A method for integrated lithium recycling across the entire supply chain

Abstract

This disclosure provides a method for integrated lithium recycling across the entire chain. The method includes the following steps: (1) taking lithium-containing materials and reducing agents from waste lithium batteries, mixing them, and then roasting them to obtain calcined sand; (2) concentrating high-calcium chloride brine and adding sodium dihydrogen phosphate, then separating the solid and liquid to obtain dicalcium hydrogen phosphate and brine solution; (3) mixing the calcined sand and brine solution, then separating the solid and liquid to obtain calcium carbonate transformation residue and mixed solution, mixing the mixed solution and alkaline solution to adjust the pH, heating and stirring, and then separating the solid and liquid to obtain lithium phosphate precipitate and recovery liquid. The method described in this disclosure can extract lithium from high-calcium chloride brine and also recover lithium from waste lithium-ion batteries, thus realizing integrated lithium recycling across the entire chain.

Description

Technical Field

[0001] This disclosure pertains to the field of resource recycling and relates to a method for integrated lithium recycling across the entire supply chain. Background Technology

[0002] In recent years, lithium and its compounds have been widely used in many fields such as aerospace, electromechanical, high-energy batteries, and nuclear power generation. It is one of the country's most valuable green resources and strategic mineral resources.

[0003] Lithium resources are mainly found in lithium ores and salt lakes. Lithium extraction from salt lakes is less costly than from ores, making it a crucial source of lithium supply. Currently, mature methods for lithium extraction from salt lakes include precipitation, adsorption, membrane extraction, and extraction. Precipitation is the most mature and has a long history. The typical process flow is: brine → evaporation and concentration → boron removal → calcium and magnesium removal → sodium carbonate precipitation of lithium. While this method has low production costs, it can only be used to treat brine with a low magnesium-to-lithium ratio and high lithium concentration, and the lithium recovery rate is relatively low.

[0004] CN114906864A discloses a method for extracting lithium from high-calcium chloride-type salt lake brine. The method includes: evaporating brine collected from brine wells in a pre-concentration tank under natural conditions, sequentially precipitating sodium chloride, potassium chloride, and carnallite (KCl·MgCl2) until the calcium ion concentration of the brine reaches 11-13%; concentration: further evaporating and concentrating the pre-concentrated brine in a concentration tank to precipitate calcium chloride crystals until the lithium ion concentration of the brine reaches 3-3.5%; boron removal by extraction: removing boron from the concentrated brine using an extraction process; calcium and magnesium removal: removing calcium and magnesium from the boron-removed brine using sodium hydroxide and sodium carbonate; lithium precipitation with sodium carbonate: continuously precipitating lithium with sodium carbonate solution in the solution after calcium and magnesium removal, with a precipitation reaction temperature of 70-95℃; centrifuging, filtering, and washing the slurry after lithium precipitation; and finally drying and packaging the washed lithium carbonate to obtain the lithium carbonate product.

[0005] CN113998715A discloses a method for extracting lithium from high-calcium lithium-containing raw materials, including the following steps: (1) Calcium precipitation: calcium-containing lithium-containing raw materials are added to a reaction vessel, and a calcium precipitant is added. The mixture is stirred to produce calcium sulfate crystals. Solid-liquid separation is performed to obtain decalcified lithium-containing mother liquor; (2) Nanofiltration: the decalcified lithium-containing mother liquor obtained in step (1) is further decalcified and other ≥2-valent ions are removed by nanofiltration through a nanofiltration system to obtain lithium-containing filtrate; (3) Evaporation and concentration: the lithium-containing filtrate obtained in step (2) is concentrated by evaporation to obtain lithium-rich concentrate.

[0006] The above-mentioned method uses precipitation to treat high-calcium chloride brine. The resulting calcium chloride has extremely strong hygroscopic properties, typically adsorbing more than 50% of its own weight in water. Therefore, during calcium chloride crystallization, a large amount of high-lithium-concentration brine is carried away through adsorption, resulting in a significant lithium loss rate, exceeding 30%. Currently, there is no effective method for recovering lithium from high-calcium chloride brine. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] The purpose of this disclosure is to provide a method for integrated lithium recycling across the entire supply chain. The method described in this disclosure can extract lithium from high-calcium-chloride salt lake brine while simultaneously recovering lithium from waste lithium-ion batteries, thus achieving integrated lithium recycling across the entire supply chain.

[0009] To achieve this purpose of disclosure, the following technical solution is adopted:

[0010] In a first aspect, embodiments of this disclosure provide a method for integrated lithium recycling across the entire supply chain, the method comprising the following steps:

[0011] (1) Take lithium-containing materials and reducing agents from waste lithium batteries, mix them together and then roast them to obtain calcined sand;

[0012] (2) After concentrating the high-calcium chloride brine, sodium dihydrogen phosphate is added, and solid-liquid separation is performed to obtain calcium phosphate salt and brine solution.

[0013] (3) The calcined sand and brine solution are mixed, and solid-liquid separation is performed to obtain calcium carbonate and mixed solution of transformation slag. The mixed solution and alkaline solution are mixed to adjust the pH, and after heating and stirring, solid-liquid separation is performed to obtain lithium phosphate precipitate and recovery solution.

[0014] The method described in this embodiment does not restrict the order of operation of steps (1) and (2). Step (1) can be performed first or step (2) can be performed first.

[0015] This embodiment of the invention adds sodium dihydrogen phosphate to the concentrated high-calcium chloride brine after evaporation, transforming the highly hygroscopic calcium chloride crystallized from the salt lake brine into non-hygroscopic calcium dihydrogen phosphate. This releases the highly concentrated brine absorbed by the calcium chloride, solving the problem of significant lithium loss caused by calcium chloride carrying high-concentration brine. The resulting brine is mixed with calcined slag obtained from the calcination of waste lithium battery cathode materials. Through precipitation conversion, residual calcium ions in the mixed solution A can be removed, while lithium carbonate in the calcined slag is dissolved, enabling the recovery of lithium from the calcined slag. This achieves two goals at once, ultimately yielding lithium dihydrogen phosphate and lithium chloride solutions. Adjusting the pH and temperature further yields lithium carbonate precipitate and lithium chloride solution, realizing integrated lithium recovery across the entire chain.

[0016] In one embodiment, the reducing agent in step (1) includes any one or a combination of at least two of carbon monoxide, coke powder, or carbon powder.

[0017] In one embodiment, the roasting temperature is 500 to 1000°C, for example: 500°C, 600°C, 700°C, 800°C, 900°C, or 1000°C.

[0018] In one embodiment, the roasting time is 2 to 4 hours, for example: 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0019] In one embodiment, the calcined sand in step (1) comprises a transition metal element and lithium carbonate.

[0020] In one embodiment, the high-calcium chloride brine in step (2) is concentrated to obtain calcium chloride crystals that have adsorbed a large amount of brine with a high lithium concentration.

[0021] In one embodiment, the concentration of brine adsorbed in the calcium chloride crystals is 25-35 g / L, for example: 25 g / L, 28 g / L, 30 g / L, 32 g / L or 35 g / L, etc.

[0022] In one embodiment, the phosphorus source comprises sodium dihydrogen phosphate.

[0023] In one embodiment, the molar ratio of the phosphorus source and calcium chloride crystals in step (2) is (2-2.1):1, for example: 2:1, 2.02:1, 2.05:1, 2.08:1 or 2.1:1, etc.

[0024] In one embodiment, the calcium phosphate salt in step (2) comprises calcium phosphate and / or calcium hydrogen phosphate.

[0025] In one embodiment, the brine solution comprises lithium chloride, lithium dihydrogen phosphate, sodium chloride, and partially dissolved calcium dihydrogen phosphate.

[0026] The equation for lithium recovery described in this embodiment is as follows:

[0027] CaCl2·2H2O+NaH2PO4==CaHPO4↓+2NaCl+2H2O+HCl

[0028] 3CaCl2·2H2O+2NaH2PO4==Ca3(PO4)2↓+2NaCl+2H2O+4HCl

[0029] Ca(H2PO4)2+Li2CO3==CaCO3↓+2LiH2PO4

[0030] 3LiH2PO4 + 6OH - ==Li3PO4+6H2O

[0031] In the recovery method described in this embodiment, a phosphorus source (e.g., sodium dihydrogen phosphate) reacts with calcium chloride to form calcium hydrogen phosphate and / or calcium phosphate precipitate. The residual calcium dihydrogen phosphate in the solution dissolves and reacts with subsequently added lithium carbonate to form calcium carbonate precipitate, which is then removed by solid-liquid separation.

[0032] In one embodiment, the roasted sand and brine in step (3) are mixed and then stirred.

[0033] In one embodiment, the stirring time is 0.5 to 1 hour, for example: 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour.

[0034] In one embodiment, sodium dihydrogen phosphate is added to the mixed solution in step (3).

[0035] In this embodiment, adding sodium dihydrogen phosphate in step (3) can maximize the complete precipitation of lithium ions in the mixed solution into lithium phosphate, reducing the residual lithium ions in the solution. If excess sodium dihydrogen phosphate is added in step (2), the solubility product formula will be used to calculate... Excessive hydrogen phosphate content will decrease the calcium ion concentration, resulting in insufficient calcium dihydrogen phosphate in the brine solution to react with the lithium phosphate in the calcined sand. This prevents the lithium carbonate from dissolving completely, thus leaving insufficient calcium ions dissolved in the water.

[0036] In one embodiment, the molar ratio of phosphorus to lithium ions in the mixed solution after the addition of sodium dihydrogen phosphate is (3.05–3.15):1, for example: 3.05:1, 3.08:1, 3.1:1, 3.12:1, or 3.15:1, etc.

[0037] In one embodiment, the alkaline solution in step (3) comprises ammonia.

[0038] In one embodiment, the molar concentration of the ammonia water is 3 to 5 mol / L, for example: 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L, etc.

[0039] In one embodiment, the pH is 8 to 9, for example: 8, 8.2, 8.5, 8.8 or 9, etc.

[0040] In one embodiment, the heating and stirring temperature in step (3) is 45 to 60°C, for example: 45°C, 48°C, 50°C, 55°C or 60°C.

[0041] In one embodiment, the heating and stirring time is 20 to 40 minutes, for example: 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0042] Compared with the prior art, this disclosure has the following beneficial effects:

[0043] (1) This disclosure solves the problem of significant lithium loss caused by calcium chloride carrying high-concentration brine after evaporation and concentration by adding sodium dihydrogen phosphate to the highly hygroscopic calcium chloride crystallized in the salt lake brine. This is achieved by converting the highly hygroscopic calcium chloride that crystallizes in the brine into non-hygroscopic calcium dihydrogen phosphate, thereby releasing the highly concentrated brine absorbed by the calcium chloride. Subsequently, solid-liquid separation is performed to obtain calcium dihydrogen phosphate precipitate and a lithium-containing mixed solution.

[0044] (2) The present invention mixes the obtained lithium mixed solution with the calcined sand of the positive electrode material of the waste lithium battery and removes the residual calcium ions in the mixed solution A by precipitation conversion, while dissolving the lithium carbonate in the calcined sand, thereby realizing the recovery of lithium in the calcined sand, achieving two goals at once.

[0045] (3) The method described in this disclosure achieves a lithium recovery rate of over 90%, which greatly reduces costs. Detailed Implementation

[0046] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0047] The solubility products of each substance in the embodiments of this disclosure are shown in Table 1 below:

[0048] Table 1

[0049]

[0050] Example 1

[0051] This embodiment provides a method for integrated lithium recycling across the entire supply chain, the method comprising the following steps:

[0052] (1) 1 kg of waste lithium-ion batteries were discharged, disassembled, crushed and screened to obtain lithium-containing materials (the average lithium content was 2%). Then carbon monoxide was added and reduced and roasted at 750°C for 3 hours to obtain calcined sand (nickel, cobalt and manganese elements and about 105.8 g of lithium carbonate).

[0053] (2) Place the high-calcium chloride brine in an evaporation and concentration tank, and collect 56.61 kg of calcium chloride crystals from the evaporation and concentration tank into a container (at this time, the calcium chloride crystals adsorb a large amount of brine with a high lithium concentration (30 g / L), the mass ratio of calcium chloride to brine is 2:1, so there are 37.74 kg of calcium chloride and 18.87 kg of brine); add 81.60 kg of sodium dihydrogen phosphate to the container (the molar ratio of calcium chloride to sodium dihydrogen phosphate is 1:2, and based on the solubility calculation, 1.45 mol of calcium dihydrogen phosphate will dissolve in the solution, and this concentration of calcium dihydrogen phosphate will just dissolve 105.8 g of lithium carbonate), stir for 30 min, at this time the solid is transformed into non-water-absorbing calcium dihydrogen phosphate, and the absorbed brine is released; at this time the brine contains lithium chloride, lithium dihydrogen phosphate, sodium chloride and partially dissolved calcium dihydrogen phosphate; then the solid and liquid are separated, the solid is calcium dihydrogen phosphate, and the solution is a brine solution of sodium chloride, lithium chloride, lithium dihydrogen phosphate and calcium dihydrogen phosphate (the brine solution contains Li + 5861g, or 87.73mol, requires 27.91mol of hydrogen phosphate to completely form a precipitate. There are already 2.9mol of hydrogen phosphate in the solution, so 25.01mol of hydrogen phosphate (equivalent to 3kg of sodium dihydrogen phosphate) needs to be added.

[0054] (3) The calcined sand and brine solution were mixed and stirred for 0.8 h. Solid-liquid separation was then performed to obtain a mixed solution containing sodium chloride, lithium dihydrogen phosphate and lithium chloride, and calcium carbonate from the transformation residue. Subsequently, 3.00 kg of sodium dihydrogen phosphate was added to the mixed solution, and after stirring evenly, 4 mol / L ammonia water was added dropwise to adjust the pH of the solution to 8.5. The solution was stirred at 50 °C for 30 min, and solid-liquid separation was performed to obtain lithium phosphate precipitate.

[0055] Example 2

[0056] This embodiment provides a method for integrated lithium recycling across the entire supply chain, the method comprising the following steps:

[0057] (1) 1 kg of waste lithium-ion batteries were discharged, disassembled, crushed and screened to obtain lithium-containing materials (the average lithium content was 2%). Then carbon powder was added and reduced and roasted at 500°C for 4 hours to obtain calcined sand (nickel, cobalt and manganese elements and about 105.8 g of lithium carbonate).

[0058] (2) Place the high-calcium chloride brine in an evaporation and concentration tank, and collect 56.61 kg of calcium chloride crystals from the evaporation and concentration tank into a container (at this time, the calcium chloride crystals adsorb a large amount of brine with a high lithium concentration (25 g / L), the mass ratio of calcium chloride to brine is 2:1, so there are 37.74 kg of calcium chloride and 18.87 kg of brine); add 85.68 kg of sodium dihydrogen phosphate to the container (the molar ratio of calcium chloride to sodium dihydrogen phosphate is 1:2.1, and based on the solubility calculation, 1.52 mol of calcium dihydrogen phosphate will dissolve in the solution, and this concentration of calcium dihydrogen phosphate will just dissolve 111.1 g of lithium carbonate), stir for 30 min, at this time the solid is transformed into non-water-absorbing calcium dihydrogen phosphate, and the absorbed brine is released; at this time the brine contains lithium chloride, lithium dihydrogen phosphate, sodium chloride and partially dissolved calcium dihydrogen phosphate; then the solid and liquid are separated, the solid is calcium dihydrogen phosphate, and the solution is a brine solution of sodium chloride, lithium chloride, lithium dihydrogen phosphate and calcium dihydrogen phosphate (the brine solution contains Li + 5861g, or 87.73mol, requires 27.91mol of hydrogen phosphate to completely form a precipitate. There are already 2.9mol of hydrogen phosphate in the solution, so 25.01mol of hydrogen phosphate (equivalent to 3kg of sodium dihydrogen phosphate) needs to be added.

[0059] (3) The calcined sand and brine solution were mixed and stirred for 0.8 h. Solid-liquid separation was then performed to obtain a mixed solution containing sodium chloride, lithium dihydrogen phosphate and lithium chloride, and calcium carbonate from the transformation residue. Subsequently, 3.00 kg of sodium dihydrogen phosphate was added to the mixed solution, and after stirring evenly, 3 mol / L ammonia water was added dropwise to adjust the pH of the solution to 8. The solution was stirred at 45 °C for 40 min, and solid-liquid separation was performed to obtain lithium phosphate precipitate.

[0060] Example 3

[0061] This embodiment provides a method for integrated lithium recycling across the entire supply chain, the method comprising the following steps:

[0062] (1) 0.3 kg of waste lithium-ion batteries were discharged, disassembled, crushed and screened to obtain lithium-containing materials (the average lithium content was 2%). Then carbon monoxide was added and reduced and roasted at 750°C for 3 h to obtain calcined sand (nickel, cobalt and manganese elements and about 31.74 g of lithium carbonate).

[0063] (2) Place the high-calcium chloride brine in an evaporation and concentration tank, and collect 56.61 kg of calcium chloride crystals from the evaporation and concentration tank into a container (at this time, the calcium chloride crystals adsorb a large amount of brine with a high lithium concentration (30 g / L), and the mass ratio of calcium chloride to brine is 2:1, so there are 37.74 kg (34 mol) of calcium chloride and 18.87 kg of brine); add 82.8 kg (69 mol) of sodium dihydrogen phosphate to the container (the molar ratio of calcium chloride to sodium dihydrogen phosphate is 1:2.03, based on the dissolution...). The calculation showed that 0.41 mol of calcium dihydrogen phosphate (19 L of aqueous solvent) would dissolve in the solution. This concentration of calcium dihydrogen phosphate would just dissolve 30.3 g of lithium carbonate (0.41 mol). After stirring for 30 min, the solid was transformed into non-hydrophilic calcium dihydrogen phosphate, releasing the absorbed brine. At this point, the brine contained lithium chloride, lithium dihydrogen phosphate, sodium chloride, and partially dissolved calcium dihydrogen phosphate. Then, solid-liquid separation was performed. The solid was calcium dihydrogen phosphate, and the solution was an aqueous solution of sodium chloride, lithium chloride, lithium dihydrogen phosphate, and calcium dihydrogen phosphate brine.

[0064] (3) The calcined sand and brine solution were mixed and stirred for 0.8 h. Solid-liquid separation was then performed to obtain a mixed solution containing sodium chloride, lithium dihydrogen phosphate and lithium chloride, and calcium carbonate from the transformation residue. Subsequently, 4 mol / L ammonia was added dropwise to the mixed solution to adjust the pH to 8.5. The solution was stirred at 50 °C for 30 min, and solid-liquid separation was performed to obtain lithium phosphate precipitate.

[0065] Example 4

[0066] This embodiment provides a method for integrated lithium recycling across the entire supply chain, the method comprising the following steps:

[0067] (1) 1 kg of waste lithium-ion batteries were discharged, disassembled, crushed and screened to obtain lithium-containing materials (the average lithium content was 2%). Then carbon monoxide was added and reduced and roasted at 750°C for 3 hours to obtain calcined sand (nickel, cobalt and manganese elements and about 105.8 g of lithium carbonate).

[0068] (2) Place the high-calcium chloride brine in an evaporation and concentration tank, and collect 56.61 kg of calcium chloride crystals from the evaporation and concentration tank into a container (at this time, the calcium chloride crystals adsorb a large amount of brine with a high lithium concentration (30 g / L), and the mass ratio of calcium chloride to brine is 2:1, so there are 37.74 kg (34 mol) of calcium chloride and 18.87 kg of brine); add 87.6 kg (73 mol) of sodium dihydrogen phosphate to the container (the molar ratio of calcium chloride to sodium dihydrogen phosphate is 1: 2.15. Based on solubility calculations, 0.127 mol of calcium dihydrogen phosphate will dissolve in the solution (this concentration of calcium dihydrogen phosphate will just dissolve 9.3 g of lithium carbonate). After stirring for 30 minutes, the solid transforms into non-hygroscopic calcium dihydrogen phosphate, releasing the absorbed brine. At this point, the brine contains lithium chloride, lithium dihydrogen phosphate, sodium chloride, and partially dissolved calcium dihydrogen phosphate. Then, solid-liquid separation is performed; the solid is calcium dihydrogen phosphate, and the solution is an aqueous solution of sodium chloride, lithium chloride, lithium dihydrogen phosphate, and calcium dihydrogen phosphate brine.

[0069] (3) The calcined sand and brine solution were mixed and stirred for 0.8 h. Solid-liquid separation was then performed to obtain a mixed solution containing sodium chloride, lithium dihydrogen phosphate and lithium chloride, and calcium carbonate from the transformation residue. Subsequently, 3.00 kg of sodium dihydrogen phosphate was added to the mixed solution, and after stirring evenly, 4 mol / L ammonia water was added dropwise to adjust the pH of the solution to 8.5. The solution was stirred at 50 °C for 30 min, and solid-liquid separation was performed to obtain lithium phosphate precipitate.

[0070] Example 5

[0071] The only difference between this embodiment and Example 1 is that the pH in step (3) is 7.5, while the other conditions and parameters are exactly the same as in Example 1.

[0072] Example 6

[0073] The only difference between this embodiment and Example 1 is that the pH in step (3) is 9.5, while the other conditions and parameters are exactly the same as in Example 1.

[0074] Comparative Example 1

[0075] The only difference between this comparative example and the embodiment is that the sodium dihydrogen phosphate in step (1) is replaced with the same amount of sodium sulfate, while the other conditions and parameters are exactly the same as in Example 1.

[0076] Performance testing:

[0077] The lithium recovery results of the methods described in Examples 1-6 are shown in Table 2:

[0078] Table 2

[0079]

[0080]

[0081] As can be seen from Table 2, the lithium recovery rate of the method described in this disclosure reaches more than 70%. By controlling the pH of step (3) and the timing of adding sodium dihydrogen phosphate, the lithium recovery rate reaches more than 90%, which greatly reduces the cost and realizes the recovery of lithium from waste lithium-ion batteries.

[0082] Comparing Examples 1 and 3, it can be seen that in step (3) of this disclosure, sodium dihydrogen phosphate is not added, which results in the lithium ions in the mixed solution not being completely precipitated into lithium phosphate, thus resulting in a large number of lithium ions remaining in the solution.

[0083] A comparison of Examples 1 and 4 shows that, in the method described in this disclosure, if excess sodium dihydrogen phosphate is added in step (2), the solubility product formula can be used to calculate... Excessive hydrogen phosphate content reduces calcium ion concentration, resulting in insufficient calcium dihydrogen phosphate in the brine solution to react with lithium phosphate in the calcined ore. This prevents complete dissolution of lithium carbonate, leading to insufficient calcium ions dissolved in the water. Of course, lithium recovery can be further improved by reducing the amount of calcined ore added or increasing the brine flow rate.

[0084] Comparing Examples 1 and 5-6, it can be seen that in the method described in this disclosure, the pH of step (3) affects the lithium recovery rate. When the pH is controlled at 8-9, the lithium recovery rate is higher. If the pH is too low, the lithium phosphate cannot be completely precipitated. If the pH is too high, it will not improve the lithium phosphate recovery rate, but may instead cause other cationic impurities to precipitate.

[0085] A comparison of Example 1 and Comparative Example 1 shows that in the Comparative Example, after adding sodium sulfate to react with calcium chloride to produce calcium sulfate, a large amount of brine remains within the calcium sulfate crystals due to the strong hygroscopicity of calcium sulfate, resulting in a low lithium recovery rate. This disclosure addresses this issue by adding sodium dihydrogen phosphate to the concentrated, high-calcium chloride brine after evaporation, transforming the highly hygroscopic calcium chloride crystallized from the salt lake brine into non-hygroscopic calcium dihydrogen phosphate. This releases the highly concentrated brine absorbed by calcium chloride, solving the problem of significant lithium loss caused by calcium chloride carrying away highly concentrated brine.

Claims

1. A method for integrated lithium recycling across the entire supply chain, the method comprising the following steps: (1) Take lithium-containing materials and reducing agents from waste lithium batteries, mix them together and then roast them to obtain calcined sand; (2) After concentrating the high-calcium chloride brine, a phosphorus source was added, and solid-liquid separation was performed to obtain calcium phosphate salt and brine solution; (3) Mix the calcined sand and brine solution, and then separate the solid and liquid to obtain calcium carbonate transformation residue and mixed solution. Mix the mixed solution and alkaline solution to adjust the pH, and then separate the solid and liquid to obtain lithium phosphate precipitate and recovery solution after heating and stirring. In step (2), the high-calcium chloride brine is concentrated to obtain calcium chloride crystals that adsorb a large amount of brine with a high lithium concentration. The concentration of brine adsorbed in the calcium chloride crystals is 25-35 g / L. The phosphorus source includes sodium dihydrogen phosphate, and the molar ratio of the phosphorus source to the calcium chloride crystals is (2-2.1):

1.

2. The method as described in claim 1, wherein, The reducing agent in step (1) includes any one or a combination of at least two of carbon monoxide, coke powder, or carbon powder.

3. The method as described in claim 1, wherein, The roasting temperature is 500–1000℃.

4. The method of claim 1, wherein, The roasting time is 2 to 4 hours.

5. The method of claim 1, wherein, The calcined sand in step (1) includes transition metal elements and lithium carbonate.

6. The method of claim 1, wherein, The brine solution in step (2) includes lithium chloride, lithium dihydrogen phosphate, sodium chloride and partially dissolved calcium dihydrogen phosphate.

7. The method of claim 1, wherein, The calcium phosphate salt includes calcium phosphate and / or calcium hydrogen phosphate.

8. The method of claim 1, wherein, The roasted sand and brine in step (3) are mixed and stirred.

9. The method of claim 8, wherein, The stirring time is 0.5 to 1 hour.

10. The method of claim 1, wherein, Sodium dihydrogen phosphate is added to the mixed solution in step (3).

11. The method of claim 10, wherein, The molar ratio of phosphorus to lithium ions in the mixed solution after the addition of sodium dihydrogen phosphate is (3.05–3.15):

1.

12. The method of claim 1, wherein, The alkaline solution in step (3) includes ammonia.

13. The method of claim 12, wherein, The molar concentration of the ammonia water is 3-5 mol / L.

14. The method of claim 1, wherein, The pH value in step (3) is 8 to 9.

15. The method of claim 1, wherein, The heating and stirring temperature in step (3) is 45-60℃.

16. The method of claim 1, wherein, The heating and stirring time in step (3) is 20 to 40 minutes.

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