Lithium slag desulfurization method with byproduct calcium sulfate and desulfurized lithium slag

Abstract

The present application belongs to the technical field of solid waste resource utilization, and provides a lithium residue desulfurization method and desulfurized lithium residue with by-product calcium sulfate. The present application mixes lithium-containing, rubidium-containing, cesium-containing ore, lithium residue, inorganic salt and limestone, roasts to obtain clinker, mixes the clinker with water, leaches to obtain preliminary desulfurized lithium residue and leaching liquor; mixes chloride salt solution with the preliminary desulfurized lithium residue, pressure cooks and desulfurizes to obtain desulfurized lithium residue and desulfurized liquor, and completes lithium residue desulfurization; mixes the leaching liquor with calcium chloride to react, obtains calcium sulfate and sulfate-removed liquor, mixes the obtained calcium sulfate with calcium sulfate obtained by concentrating the desulfurized liquor, and realizes by-product calcium sulfate. The method not only realizes efficient desulfurization treatment of lithium residue while by-product calcium sulfate is produced, but also solves the problems of easy burning and melting of lithium-containing, rubidium-containing and cesium-containing ore roasting and hydrogen fluoride overflow; at the same time, the method is simple, low in cost, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a method for desulfurizing lithium slag produced as a byproduct of calcium sulfate and the desulfurized lithium slag. Background Technology

[0002] Lithium is mainly found in minerals such as spodumene and lepidolite, as well as in salt lake brines. Lithium slag is a general term for the waste residue generated after lithium extraction from lithium-rich resources. Its type varies depending on the lithium extraction process, and it is mainly divided into spodumene lithium extraction slag and lepidolite lithium extraction slag.

[0003] With the booming development of the lithium industry, the amount of lithium slag generated is also increasing daily. Currently, most of this waste is disposed of through stockpiling or landfilling, which not only wastes valuable resources but also, if not properly managed, may damage the geological environment and pose a risk of environmental pollution. At present, lithium slag is mainly used in the cement and building materials industry, but its added value is relatively low, and the small amounts of lithium, niobium, tantalum metal, and gypsum it contains are not effectively recycled. Furthermore, due to the low proportion of lithium slag added to cement and building materials, the industry struggles to achieve its goal of large-scale lithium slag disposal. Therefore, exploring more efficient, environmentally friendly, and economically feasible comprehensive utilization methods for lithium slag is particularly important.

[0004] Currently, high-value-added applications of lithium slag are mainly concentrated in ceramics, glass fiber, papermaking, and adsorption materials. However, these applications require that the sulfur trioxide content in lithium slag not exceed 0.3%, while the standard YB / T4230-2010 for lithium slag powder used in cement and concrete requires an SO3 content (mass concentration) of 2.3% to 2.8%. Therefore, corresponding measures need to be taken to desulfurize lithium slag.

[0005] During ore roasting, the high temperatures cause added auxiliary materials, such as inorganic salts, with low melting points to easily melt. The fluorine they contain may also escape as hydrogen fluoride, which not only pollutes the environment but also corrodes equipment. Furthermore, many valuable metals contained in the ore fail to be effectively extracted, leading to resource waste.

[0006] In conclusion, developing a lithium slag desulfurization method that can fully utilize lithium slag resources and simultaneously produce calcium sulfate as a byproduct to assist in ore roasting is of great significance. Summary of the Invention

[0007] In view of this, the present invention provides a method for desulfurizing lithium slag with calcium sulfate as a byproduct and desulfurized lithium slag, so as to solve the problems of high sulfur content in existing lithium slag and the inability to fully utilize lithium slag resources.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for desulfurizing lithium slag containing calcium sulfate as a byproduct, comprising the following steps:

[0010] 1) Mix lithium-, rubidium-, and cesium-containing ores, lithium slag, inorganic salts, and limestone, and roast them to obtain clinker. Mix the clinker with water and leach it to obtain preliminary desulfurized lithium slag and leachate.

[0011] 2) Mix the chloride salt solution with the pre-desulfurized lithium slag and perform pressure boiling desulfurization to obtain desulfurized lithium slag and desulfurization liquid, thus completing the lithium slag desulfurization;

[0012] 3) The leachate obtained in step 1) is mixed with calcium chloride and reacted to obtain calcium sulfate and desulfate solution. The obtained calcium sulfate is then mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to produce calcium sulfate as a byproduct.

[0013] Preferably, in step 1), the mass ratio of lithium-containing rubidium-containing ore, cesium-containing slag, inorganic salt, and limestone is 1:0.2-1.0:0.2-1.0:0.05-0.3; the liquid-to-solid ratio of water to clinker is 2-5 mL / g; the roasting temperature in step 1) is 750-950℃, and the time is 10-120 min; the leaching temperature is 25-95℃, and the time is 30-90 min.

[0014] Preferably, the lithium-, rubidium-, and cesium-containing ore in step 1) includes one or more of lepidolite, lithium-containing clay, and cesium garnet; the lithium slag includes spodumene smelting slag and / or lepidolite smelting slag; and the inorganic salt includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium sulfate, and potassium sulfate.

[0015] Preferably, the mass concentration of sulfur in the lithium slag in step 1) is 2-30 wt% based on sulfate; and the particle size of the lithium slag is 5-300 μm.

[0016] Preferably, in step 2), the liquid-to-solid ratio of the chloride salt solution to the preliminary desulfurized lithium slag is 5–25 mL / g; the mass concentration of the chloride salt solution is 5–30 wt%; and the temperature for pressure boiling desulfurization in step 2) is 100–200 °C, and the time is 5–20 min.

[0017] Preferably, the chloride salt solution in step 2) includes a sodium chloride solution and / or a potassium chloride solution.

[0018] Preferably, in step 3), the molar ratio of calcium chloride to sulfate ions in the leachate is 1.0–1.2:1; the reaction temperature is 10–50°C, and the reaction time is 10–30 min.

[0019] Preferably, step 3) further includes removing impurities from the sulfate-removing solution for use in preparing valuable metal salts.

[0020] The present invention also provides a desulfurized lithium slag obtained by the above-mentioned desulfurization method of lithium slag with calcium sulfate as a by-product, wherein the mass concentration of sulfur in the desulfurized lithium slag is 0.05 to 0.2 wt% based on sulfate.

[0021] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The method described in this invention employs a two-stage desulfurization process, achieving highly efficient desulfurization of lithium slag. The sulfur removal rate can reach up to 96.3%, while simultaneously controlling the sulfate content in the desulfurized lithium slag to 0.05–0.2%, equivalent to an SO3 mass concentration of 0.04–0.17%. This means the sulfur content in the lithium slag obtained by this invention fully meets the standard of 2.3%–2.8% SO3 content. This not only makes the large-scale conversion of lithium slag into building materials possible but also facilitates the high-value utilization of desulfurized lithium slag. It can be used to prepare lithium slag roadbeds, synthetic sand, auxiliary cementitious materials, molecular sieves, porous ceramics, foam glass, and catalysts. Adding lithium slag to these applications not only effectively reduces costs but also promotes the recycling of lithium slag resources and environmental protection.

[0023] The method described in this invention not only achieves efficient desulfurization of lithium slag, reducing the sulfate content in the desulfurized lithium slag to below 0.2%, but also realizes the recovery of calcium sulfate with a yield of over 93% and a purity of over 95.8%. At the same time, the method described in this invention also solves the problems of easy melting and hydrogen fluoride overflow during roasting of lithium, rubidium, and cesium-containing ores.

[0024] The method described in this invention is simple and low-cost, realizing the comprehensive utilization of lithium slag resources, demonstrating significant economic value and environmental friendliness, and has broad application prospects. Detailed Implementation

[0025] This invention provides a method for desulfurizing lithium slag containing calcium sulfate as a byproduct, comprising the following steps:

[0026] 1) Mix lithium-, rubidium-, and cesium-containing ores, lithium slag, inorganic salts, and limestone, and roast them to obtain clinker. Mix the clinker with water and leach it to obtain preliminary desulfurized lithium slag and leachate.

[0027] 2) Mix the chloride salt solution with the pre-desulfurized lithium slag and perform pressure boiling desulfurization to obtain desulfurized lithium slag and desulfurization liquid, thus completing the lithium slag desulfurization;

[0028] 3) The leachate obtained in step 1) is mixed with calcium chloride and reacted to obtain calcium sulfate and desulfate solution. The obtained calcium sulfate is then mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to produce calcium sulfate as a byproduct.

[0029] In this invention, the mass ratio of lithium, rubidium, cesium ore, lithium slag, inorganic salts, and limestone in step 1) is 1:0.2-1.0:0.2-1.0:0.05-0.3, preferably 1:0.25-0.98:0.3-0.98:0.1-0.28, more preferably 1:0.3-0.8:0.35-0.65:0.12-0.25, and even more preferably 1:0.5-0.6:0.4-0.5:0.15-0.2; the liquid-solid ratio of water to clinker is 2-5 mL / g, preferably 2.2-4.5 mL / g, more preferably 2.5-4 mL / g, and even more preferably 3 mL / g.

[0030] In this invention, the roasting temperature in step 1) is 750–950°C, preferably 780–920°C, more preferably 800–900°C, and even more preferably 850°C; the roasting time is 10–120 min, preferably 20–100 min, more preferably 35–70 min, and even more preferably 45–60 min; the leaching temperature is 25–95°C, preferably 35–85°C, more preferably 40–75°C, and even more preferably 50–65°C; the leaching time is 30–90 min, preferably 40–80 min, more preferably 45–75 min, and even more preferably 55–60 min.

[0031] In this invention, the lithium, rubidium, and cesium-containing ore in step 1) includes one or more of lepidolite, lithium-containing clay, and cesium garnet; the lithium slag includes spodumene smelting slag and / or lepidolite smelting slag; and the inorganic salt includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium sulfate, and potassium sulfate.

[0032] In this invention, based on sulfate, the mass concentration of sulfur in the lithium slag in step 1) is 2-30 wt%, preferably 5-25 wt%, more preferably 10-20 wt%, and even more preferably 15 wt%; the particle size of the lithium slag is 5-300 μm, preferably 80-250 μm, more preferably 100-200 μm, and even more preferably 150 μm.

[0033] In this invention, the lithium slag in step 1) contains calcium sulfate. During roasting, the calcium ions in the calcium sulfate undergo ion exchange with the valuable metal ions such as lithium, rubidium, and cesium in the lithium, rubidium, and cesium-containing ores, transforming the calcium sulfate into lithium sulfate, rubidium sulfate, and cesium sulfate. The lithium slag also contains a large amount of alumina and silicon dioxide. According to thermodynamic calculations, when alumina and silicon dioxide are present, the Gibbs free energy of the ion exchange reaction is lower, which can promote the ion exchange reaction and realize the extraction of valuable metals from the lithium, rubidium, and cesium-containing ores.

[0034] In this invention, the problem of inorganic salts having low melting points and being easily melted is avoided by adding lithium slag. This is because lithium slag contains calcium sulfate (melting point 1297℃) and a large amount of aluminosilicates, both of which have high melting points and will not become molten during the roasting process. However, the inorganic salts added in this invention have low melting points and will become molten during the roasting process. Therefore, lithium slag can provide a kind of "skeletal function" for the easily molten inorganic salts, effectively avoiding the melting phenomenon of inorganic salts (during the roasting process, lithium slag can be compared to a sponge, and the easily molten inorganic salts can be compared to water. A sponge can absorb water, and lithium slag has a similar effect).

[0035] In this invention, by adding limestone and lithium slag, the calcium sulfate contained therein can react with the hydrogen fluoride generated during the roasting of lithium, rubidium, and cesium ores to generate calcium fluoride, thereby achieving solid fluoride and solving the problem of hydrogen fluoride overflow during the roasting of lithium, rubidium, and cesium ores.

[0036] In this invention, the liquid-to-solid ratio of the chloride salt solution to the preliminary desulfurized lithium slag in step 2) is 5-25 mL / g, preferably 8-20 mL / g, more preferably 10-16 mL / g, and even more preferably 15 mL / g; the mass concentration of the chloride salt solution is 5-30 wt%, preferably 8-25 wt%, more preferably 10-20 wt%, and even more preferably 15 wt%.

[0037] In this invention, the temperature of the pressure boiling desulfurization in step 2) is 100-200°C, preferably 120-180°C, more preferably 130-150°C, and even more preferably 140°C; the time is 5-20 min, preferably 8-18 min, more preferably 10-15 min, and even more preferably 12 min.

[0038] In this invention, the chloride salt solution in step 2) includes sodium chloride solution and / or potassium chloride solution.

[0039] In this invention, the core principle of pressure cooking desulfurization in step 2) lies in utilizing the unique porous structure of lithium slag. In this structure, some sulfate ions are adsorbed in the pores of lithium slag in the form of calcium sulfate, and the sulfate ions in the initially desulfurized lithium slag exist in this form. This invention uses a chloride salt solution and pressure cooking to replace the calcium sulfate hidden in the pores of lithium slag, thereby achieving the purpose of deep desulfurization.

[0040] In this invention, the molar ratio of calcium chloride to sulfate ions in the leachate in step 3) is 1.0 to 1.2:1, preferably 1.1 to 1.18:1, and more preferably 1.15:1; the calcium chloride is preferably industrial grade dihydrate calcium chloride.

[0041] In this invention, the reaction temperature in step 3) is 10-50°C, preferably 15-40°C, more preferably 20-35°C, and even more preferably 30°C; the reaction time is 10-30 min, preferably 12-28 min, more preferably 15-25 min, and even more preferably 20 min.

[0042] In this invention, step 3) further includes removing impurities from the sulfate-removing solution for the preparation of valuable metal salts. Specifically, the solution after sulfate removal (containing relatively pure lithium, rubidium, cesium, potassium, and sodium) is subjected to crystallization, extraction, adsorption, or precipitation to obtain the corresponding valuable metal salts. Different valuable metal salts can be obtained depending on the system and the methods used. For example, crystallization can yield sodium sulfate, sodium chloride, potassium sulfate, and potassium chloride; extraction can yield rubidium sulfate, cesium sulfate, rubidium chloride, and cesium chloride; and precipitation can yield lithium carbonate.

[0043] In this invention, step 3) further includes purifying the calcium sulfate obtained by mixing. The preferred step is to mix calcium sulfate with water and stir and wash to obtain calcium sulfate product. The solid-liquid ratio of calcium sulfate to water is preferably 3 to 15 mL / g, more preferably 5 to 12 mL / g, and more preferably 10 mL / g.

[0044] In this invention, after the desulfurization liquid in step 3) is concentrated to obtain calcium sulfate, the remaining desulfurization liquid and the evaporated water are preferably returned to the pressure boiling desulfurization process for recycling.

[0045] The present invention also provides a desulfurized lithium slag obtained by the above-mentioned desulfurization method of lithium slag with calcium sulfate as a by-product. The mass concentration of sulfur in the desulfurized lithium slag is 0.05-0.2 wt%, preferably 0.1-0.18 wt%, and more preferably 0.15 wt%, based on sulfate. The desulfurized lithium slag can be used to prepare lithium slag roadbed, synthetic sand, auxiliary cementing materials, molecular sieves, porous ceramics, foam glass, and catalysts.

[0046] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] 1) Lithium iron ore mica (grade 2.7%), spodumene smelting slag (particle size 150μm, sulfate concentration 25wt%), industrial grade sodium chloride and industrial grade limestone were mixed in a mass ratio of 1:0.6:0.3:0.1 and calcined at 900℃ for 10min to obtain clinker. Then, water was added to the clinker with a liquid-solid ratio of 3mL / g and leached at 95℃ for 60min to obtain preliminary desulfurized lithium slag (sulfate ion concentration 2.53wt%) and leachate (sulfate ion concentration 22.46g / L).

[0049] 2) Mix a 10wt% sodium chloride solution with the pre-desulfurized lithium slag and control the liquid-solid ratio at 12mL / g. Then, boil the mixture at 140℃ for 5min and filter to obtain a desulfurized lithium slag and desulfurization liquid with a sulfate ion concentration of 0.15wt%, thus completing the lithium slag desulfurization.

[0050] 3) The leachate obtained in step 1) is mixed with industrial-grade dihydrate calcium chloride at a molar ratio of sulfate ions to calcium chloride of 1:1.2. The mixture is reacted at 30°C for 20 min to obtain calcium sulfate and a sulfate-removing solution. The obtained calcium sulfate is mixed with the calcium sulfate obtained from the concentration of the desulfurization solution in step 2) to produce calcium sulfate as a byproduct. The solid-liquid ratio is controlled at 10 mL / g. The mixed calcium sulfate is then mixed with water and purified by stirring and washing at 25°C to obtain the calcium sulfate product. The water evaporated during the concentration of the desulfurization solution and the remaining desulfurization solution after concentration are returned to the pressure boiling desulfurization process for recycling. The calcium ion mass concentration in the sulfate-removing solution is 1.06 g / L, and the sulfate ion mass concentration is 0.93 g / L. The leachate contains a large amount of lithium, sodium, and potassium salts and a small amount of rubidium and cesium salts.

[0051] After removing impurities from the sulfate-free solution, it is evaporated and crystallized to obtain sodium chloride; then cooled and crystallized to obtain potassium chloride; then precipitated and filtered to obtain lithium carbonate and primary precipitate mother liquor; the primary precipitate mother liquor is acidified and evaporated and crystallized to obtain sodium chloride and concentrate; the concentrate is precipitated and filtered to obtain lithium carbonate and secondary precipitate mother liquor; the secondary precipitate mother liquor is treated and extracted (extractant is t-BAMBP) to obtain rubidium chloride and cesium chloride.

[0052] According to the test results, the sulfate removal rate of the lithium slag in Example 1 was 96.3%, the calcium sulfate yield was 94.5%, and the purity of calcium sulfate was 96.8%.

[0053] Example 2

[0054] 1) Lithium-containing clay (grade 1.0%), lepidolite smelting slag (particle size 150μm, sulfate concentration 15wt%), industrial-grade potassium chloride and industrial-grade limestone were mixed in a mass ratio of 1:0.8:0.2:0.15 and calcined at 800℃ for 45min to obtain clinker. Then, water was added to the clinker with a liquid-solid ratio of 3mL / g and leached at 65℃ for 45min to obtain preliminary desulfurized lithium slag (sulfate ion concentration 2.00wt%) and leachate (sulfate ion concentration 20.36g / L).

[0055] 2) Mix a 25wt% potassium chloride solution with the pre-desulfurized lithium slag and control the liquid-solid ratio at 14mL / g. Then, pressure cook at 180℃ for 15min and filter to obtain a desulfurized lithium slag and desulfurization liquid with a sulfate ion concentration of 0.16wt%, thus completing the lithium slag desulfurization.

[0056] 3) The leachate obtained in step 1) is mixed with industrial-grade dihydrate calcium chloride at a molar ratio of sulfate ions to calcium chloride of 1:1.15. The mixture is reacted at 20°C for 20 min to obtain calcium sulfate and a sulfate-removing solution. The obtained calcium sulfate is mixed with the calcium sulfate obtained from the concentration of the desulfurization solution in step 2) to produce calcium sulfate as a byproduct. The solid-liquid ratio is controlled at 10 mL / g. The mixed calcium sulfate is then mixed with water and purified by stirring and washing at 25°C to obtain the calcium sulfate product. The water evaporated during the concentration of the desulfurization solution and the remaining desulfurization solution after concentration are returned to the pressure boiling desulfurization process for recycling. The calcium ion mass concentration in the sulfate-removing solution is 0.74 g / L, and the sulfate ion mass concentration is 1.05 g / L. The leachate contains a large amount of lithium and potassium salts.

[0057] After removing impurities from the sulfate-free solution, it is cooled and crystallized to obtain potassium chloride; then, after precipitation and filtration, lithium carbonate and a primary precipitate mother liquor are obtained; the primary precipitate mother liquor is acidified and then evaporated and crystallized to obtain sodium chloride and a concentrated solution; the concentrated solution is adsorbed and desorbed by a titanium-based adsorbent to obtain lithium chloride.

[0058] According to the test results, the sulfate removal rate of lithium slag in Example 2 was 94.2%, the calcium sulfate yield was 93.1%, and the purity of calcium sulfate was 95.8%.

[0059] Example 3

[0060] 1) Cesium garnet (grade 25%), spodumene smelting slag (particle size 150μm, sulfate concentration 20wt%), industrial grade sodium chloride and industrial grade limestone were mixed in a mass ratio of 1:0.5:0.4:0.2 and then calcined at 850℃ for 120min to obtain clinker. Then, water was added to the clinker with a liquid-solid ratio of 3mL / g and leached at 25℃ for 90min to obtain preliminary desulfurized lithium slag (sulfate ion concentration 1.86wt%) and leachate (sulfate ion concentration 16.27g / L).

[0061] 2) Mix a 10wt% sodium chloride solution with the pre-desulfurized lithium slag and control the liquid-solid ratio at 14mL / g. Then, pressure cook at 120℃ for 20min and filter to obtain desulfurized lithium slag and desulfurization liquid with a sulfate ion concentration of 0.08wt%, thus completing the lithium slag desulfurization.

[0062] 3) The leachate obtained in step 1) is mixed with industrial-grade calcium chloride dihydrate at a molar ratio of sulfate ions to calcium chloride of 1:1.15. The mixture is reacted at 45°C for 20 min to obtain calcium sulfate and a sulfate-removing solution. The obtained calcium sulfate is mixed with the calcium sulfate obtained from the desulfurization solution concentration in step 2) to produce calcium sulfate as a byproduct. The solid-liquid ratio is controlled at 10 mL / g. The mixed calcium sulfate is then mixed with water and purified by stirring and washing at 25°C to obtain the calcium sulfate product. The water evaporated during the desulfurization solution concentration process and the remaining desulfurization solution after concentration are returned to the pressure boiling desulfurization process for recycling. The calcium ion mass concentration in the sulfate-removing solution is 1.05 g / L, and the sulfate ion mass concentration is 0.78 g / L. The leachate contains a large amount of cesium, sodium, and potassium salts, as well as a small amount of lithium salts.

[0063] After removing impurities from the sulfate-free solution, extraction was performed (using t-BAMBP as the extraction solvent) to obtain rubidium chloride and cesium chloride; the raffinate was evaporated, concentrated, and then cooled to crystallize, yielding potassium chloride and a concentrate; the concentrate was extracted with TBP to obtain lithium chloride.

[0064] According to the test results, the sulfate removal rate of the lithium slag in Example 3 was 95.7%, the calcium sulfate yield was 94.0%, and the purity of calcium sulfate was 96.3%.

[0065] As can be seen from Examples 1-3 above, the method described in this invention for desulfurizing lithium slag not only reduces the sulfate content in the lithium slag to below 0.2%, but also achieves the recovery of calcium sulfate, with a recovery rate of over 93% and a purity of over 95.8%. Simultaneously, the method described in this invention can also extract valuable metals from lithium, rubidium, and cesium-containing ores, solving the problems of easy melting and hydrogen fluoride leakage during roasting of lithium, rubidium, and cesium-containing ores. The method described in this invention is simple, low-cost, and achieves comprehensive utilization of lithium slag resources, demonstrating significant economic value and environmental friendliness, and has broad application prospects.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for desulfurization of lithium slag with by-product calcium sulfate, characterized by, Includes the following steps: 1) Lithium-, rubidium-, and cesium-containing ores, lithium slag, inorganic salts, and limestone are mixed and roasted to obtain clinker. The clinker is then mixed with water and leached to obtain preliminary desulfurized lithium slag and leachate. 2) Mix the chloride salt solution with the pre-desulfurized lithium slag and perform pressure boiling desulfurization to obtain desulfurized lithium slag and desulfurization liquid, thus completing the lithium slag desulfurization; 3) The leachate obtained in step 1) is mixed with calcium chloride and reacted to obtain calcium sulfate and desulfate solution. The obtained calcium sulfate is then mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to produce calcium sulfate as a byproduct.

2. The method according to claim 1, wherein the method is characterized by, The mass ratio of lithium-containing, rubidium-, and cesium-containing ore, lithium slag, inorganic salts, and limestone mentioned in step 1) is 1:0.2~1.0:0.2~1.0:0.05~0.3; The liquid-to-solid ratio of the water to the clinker is 2~5 mL / g; The roasting temperature in step 1) is 750~950℃ and the time is 10~120min; the leaching temperature is 25~95℃ and the time is 30~90min.

3. The method according to claim 2, wherein the calcium sulfate is produced as a byproduct. The lithium, rubidium, and cesium-containing ores mentioned in step 1) include one or more of lepidolite, lithium-containing clay, and cesium garnet; The lithium slag includes spodumene smelting slag and / or lepidolite smelting slag. The inorganic salts include one or more of sodium chloride, potassium chloride, calcium chloride, sodium sulfate, and potassium sulfate.

4. The method according to any one of claims 1 to 3, wherein the method is characterized by, The mass concentration of sulfur in the lithium slag in step 1) is 2-30 wt% based on sulfate; the particle size of the lithium slag is 5-300 μm.

5. The method according to claim 4, wherein the calcium sulfate is recovered as a byproduct. The liquid-to-solid ratio of the chloride salt solution to the preliminary desulfurized lithium slag in step 2) is 5~25 mL / g; The mass concentration of the chloride solution is 5-30 wt%; The temperature for pressure boiling desulfurization in step 2) is 100~200℃, and the time is 5~20min.

6. The method according to claim 5, wherein the calcium sulfate is recovered as a byproduct. The chloride salt solution mentioned in step 2) includes sodium chloride solution and / or potassium chloride solution.

7. The method according to claim 6, wherein the calcium sulfate is recovered as a byproduct. In step 3), the molar ratio of calcium chloride to sulfate ions in the leachate is 1.0~1.2:1; The reaction is carried out at a temperature of 10-50°C for a time of 10-30 minutes.

8. The method according to claim 7, wherein the calcium sulfate is recovered from the lithium slag. Step 3) also includes removing impurities from the sulfate-free solution for the preparation of valuable metal salts.

9. The desulfurized lithium slag obtained by the desulfurization method for lithium slag with calcium sulfate as a byproduct according to any one of claims 1 to 8, characterized in that, The mass concentration of sulfur in the desulfurized lithium slag is 0.05~0.2wt% based on sulfate.