Resource utilization method of potassium-sodium-lithium mixed salt

Abstract

The invention discloses a potassium-sodium-lithium mixed salt resource utilization method, and belongs to the technical field of industrial waste treatment. According to the method, low-content lithium in the mixed salt is efficiently recovered at a low cost, potassium and sodium are effectively separated and sodium carbonate is recovered by a reasonable technology, so that high-purity anhydrous sodium sulphate is prepared, the lithium recovery rate is greater than 90%, the sodium carbonate recovery rate is greater than 80%, the potassium recovery rate is greater than 90%, the content of lithium carbonate in crude lithium is 10-60%, and the purity of sodium bicarbonate is gt; the purity of the anhydrous sodium sulphate is gt; the average value gt of the K2SO4 content in the recovered sylvite; 38%. The process provided by the invention is low in overall energy consumption, greatly reduces the investment cost, is green and environment-friendly, has excellent economic benefits, and provides a systematic solution for treatment of lithium potassium sodium mixed salt or lithium precipitation mother liquor.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial waste treatment, and in particular relates to a method for resource utilization of potassium, sodium and lithium mixed salts. Background Art

[0002] When extracting lithium from spodumene or lepidolite ore, a lithium sulfate solution is obtained through roasting, leaching, and impurity removal. Lithium carbonate is then precipitated using an excess of sodium carbonate. The post-precipitation solution is primarily sodium sulfate, but also contains sodium carbonate, potassium introduced from the ore, dissolved lithium carbonate, and other impurities. A common treatment method for this post-precipitation solution is a double evaporation and crystallization process. The first evaporation and crystallization process produces relatively pure sodium sulfate solids. The mother liquor undergoes a second evaporation and crystallization process, producing a slightly yellowish mixed salt containing sodium sulfate, sodium carbonate, potassium sulfate, and a small amount of lithium. Currently, the treatment of this type of mixed salt or the mother liquor from the first evaporation crystallization is quite difficult for several reasons: First, the lithium content in the mixed salt is only about 0.1%, and conventional lithium extraction processes, such as adsorption or extraction, are not economically effective due to the falling price of lithium salts. Second, the use of potassium-containing sodium sulfate products is limited and difficult to process, and the potassium-sodium separation process needs to be improved. Third, some companies use sulfuric acid to neutralize sodium carbonate, converting the economically valuable sodium carbonate into low-value sodium sulfate, which is not worth the effort. A low-cost process for extracting sodium carbonate is urgently needed. To address the current difficulties in treating potassium-sodium-lithium mixed salts, the present invention provides a systematic solution. Summary of the Invention

[0003] In view of the above-mentioned prior art, the present invention provides a method for resource utilization of potassium, sodium and lithium mixed salts to solve the technical problem of difficulty in treating potassium, sodium and lithium mixed salts.

[0004] In order to achieve the above object, the present invention provides a method for resource utilization of potassium, sodium and lithium mixed salts, comprising the following steps:

[0005] S1: Mixing a potassium, sodium, and lithium mixed salt with a solvent 1, wherein the solvent 1 is a crystallization mother liquor 2 or water, and the crystallization mother liquor 2 is obtained from the subsequent S4; then heating the mixed system to 70-100°C, stirring at this temperature for 20-100 minutes, and filtering while hot to obtain a solid 1 and a filtrate 1; stirring the filtrate 1 and cooling it to 20-40°C and maintaining it for 1-2 hours, and then filtering it to obtain a potassium-containing salt 1 and a crystallization mother liquor 1; introducing CO2 into the crystallization mother liquor 1 under stirring to carbonize the sodium carbonate in the crystallization mother liquor 1, filtering it to obtain a solid 3 and a filtrate 3; washing and drying the solid 3 to obtain sodium bicarbonate; adjusting the pH of the filtrate 3 to 6.5-7.5, and then evaporating and crystallizing it to obtain a potassium-containing salt 2;

[0006] S2: mixing the solid 1 with the solvent 2, stirring and dissolving at 40-65°C for 30-60 minutes, and filtering while hot to obtain a lithium-containing residue and a filtrate 2, wherein the solvent 2 is a mixture of water and the crystallization mother liquor 2 or water;

[0007] S3: Adjust the temperature of filtrate 2 to 32-45°C, and introduce CO2 under stirring to carbonize the sodium carbonate in filtrate 2, filter, and obtain solid 4 and filtrate 4; wash and dry solid 4 to obtain sodium bicarbonate;

[0008] S4: Cool the filtrate (4) to 5-10°C, keep warm and allow to crystallize until the amount of crystals no longer increases; then filter to obtain the crystallization mother liquor (2) and crude thenardite; heat the crude thenardite to 40-60°C, then adjust the pH to neutral, keep warm and react for 45-90 minutes, filter to obtain solid (5) and filtrate (5); dry the solid (5) at 100-130°C to obtain glauber's salt.

[0009] On the basis of the above technical solution, the present invention can also be improved as follows.

[0010] Furthermore, the mass ratio of water to potassium in the system obtained by mixing the potassium, sodium and lithium mixed salt in S1 with solvent 1 is 10~18:1.

[0011] Furthermore, the ratio of water to all solid solutes in the mixed system of solid 1 and solvent 2 in S2 is 2~2.8.

[0012] Furthermore, in S1 and S3, the CO2 ventilation rate during sodium carbonate carbonization was 2~10 L.min -1 . L -1 .

[0013] Furthermore, in S1 and S3, the pH value at the end point of sodium carbonate carbonization was 7.5-8.3.

[0014] Furthermore, the drying temperature of solid five in S4 is 110-120°C, and the drying time is 40-60 min.

[0015] Furthermore, the potassium sulfate content in the potassium, sodium and lithium mixed salt is 5-20 wt%, and the sodium carbonate content is 20-45 wt%.

[0016] The treatment process of the present invention can produce the following effects on the awakening treatment of potassium, sodium and lithium mixed salts:

[0017] 1. Potassium-Sodium Separation: The inventors discovered through experiments that when sodium carbonate, potassium sulfate, and sodium sulfate coexist, the actual solubility of sodium sulfate significantly decreases at higher temperatures. Therefore, temperatures above 70°C favor the removal of potassium sulfate, while the dissolution of sodium sulfate is inhibited. Most of the dissolved sodium ions precipitate as sodium bicarbonate after carbonization, thus achieving potassium-sodium separation. When the potassium eluent (filtrate 2) is cooled to 35-40°C, the solubility of potassium sulfate decreases, while the solubility of both sodium carbonate and sodium sulfate increases, resulting in the precipitation of potassium-rich glauberite (K3Na(SO4)2). Further cooling to 25°C precipitates sodium sulfate (K2SO4.Na2SO4.6H2O), while sodium carbonate and sodium sulfate rarely precipitate. The nearly saturated sodium carbonate solution then enters a carbonization tower for a carbonization reaction, generating a large amount of sodium bicarbonate, which is separated by filtration. The filtrate is then pH-adjusted with sulfuric acid and evaporated for crystallization, yielding a potassium-sodium mixed salt with a potassium sulfate content exceeding 20%, which can be used for purification to prepare potassium sulfate. The technical solution provided by the present invention is suitable for extracting potassium from a potassium-sodium mixed salt with a potassium sulfate content of 5% to 20% and a sodium carbonate content of 20% to 50%.

[0018] 2. Lithium Extraction: The solid after potassium extraction (Solid 1) is dissolved at 40-60°C to obtain a nearly saturated solution. This solution is then filtered, and approximately 70% of the lithium carbonate enters the residue (Solid 2). The lithium carbonate content in the residue is as high as 10-60%, resulting in a lithium enrichment of over 100 times. The lithium carbonate that does not remain in the residue enters the solution and, after subsequent carbonization and other steps, is concentrated in the mother liquor (crystallization mother liquor 2). The mother liquor is then returned to the dissolution process, reforming the lithium carbonate and remaining in the residue. This results in a lithium recovery rate exceeding 90%. Compared to lithium extraction methods such as extraction and adsorption, this lithium recovery method, synergistically coupled with sodium carbonate recovery and sodium sulfate crystallization, offers the advantages of low cost, simple process, and high economic efficiency.

[0019] 3. Sodium carbonate recovery: The sodium carbonate in the potassium eluate (filtrate 2) and the lithium extraction solution (crystallization mother liquor 1) is recovered by carbonization. The reaction equation is as follows:

[0020] Na2CO3+CO2+H2O=2NaHCO3↓

[0021] During the carbonization stage, a certain temperature is maintained to avoid the temperature drop during the initial reaction, which may cause sulfate crystallization. +The common ion effect improves the yield of sodium bicarbonate. The present invention sets two carbonization towers, which are used for carbonization of potassium eluent and lithium-extracted liquid respectively. The initial reaction temperature is controlled at 30-40°C, and the pH value of carbonization endpoint is controlled at 7.5-8.3, which can effectively improve the purity and yield of the product sodium bicarbonate. After testing, the purity of sodium bicarbonate obtained from the two solutions is more than 99%, the potassium content is less than 0.012% and 0.002% respectively, the sulfate ion content is less than 0.07%, the lithium content is less than 0.0001%, and the recovery rate of sodium carbonate is more than 80%.

[0022] 4. Preparation of high-quality sodium sulfate: The post-lithium extraction solution is carbonized to extract sodium bicarbonate, then cooled to 5-10°C. Na2SO4 precipitates in large quantities as heptahydrate or decahydrate. The lithium in the carbonized solution enters the crystallization mother liquor II and is reused to dissolve the mixed salt, allowing for efficient lithium recovery. The crude sodium sulfate is directly heated to 40-60°C to convert it into anhydrous sodium sulfate. Part of the sodium sulfate dissolves in its own crystallization water, and the potassium impurity in the sodium sulfate is also transferred to the solution. A small amount of sulfuric acid is added to adjust the slurry pH to neutral. After hot filtration and drying, high-quality sodium sulfate is obtained with a purity greater than 99%. The filtrate is then added to the carbonized solution (filtrate IV) and cooled for crystallization.

[0023] 5. Water balance and potassium circulation accumulation: Throughout the process design, to reduce energy consumption, most mother liquor is recycled after heat exchange. The mixed salt contains 10% to 20% water, and all water in the process is recycled. Once the process stabilizes, no additional water is added. However, the following three issues must be considered: first, the water balance between the potassium extraction process, the lithium extraction process, and the product washing process; second, the potassium remaining in the mixed salt after potassium extraction enters the sodium sulfate preparation process, requiring a solution to the potassium circulation accumulation problem; and third, the accumulation of other small amounts of soluble impurities in the mixed salt. The solution of the present invention is as follows: all mother liquor generated in the crystallization stage after carbonization in the potassium extraction process is evaporated and crystallized to obtain a mixed salt of potassium sulfate and sodium sulfate. The evaporated water vapor is combined with the mother liquor to be flexibly distributed and used as replenishing water, thereby saving some energy consumption. Residual potassium is contained in the crystallization mother liquor generated in the sodium sulfate process. A portion of the mother liquor is reacted with sodium hydroxide to convert a small amount of sodium bicarbonate therein into sodium carbonate, which is then returned to the potassium extraction process (to prevent sodium bicarbonate from decomposing and releasing CO2 at a high temperature), effectively solving the problem of potassium circulation accumulation. The sodium bicarbonate washing water is graded and used before being returned to the lithium extraction and dissolution process, effectively solving the problem of water distribution balance in various processes and potassium accumulation.

[0024] The beneficial effects of the present invention are:

[0025] The present invention efficiently recovers low-content lithium from mixed salts at a low cost, effectively separating potassium and sodium and recovering sodium carbonate using reasonable technology, thereby producing high-purity sodium sulfate. The process has a lithium recovery rate greater than 90%, a sodium carbonate recovery rate greater than 80%, and a potassium recovery rate greater than 90%. The crude lithium contains a lithium carbonate content of 10-60%, the purity of sodium bicarbonate is greater than 99%, the purity of sodium sulfate is greater than 99%, and the average K2SO4 content in the recovered potassium salt is greater than 38%. The process of the present invention has low overall energy consumption, significantly reduces investment costs, is environmentally friendly, and has excellent economic benefits. It provides a systematic solution for the treatment of lithium-potassium-sodium mixed salts or lithium precipitation mother liquor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a process flow chart for the resource utilization method of potassium, sodium and lithium mixed salt. DETAILED DESCRIPTION

[0027] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

[0028] Example 1

[0029] A method for resource utilization of potassium, sodium and lithium mixed salts, comprising the following steps:

[0030] S1: Weigh 2 kg of potassium, sodium and lithium mixed salt (the composition of the mixed salt is shown in Table 1), add 1.2 kg of water, and stir to mix evenly. The resulting system contains w 总H2O / w K =16.6; heat the mixed system to 75°C, keep stirring for 40 min, and filter while hot to obtain solid 1 (wet weight 1.31 kg, water content 16.8%) and filtrate 1;

[0031] Table 1 Composition of potassium, sodium and lithium mixed salt (%)

[0032] Ingredients <![CDATA[Na2SO4]]> <![CDATA[K2SO4]]> <![CDATA[Na2CO3]]> <![CDATA[Li2O]]> moisture content / % 46.4 9.8 30.5 0.21 13

[0033] S2: Solid 1 was mixed with water, with a water-solid ratio of 2.48; then the mixture was stirred and dissolved at 50 °C for 40 min, and filtered while hot to obtain 15.6 g of solid 2 (crude lithium carbonate) and 2.94 L of filtrate 2; the filtrate 1 was stirred and cooled to 25 °C and maintained for 1.5 h, and then filtered to obtain 161 g of potassium salt 1 (mainly composed of K2SO4.Na2SO4.6H2O) and crystallization mother liquor 1; the crystallization mother liquor 1 was placed in a carbonization tower, heated to 30 °C, and then stirred at 3.5 L.min using a microporous aeration head. -1 .L -1CO2 was introduced at a rate of 1000 ℃ until the pH value of the solution reached 8.2, and then filtered to obtain solid 3 and filtrate 3; solid 3 was washed (the washing liquid was water, and the water-solid ratio during washing was 0.5:1) and dried at 50°C to obtain sodium bicarbonate solid (422 g); the pH of filtrate 3 was adjusted to 7.0 with sulfuric acid (1 mol / L), and then evaporated and crystallized to obtain 285 g of potassium salt 2 (a mixture of potassium sulfate and sodium sulfate);

[0034] S3: Place the filtrate 2 in a carbonization tower, heat it to 38°C, and use a microporous aeration head at 3.5L.min under stirring. -1 .L -1 CO2 was introduced at a rate until the pH value of the solution reached 8.0, aeration was stopped, and the solution was filtered to obtain solid 4 and filtrate 4; solid 4 was washed (the washing liquid was water, and the water-solid ratio during washing was 0.5:1) and dried at 50°C to obtain sodium bicarbonate solid (342g);

[0035] S4: Cool the filtrate four to 8 °C, keep warm and allow to crystallize until the amount of crystals no longer increases; then filter to obtain the crystallization mother liquor two and crude Sodium Sulfate; add a small amount of concentrated sulfuric acid (98%) to the crude Sodium Sulfate, and simultaneously raise the temperature to 40 °C, then add sulfuric acid until the pH of the system reaches 7.0, keep warm and react for 50 min, filter to obtain Solid Five and Filtrate Five; Dry the Solid Five at 120 °C for 40 min to obtain Sodium Sulfate (398 g).

[0036] Example 2

[0037] A method for resource utilization of potassium, sodium and lithium mixed salts, comprising the following steps:

[0038] S1: Weigh 2 kg of potassium, sodium and lithium mixed salt (the composition of the mixed salt is shown in Table 1), add 1.5 kg of the crystallization mother solution 2 obtained in S4 of Example 1, and then add 10 g of sodium hydroxide, stir and mix evenly, and the resulting system is w 总H2O / w K =11.1; heat the mixed system to 90°C, keep stirring for 40 min, and filter while hot to obtain solid 1 (wet weight 1.56 kg, water content 17.5%) and filtrate 1;

[0039] S2: Solid 1 was mixed with water and the crystallization mother liquor 2 obtained in Example 1 S4 (the mass ratio of water to crystallization mother liquor 2 was 1.8:1), and the water-solid ratio of the mixed system was 2.51; then, the mixture was stirred and dissolved at 50 °C for 40 min, and filtered while hot to obtain 26.8 g of solid 2 (crude lithium carbonate) and 3.34 L of filtrate 2; the filtrate 1 was stirred and cooled to 25 °C and maintained for 1.5 h, and then filtered to obtain 207 g of potassium salt 1 (mainly composed of K2SO4.Na2SO4.6H2O) and crystallization mother liquor 1; the crystallization mother liquor 1 was placed in a carbonization tower, heated to 35 °C, and then stirred at 3.5 L.min using a microporous aeration head. -1 .L -1 CO2 was introduced at a rate of 1000 rpm until the pH value of the solution reached 8.3, and then filtered to obtain solid 3 and filtrate 3; solid 3 was washed (the washing liquid was water, and the water-to-solid ratio during washing was 0.5:1) and dried at 50°C to obtain sodium bicarbonate solid (427 g); the pH of filtrate 3 was adjusted to 7.5 with sulfuric acid (1 mol / L), and then evaporated and crystallized to obtain 336 g of potassium salt 2 (a mixture of potassium sulfate and sodium sulfate);

[0040] S3: Place the filtrate 2 in a carbonization tower, heat it to 38°C, and use a microporous aeration head at 3.5L.min under stirring. -1 .L -1 CO2 was introduced at a rate until the pH value of the solution reached 8.0, aeration was stopped, and the solution was filtered to obtain solid 4 and filtrate 4; solid 4 was washed (the washing liquid was water, and the water-solid ratio during washing was 0.5:1) and dried at 50°C to obtain sodium bicarbonate solid (404g);

[0041] S4: Filtrate 4 was mixed with filtrate 5 obtained in Example 1 S4, and the mixture was cooled to 5°C and kept warm for crystallization until the amount of crystals no longer increased; then filtered to obtain crystallization mother liquor 2 and crude Sodium Sulfate; a small amount of concentrated sulfuric acid (98%) was added to the crude Sodium Sulfate, and the temperature was raised to 50°C, and then sulfuric acid was added until the pH of the system reached 7.5. The mixture was kept warm for reaction for 35 minutes, and filtered to obtain Solid 5 and Filtrate 5; Solid 5 was dried at 120°C for 40 minutes to obtain Sodium Sulfate (685 g).

[0042] Example 3

[0043] A method for resource utilization of potassium, sodium and lithium mixed salts, comprising the following steps:

[0044] S1: Weigh 2 kg of potassium, sodium and lithium mixed salt (the composition of the mixed salt is shown in Table 2), add 1.2 kg of water, and stir to mix evenly. The resulting system contains w 总H2O / w K=14; the mixed system was heated to 80°C, stirred at this temperature for 40 min, and filtered while hot to obtain a solid 1 (wet weight 1.40 Kg, water content 15.7%) and a filtrate 1;

[0045] Table 2 Composition of potassium, sodium and lithium mixed salt (%)

[0046] Ingredients <![CDATA[Na2SO4]]> <![CDATA[K2SO4]]> <![CDATA[Na2CO3]]> <![CDATA[Li2O]]> moisture content / % 40.1 11.5 34.5 0.21 12

[0047] S2: Solid 1 was mixed with water, with a water-solid ratio of 2.45; then the mixture was stirred and dissolved at 50 °C for 40 min, and filtered while hot to obtain 22.6 g of solid 2 (crude lithium carbonate) and 2.94 L of filtrate 2; the filtrate 1 was stirred and cooled to 25 °C and maintained for 1 h, and then filtered to obtain 204 g of potassium salt 1 (mainly composed of K2SO4.Na2SO4.6H2O) and crystallization mother liquor 1; the crystallization mother liquor 1 was placed in a carbonization device, heated to 30 °C, and then stirred at 6 L.min using a microporous aeration head. -1 .L -1 CO2 was introduced at a rate of 1000 rpm until the pH value of the solution reached 8.2, and then filtered to obtain solid 3 and filtrate 3; solid 3 was washed (the washing liquid was water, and the water-to-solid ratio during washing was 0.5:1) and dried at 55°C to obtain sodium bicarbonate solid (526 g); the pH of filtrate 3 was adjusted to 6.5 with sulfuric acid (1 mol / L), and then evaporated and crystallized to obtain 298 g of potassium salt 2 (a mixture of potassium sulfate and sodium sulfate);

[0048] S3: Place the filtrate 2 in a carbonization tower, heat it to 38°C, and use a microporous aeration head at 4 L.min under stirring. -1 .L -1 CO2 was introduced at a rate until the pH value of the solution reached 8.0, aeration was stopped, and the solution was filtered to obtain solid 4 and filtrate 4; solid 4 was washed (the washing liquid was water, and the water-solid ratio during washing was 0.5:1) and dried at 50°C to obtain sodium bicarbonate solid (381g);

[0049] S4: Cool the filtrate four to 10 °C, keep warm and allow to crystallize until the amount of crystals no longer increases; then filter to obtain the crystallization mother liquor two and crude Sodium Sulfate; add a small amount of concentrated sulfuric acid (98%) to the crude Sodium Sulfate, and simultaneously raise the temperature to 50 °C, then add sulfuric acid (1 mol / L) until the pH of the system reaches 6.5, keep warm and react for 60 min, filter to obtain Solid Five and Filtrate Five; Dry the Solid Five at 120 °C for 40 min to obtain Sodium Sulfate (398 g).

[0050] Experimental example:

[0051] 1. Product test results

[0052] The test results of the product obtained by the method in the embodiment of the present invention are shown in Table 3.

[0053] Table 3 Test results of Examples 1 to 3

[0054]

[0055] Note: 1 Example S2 Carbonization recovery of sodium bicarbonate purity; 2 Purity of sodium bicarbonate recovered by carbonization in Example S3; 3 Weighted average of the K2SO4% in the two potassium-containing salts recovered.

[0056] As can be seen from Table 3, the treatment method of the present invention can directly obtain two products, industrial-grade sodium bicarbonate and high-quality sodium sulfate. The crude lithium carbonate can be used to prepare lithium carbonate. The method that can be adopted is water slurry-CO2 carbonization-impurity removal-pyrolysis to obtain battery-grade lithium carbonate; the potassium sulfate contents of the two potassium-containing salts obtained are 35% to 60% and 18% to 25%, respectively, and can be used to prepare potassium sulfate.

[0057] 2. Economic Benefit Analysis of the Method for Resource Utilization of Potassium, Sodium and Lithium Mixed Salts in the Present Invention

[0058] The economic benefit analysis results of using the method of the present invention to process 30,000 tons / year of lithium-sodium-potassium mixed salt are shown in Table 4.

[0059] Table 4 Economic Benefit Analysis of Processing 30,000 Tons / Year of Lithium-Sodium-Potassium Mixed Salt

[0060]

[0061] As can be seen from Table 3, the method of the present invention for treating lithium-sodium-potassium mixed salt can produce good economic benefits and has good practical value.

[0062] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for resource utilization of potassium, sodium and lithium mixed salts, characterized in that: The following steps are involved: S1: Mixing a potassium, sodium, and lithium mixed salt with a solvent 1, wherein the solvent 1 is a crystallization mother liquor 2 or water, and the crystallization mother liquor 2 is obtained from the subsequent S4; then heating the mixed system to 70-100°C, stirring at this temperature for 20-100 minutes, and filtering while hot to obtain a solid 1 and a filtrate 1; stirring the filtrate 1 and cooling it to 20-40°C and maintaining it for 1-2 hours, and then filtering it to obtain a potassium-containing salt 1 and a crystallization mother liquor 1; introducing CO2 into the crystallization mother liquor 1 under stirring to carbonize the sodium carbonate in the crystallization mother liquor 1, filtering it to obtain a solid 3 and a filtrate 3; washing and drying the solid 3 to obtain sodium bicarbonate; adjusting the pH of the filtrate 3 to 6.5-7.5, and then evaporating and crystallizing it to obtain a potassium-containing salt 2; S2: mixing the solid 1 with the solvent 2, stirring and dissolving at 40-65°C for 30-60 minutes, and filtering while hot to obtain a lithium-containing residue and a filtrate 2, wherein the solvent 2 is a mixture of water and the crystallization mother liquor 2 or water; S3: adjusting the temperature of the filtrate 2 to 32-45°C, and introducing CO2 under stirring to carbonize the sodium carbonate in the filtrate 2, filtering to obtain solid 4 and filtrate 4; The solid is washed and dried to obtain sodium bicarbonate; S4: Cool the filtrate (4) to 5-10°C, keep warm and allow to crystallize until the amount of crystals no longer increases; then filter to obtain the crystallization mother liquor (2) and crude thenardite; heat the crude thenardite to 40-60°C, then adjust the pH to neutral, keep warm and react for 45-90 minutes, filter to obtain solid (5) and filtrate (5); dry the solid (5) at 100-130°C to obtain glauber's salt.

2. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: The mass ratio of water to potassium in the system obtained by mixing the potassium, sodium and lithium mixed salt in S1 with solvent 1 is 10~18:

1.

3. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: The ratio of water to all solid solutes in the mixed system of solid 1 and solvent 2 in S2 is 2~2.

8.

4. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: In S1 and S3, the CO2 ventilation rate during sodium carbonate carbonation was 2-10 L. min -1 . L -1 .

5. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: In S1 and S3, the pH value at the end point of sodium carbonate carbonization was 7.5~8.

3.

6. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: The drying temperature of solid 5 in S4 is 110~120℃, and the drying time is 40~60 min.

7. The method for resource utilization of potassium, sodium and lithium mixed salt according to claim 1, characterized in that: The potassium sulfate content in the potassium, sodium and lithium mixed salt is 5-20 wt %, and the sodium carbonate content is 20-45 wt %.

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