Method for preparing lithium dihydrogen phosphate from lithium-containing brine and recycling lithium dihydrogen phosphate

Abstract

The invention belongs to the field of lithium extraction, and particularly relates to a method for preparing lithium dihydrogen phosphate and recycling lithium dihydrogen phosphate from lithium-containing brine, which comprises the following steps: capturing the lithium-containing brine by using modified silicon dioxide aerogel, and then eluting by using acid liquor to obtain a lithium-rich solution; carrying out first-stage precipitation treatment on the lithium-rich solution and water-soluble phosphate to obtain a first-stage precipitate; carrying out transformation treatment on the first-section precipitate by adopting a phosphoric acid solution to obtain lithium dihydrogen phosphate; the modified silicon dioxide aerogel is obtained by carrying out high-temperature and high-pressure modification treatment on a modifier and silicon dioxide gel in an oxygen-containing atmosphere; the modifier comprises a Mn source and / or a Ti source; the temperature of the modification treatment is 300-450 DEG C, and the pressure of the modification treatment is 15-35 MPa; the pH value of the first-stage precipitation process is 10-13. According to the method, lithium in the lithium-containing brine can be selectively extracted, lithium dihydrogen phosphate can be obtained at high yield, and lithium dihydrogen phosphate can be subjected to physical and chemical modification, so that ORR, photocatalysis and electrochemical performance of materials prepared by recycling can be accidentally improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium recovery, and particularly relates to the field of resource utilization of lithium-containing brine. BACKGROUND

[0002] Lithium is an important resource, which is widely used in electronic products, electric vehicles, aerospace, military equipment and other fields.

[0003] Lithium leaching and recovery from lithium ore is the main way to obtain lithium materials, but lithium ore is a non-renewable resource, so recovering lithium from lithium-containing waste such as waste batteries also has specific industrial value.

[0004] The existing methods for recovering lithium mainly include physical method, chemical method and biological method. The physical method mainly includes adsorption, extraction, etc. The chemical method mainly includes roasting, precipitation, electrolysis, etc. The biological method uses the action of microorganisms or enzymes to selectively dissolve and precipitate lithium ions.

[0005] The physical method has great application prospect in industry due to its simple operation and easy industrialization. The existing technology also reports many adsorption recovery processes of lithium. For example, the Chinese patent document with publication number CN114558557A discloses a lithium extraction adsorption particle for lithium in natural brine based on molecular sieve adsorbent and a preparation method thereof, which specifically records that the adsorption particle includes sodium silicate bonded aluminum hydroxide molecular sieve or molecular sieve coupled with silicon dioxide aerogel. For another example, the patent document with publication number WO2025129489A1 discloses a lithium-containing salt water through lithium adsorbent.

[0006] In summary, the existing technology reports some lithium extraction methods for lithium solution, but the existing methods mainly focus on the recovery effect of lithium, and less attention is paid to how to directly and efficiently resource utilization. The existing technology has not solved the problem of preparing lithium dihydrogen phosphate from lithium solution and resource utilization in ORR, photocatalysis and other aspects. SUMMARY

[0007] In view of the problems existing in the prior art, the first object of the present application is to provide a method for preparing lithium dihydrogen phosphate from lithium-containing brine, which aims to prepare lithium dihydrogen phosphate from lithium-containing brine.

[0008] The second object of the present application is to provide a method for preparing lithium dihydrogen phosphate from lithium-containing brine and resource utilization, which aims to resource utilization of the prepared lithium dihydrogen phosphate to prepare ORR, photocatalysis, LFP material and other materials.

[0009] The lithium-containing brine targeted by the present application is an aqueous solution containing lithium ions, impurity ions and halogen ions, which is usually the residual solution after lithium extraction from lithium leaching solution, and the lithium content thereof is usually low, which is difficult to be directly carbonized and precipitated. For this low-grade lithium-containing brine, using adsorption materials to enrich it is beneficial to its resource recovery, but the existing adsorption materials are usually not suitable for the enrichment and extraction of this type of low-grade lithium-containing brine, in addition, the existing recovery ideas are usually to extract high-quality lithium products, and there are few ideas for direct high-value resource utilization. In view of the current situation of the industry, the present application provides the following improved ideas:

[0010] The method for preparing lithium dihydrogen phosphate from lithium-containing brine comprises the following steps: the lithium-containing brine is captured and treated (also referred to as adsorption treatment) by modified silica aerogel, and then eluted by acid solution to obtain a lithium-rich solution; the lithium-rich solution and a water-soluble phosphate are subjected to first-stage precipitation treatment to obtain a first-stage precipitate; and the first-stage precipitate is subjected to transformation treatment by a phosphoric acid solution to obtain lithium dihydrogen phosphate;

[0011] The modified silica aerogel is obtained by high-temperature and high-pressure modification treatment of a modifier and a silica gel in an oxygen-containing atmosphere; the modifier comprises a Mn source and / or a Ti source; the temperature of the modification treatment is 300-450℃, and the pressure is 15-35MPa;

[0012] The pH of the first-stage precipitation process is 10-13.

[0013] The present application innovatively shows that the use of the modified silica aerogel can selectively extract lithium from the lithium-containing brine, improve the recovery rate of lithium, and in combination with subsequent elution, first-stage precipitation and transformation treatment, obtain lithium dihydrogen phosphate at a high yield, and further facilitate the physicochemical modification of lithium dihydrogen phosphate to prepare functional materials such as ORR, photocatalysis and LFP with excellent performance.

[0014] In the present application, the lithium-containing brine is an aqueous solution containing lithium ions, impurity elements and halogen elements, the impurity elements include at least one of N, S and P, and the halogen elements include at least one of F and Cl; the content of lithium is below 0.2 g / L (for example, it can be 0.05-0.2 g / L), the content of impurity elements is 10-100 ppm, and the content of halogen is 0.05-0.2 g / L.

[0015] The silica gel can be prepared based on known methods, for example, the silica gel can be obtained by acid treatment of a silicate. The silicate can be at least one of ethyl silicate, propyl silicate and butyl silicate. The acid in the acid treatment process can be a mineral acid, for example, it can be hydrochloric acid.

[0016] The molar ratio of the silicate to the acid can be 1:0.01-0.05.

[0017] The solvent of the acid treatment process can be an alcohol-water mixed solvent, wherein the alcohol can be, for example, ethanol. The molar ratio of the alcohol and water in the alcohol-water solvent can be reasonably controlled as required, for example, can be 0.5-2:1.

[0018] In the present application, the silica aerogel is treated at high temperature and high pressure under a modifier, which is beneficial to optimize the physicochemical structure and network of the material, thus being beneficial to the extraction and elution of lithium and beneficial to beneficial modification thereof, thus being beneficial to obtaining lithium dihydrogen phosphate with greater resource value in high yield.

[0019] The modifier is one of tetrabutyl titanate, manganese sulfate and potassium permanganate.

[0020] The weight ratio of the modifier to the silica in the silica gel is 0.01-0.15:1; further can be 0.05-0.1:1.

[0021] The oxygen-containing atmosphere can be, for example, air.

[0022] In the present application, the temperature of the modification treatment is 350-450℃, and the pressure is 20-30MPa.

[0023] The modification time is 1-10h, further can be 3-6h.

[0024] In the present application, the acid liquid is at least one of hydrochloric acid and sulfuric acid; the concentration of the solute thereof is not particularly required, for example, can be 0.1-1M.

[0025] In the present application, the water-soluble phosphate salt includes at least one of sodium phosphate and ammonium phosphate.

[0026] In the present application, the amount of the water-soluble phosphate salt is not less than the theoretical amount of precipitating lithium in the lithium-rich solution, for example, considering the cost, can be 1-1.5 times of the theoretical amount; further can be 1-1.1 times.

[0027] In the present application, based on known means, the obtained first-stage precipitate is transformed into lithium dihydrogen phosphate with a phosphoric acid solution. For example, the first-stage precipitate and the phosphoric acid solution can be mixed to transform and prepare lithium dihydrogen phosphate; then can be directly used in the form of a solution, or based on conventional means such as evaporation, the lithium dihydrogen phosphate solid product is recovered.

[0028] In the present application, the amount of the phosphoric acid is 1-1.1 times, further can be 1-1.05 times of the molar amount of converting lithium phosphate into lithium dihydrogen phosphate.

[0029] In the present application, the pH at the transformation endpoint can be 4-5.

[0030] The application also provides a method for preparing lithium dihydrogen phosphate and recycling by using lithium-containing brine, wherein the lithium-containing brine is treated by the method to obtain lithium dihydrogen phosphate, and then the lithium dihydrogen phosphate is used in at least one of ORR materials, photocatalytic materials and lithium iron phosphate.

[0031] In the application, the step of recycling to prepare the ORR material is that the Pt nanomaterial and the prepared lithium dihydrogen phosphate are mixed in liquid phase, dried, and then calcined under an oxygen-containing atmosphere to obtain the ORR material.

[0032] In the application, the Pt nanomaterial and the prepared lithium dihydrogen phosphate are mixed and then calcined under an oxygen-containing atmosphere at a low temperature, so that a modified layer with excellent interface stability is formed based on the in-situ conversion of lithium dihydrogen phosphate, thereby improving the ORR performance.

[0033] In the application, the solvent for the liquid phase mixing can be water.

[0034] In the application, the weight ratio of the Pt nanomaterial to the lithium dihydrogen phosphate is 0.5-2:1.

[0035] Preferably, the oxygen-containing atmosphere is air.

[0036] Preferably, the calcination temperature is 300-500 ℃.

[0037] Preferably, the calcination time is 2-4 h.

[0038] In the application, the step of recycling to prepare the photocatalytic material is that a zinc hydroxide colloid is obtained, then the zinc hydroxide colloid and the prepared LiH2PO4 are mixed to obtain a hydrothermal reaction, and then the Li3PO4@ZnO photocatalytic material is prepared through heat treatment.

[0039] In the application, the preparation step of the zinc hydroxide colloid is that Zn(NO3)2 is dissolved in deionized water to prepare a solution with a certain concentration, ammonia water is slowly added dropwise under stirring until the pH of the solution is 9-10, and the solution is continuously stirred and aged for 1-2 hours to obtain the zinc hydroxide colloid.

[0040] In the application, the molar ratio of LiH2PO4 to zinc hydroxide is 0.5-2:10.

[0041] The temperature of the hydrothermal reaction is 120-180 ℃.

[0042] The time of the hydrothermal reaction is 12-24 hours.

[0043] The temperature of the heat treatment is 300-500 ℃.

[0044] The time of the heat treatment is 1-5 h.

[0045] In the present application, the step of preparing the lithium iron phosphate material in a resourceful manner is as follows: subjecting the prepared LiH2PO4, ferrous source, carbon source and reducing agent to two-stage calcination treatment to prepare the lithium iron phosphate;

[0046] Preferably, the ferrous source is at least one of ferrous organic acid salt, ferrous sulfate, ferrous nitrate.

[0047] The carbon source includes at least one of monosaccharide, disaccharide, polysaccharide and polymer.

[0048] The reducing agent is, for example, an organic reducing agent, which can include components such as ascorbic acid.

[0049] In the present application, the molar ratio of LiH2PO4, ferrous source, carbon source and reducing agent can be reasonably controlled as required, for example, it can be 1:0.95~1.05:0.1~1:0.05~0.2; further, it can be 1:1:0.4~0.6:0.1~0.15.

[0050] The two-stage calcination process includes a first-stage calcination process at a temperature of 300~400℃ and a second-stage calcination process at a temperature of 600~700℃.

[0051] The time of the first-stage calcination process is 1~8h; the time of the second-stage calcination process is 5~15h.

[0052] Beneficial effects

[0053] The present application innovatively shows that, in addition to being able to selectively extract lithium from lithium-containing brine and improve the recovery rate of lithium, the modified silica aerogel can also be used for subsequent elution, first-stage precipitation and transformation treatment, which is beneficial to the physicochemical modification and optimization of lithium dihydrogen phosphate, and can unexpectedly improve the performance of the ORR, photocatalysis and lithium iron phosphate functional materials of the resourcefully prepared material. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 XRD pattern of lithium dihydrogen phosphate prepared in Example 1;

[0055] Figure 2 Thermogravimetric pattern of silica aerogel before and after Mn modification in Example 1. DETAILED DESCRIPTION

[0056] The present application will be further described in detail below in combination with specific embodiments, but the present application is not limited to the following embodiments.

[0057] As a scheme that can be cited in the present application, the lithium-containing brine after lithium precipitation from the spent battery acid leaching solution is a brine containing 0.05-0.1 g / L of Li, 20-50 ppm of total content of N, S and P heteroelements, and 0.05-0.1 g / L of total content of F and Cl.

[0058] The silica gel preparation method is as follows: taking tetraethyl orthosilicate (TEOS) as a precursor, and using an acid catalysis sol-gel method to prepare a silica wet gel: first, accurately take reagents according to the molar ratio of TEOS:EtOH:H2O:HCl = 1:4:4:0.01. Mix the deionized water, ethanol and dilute hydrochloric acid and stir, and use a pH meter to confirm that the pH value of the mixed solution is in the acidic range of 2-4. Then, slowly add TEOS to the mixed solution under continuous stirring, and react in a 40-60°C water bath for 1-2 hours until the solution becomes a clear transparent sol. Stop stirring, transfer the sol into a wide-mouth container and loosely cover, and place in a vibration-free environment for standing. After several hours to several days, the sol loses fluidity and forms a transparent jelly-like wet gel. Finally, age the wet gel in the original solution for 24-48 hours to strengthen its network structure, and obtain the final silica wet gel product.

[0059] The weight of the silica gel is calculated based on the silica therein.

[0060] The amount of the modified aerogel can be reasonably adjusted according to conventional adsorption means, and lithium therein can be fully captured (for example, the lithium in the mother liquor after adsorption is below 30 ppm). Considering the cost, it can be 3-5 g / L.

[0061] Example 1

[0062] Step (1):

[0063] After mixing the silica wet gel with the modifier (manganese sulfate, wherein the weight ratio of the modifier to the silica is 0.05:1), heat treatment is performed in air at 380°C under a closed condition of 22.5 MPa for 5 hours to obtain the Mn-based modified silica aerogel, which has better thermal stability than the unmodified silica aerogel.

[0064] The lithium-containing brine is placed in a beaker, and the Mn-based silica aerogel is added, and enrichment is performed for 30 minutes, and then filtration is performed to obtain a lithium-rich solid phase.

[0065] Step (2):

[0066] The lithium-rich solid phase is placed in a beaker, 0.5M dilute hydrochloric acid is added for sufficient washing, and then filtration is performed to obtain a lithium-rich solution.

[0067] Step (3):

[0068] The lithium-rich solution was placed in a beaker, sodium phosphate was added (1.05-1.1 times the theoretical molar amount of precipitated lithium), the pH was adjusted to 11 with sodium hydroxide, and it was allowed to stand for 30 min, then filtered to obtain lithium phosphate filter residue;

[0069] Step (4):

[0070] The lithium phosphate filter residue from step (3) was placed in a beaker, 20wt.% phosphoric acid solution (1.02-1.05 times the theoretical amount) was added, and it was allowed to stand for 3 h, then vacuum evaporation was performed at 90±10°C to obtain LiH2PO4.

[0071] ICP detected that the yield of lithium dihydrogen phosphate (LiH2PO4) was 97%, and the purity was 97.8%.

[0072] Step (5): Resource preparation of LFP:

[0073] The LiH2PO4: FeSO4·7H2O: ascorbic acid prepared in step 4 were mixed in a molar ratio of 1:1:0.5:0.1 to obtain a slurry, the slurry was dried in a vacuum oven or a forced air drying oven at 60-80°C to obtain a dry gel or a solid mixture, and the dried precursor powder was subjected to first-stage heat treatment under an inert atmosphere (N2or Ar). The temperature was 350°C, and the reaction time was 4 h. After grinding the pre-sintered powder, final heat treatment was performed under an inert atmosphere (Ar) at a temperature of 650°C for 10 h to obtain regenerated LFP. 12

[0074] In an argon atmosphere in a glove box, an aluminum foil was used as a current collector to coat a positive electrode sheet containing 90% of a regenerated positive electrode active material (weight ratio of regenerated positive electrode active material: conductive carbon black: PVDF was 90:5:5), a lithium sheet was used as a negative electrode, 1 mol / L LiPF6 in EC / EMC (volume ratio 1:1) was used as an electrolyte, and it was tested at room temperature.

[0075] The prepared lithium iron phosphate showed a reversible specific capacity of 175.3 mAh g -1 when used as a battery positive electrode.

[0076] Step (6): Resource preparation of ORR catalytic material:

[0077] ​The mixture of the Pt nanomaterial and the lithium dihydrogen phosphate prepared in step 4 in a weight ratio of 1:1 was calcined in an air atmosphere, wherein the calcination temperature was 400 ℃, and the calcination time was 3 h. The Pt nanoparticles were loaded on the lithium dihydrogen phosphate product carrier to prepare an ORR catalytic material. The proton conductivity of the prepared catalytic material was 0.035 S / cm.

[0078] Example 2

[0079] Compared with Example 1, the only difference is that in step 1, the modifier is potassium permanganate, the weight ratio of the modifier to the silica is 0.08:1, the modification temperature is 400 ℃, the modification pressure is 25.0 MPa, and the modification time is 4 h, to obtain the modified silica aerogel. The remaining steps are unchanged.

[0080] The yield of lithium dihydrogen phosphate was 97.7%, and the purity was 98.1%.

[0081] The regenerated LFP has a reversible specific capacity of 176.7 mAh g -1 .

[0082] The proton conductivity of the ORR catalytic material was 0.036 S / cm.

[0083] Example 3

[0084] Compared with Example 1, the only difference is that the modifier in step (1) is changed to tetrabutyl titanate, and the remaining steps are unchanged.

[0085] The yield of lithium dihydrogen phosphate was 98.5%, and the purity was 98.9%.

[0086] The regenerated LFP has a reversible specific capacity of 178 mAh g -1 .

[0087] The proton conductivity of the ORR catalytic material was 0.037 S / cm.

[0088] Example 4

[0089] Compared with Example 1, the only difference is that the modifier in step (1) is changed to a mixture of manganese sulfate and potassium permanganate in a ratio of 1:1, and the amount of the modifier and the remaining steps are unchanged.

[0090] The yield of lithium dihydrogen phosphate was 97.7%, and the purity was 98.1%.

[0091] The regenerated LFP has a reversible specific capacity of 179 mAh g -1 .

[0092] The proton conductivity of the ORR catalytic material was 0.041 S / cm.

[0093] Comparative Example 1

[0094] Comparative Example 1 except that in step 1, no modifier was added, and the rest of the steps were unchanged.

[0095] The yield of lithium dihydrogen phosphate was 53%, and the regenerated LFP had a reversible specific capacity of 114 mAh g

[0096] The yield of lithium dihydrogen phosphate was 53%, and the regenerated LFP had a reversible specific capacity of 114 mAh g -1 The proton conductivity of the ORR catalytic material was 0.014 S / cm.

[0097] Comparative Example 2

[0098] Comparative Example 1 except that in step 1, the active carbon was used as the modifier, and the modification step was that the modifier was mechanically dispersed inside the silica aerogel, which was used as an adsorbent to extract lithium from the lithium-containing brine, and the rest of the operations and parameters were the same as in Example 1.

[0099] The yield of lithium dihydrogen phosphate was 73.1%, and the regenerated LFP had a reversible specific capacity of 125 mAh g -1 The proton conductivity of the ORR catalytic material was 0.017 S / cm.

[0100] Comparative Example 3

[0101] Comparative Example 1 except that in step 1, 75% alcohol was used to extract the lithium-containing brine, followed by back extraction with 0.5M hydrochloric acid in step 2 to obtain a lithium-rich solution.

[0102] The yield of lithium dihydrogen phosphate was 89.7%, and the regenerated LFP had a reversible specific capacity of 143 mAh g -1 The proton conductivity of the ORR catalytic material was 0.029 S / cm.

[0103] Comparative Example 4

[0104] Comparative Example 1 except that in step 1, the modified silica aerogel was replaced with active carbon to solidify lithium from the lithium-containing brine, and the rest of the operations and parameters were the same as in Example 1.

[0105] The yield of lithium dihydrogen phosphate was 75.3%, and the regenerated LFP had a reversible specific capacity of 137 mAh g -1 The proton conductivity of the ORR catalytic material was 0.026 S / cm.

[0106] Comparative Example 5

[0107] Comparative Example 1 except that in step (1), the modifier was changed to iron chloride, and the rest of the steps were unchanged.

[0108] The yield of lithium dihydrogen phosphate is 80%, and the regenerated LFP has a reversible specific capacity of 140 mAh g -1 The proton conductivity of the ORR catalytic material is 0.028 S / cm.

[0109] Comparative Example 6

[0110] Compared with Example 1, the only difference is that in step 1, 5% H2-Ar atmosphere is used instead of air for modification, and other operations and parameters are the same as those in Example 1.

[0111] The yield of lithium dihydrogen phosphate is 53.4%, and the regenerated LFP has a reversible specific capacity of 119 mAh g -1 The proton conductivity of the ORR catalytic material is 0.021 S / cm.

[0112] Comparative Example 7

[0113] Compared with Example 1, the only difference is that in step 1, the pressure during modification is 1-2 MPa, and other operations and parameters are the same as those in Example 1.

[0114] The yield of lithium dihydrogen phosphate is 73.2%, and the regenerated LFP has a reversible specific capacity of 131 mAh g -1 The proton conductivity of the ORR catalytic material is 0.024 S / cm.

[0115] In summary, for the lithium-containing brine according to the present application, the special modified silica aerogel is used for treatment, which can obtain good low-grade brine capture and enrichment ability, in addition, it is also beneficial to retain some beneficial ingredients such as impurity elements and appropriate halogens, and the resources are prepared to obtain lithium dihydrogen phosphate, and it is not necessary to carry out deep purification, directly resources are prepared to obtain LFP and ORR catalytic material, which can synergistically improve the performance of regenerated LFP and ORR.

Claims

1. A method for preparing lithium dihydrogen phosphate using lithium-containing brine, characterized in that, Lithium-containing brine was captured by modified silica aerogel, followed by acid elution to obtain a lithium-rich solution. The lithium-rich solution and water-soluble phosphate were subjected to a first-stage precipitation treatment to obtain a first-stage precipitate. The first-stage precipitate was then transformed with phosphoric acid solution to obtain lithium dihydrogen phosphate. The modified silica aerogel is obtained by high-temperature and high-pressure modification of a modifier and silica gel in an oxygen-containing atmosphere; the modifier includes Mn source and / or Ti source; the modification temperature is 300~450℃ and the pressure is 15~35MPa. The pH during the first precipitation stage is 10-13.

2. The method for preparing lithium dihydrogen phosphate using lithium-containing brine as described in claim 1, characterized in that, The lithium-containing brine is an aqueous solution containing lithium ions, impurities, and halogens. The impurities include at least one of N, S, and P, and the halogens include at least one of F and Cl. The lithium content is below 0.2 g / L, the impurity element content is 10~100 ppm, and the halogen content is 0.05~0.2 g / L.

3. The method for preparing lithium dihydrogen phosphate using lithium-containing brine as described in claim 1, characterized in that, The modifier is one of tetrabutyl titanate, manganese sulfate, and potassium permanganate; Preferably, the weight ratio of the modifier to the silica gel is 0.01 to 0.15:

1.

4. The method for preparing lithium dihydrogen phosphate using lithium-containing brine as described in claim 3, characterized in that, In the modified silica aerogel, the modification treatment temperature is 350~450℃ and the pressure is 20~30MPa.

5. The method for preparing lithium dihydrogen phosphate using lithium-containing brine as described in claim 1, characterized in that, The acid solution is at least one of hydrochloric acid and sulfuric acid; the concentration of its solute is 0.1~1M.

6. The method for preparing lithium dihydrogen phosphate using lithium-containing brine as described in claim 1, characterized in that, Water-soluble phosphates include at least one of sodium phosphate and ammonium phosphate.

7. A method for preparing and utilizing lithium dihydrogen phosphate from lithium-containing brine, characterized in that, Lithium dihydrogen phosphate is obtained by treating lithium-containing brine using the method described in any one of claims 1 to 6, and then the lithium dihydrogen phosphate is used in at least one functional material among ORR materials, photocatalytic materials, and lithium iron phosphate.

8. The method for preparing and utilizing lithium dihydrogen phosphate from lithium-containing brine as described in claim 7, characterized in that, The steps for resource-based preparation of ORR materials are as follows: Pt nanomaterials and the prepared lithium dihydrogen phosphate liquid phase are mixed and dried, and then calcined in an oxygen-containing atmosphere to obtain the ORR materials. Preferably, the weight ratio of the Pt nanomaterial to lithium dihydrogen phosphate is 0.5~2:1; Preferably, the oxygen-containing atmosphere is air; Preferably, the roasting temperature is 300~500 ℃; Preferably, the roasting time is 2 to 4 hours.

9. The method for preparing and utilizing lithium dihydrogen phosphate from lithium-containing brine as described in claim 7, characterized in that, The steps for resource-based preparation of photocatalytic materials are as follows: zinc hydroxide colloid is obtained, then the zinc hydroxide colloid and the prepared LiH2PO4 are mixed and subjected to hydrothermal reaction, followed by heat treatment to obtain Li3PO4@ZnO photocatalytic material; The molar ratio of LiH2PO4 to zinc hydroxide is 0.5~2:10; The temperature for hydrothermal reactions is 120~180℃; The hydrothermal reaction takes 12 to 24 hours; The heat treatment temperature is 300~500℃; The heat treatment time is 1 to 5 hours.

10. The method for preparing and utilizing lithium dihydrogen phosphate from lithium-containing brine as described in claim 7, characterized in that, The steps for resource-based preparation of lithium iron phosphate materials are as follows: the obtained LiH2PO4, ferrous source, carbon source and reducing agent are subjected to two-stage calcination treatment to obtain lithium iron phosphate; Preferably, the ferrous source is at least one of ferrous organic acid salts, sulfates, and nitrates; The two-stage calcination process includes a first-stage calcination process at a temperature of 300~400℃ and a second-stage calcination process at a temperature of 600~700℃; The first calcination process takes 1-8 hours; the second calcination process takes 5-15 hours.

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