A high-value conversion process and system for the resource utilization of potassium sodium sulfate mixed salt

Abstract

A process and system for the high-value conversion of potassium sodium sulfate mixed salt resources. First, the potassium sodium sulfate mixed salt is fed into a potassium sulfate dissolution device, and saturated sodium sulfate solution is added to completely dissolve the potassium sulfate. Then, it is sent to a cooling crystallization device to crystallize out potassium sulfate, and through solid-liquid separation and drying, potassium sulfate products are obtained. The solid of the potassium sodium sulfate mixed salt after potassium sulfate dissolution is sent to a sodium sulfate dissolution device, and water is added to fully dissolve sodium sulfate and sent to an alkali-making reaction device to react with ammonium bicarbonate solution prepared through ammonia absorption and carbonation reaction to obtain sodium bicarbonate and ammonium sulfate. Sodium bicarbonate crystallizes out and is directly used as a raw material for lithium precipitation or calcined at 240°C to form sodium carbonate as a raw material for lithium precipitation. The mother liquor containing ammonium sulfate is sent to an alkalization device, and calcium oxide is added to precipitate ammonia for recycling, and the sulfate radical is converted into calcium sulfate as a raw material for roasting lepidolite ore. The present invention realizes the high-value conversion of potassium sodium sulfate mixed salt resources and saves the production cost of extracting lithium from lepidolite ore.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of potassium sodium sulfate mixed salt, and particularly relates to a high-value conversion process and system for the resource utilization of potassium sodium sulfate mixed salt. Background Art

[0002] With the release of carbon neutrality goals by various countries, the global energy transition has been rapidly advancing. Lithium has evolved from an "industrial flavor enhancer" to an "energy metal" and "white oil", and the global demand for lithium has shown an explosive growth. In nature, lithium mainly exists in the form of salt lake lithium and ore lithium. Ore lithium has advantages such as high grade and simple composition compared to salt lake lithium, and it is easier to meet the standard of battery-grade lithium carbonate after enrichment and separation. Lithium ores include spodumene and lepidolite, among which the mining cost of lepidolite is low and it has gradually received attention.

[0003] Currently, the relatively mature production process is to extract lithium from lepidolite ore by sulfate roasting method to prepare battery-grade lithium carbonate. However, a large amount of potassium sodium sulfate mixed salt will be generated during the process of extracting lithium from lepidolite. Although part of the potassium sodium sulfate mixed salt is recycled to the lepidolite roasting unit for utilization, lepidolite contains K2O. In addition, an excessive amount of sodium carbonate needs to be added during the lithium precipitation process to ensure the lithium precipitation rate. Therefore, the potassium sodium sulfate mixed salt must be discharged from the lepidolite sulfate roasting process system, becoming solid waste of potassium sodium sulfate mixed salt. Previously, the research team proposed a resource utilization system for solid waste of potassium sulfate and sodium sulfate mixed salt (application number: 202323600424.5). This patent proposed a separation process for potassium sulfate and sodium sulfate in the potassium sodium sulfate mixed salt. Among them, the potassium sulfate product can be used as a potash fertilizer, while the market value of the sodium sulfate decahydrate product is relatively low. In addition, this patent has good effects on recovering potassium sulfate products from potassium sodium sulfate mixed salts with a high potassium sulfate mass content (≥25%). However, the difference in potassium content in lepidolite ore leads to a large difference in the potassium sulfate content in the potassium sodium sulfate mixed salt generated during the lithium extraction process. Therefore, recovering potassium sulfate products from potassium sodium sulfate mixed salts with a low potassium sulfate mass content and converting sodium sulfate into high-value-added products is of great significance for reducing the costs of lithium ore lithium extraction enterprises and green production. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a high-value conversion process and system for the resource utilization of potassium sodium sulfate mixed salt, realizing the separation and recovery of potassium sulfate in the potassium sodium sulfate mixed salt, and at the same time realizing the high-value conversion of sodium sulfate resources.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A high-value conversion system for the resource utilization of potassium sodium sulfate mixed salt, comprising a potassium sulfate dissolution device 1, wherein the first feed inlet of the potassium sulfate dissolution unit 1 is connected to the outlet of the potassium sodium sulfate mixed salt, the outlet of the potassium sulfate dissolution device 1 is connected to the inlet of the first solid-liquid separation device 2, the liquid outlet of the first solid-liquid separation device 2 is connected to the tube-side feed inlet of the heat exchanger 3, the tube-side outlet of the heat exchanger 3 is connected to the inlet of the cooling crystallization device 4, the crystallization outlet of the cooling crystallization device 4 is connected to the inlet of the second solid-liquid separation device 5, the liquid outlet of the cooling crystallization device 4 is connected to the first inlet of the first buffer tank 6, the liquid outlet of the second solid-liquid separation device 5 is connected to the second inlet of the first buffer tank 6, the solid outlet of the second solid-liquid separation device 5 is connected to the inlet of the drying device 7, the first outlet of the first buffer tank 6 is connected to the shell-side inlet of the heat exchanger 3, the shell-side outlet of the heat exchanger 3 is connected to the second inlet of the potassium sulfate dissolution device 1, and the second inlet of the first buffer tank 6 is connected to the feed inlet of the rare metal recovery unit 8; the solid outlet of the first solid-liquid separation device 2 is connected to the first feed inlet of the sodium sulfate dissolution device 9, the second feed inlet of the sodium sulfate dissolution device 9 is connected to the first discharge outlet of the second buffer tank 17, the outlet of the sodium sulfate dissolution device 9 is connected to the first inlet of the alkali production reaction device 10, the second inlet of the alkali production reaction device 10 is connected to the outlet of the carbonization reaction device 13, the first inlet of the carbonization reaction device 13 is connected to the outlet of the ammonia absorption device 12, the second inlet of the carbonization reaction device 13 is connected to the carbon dioxide outlet, the first inlet of the ammonia absorption device 12 is connected to the outlet of the liquid ammonia storage tank 11, the second inlet of the ammonia absorption device 12 is connected to the second discharge outlet of the second buffer tank 17, the first inlet of the liquid ammonia storage tank 11 is connected to the liquid ammonia outlet, and the second inlet of the liquid ammonia storage tank 11 is connected to the gas outlet of the alkalization device 15; the solid outlet of the alkali production reaction device 10 is connected to the feed inlet of the washing / filtering device 14, the liquid outlet of the washing / filtering device 14 is connected to the first feed inlet of the alkalization device 15, the liquid outlet of the alkali production reaction device 10 is connected to the second feed inlet of the alkalization device 15, the third feed inlet of the alkalization device 15 is connected to the calcium oxide outlet, the solid outlet of the alkalization device 15 is connected to the inlet of the third solid-liquid separation device 16, and the liquid outlet of the alkalization device 15 and the liquid outlet of the third solid-liquid separation device 16 are connected to the feed inlet of the second buffer tank 17.

[0007] A high-value conversion process for the resource utilization of potassium sodium sulfate mixed salt, comprising the following steps:

[0008] First step: Feed the potassium sodium sulfate mixed salt into the potassium sulfate dissolution device 1. At the same time, part of the saturated sodium sulfate solution in the first buffer tank 6 is circulated to the potassium sulfate dissolution device 1 after heat exchange through the heat exchanger 3, and industrial water is supplemented to the potassium sulfate dissolution device 1 to dissolve all the potassium sulfate in the potassium sodium sulfate mixed salt, and the sodium sulfate in the dissolution solution is in a saturated state. Then, the dissolution solution and the undissolved sodium sulfate solid are sent together into the first solid-liquid separation device 2 to separate the dissolution solution and the undissolved sodium sulfate solid. The separated dissolution solution is discharged from the liquid outlet of the first solid-liquid separation device 2 and sent to the heat exchanger 3 for countercurrent heat exchange and cooling with the saturated sodium sulfate solution from the first buffer tank 6, and then sent to the cooling crystallization device 4 to crystallize out potassium sulfate. The crystal particles crystallized out are discharged from the crystallization outlet of the cooling crystallization device 4 and sent to the second solid-liquid separation device 5 for solid-liquid separation. The separated potassium sulfate solid is discharged from the solid outlet of the second solid-liquid separation device 5 and sent to the drying device 7 for drying to obtain potassium sulfate products. The mother liquor in the cooling crystallization device 4, that is, the sodium sulfate saturated solution containing potassium sulfate and the liquid discharge from the second solid-liquid separation device 5 are sent together into the first buffer tank 6. Then, part of the sodium sulfate saturated solution in the first buffer tank 6 is sent into the heat exchanger 3 for heat exchange and temperature increase and then sent into the potassium sulfate dissolution device 1, and the remaining part is sent to the rare metal recovery unit 8 for recovering rare metals such as rubidium, strontium, thallium, and beryllium contained in the potassium sodium sulfate mixed salt;

[0009] Second step: The sodium sulfate solid separated by the first solid-liquid separation device 2 is sent into the sodium sulfate dissolution device 9. At the same time, part of the circulating liquid in the second buffer tank 17 is circulated to the sodium sulfate dissolution device 9, and water is supplemented to the sodium sulfate dissolution device 9 to fully dissolve sodium sulfate, and then it is sent into the alkali-making reaction device 10. At the same time, liquid ammonia is fed from the liquid ammonia storage tank 11 into the ammonia absorption device 12, and part of the circulating liquid in the second buffer tank 17 is fed into the ammonia absorption device 12 to absorb liquid ammonia and become ammonia water with a mass content of 20%. Then, the ammonia water with a mass content of 20% is fed into the carbonation reaction device 13 to react with carbon dioxide to generate ammonium bicarbonate; then the ammonium bicarbonate solution is fed into the alkali-making reaction device 10 to react with sodium sulfate to generate sodium bicarbonate and ammonium sulfate, and sodium bicarbonate crystallizes out due to its low solubility in water;

[0010] Step 3: The sodium bicarbonate crystals precipitated in the alkali-making reaction device 10 are discharged from the solid discharge port and sent into the washing / filtering device 14. Then, the liquid after washing and filtering is discharged from the liquid outlet of the washing / filtering device 14 and sent into the alkalization device 15. At the same time, the mother liquor of the alkali-making reaction device 10 is sent into the alkalization device 15. Calcium oxide reacts with water to generate calcium hydroxide, and then reacts with ammonium sulfate to generate ammonia and calcium sulfate. The washed and filtered sodium bicarbonate solid is discharged from the solid outlet of the washing / filtering device 14 and directly used as the raw material for lithium precipitation, or the sodium bicarbonate solid is calcined at 240 °C to form sodium carbonate and then used as the raw material for lithium precipitation. The ammonia in the alkalization device 15 is recycled to the liquid ammonia storage tank 11, and liquid ammonia is supplemented into the liquid ammonia storage tank 11. The solid materials in the alkalization device 15 are sent into the third solid-liquid separation device 16 for solid-liquid separation. The separated solid is discharged from the solid outlet of the third solid-liquid separation device 16, and calcium sulfate products are obtained after natural air drying and used as raw materials in the roasting process of lithium mica ore. The clear liquid of the alkalization device 15 and the liquid of the third solid-liquid separation device 16 are sent into the second buffer tank 17 for recycling. Part of it is recycled to the ammonia absorption device 12, and the remaining part is recycled to the sodium sulfate dissolution device 9.

[0011] The potassium sulfate dissolution device 1 is provided with an electric heating system and a stirring device. The stirring speed is 450 - 600 rpm, the residence time is 1 - 1.5 h, and the operating temperature is 90 - 100 °C.

[0012] The sodium sulfate dissolution device 9 is provided with an electric heating system and a stirring device. The stirring speed is 300 - 400 rpm, the residence time is 0.5 - 1 h, and the operating temperature is 30 - 50 °C.

[0013] The alkali-making reaction device 10 is provided with an electric heating system, a cooling system and a stirring device. The stirring speed is 500 - 600 rpm, the residence time is 2 - 3 h, and the reaction temperature is 45 - 55 °C.

[0014] The operating pressure of the carbonization reaction device 13 is 0.18 - 0.22 MPa (gauge pressure), the operating temperature is 30 - 35 °C, the residence time is 3 - 4 h, the molar ratio of excessive carbon dioxide to ammonia water ≥ 2.5, and the flue gas generated in the roasting process of lithium mica is recycled as the raw material for the carbonization reaction.

[0015] The alkalization device 15 is provided with an ammonia stripping device. The operating pH is 8 - 9, the residence time is 1 - 2 h, and the molar ratio of calcium oxide to sodium sulfate in the reaction liquid is 1.1:1.

[0016] The cooling crystallization device 4 includes a cooling crystallizer and a refrigeration system, uses cooling water circulation for refrigeration, the operating temperature is 30 - 35 °C, and the residence time is 1.5 - 2 h.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The present invention adds a sodium sulfate saturated solution at 30-35°C into the potassium sulfate dissolving device 1, which can dissolve potassium sulfate and other soluble impurities in the potassium sodium sulfate mixed salt, realizing the separation of potassium sulfate and sodium sulfate in the potassium sodium sulfate mixed salt.

[0019] 2. By circulating the mother liquor of the cooling crystallization device 4 and the clear liquid of the second solid-liquid separation device 5 to the potassium sulfate dissolving device 1 as the dissolving liquid for the potassium sodium sulfate mixed salt, the present invention not only reduces the consumption of the sodium sulfate saturated solution, improves the recovery rate of potassium sulfate, but also increases the concentration of rare metals such as rubidium, strontium, thallium and beryllium in the solution through continuous circulation, providing conditions for the recycling and resource utilization of rare metals.

[0020] 3. The present invention prepares sodium bicarbonate or sodium carbonate with high added value by using sodium sulfate with low added value, realizing the high-value conversion of sodium sulfate. At the same time, ammonia is recovered by using calcium oxide, reducing the operation cost of the process, and obtaining calcium sulfate products, which can be used as raw materials for roasting lithium mica ore, saving the production cost of lithium mica lithium extraction enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the system and process of the embodiment of the present invention.

[0022] Figure 2 It is the result of converting sodium sulfate into sodium bicarbonate in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described below in conjunction with the embodiments and the drawings.

[0024] Example: The mass content of potassium sulfate in the potassium sodium sulfate mixed salt is 20%, and the mass content of sodium sulfate is 80%. The treatment scale is 15 tons / h. Refer to Figure 1, A high-value conversion system for the resource utilization of potassium sodium sulfate mixed salt, comprising a potassium sulfate dissolving device 1. The first feed inlet of the potassium sulfate dissolving unit 1 is connected to the outlet of the potassium sodium sulfate mixed salt. The outlet of the potassium sulfate dissolving device 1 is connected to the inlet of the first solid-liquid separation device 2. The liquid outlet of the first solid-liquid separation device 2 is connected to the feed inlet of the tube side of the heat exchanger 3. The outlet of the tube side of the heat exchanger 3 is connected to the inlet of the cooling crystallization device 4. The crystallization outlet of the cooling crystallization device 4 is connected to the inlet of the second solid-liquid separation device 5. The liquid outlet of the cooling crystallization device 4 is connected to the first inlet of the first buffer tank 6. The liquid outlet of the second solid-liquid separation device 5 is connected to the second inlet of the first buffer tank 6. The solid outlet of the second solid-liquid separation device 5 is connected to the inlet of the drying device 7. The first outlet of the first buffer tank 6 is connected to the inlet of the shell side of the heat exchanger 3. The outlet of the shell side of the heat exchanger 3 is connected to the second inlet of the potassium sulfate dissolving device 1. The second inlet of the first buffer tank 6 is connected to the feed inlet of the rare metal recovery unit 8; The solid outlet of the first solid-liquid separation device 2 is connected to the first feed inlet of the sodium sulfate dissolving device 9. The second feed inlet of the sodium sulfate dissolving device 9 is connected to the first discharge outlet of the second buffer tank 17. The outlet of the sodium sulfate dissolving device 9 is connected to the first inlet of the alkali-making reaction device 10. The second inlet of the alkali-making reaction device 10 is connected to the outlet of the carbonization reaction device 13. The first inlet of the carbonization reaction device 13 is connected to the outlet of the ammonia absorption device 12. The second inlet of the carbonization reaction device 13 is connected to the carbon dioxide outlet. The first inlet of the ammonia absorption device 12 is connected to the outlet of the liquid ammonia storage tank 11. The second inlet of the ammonia absorption device 12 is connected to the second outlet of the second buffer tank 17. The first inlet of the liquid ammonia storage tank 11 is connected to the liquid ammonia outlet. The second inlet of the liquid ammonia storage tank 11 is connected to the gas outlet of the alkalization device 15; The solid outlet of the alkali-making reaction device 10 is connected to the feed inlet of the washing / filtering device 14. The liquid outlet of the washing / filtering device 14 is connected to the first feed inlet of the alkalization device 15. The liquid outlet of the alkali-making reaction device 10 is connected to the second feed inlet of the alkalization device 15. The third feed inlet of the alkalization device 15 is connected to the calcium oxide outlet. The solid outlet of the alkalization device 15 is connected to the inlet of the third solid-liquid separation device 16. The liquid outlet of the alkalization device 15 and the liquid outlet of the third solid-liquid separation device 16 are connected to the feed inlet of the second buffer tank 17.

[0025] A high-value conversion process for the resource utilization of potassium sodium sulfate mixed salt, comprising the following steps:

[0026] First step: Feed the potassium sodium sulfate mixed salt into the potassium sulfate dissolving device 1 at a flow rate of 15 t / h. At the same time, circulate the saturated sodium sulfate solution at 30 - 35 °C in the first buffer tank 6 to the potassium sulfate dissolving device 1 through the heat exchanger 3 at a flow rate of 46 t / h after heating it to 50 - 55 °C, and supplement industrial water to the potassium sulfate dissolving device 1 at a flow rate of 3.2 t / h to dissolve all the potassium sulfate in the potassium sodium sulfate mixed salt, and keep the sodium sulfate in the dissolved solution in a saturated state. Then, send the dissolved solution and the undissolved sodium sulfate solid together to the first solid-liquid separation device 2 at a flow rate of 64.2 t / h to separate the dissolved solution and the undissolved sodium sulfate solid. The separated dissolved solution is discharged from the liquid discharge port of the first solid-liquid separation device 2 at a flow rate of 50 t / h, sent to the heat exchanger 3 to counter-currently exchange heat with the saturated sodium sulfate solution from the first buffer tank 6 and cooled to 60 - 65 °C, and then sent to the cooling crystallization device 4 to crystallize out potassium sulfate. The crystallized crystal particles are discharged from the crystallization discharge port of the cooling crystallization device 4 at a flow rate of 4 t / h and sent to the second solid-liquid separation device 5 for solid-liquid separation. The separated potassium sulfate solid is discharged from the solid discharge port of the second solid-liquid separation device 5 at a flow rate of 3.5 t / h and sent to the drying device 7 for drying to obtain potassium sulfate products at a rate of 3 t / h. The mother liquor in the cooling crystallization device 4 (i.e., the saturated sodium sulfate solution containing potassium sulfate) and the liquid discharge in the second solid-liquid separation device 5 are sent into the first buffer tank 6 together at a flow rate of 46.5 t / h. Then, the saturated sodium sulfate solution in the first buffer tank 6 is sent into the heat exchanger 3 at a flow rate of 46 t / h for heat exchange and temperature increase and then sent into the potassium sulfate dissolving device 1. The remaining part is sent to the rare metal recovery unit 8 at a flow rate of 0.5 t / h to recover rare metals such as rubidium, strontium, thallium, and beryllium contained in the potassium sodium sulfate mixed salt;

[0027] Second step: Feed the sodium sulfate solid separated by the first solid-liquid separation device 2 into the sodium sulfate dissolving device 9 at a flow rate of 14.2 t / h. At the same time, circulate part of the circulating liquid in the second buffer tank 17 to the sodium sulfate dissolving device 9 at a flow rate of 30.5 t / h, and supplement a small amount of industrial water to the sodium sulfate dissolving device 9 at a flow rate of 0.3 t / h to fully dissolve the sodium sulfate, and then send it into the alkali-making reaction device 10 at a flow rate of 45 t / h. Meanwhile, feed liquid ammonia from the liquid ammonia storage tank 11 into the ammonia absorption device 12 at a flow rate of 3.5 t / h, and send part of the circulating liquid in the second buffer tank 17 into the ammonia absorption device 12 at a flow rate of 14 t / h to absorb the liquid ammonia and turn it into ammonia water with a mass content of 20%. Then, send the ammonia water with a mass content of 20% into the carbonization reaction device 13 at a flow rate of 14.5 t / h to react with carbon dioxide to generate ammonium bicarbonate. The reaction equation is as shown in Equation (1). Then, send the ammonium bicarbonate solution into the alkali-making reaction device 10 at a flow rate of 30.3 t / h to react with sodium sulfate to generate sodium bicarbonate and ammonium sulfate. The reaction equation is as shown in Equation (2), where sodium bicarbonate has a low solubility in water and crystallizes out;

[0028] NH3·H2O + CO2 = NH4HCO3 1)

[0029] 2NH4HCO3 + Na2SO4 = 2NaHCO3 + (NH4)2SO4 2)

[0030] In the third step, the sodium bicarbonate crystals precipitated in the alkali-making reaction device 10 are discharged from the solid discharge port at a flow rate of 20 tons / h and sent into the washing / filtering device 14. Then, the washed and filtered liquid is discharged from the liquid outlet of the washing / filtering device 14 and sent into the alkalization device 15 at a flow rate of 3 tons / h. At the same time, the mother liquor of the alkali-making reaction device 10 is sent into the alkalization device 15 at a flow rate of 55.3 tons / h, and calcium hydroxide formed by the reaction of calcium oxide and water is added at a flow rate of 5.2 tons / h, and then reacts with ammonium sulfate to form ammonia and calcium sulfate. The reaction equations are shown in equations 3) and 4). The washed and filtered sodium bicarbonate solid is discharged from the solid outlet of the washing / filtering device 14 and directly used as the raw material for lithium precipitation or the sodium bicarbonate is calcined at 240 °C to form sodium carbonate and then used as the raw material for lithium precipitation; the ammonia in the alkalization device 15 is circulated to the liquid ammonia storage tank 11 at a flow rate of 3.2 tons / h, and liquid ammonia is supplemented into the liquid ammonia storage tank 11 at a flow rate of 0.3 tons / h. The solid materials in the alkalization device 15 are sent into the third solid-liquid separation device 16 at a flow rate of 16 tons / h for solid-liquid separation. The separated solid is discharged from the solid outlet of the third solid-liquid separation device 16 at a flow rate of 13.8 tons / h, and calcium sulfate products are obtained after natural air drying and can be used as raw materials in the roasting process of lepidolite ore. The clear liquid of the alkalization device 15 and the liquid of the third solid-liquid separation device 16 are sent into the second buffer tank 17 together at a flow rate of 44.5 tons / h for recycling. Among them, part of it is circulated to the ammonia absorption device 12 at a flow rate of 14 tons / h, and the remaining part is circulated to the sodium sulfate dissolution device 9 at a flow rate of 30.5 tons / h;

[0031] CaO + H2O = Ca(OH)2 3)

[0032] (NH4)2SO4 + Ca(OH)2 = 2NH3 + CaSO4 + 2H2O 4)

[0033] The potassium sulfate dissolution device 1 is provided with an electric heating system and a stirring device. The stirring speed is 450 - 600 rpm, the residence time is 1 - 1.5 h, and the operating temperature is 90 - 100 °C;

[0034] The sodium sulfate dissolution device 9 is provided with an electric heating system and a stirring device. The stirring speed is 300 - 400 rpm, the residence time is 0.5 - 1 h, and the operating temperature is 30 - 50 °C;

[0035] The described alkali-making reaction device 10 is provided with an electric heating system, a cooling system and a stirring device. The stirring speed is 500 - 600 rpm, the residence time is 2 - 3 h, and the reaction temperature is 45 - 55 °C;

[0036] The described carbonization reaction device 13 has an operating pressure of 0.18 - 0.22 MPa (gauge pressure), an operating temperature of 30 - 35 °C, a residence time of 3 - 4 h, and the molar ratio of excess carbon dioxide to ammonia water ≥ 2.5. The flue gas generated during the roasting process of lepidolite can be recycled as a raw material for the carbonization reaction;

[0037] The described alkalization device 15 is provided with an ammonia stripping device, an operating pH of 8 - 9, a residence time of 1 - 2 h, and the molar ratio of calcium oxide to sodium sulfate in the reaction solution is 1.1:1;

[0038] The described cooling and crystallization device 4 includes a cooling crystallizer and a refrigeration system, uses cooling water circulation for refrigeration, has an operating temperature of 30 - 35 °C, and a residence time of 1.5 - 2 h.

[0039] Through this embodiment, the separation and recovery of potassium sulfate products from the potassium - sodium sulfate mixed salt can be achieved. The potassium oxide content of the prepared potassium sulfate product is above 51.6%, meeting the requirements of first - grade powder crystal and premium - grade granular products in the national standard for agricultural potassium sulfate, and can be sold as potash fertilizer, creating a new economic growth point for lithium - mica lithium - extraction enterprises; at the same time, sodium sulfate is converted into sodium bicarbonate, and under certain conditions, the conversion rate of sodium sulfate can reach above 84% (as Figure 2 shown), and sodium bicarbonate can be directly used as a raw material for lithium precipitation, saving the production cost of lithium - mica lithium - extraction enterprises; in addition, this embodiment uses calcium oxide to recover ammonia, reducing the raw material cost, and the prepared calcium sulfate product can be used as a raw material for lepidolite roasting, saving the production cost of lithium - mica lithium - extraction enterprises.

[0040] When the treatment scale of the potassium - sodium sulfate mixed salt is 15 tons / h and calculated based on 300 days of operation per year, the economic benefits that can be created by the system and process of this embodiment are shown in Table 1, and the annual economic benefits that can be created are approximately 173.827 million yuan.

[0041] Table 1 Economic benefit budget table of the system and process of this embodiment

[0042]

[0043]

[0044] The above - described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those skilled in the art to the technical solutions of the present invention all fall within the protection scope determined by the claims of the present invention.

Claims

1. A potassium sulfate sodium mixed salt resource conversion high value system, comprising a potassium sulfate dissolving device (1), wherein a first feed port of the potassium sulfate dissolving unit (1) is connected to a potassium sulfate sodium mixed salt outlet, a discharge port of the potassium sulfate dissolving device (1) is connected to an inlet of a first solid-liquid separation device (2), a liquid discharge port of the first solid-liquid separation device (2) is connected to a pipe-side feed port of a heat exchanger (3), a pipe-side discharge port of the heat exchanger (3) is connected to an inlet of a cooling crystallization device (4), a crystallization discharge port of the cooling crystallization device (4) is connected to an inlet of a second solid-liquid separation device (5), a liquid discharge port of the cooling crystallization device (4) is connected to a first inlet of a first buffer tank (6), and a second The liquid discharge port of the solid-liquid separation device (5) is connected to the second inlet of the first buffer tank (6), the solid discharge port of the second solid-liquid separation device (5) is connected to the inlet of the drying device (7), the first outlet of the first buffer tank (6) is connected to the shell side inlet of the heat exchanger (3), the shell side outlet of the heat exchanger (3) is connected to the second inlet of the potassium sulfate dissolving device (1), the second inlet of the first buffer tank (6) is connected to the feed port of the rare metal recovery unit (8); the solid discharge port of the first solid-liquid separation device (2) is connected to the first feed port of the sodium sulfate dissolving device (9), and the second feed port of the sodium sulfate dissolving device (9) is connected to the first discharge port of the second buffer tank (17). The discharge port of the sodium sulfate dissolving device (9) is connected to the first inlet of the alkali-making reaction device (10), the second inlet of the alkali-making reaction device (10) is connected to the discharge port of the carbonization reaction device (13), the first inlet of the carbonization reaction device (13) is connected to the discharge port of the ammonia absorption device (12), the second inlet of the carbonization reaction device (13) is connected to the carbon dioxide outlet, the first inlet of the ammonia absorption device (12) is connected to the outlet of the liquid ammonia storage tank (11), the second inlet of the ammonia absorption device (12) is connected to the second outlet of the second buffer tank (17), the first inlet of the liquid ammonia storage tank (11) is connected to the liquid ammonia outlet, and the second inlet of the liquid ammonia storage tank (11) is connected to the outlet of the alkali-making reaction device (12). The gas outlet of the device (15) is connected; the solid outlet of the alkali-making reaction device (10) is connected to the feed port of the washing / filtering device (14); the liquid outlet of the washing / filtering device (14) is connected to the first feed port of the alkalization device (15); the liquid outlet of the alkali-making reaction device (10) is connected to the second feed port of the alkalization device (15); the third feed port of the alkalization device (15) is connected to the calcium oxide outlet; the solid outlet of the alkalization device (15) is connected to the feed port of the third solid-liquid separation device (16); the liquid outlet of the alkalization device (15) and the liquid outlet of the third solid-liquid separation device (16) are connected to the feed port of the second buffer tank (17); The potassium sulfate dissolving device (1) is provided with an electric heating system and a stirring device, with a stirring speed of 450-600 rpm, a residence time of 1-1.5 hours, and an operating temperature of 90-100° C.; The sodium sulfate dissolving device (9) is provided with an electric heating system and a stirring device, with a stirring speed of 300-400 rpm, a residence time of 0.5-1 h, and an operating temperature of 30-50° C.; The alkali production reaction device (10) is provided with an electric heating system, a cooling system and a stirring device, with a stirring speed of 500-600 rpm, a residence time of 2-3 hours, and a reaction temperature of 45-55°C; The cooling crystallization device (4) comprises a cooling crystallizer and a refrigeration system, adopts cooling water circulation refrigeration, has an operating temperature of 30-35°C, and a residence time of 1.5-2h.

2. A process for utilizing the potassium and sodium sulfate mixed salt resource high-value conversion system according to claim 1, characterized in that: The following steps are involved: In the first step, the potassium sulfate and sodium sulfate mixed salt is fed into the potassium sulfate dissolving device (1), and at the same time, a portion of the saturated sodium sulfate solution in the first buffer tank (6) is circulated to the potassium sulfate dissolving device (1) after heat exchange through the heat exchanger (3), and industrial water is added to the potassium sulfate dissolving device (1) to dissolve all the potassium sulfate in the potassium sulfate and sodium sulfate mixed salt, and the sodium sulfate in the dissolved liquid is saturated, and then the dissolved liquid and the undissolved sodium sulfate solid are fed together into the first solid-liquid separation device (2) to separate the dissolved liquid and the undissolved sodium sulfate solid, and the separated dissolved liquid is discharged from the liquid outlet of the first solid-liquid separation device (2) and fed into the heat exchanger (3) to countercurrently exchange heat with the saturated sodium sulfate solution from the first buffer tank (6) to cool, and then fed into the cooling crystallization device (4) to crystallize potassium sulfate, and the result is as follows: The crystal particles are discharged from the crystallization outlet of the cooling crystallization device (4) and then sent to the second solid-liquid separation device (5) for solid-liquid separation. The separated potassium sulfate solid is discharged from the solid outlet of the second solid-liquid separation device (5) and then sent to the drying device (7) for drying to obtain a potassium sulfate product. The mother liquor in the cooling crystallization device (4), i.e., the saturated sodium sulfate solution containing potassium sulfate, and the liquid discharge from the second solid-liquid separation device (5) are sent to the first buffer tank (6) together. Then, part of the saturated sodium sulfate solution in the first buffer tank (6) is sent to the heat exchanger (3) for heat exchange and temperature increase, and then sent to the potassium sulfate dissolving device (1). The remaining part is sent to the rare metal recovery unit (8) for recovering the rare metals of rubidium, strontium, thallium and beryllium contained in the potassium sodium sulfate mixed salt. In the second step, the sodium sulfate solid separated by the first solid-liquid separation device (2) is sent to the sodium sulfate dissolving device (9), and at the same time, the circulating liquid in the second buffer tank (17) is circulated to the sodium sulfate dissolving device (9), and water is added to the sodium sulfate dissolving device (9) to fully dissolve the sodium sulfate, and then sent to the alkali reaction device (10). At the same time, liquid ammonia is sent from the liquid ammonia storage tank (11) to the ammonia absorption device (12), and the circulating liquid in the second buffer tank (17) is sent to the ammonia absorption device (12) to absorb the liquid ammonia to become ammonia water with a mass content of 20%. The ammonia water with a mass content of 20% is then sent to the carbonization reaction device (13) to react with carbon dioxide to generate ammonium bicarbonate. The ammonium bicarbonate solution is then sent to the alkali reaction device (10) to react with sodium sulfate to generate sodium bicarbonate and ammonium sulfate. The solubility of sodium bicarbonate in water is low and crystals are precipitated. In the third step, the sodium bicarbonate crystals precipitated in the alkali reaction device (10) are discharged from the solid discharge port into the washing / filtering device (14), and the washed and filtered liquid is discharged from the liquid outlet of the washing / filtering device (14) and sent to the alkalization device (15). At the same time, the mother liquor of the alkali reaction device (10) is sent to the alkalization device (15), calcium oxide is added to react with water to generate calcium hydroxide, and then reacted with ammonium sulfate to generate ammonia and calcium sulfate. The washed and filtered sodium bicarbonate solid is discharged from the solid outlet of the washing / filtering device (14) and directly used as a raw material for lithium precipitation or the sodium bicarbonate is calcined at 240°C to form sodium carbonate, which is then used as a raw material for lithium precipitation. The ammonia gas in the alkalization device (15) is circulated to the liquid ammonia storage tank (11), and liquid ammonia is added to the liquid ammonia storage tank (11). The solid material in the alkalization device (15) is sent to the third solid-liquid separation device (16) for solid-liquid separation. The separated solid is discharged from the solid outlet of the third solid-liquid separation device (16). After natural air drying, a calcium sulfate product is obtained, which is used as a raw material in the roasting process of lepidolite ore. The clear liquid of the alkalization device (15) and the liquid of the third solid-liquid separation device (16) are sent to the second buffer tank (17) for recycling, part of which is recycled to the ammonia absorption device (12), and the remaining part is recycled to the sodium sulfate dissolution device (9).

3. The process according to claim 2, characterized in that: The carbonization reaction device (13) has an operating pressure of 0.18-0.22 MPa, an operating temperature of 30-35° C., a residence time of 3-4 hours, a molar ratio of excess carbon dioxide to ammonia water of ≥2.5, and the flue gas generated during the calcination of lepidolite is recycled as a raw material for the carbonization reaction.

4. The process according to claim 2, characterized in that: The alkalization device (15) is provided with an ammonia stripping device, the operating pH is 8-9, the residence time is 1-2 hours, and the molar ratio of calcium oxide to sodium sulfate in the reaction solution is 1.1:1.

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