpm for precipitation reaction, and an ultrasonic wave of 10 kHz and a power of 100 W is turned on during the feeding nucleation stage, and the ultrasonic time is 10 min; after the reaction, the solution is filtered, washed, and dried to obtain battery-grade lithium phosphate. The main lithium phosphate content of the battery-grade lithium phosphate prepared by washing twice and adding a small amount of polyethylene glycol dispersant is 99.2%, and the boron impurity content is 1000 ppm, which does not meet the requirements of battery-grade lithium phosphate.

[0121] 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.

[0122] 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 co-producing lithium phosphate and boric acid from a carbonate salt lake or lithium carbonate precipitation mother liquor, characterized in that: include: Provide carbonate salt lake raw brine or lithium carbonate precipitation mother liquor; The carbonate salt lake raw brine or lithium carbonate lithium precipitation mother liquor is subjected to adsorption and desorption treatment to obtain a desorption liquid; wherein the concentration of lithium ions in the carbonate salt lake raw brine is 0.01-2.5 g / L, the concentration of carbonate is 30-40 g / L, the concentration of sulfate is 7-10 g / L, and the concentration of boron trioxide is 8-10 g / L; the concentration of lithium ions in the lithium carbonate lithium precipitation mother liquor is 0.3-3.0 g / L, the concentration of carbonate is 15-25 g / L, and the concentration of boron trioxide is 1-2 g / L; the concentration of carbonate in the desorption liquid is 1-3 g / L, the concentration of sulfate is 0.5-1 g / L, and the concentration of boron trioxide is 0.5-1 g / L; The desorbed liquid is subjected to a forward osmosis primary concentration treatment to obtain a primary concentrated liquid and forward osmosis fresh water; The primary concentrated solution is subjected to a nanofiltration deep separation treatment to obtain a lithium-containing solution and a low-lithium solution; wherein the nanofiltration deep separation treatment at least achieves a deep separation of carbonate, sulfate and lithium ions; The lithium-containing solution is subjected to a high-pressure reverse osmosis secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water; The secondary concentrated lithium-rich solution is subjected to a boron removal treatment by an ion exchange method to obtain a boron-removed lithium-rich solution and boric acid; And, adding sodium phosphate solution to the boron-removed lithium-rich solution, and using ultrasonic precipitation-ultrasonic coupling method to precipitate lithium on the obtained solution to obtain battery-grade lithium phosphate.

2. The method according to claim 1, characterized in that Specifically include: The carbonate salt lake raw brine or lithium carbonate precipitation mother liquor is placed in an adsorption system for adsorption treatment, and then the saturated adsorption column is washed with water, and then the saturated adsorption column is desorbed by a desorbent to obtain a desorption liquid.

3. The method according to claim 2, characterized in that: The water washing liquid produced by the water washing saturated adsorption column is used for lithium recovery.

4. The method according to claim 2, characterized in that: The adsorption system is an adsorption system filled with titanium-based or manganese-based adsorbent.

5. The method according to claim 2, characterized in that: The adsorption treatment uses 3 to 10 multi-columns for adsorption; the desorption treatment uses 2 to 5 multi-columns for desorption.

6. The method according to claim 2, characterized in that: The desorbent is selected from hydrochloric acid and / or sulfuric acid; the concentration of the desorbent is 0.05-2.0 mol / L.

7. The method according to claim 2, characterized in that: The lithium concentration in the adsorption tail liquid generated after the adsorption treatment is less than 20 ppm.

8. The method according to claim 1, characterized in that Specifically include: The 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 0.5-5.0 g / L, the concentration of carbonate is 2-12 g / L, the concentration of sulfate is 2-4 g / L, and the concentration of boron trioxide is 2-4 g / L.

9. The method according to claim 8, characterized in that: The forward osmosis extraction liquid used in the forward osmosis system is selected from saturated magnesium chloride solution or saturated sodium chloride solution; the concentration of lithium ions in the forward osmosis fresh water is 0.005-0.10 g / L.

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

1.

11. The method according to claim 8, characterized in that: The forward osmosis membrane used in the forward osmosis system is selected from CTA membrane and / or TFC membrane.

12. The method according to claim 1, characterized in that Specifically include: 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.

13. The method according to claim 12, characterized in that: The concentration of lithium ions in the lithium-containing solution is 2.5-4.5 g / L.

14. The method according to claim 12, 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; the operating pressure of the nanofiltration depth separation unit is 0.5~5.0MPa.

15. The method according to claim 12, characterized in that: The nanofiltration membrane used in the nanofiltration deep separation system is selected from any one of DK membrane, DL membrane and NF membrane or a combination of two or more thereof.

16. The method according to claim 1, characterized in that Specifically include: Placing the lithium-containing solution in a high-pressure reverse osmosis system for secondary concentration treatment to obtain a secondary concentrated lithium-rich solution and reverse osmosis fresh water; wherein the high-pressure reverse osmosis system adopts a multi-stage reverse osmosis device; The concentration of lithium ions in the secondary concentrated lithium-rich solution is 5-10 g / L.

17. The method according to claim 16, characterized in that: The volume ratio of the lithium-containing solution to the secondary concentrated lithium-rich solution is 1:1-4:1; the concentration of lithium ions in the reverse osmosis fresh water is 0.005-0.10 g / L; and the mass ratio of Mg to Li in the reverse osmosis fresh water is 0.1-0.4:

1.

18. The method according to claim 16, characterized in that: The secondary concentration unit in the high-pressure reverse osmosis system adopts a two-stage series connection form; the operating pressure of the secondary concentration unit in the high-pressure reverse osmosis system is 1.0~10.0MPa; the reverse osmosis membrane used in the high-pressure reverse osmosis system is selected from Dow BW membrane and / or SW membrane.

19. The 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; the concentration of lithium ions in the deborated lithium-rich solution is 5-10 g / L; the boron-saturated adsorption column is subjected to acid desorption and evaporation crystallization treatment to obtain boric acid.

20. The method according to claim 19, 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.

21. The method according to claim 1, characterized in that Specifically include: A sodium phosphate solution is added to the boron-removed lithium-rich solution, and a co-precipitation reaction is carried out under the conditions of an ultrasonic frequency of 10-50 kHz, an ultrasonic power of 100-1000 W, a pH of 8-12, a stirring rate of 50-200 rpm, and a temperature of 80-110° C., followed by nucleation, aging, filtering, washing, and drying to obtain battery-grade lithium phosphate.

22. The method according to claim 21, characterized in that: The ultrasonic frequency is 20-40 kHz; the ultrasonic power is 300-800 W; the stirring rate is 100-150 rpm; the temperature is 90-100° C.; and the ultrasonic time during the coprecipitation reaction is 10-60 min.

23. The method according to claim 21, characterized in that: The mass concentration of the sodium phosphate solution is 10-30%.

24. The method according to claim 21, characterized in that: The washing liquid used in the washing treatment includes water and a dispersant, and the dispersant is selected from polyethylene glycol and / or ethanol dispersant.

25. The method according to claim 1, characterized in that: The purity of the battery-grade lithium phosphate is above 99.5%, and the particle size of the battery-grade lithium phosphate is below 8 μm.

26. The method according to claim 1, characterized in that Also includes: Firstly, the carbonate salt lake raw brine or lithium carbonate precipitation mother liquor is 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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