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

Abstract

The invention belongs to the technical field of solid waste resource utilization, and provides a lithium slag desulfurization method for byproduct calcium sulfate and desulfurized lithium slag. The method comprises the following steps: mixing ores containing lithium, rubidium and cesium, lithium slag, inorganic salt and limestone, roasting to obtain clinker, mixing the clinker with water, and leaching to obtain primary desulfurized lithium slag and leachate; mixing a chlorate solution with the preliminarily desulfurized lithium slag, and carrying out autoclave desulfurization to obtain desulfurized lithium slag and a desulfurized solution, thereby completing lithium slag desulfurization; and mixing the leachate with calcium chloride for reaction to obtain calcium sulfate and a sulfate radical removal solution, and mixing the obtained calcium sulfate with calcium sulfate obtained by concentrating the desulfurization solution to obtain a byproduct calcium sulfate. According to the method, calcium sulfate is produced as a byproduct while the lithium slag is subjected to efficient desulfurization treatment, and the problems that ores containing lithium, rubidium and cesium are easy to burn and melt and hydrogen fluoride overflows during roasting are solved; meanwhile, the method is simple, low in cost and wide in application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, and in particular to a lithium slag desulfurization method with by-product calcium sulfate and desulfurized lithium slag. Background Art

[0002] Lithium mainly exists in minerals such as spodumene and lepidolite and in salt lake brine. Lithium slag is a general term for waste residues produced after lithium is extracted from lithium-rich resources. Its type varies depending on the lithium extraction process and is mainly divided into spodumene lithium slag and lepidolite lithium slag.

[0003] With the booming development of the lithium industry, the amount of lithium slag generated is also increasing. At present, most of these wastes are handled by stacking or landfilling, which not only wastes precious resources, but also may damage the geological environment and bring risks of environmental pollution if not managed properly. At present, lithium slag is mainly used in the cement and building materials industry, but its added value is relatively low, and the small amount of lithium, niobium and tantalum metals and gypsum contained in it are not effectively recycled. In addition, due to the low proportion of lithium slag added in cement and building materials, it is difficult for the industry to achieve the goal of large-scale disposal of lithium slag. Therefore, it is particularly important to explore more efficient, environmentally friendly and economically feasible ways to comprehensively utilize lithium slag.

[0004] At present, the high value-added applications of lithium slag are mainly concentrated in the fields of ceramics, glass fiber, papermaking and adsorption materials. However, these applications require that the sulfur trioxide content in lithium slag should not exceed 0.3%. The standard "YB / T4230-2010 Lithium Slag Powder for Cement and Concrete" requires the SO3 content (mass concentration) to be 2.3% to 2.8%, so corresponding measures need to be taken to desulfurize the lithium slag.

[0005] During the ore roasting process, due to the high temperature, the added auxiliary materials such as inorganic salts have a low melting point and are prone to melting. The fluorine contained in them may also escape in the form of hydrogen fluoride, which not only pollutes the environment but also may corrode the equipment. In addition, the various valuable metals contained in the ore have not been effectively extracted, resulting in a waste of resources.

[0006] In summary, it is of great significance to develop a lithium slag desulfurization method that can fully utilize lithium slag resources, produce calcium sulfate as a by-product and assist in ore roasting. Summary of the invention

[0007] In view of this, the present invention provides a lithium slag desulfurization method with by-product calcium sulfate and desulfurized lithium slag to solve the problems of high sulfur content in existing lithium slag and insufficient utilization of lithium slag resources.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] The present invention provides a method for desulfurizing lithium slag with by-product calcium sulfate, comprising the following steps:

[0010] 1) mixing lithium, rubidium, cesium ore, lithium slag, inorganic salt and limestone, roasting to obtain clinker, mixing the clinker with water, leaching to obtain preliminary desulfurized lithium slag and leachate;

[0011] 2) mixing the chloride solution with the preliminary desulfurized lithium slag, performing pressure cooking desulfurization, obtaining desulfurized lithium slag and desulfurization liquid, and completing lithium slag desulfurization;

[0012] 3) The leaching solution obtained in step 1) is mixed with calcium chloride for reaction to obtain calcium sulfate and sulfate removal solution, and the obtained calcium sulfate is mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to achieve by-production of calcium sulfate.

[0013] Preferably, the mass ratio of the lithium-, rubidium-, cesium-containing ore, lithium slag, inorganic salt and limestone in step 1) is 1: 0.2-1.0: 0.2-1.0: 0.05-0.3; the liquid-solid ratio of water to clinker is 2-5 mL / g; the roasting temperature in step 1) is 750-950° C. and the time is 10-120 min; the leaching temperature is 25-95° C. 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 2-30wt% in terms of sulfate radical; and the particle size of the lithium slag is 5-300 μm.

[0016] Preferably, the liquid-to-solid ratio of the chloride 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 of the autoclave 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 sodium chloride solution and / or potassium chloride solution.

[0018] Preferably, in step 3), the molar ratio of calcium chloride to sulfate ions in the leaching solution 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 comprises removing impurities from the sulfate removal solution for preparing valuable metal salts.

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

[0021] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0022] The method of the present invention adopts a two-stage desulfurization method to achieve efficient desulfurization treatment of lithium slag, and the sulfur removal rate can reach up to 96.3%. At the same time, the sulfate content in the lithium slag after desulfurization can be controlled to 0.05-0.2%, which is converted into a mass concentration of SO3 of 0.04-0.17%, that is, the sulfur content in the lithium slag obtained by the present invention fully meets the standard of SO3 content of 2.3%-2.8%. This not only provides the possibility of large-scale conversion of lithium slag into building materials, but also helps to achieve high-value utilization of desulfurized lithium slag, which can be used to prepare lithium slag roadbed, synthetic sand, auxiliary cementitious materials, molecular sieves, porous ceramics, foam glass and catalysts. Adding lithium slag in these applications can not only effectively reduce costs, but also promote the recycling of lithium slag resources and environmental protection.

[0023] The method of the present invention not only realizes the efficient desulfurization of lithium slag, so that the sulfate content in the desulfurized lithium slag is reduced to below 0.2%, but also realizes the recovery of calcium sulfate, with a yield of more than 93% and a purity of more than 95.8%; at the same time, the method of the present invention also solves the problems of easy melting and hydrogen fluoride overflow during roasting of lithium, rubidium and cesium ores.

[0024] The method of the present invention is simple and low-cost, realizes the comprehensive utilization of lithium slag resources, shows significant economic value and environmental friendliness, and has broad application prospects. DETAILED DESCRIPTION

[0025] The present invention provides a method for desulfurizing lithium slag with by-product calcium sulfate, comprising the following steps:

[0026] 1) mixing lithium, rubidium, cesium ore, lithium slag, inorganic salt and limestone, roasting to obtain clinker, mixing the clinker with water, leaching to obtain preliminary desulfurized lithium slag and leachate;

[0027] 2) mixing the chloride solution with the preliminary desulfurized lithium slag, performing pressure cooking desulfurization, obtaining desulfurized lithium slag and desulfurization liquid, and completing lithium slag desulfurization;

[0028] 3) The leaching solution obtained in step 1) is mixed with calcium chloride for reaction to obtain calcium sulfate and sulfate removal solution, and the obtained calcium sulfate is mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to achieve by-production of calcium sulfate.

[0029] In the present invention, the mass ratio of the lithium-containing, rubidium-containing, cesium-containing ore, lithium slag, inorganic salt 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, further preferably 1: 0.3-0.8: 0.35-0.65: 0.12-0.25, more preferably 1: 0.5-0.6: 0.4-0.5: 0.15-0.2; the liquid-solid ratio of the water to the clinker is 2-5 mL / g, preferably 2.2-4.5 mL / g, further preferably 2.5-4 mL / g, and more preferably 3 mL / g.

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

[0031] In the present invention, the lithium, rubidium and cesium 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; the inorganic salt includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium sulfate and potassium sulfate.

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

[0033] In the present invention, the lithium slag in step 1) contains calcium sulfate. During roasting, the calcium ions in the calcium sulfate are exchanged with valuable metal ions such as lithium, rubidium, and cesium in the lithium, rubidium, and cesium ores, and the calcium sulfate is converted into lithium sulfate, rubidium sulfate, and cesium sulfate. The lithium slag also contains a large amount of aluminum oxide and silicon dioxide. According to thermodynamic calculations, when aluminum oxide and silicon dioxide are present, the Gibbs free energy of the ion exchange reaction is lower, thereby promoting the ion exchange reaction and realizing the extraction of valuable metals in the lithium, rubidium, and cesium ores.

[0034] In the present invention, the problem of low melting point and easy sintering of inorganic salts is avoided by adding lithium slag. This is because lithium slag contains calcium sulfate (melting point 1297°C) and a large amount of aluminosilicate, both of which have high melting points and will not become a molten state during the roasting process; while the inorganic salt added in the present invention has a low melting point and will become a molten state during the roasting process; therefore, lithium slag can provide a similar "skeleton function" for the easily sintered inorganic salt, effectively avoiding the sintering phenomenon of the inorganic salt (in the roasting process, lithium slag can be compared to a sponge, and the easily sintered inorganic salt can be compared to water. The sponge can absorb water, and lithium slag also has a similar effect).

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

[0036] In the present invention, the liquid-to-solid ratio of the chloride 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 more preferably 15 mL / g; the mass concentration of the chloride solution is 5-30 wt%, preferably 8-25 wt%, more preferably 10-20 wt%, and more preferably 15 wt%.

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

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

[0039] In the present invention, the core principle of the pressure cooking desulfurization in step 2) is to utilize the unique porous structure characteristics of lithium slag; in this structure, part of the sulfate is adsorbed in the pores of the lithium slag in the form of calcium sulfate, and the sulfate in the initial desulfurized lithium slag exists in this form; the present invention selects chloride solution and adopts pressure cooking to replace the calcium sulfate hidden in the pores of the lithium slag, thereby achieving the purpose of deep desulfurization.

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

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

[0042] In the present invention, step 3) further comprises removing impurities from the sulfate removal solution for preparing valuable metal salts, specifically, the solution after the sulfate removal solution is removed (containing relatively pure lithium, rubidium, cesium, potassium, sodium) is crystallized, extracted, adsorbed or precipitated to obtain the corresponding valuable metal salts; different valuable metal salts can be obtained according to different systems and different measures. For example, crystallization can obtain sodium sulfate, sodium chloride, potassium sulfate and potassium chloride; extraction can obtain rubidium sulfate, cesium sulfate, rubidium chloride and cesium chloride; precipitation can obtain lithium carbonate.

[0043] In the present invention, step 3) also includes an operation of purifying the mixed calcium sulfate, and the specific step is preferably to mix the calcium sulfate with water and stir and wash to obtain a calcium sulfate product; the solid-to-liquid ratio of the calcium sulfate to water is preferably 3-15 mL / g, more preferably 5-12 mL / g, and more preferably 10 mL / g.

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

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

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

[0047] Example 1

[0048] 1) After mixing lithium iron mica (grade of 2.7%), spodumene smelting slag (particle size of 150 μm, mass concentration of sulfate ion of 25 wt%), industrial grade sodium chloride and industrial grade limestone in a mass ratio of 1:0.6:0.3:0.1, the mixture was calcined at 900°C for 10 min to obtain clinker, and then water was added to the clinker at a liquid-solid ratio of 3 mL / g, and leaching was carried out at 95°C for 60 min to obtain preliminary desulfurized lithium slag (mass concentration of sulfate ion of 2.53 wt%) and leaching solution (mass concentration of sulfate ion of 22.46 g / L).

[0049] 2) A sodium chloride solution with a mass concentration of 10 wt% is mixed with the preliminary desulfurized lithium slag and the liquid-to-solid ratio is controlled to be 12 mL / g, and then pressure-cooked at 140° C. for 5 min, filtered to obtain desulfurized lithium slag and desulfurization liquid with a mass concentration of sulfate ions of 0.15 wt%, and the desulfurization of the lithium slag is completed.

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

[0051] The sulfate-removing liquid is decontaminated and then evaporated and crystallized to obtain sodium chloride; then cooled and crystallized to obtain potassium chloride; then filtered through precipitation to obtain lithium carbonate and a first precipitation mother liquor; the first precipitation mother liquor is acidified and then evaporated and crystallized to obtain sodium chloride and a concentrated solution; the concentrated solution is filtered through precipitation to obtain lithium carbonate and a second precipitation mother liquor; the second precipitation mother liquor is treated and then extracted (the extractant is t-BAMBP) to obtain rubidium chloride and cesium chloride.

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

[0053] Example 2

[0054] 1) Lithium-containing clay (grade 1.0%), lithium mica smelting slag (particle size 150 μm, mass concentration of sulfate ion 15 wt%), 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°C for 45 min to obtain clinker, and then water was added to the clinker at a liquid-solid ratio of 3 mL / g, and leached at 65°C for 45 min to obtain preliminary desulfurized lithium slag (mass concentration of sulfate ion 2.00 wt%) and leachate (mass concentration of sulfate ion 20.36 g / L).

[0055] 2) A potassium chloride solution with a mass concentration of 25 wt% is mixed with the preliminary desulfurized lithium slag and the liquid-to-solid ratio is controlled to be 14 mL / g, and then pressure-cooked at 180° C. for 15 min, filtered to obtain desulfurized lithium slag and desulfurization liquid with a mass concentration of sulfate ions of 0.16 wt%, and the desulfurization of the lithium slag is completed.

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

[0057] The sulfate-removing liquid is decontaminated and then cooled for crystallization to obtain potassium chloride; then lithium carbonate and a precipitated mother liquor are obtained through precipitation filtration; the precipitated mother liquor is acidified and then evaporated for crystallization to obtain sodium chloride and a concentrated solution; the concentrated solution is adsorbed and analyzed by a titanium-based adsorbent to obtain lithium chloride.

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

[0059] Example 3

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

[0061] 2) A sodium chloride solution with a mass concentration of 10 wt% is mixed with the preliminary desulfurized lithium slag and the liquid-to-solid ratio is controlled to be 14 mL / g, and then pressure-cooked at 120° C. for 20 min, filtered to obtain desulfurized lithium slag and desulfurization liquid with a mass concentration of sulfate ions of 0.08 wt%, and the desulfurization of the lithium slag is completed.

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

[0063] After the sulfate removal liquid is impurity-removed, extraction is performed (the extraction solvent is t-BAMBP) to obtain rubidium chloride and cesium chloride; the raffinate is evaporated and concentrated, and then cooled and crystallized to obtain potassium chloride and concentrated liquid; the concentrated liquid is extracted with an extractant TBP to obtain lithium chloride.

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

[0065] As can be seen from the above examples 1 to 3, the method of the present invention can be used to desulfurize lithium slag, which can not only reduce the sulfate content in the lithium slag to less than 0.2%, but also realize the recovery of calcium sulfate, the yield of calcium sulfate can reach more than 93%, and the purity can reach more than 95.8%; at the same time, the method of the present invention can also realize the extraction of valuable metals in lithium, rubidium, and cesium ores, and solve the problem of easy melting and hydrogen fluoride overflow during the roasting of lithium, rubidium, and cesium ores. The method of the present invention is simple, low-cost, realizes the comprehensive utilization of lithium slag resources, shows significant economic value and environmental friendliness, and has broad application prospects.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium slag desulfurization method with by-product calcium sulfate, characterized in that: The steps include: 1) mixing lithium, rubidium, cesium ore, lithium slag, inorganic salt and limestone, roasting to obtain clinker, mixing the clinker with water, leaching to obtain preliminary desulfurized lithium slag and leachate; 2) mixing the chloride solution with the preliminary desulfurized lithium slag, performing pressure cooking desulfurization, obtaining desulfurized lithium slag and desulfurization liquid, and completing lithium slag desulfurization; 3) The leaching solution obtained in step 1) is mixed with calcium chloride for reaction to obtain calcium sulfate and sulfate removal solution, and the obtained calcium sulfate is mixed with the calcium sulfate obtained by concentrating the desulfurization solution in step 2) to achieve by-production of calcium sulfate.

2. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 1, characterized in that: The mass ratio of the lithium, rubidium, cesium ore, lithium slag, inorganic salt and limestone in step 1) 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; In step 1), the calcination temperature is 750-950° C. and the time is 10-120 min; the leaching temperature is 25-95° C. and the time is 30-90 min.

3. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 2, characterized in that: The lithium, rubidium and cesium 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; The inorganic salt includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium sulfate and potassium sulfate.

4. A lithium slag desulfurization method with by-product calcium sulfate according to any one of claims 1 to 3, characterized in that: Calculated as sulfate, the mass concentration of sulfur in the lithium slag in step 1) is 2-30wt%; the particle size of the lithium slag is 5-300 μm.

5. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 4, characterized in that: The liquid-to-solid ratio of the chloride solution to the preliminary desulfurized lithium slag in step 2) is 5-25 mL / g; The mass concentration of the chloride salt solution is 5 to 30 wt%; The pressure boiling desulfurization in step 2) is carried out at a temperature of 100 to 200° C. and for a time of 5 to 20 minutes.

6. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 5, characterized in that: The chloride salt solution in step 2) includes sodium chloride solution and / or potassium chloride solution.

7. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 6, characterized in that: The molar ratio of calcium chloride to sulfate ions in the leaching solution in step 3) is 1.0-1.2:1; The reaction temperature is 10-50°C and the reaction time is 10-30 minutes.

8. The method for desulfurizing lithium slag with by-product calcium sulfate according to claim 7, characterized in that: Step 3) also includes removing impurities from the sulfate removal solution for preparing valuable metal salts.

9. The desulfurized lithium slag obtained by desulfurization using the method for desulfurization of lithium slag with by-product calcium sulfate according to any one of claims 1 to 8, characterized in that: The mass concentration of sulfur in the desulfurized lithium slag is 0.05-0.2 wt % calculated as sulfate radical.