Method for recovering lithium and calcium sulfate from lithium smelting slag

Abstract

The invention provides a method for recycling lithium and calcium sulfate from lithium smelting slag, and belongs to the technical field of resource utilization of metal smelting waste slag, the method comprises the following steps: step S1, mixing the lithium smelting slag and a first solution to obtain a primary leaching system, and filtering and separating after reaction to obtain a primary leachate and primary leaching slag; s2, the primary leachate is added into a primary leaching system for primary leaching circulation, and lithium-enriched liquid is obtained; the concentration of lithium ions in the lithium enrichment liquid is 0.2-3 g / L; s3, mixing the primary leaching residues with a second solution to obtain a secondary leaching system, and filtering and separating after reaction to obtain secondary leaching liquid and purified residues; and S4, the secondary leaching solution is subjected to crystallization separation, calcium sulfate dihydrate and crystallization mother liquor are obtained, and the crystallization mother liquor is added into a secondary leaching system for secondary leaching circulation. According to the method, lithium can be efficiently recycled, and the removal rate of sulfur and calcium in the lithium smelting slag and the purity of calcium sulfate are improved.

Description

Technical Field

[0001] The present application belongs to the technical field of resource utilization of metal smelting waste slag, and specifically relates to a method for recovering lithium and calcium sulfate from lithium smelting slag. Background Art

[0002] With the development of my country's new energy vehicle industry, the demand for lithium, as a key raw material for battery manufacturing, has risen sharply. However, China's lithium resources are relatively scarce, accounting for only 7% of the world's total reserves. The production capacity of the upstream and downstream of the lithium industry is mismatched, and the external dependence exceeds 70%. In this context, it is particularly important to fully develop and utilize the country's lithium ore resources. At present, lithium is mainly extracted from ores such as spodumene and lithium mica in China. However, the process of lithium ore extraction will produce a large amount of lithium smelting slag, which contains a certain amount of lithium and rich elements such as calcium, sulfur, aluminum, and silicon. If it cannot be effectively utilized, it will not only cause resource waste, but also cause environmental pollution problems. In addition, during the roasting process of lithium ore, the incomplete transformation / decomposition of the ore phase will lead to incomplete leaching of lithium smelting slag, entrainment during the neutralization process, etc., resulting in more than 0.05% of lithium in the lithium smelting slag not being utilized. Existing lithium smelting slag is mainly used in the cement building materials industry, with low product added value, and valuable metal elements such as lithium and calcium have not been comprehensively utilized. Therefore, it is particularly urgent to develop a technology that can not only efficiently recover lithium but also make full use of other valuable elements in lithium smelting slag.

[0003] At present, for the treatment of lithium smelting slag, a variety of methods have been proposed, but there are still many deficiencies in practical applications. CN202210370700.4 discloses a method for comprehensive recovery of valuable elements in spodumene industrial leaching slag, in which spodumene smelting slag is washed at room temperature, but due to the use of harmless water leaching, a larger liquid-solid ratio is required, reaching 10~100, and the leaching time is as long as 18~30h. At the same time, the concentration of calcium sulfate in the leachate is low, and calcium sulfate products need to be obtained by evaporation enrichment, which increases energy consumption and cost. More importantly, this method is not specifically aimed at the recovery of lithium.

[0004] CN202410113567.3 discloses a method for extracting lithium from spodumene smelting slag, which uses fluorides such as calcium fluoride, sodium fluoride, potassium fluoride, etc. as leaching aids and is leached with sulfuric acid. The use of fluorides in this method may bring environmental and health risks, and the final treatment process of the leachate is relatively cumbersome, which increases the process difficulty and operating cost.

[0005] CN202410530351.7 discloses a new process for desulfurization of spodumene smelting slag using EDTA. During the treatment process of this process, multiple rotary evaporation and recovery are required, which increases the complexity of operation and energy consumption. In addition, the method mainly focuses on desulfurization, and there is no detailed description of lithium recovery.

[0006] In summary, although the existing lithium smelting slag treatment methods have solved the problem of recycling lithium and other valuable elements to a certain extent, none of them have achieved the combined synchronous or cascade recovery of lithium and calcium sulfate components. There are problems such as insufficient lithium recovery rate, insufficient purity of calcium sulfate, complex process, high cost and potential environmental impact.

[0007] Therefore, there is an urgent need to develop a method for recovering lithium and calcium sulfate that can efficiently recover lithium and improve the sulfur and calcium removal rate and calcium sulfate purity in lithium smelting slag. Summary of the invention

[0008] In view of this, the present application provides a method for recovering lithium and calcium sulfate from lithium smelting slag. According to the differences in the leaching conditions of lithium, aluminum, iron and calcium components in lithium smelting slag, the leaching of easily soluble impurities aluminum, iron and lithium is achieved through a low-acid high-temperature leaching. The primary leached slag is subjected to a secondary leaching under high-acid and low-temperature conditions to further remove the sulfur and calcium components, thereby achieving the removal of the sulfur and calcium components in the smelting slag and the preparation of high-purity calcium sulfate. This method can efficiently recover lithium and improve the sulfur and calcium removal rate and the purity of calcium sulfate in lithium smelting slag.

[0009] In a first aspect, the present application provides a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps: Step S1, mixing lithium smelting slag and a first solution to obtain a primary leaching system, filtering and separating after the reaction to obtain a primary leaching solution and a primary leaching slag; Step S2, adding the primary leaching solution into a primary leaching system to perform a primary leaching cycle to obtain a lithium-enriched solution; the lithium ion concentration in the lithium-enriched solution is 0.2-3 g / L; Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; Step S4, subjecting the secondary leachate to crystallization separation to obtain calcium sulfate dihydrate and a crystallization mother liquor, and adding the crystallization mother liquor to a secondary leaching system for a secondary leaching cycle.

[0010] By adopting the above technical scheme, the method of the present application can efficiently recover lithium, improve the sulfur-calcium removal rate and calcium sulfate purity in lithium smelting slag, the lithium removal rate can reach 70% or more, and the sulfur-calcium removal rate can reach 90% or more.

[0011] According to the differences in leaching characteristics of different components (lithium, aluminum, iron, calcium, etc.) in lithium smelting slag under acidic composite media, the primary leaching is mainly used to remove lithium and pre-remove aluminum and iron, and the secondary leaching is mainly used to remove sulfur and calcium. Through a two-step cascade leaching process, lithium is efficiently recovered and sulfur and calcium components are removed at the same time to prepare high-purity calcium sulfate. The purified slag is used in cement building materials, glass fiber or plastic additives.

[0012] At low acidity and high temperature, soluble impurities such as lithium, aluminum, and iron are preferentially leached. At the same time, the leaching of aluminum and iron also helps to reduce impurities in subsequent treatments. In this application, a single leaching cycle refers to adding a primary leaching solution to a primary leaching system formed by mixing subsequent batches of lithium smelting slag and the first solution, and enriching lithium ions and increasing lithium concentration through multiple cycles of leaching, thereby realizing lithium recovery.

[0013] Under high acidity and low temperature, calcium and sulfur components are more likely to enter the liquid phase. Through crystallization separation, calcium sulfate can be further purified to obtain a high-purity calcium sulfate product, thereby realizing the removal of sulfur and calcium components in lithium smelting slag and the preparation of high-purity calcium sulfate.

[0014] The method of the present application does not involve complicated processes such as sorting, roasting, and evaporation, is simple to operate, and is convenient for industrial application. It also reduces wastewater and waste gas emissions in traditional methods, and is beneficial to environmental protection.

[0015] Optionally, in step S1, the lithium smelting slag is selected from at least one of spodumene smelting slag and lepidolite smelting slag.

[0016] By adopting the above technical solution, the method of the present application can adapt to the waste residues generated in the process of extracting lithium from lithium ores of different sources, enhance the versatility and flexibility of the technology, and reduce the processing cost. The processing of these lithium smelting slags can reduce the emission of harmful substances and reduce pollution to the environment.

[0017] Optionally, in step S1, the content of SO3 in the lithium smelting slag is 2-30%, the content of CaO is 5-33%, and the content of lithium element is 0.05-0.5%.

[0018] By adopting the above technical solution, the content composition of the lithium smelting slag of the present application can simultaneously recover multiple valuable elements such as lithium, sulfur and calcium, thereby improving the comprehensive utilization value of resources. High content of sulfur and calcium can be converted into high-purity calcium sulfate products, increasing the added value of by-products. At the same time, the recovery of lithium also brings additional economic benefits.

[0019] Optionally, the first solution in step S1 is selected from at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid; The second solution in step S3 is a mixed solution prepared by a compounding agent and at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid; The compounding agent is selected from at least one of potassium nitrate, sodium nitrate, sodium chloride, potassium chloride, sodium acetate, potassium acetate, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate.

[0020] By adopting the above technical solution, the first solution of the present application has high leaching conversion characteristics for elements such as lithium, aluminum and iron. Under appropriate acidity and temperature conditions, the first solution can efficiently leach easily convertible lithium, aluminum and iron, thereby achieving lithium enrichment and pre-removal of aluminum and iron in a single leaching process.

[0021] In the primary leaching process, the leaching process of aluminum, iron and lithium by the first solution is less affected by acidity, but more affected by temperature. Therefore, the conversion and extraction efficiency of these elements is optimized by adjusting the temperature. The extraction of calcium ions is significantly affected by the properties of the solution. Therefore, by selecting a suitable compounding agent, calcium ions can be efficiently extracted in the secondary leaching process, and crystallization can be efficiently carried out, providing a basis for the separation of calcium sulfate.

[0022] Optionally, in step S1, the concentration of the first solution is 0.1-1.5 mol / L, the reaction temperature is 30-160° C., the reaction time is 10-180 min, and the reaction liquid-solid ratio is 2-10 mL / g.

[0023] By adopting the above technical solution, the present application selects appropriate parameters such as the concentration of the first solution, reaction temperature, reaction time, etc., to achieve efficient leaching and recovery of lithium, aluminum, iron and other elements in lithium smelting slag, while reducing processing costs and improving the economy and environmental friendliness of the overall process. A reasonable liquid-to-solid ratio can ensure full conversion of solid materials while reducing waste of the first solution and the complexity of subsequent processing.

[0024] Optionally, the lithium ion concentration in the primary leaching solution is greater than 0.05 g / L, the aluminum ion concentration is greater than 1 g / L, the iron ion concentration is greater than 1 g / L, and the calcium ion concentration is less than 6 g / L.

[0025] Optionally, in step S2, the number of cycles of one leaching cycle is 3 to 8 times.

[0026] By adopting the above technical solution, the present application can increase the concentration of lithium ions from an initial low level to a higher level through multiple cycles, thereby realizing lithium recovery. The number of leaching cycles in step S2 of the present application can ensure that the concentration of lithium ions reaches a higher level, while not increasing unnecessary processing time and cost due to excessive cycles.

[0027] Optionally, the lithium ion concentration in the lithium-enriched solution is 0.2-3 g / L, the aluminum ion concentration is 2-10 g / L, and the iron ion concentration is 2-10 g / L.

[0028] Optionally, in step S3, the concentration of the second solution is 2-8 mol / L, the reaction temperature is 50-95° C., the reaction time is 10-180 min, the reaction liquid-solid ratio is 3-10 mL / g, and the concentration of the compounding agent is 0.25-0.75 mol / L.

[0029] By adopting the above technical solution, the concentration of the second solution in step S3 of the present application directly affects the leaching capacity of calcium and sulfur. A higher concentration can accelerate the leaching rate and improve the extraction efficiency of calcium and sulfur. If the concentration of the second solution is too high, it may cause unnecessary solution consumption, increase processing costs, and may leach more impurities, affecting the purity of calcium sulfate; if the concentration of the second solution is too low, it may cause a decrease in the extraction rate, prolong the reaction time, reduce the leaching efficiency of calcium and sulfur, and affect the yield and purity of calcium sulfate.

[0030] The reaction temperature and reaction time of step S3 of the present application can ensure that calcium and sulfur are fully leached and improve the leaching efficiency of calcium and sulfur. The reaction liquid-solid ratio of step S3 of the present application can ensure that the solid material fully contacts the solution and improve the efficiency. The compounding agent promotes the leaching of calcium sulfate through the salt effect.

[0031] Optionally, in step S4, the crystallization temperature of the crystallization separation is 0-50° C., and the crystallization time is 3-24 h.

[0032] By adopting the above technical scheme, the specific crystallization temperature and crystallization time of the present application can ensure the uniform growth of calcium sulfate crystals and improve the purity and morphology of the crystals. If the crystallization temperature is too high, the solubility of calcium sulfate may be higher, the crystallization rate may be slower, and the crystal particles may be smaller and uneven, affecting the purity and morphology of the crystals. If the crystallization temperature is too low, the crystallization rate may be too fast, resulting in an incomplete crystal structure, affecting the purity and morphology of the crystals. If the crystallization time is too long, excessive crystal growth may be caused, affecting the uniformity and purity of the crystals. If the crystallization time is too short, insufficient crystal growth may be caused, and the crystal particles may be smaller and uneven, affecting the purity and morphology of the crystals. By adding a compounding agent during the crystallization process, when the salt effect and the common ion effect act together, the common ion effect is regulated to dominate and promote the precipitation of calcium sulfate.

[0033] Optionally, the step S4 further includes: adding the crystallization mother liquor replenishment solution to a secondary leaching system for a secondary leaching cycle; in the step S4, the crystallization mother liquor replenishment solution is adjusted to a concentration of 2 to 8 mol / L; and the number of cycles of the secondary leaching cycle is 3 to 5 times.

[0034] By adopting the above technical solution, step S4 of the present application restores the concentration of the crystallization mother liquor by replenishing the solution, so that it can be used again in the leaching process, thereby ensuring the leaching amount of the sulfur and calcium components and realizing the recycling of the medium.

[0035] Optionally, in step S4, the calcium sulfate yield is ≥65%, and the calcium sulfate purity is ≥99%.

[0036] By adopting the above technical scheme, the method for recovering lithium and calcium sulfate from lithium smelting slag of the present application can make the calcium sulfate yield ≥65% and the calcium sulfate purity ≥99%.

[0037] In summary, the present invention includes at least one of the following beneficial technical effects: 1. The method of the present application can efficiently recover lithium and improve the sulfur and calcium removal rate and the purity of calcium sulfate in lithium smelting slag.

[0038] 2. The lithium removal rate of the method of the present application can reach 70% or more, and the sulfur and calcium removal rate can reach 90% or more.

[0039] 3. The method of the present application can make the calcium sulfate yield ≥65% and the calcium sulfate purity ≥99%.

[0040] 4. The method of the present application can obtain calcium sulfate products without evaporation enrichment, thereby realizing the recycling of the medium and reducing the cost of smelting slag disposal.

[0041] 5. The method of the present application does not involve complicated processes such as sorting, roasting, and evaporation, is simple to operate, and is convenient for industrial application. It also reduces wastewater and waste gas emissions in traditional methods, which is beneficial to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A process flow chart of a method for recovering lithium and calcium sulfate from lithium smelting slag provided in Example 1 of the present application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0044] The inventors of the present application found in their research on the recovery of lithium and calcium sulfate from lithium smelting slag that although the existing lithium smelting slag treatment methods have solved the problem of recovery of lithium and other valuable elements to a certain extent, none of them have achieved the combined synchronous or cascade recovery of lithium and calcium sulfate components, and there are problems such as insufficient lithium recovery rate, insufficient purity of calcium sulfate, complex process, high cost and potential environmental impact.

[0045] In order to solve the above problems, the present application proposes a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps: Step S1, mixing lithium smelting slag and a first solution to obtain a primary leaching system, filtering and separating after the reaction to obtain a primary leaching solution and a primary leaching slag; Step S2, adding the primary leaching solution into a primary leaching system to perform a primary leaching cycle to obtain a lithium-enriched solution; the lithium ion concentration in the lithium-enriched solution is 0.2-3 g / L; Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; Step S4, subjecting the secondary leachate to crystallization separation to obtain calcium sulfate dihydrate and a crystallization mother liquor, and adding the crystallization mother liquor to a secondary leaching system for a secondary leaching cycle.

[0046] The scheme of the present application is described below in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels. Specific embodiments Example 1 This embodiment provides a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps: Step S1, mixing spodumene smelting slag and the first solution to obtain a primary leaching system, filtering and separating after the reaction, to obtain a primary leaching solution and a primary leaching slag; wherein the content of SO3 in the spodumene smelting slag is 30%, the content of CaO is 33%, and the content of lithium element is 0.5%; the first solution is hydrochloric acid, the concentration of the first solution is 1.5 mol / L, the reaction temperature is 160°C, the reaction time is 180min, and the reaction liquid-solid ratio is 10mL / g; the lithium ion concentration in the primary leaching solution is 0.45g / L, the aluminum ion concentration is 3g / L, the iron ion concentration is 3.5g / L, and the calcium ion concentration is 6g / L.

[0048] Step S2, adding the primary leaching solution into the primary leaching system to carry out a leaching cycle, the number of cycles of the primary leaching cycle is 3 times, and a lithium-enriched solution is obtained; the lithium ion concentration in the lithium-enriched solution is 1.25 g / L, the aluminum ion concentration is 10 g / L, and the iron ion concentration is 10 g / L.

[0049] Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; wherein the second solution is a mixed solution of sodium chloride (compounding agent) and hydrochloric acid, the concentration of the second solution is 8 mol / L, the concentration of the compounding agent is 0.25 mol / L, the reaction temperature is 50°C, the reaction time is 10 min, and the reaction liquid-solid ratio is 3 mL / g; the calcium ion concentration in the secondary leaching solution is 50 g / L, the aluminum ion concentration is 0.3 g / L, and the iron ion concentration is 0.2 g / L.

[0050] Step S4, the secondary leachate is crystallized and separated, the crystallization temperature is 0°C, the crystallization time is 3h, calcium sulfate dihydrate and crystallization mother liquor are obtained, the crystallization mother liquor is supplemented with the second solution to a solution concentration of 8 mol / L, and added to the secondary leaching system for secondary leaching cycle, and the number of cycles of the secondary leaching cycle is 3 times.

[0051] Example 2 This embodiment provides a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps: Step S1, mixing spodumene smelting slag and the first solution to obtain a primary leaching system, filtering and separating after the reaction, to obtain a primary leaching solution and a primary leaching slag; wherein the content of SO3 in the spodumene smelting slag is 2%, the content of CaO is 5%, and the content of lithium element is 0.05%; the first solution is hydrochloric acid, the concentration of the first solution is 0.1 mol / L, the reaction temperature is 30°C, the reaction time is 10min, and the reaction liquid-solid ratio is 2mL / g; the lithium ion concentration in the primary leaching solution is 0.17g / L, the aluminum ion concentration is 1g / L, the iron ion concentration is 1g / L, and the calcium ion concentration is 1g / L.

[0052] Step S2, adding the primary leaching solution into the primary leaching system to carry out a leaching cycle, the number of cycles of the primary leaching cycle is 8 times, and a lithium-enriched solution is obtained; the lithium ion concentration in the lithium-enriched solution is 0.88 g / L, the aluminum ion concentration is 2 g / L, and the iron ion concentration is 2 g / L.

[0053] Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; wherein the second solution is a mixed solution of sodium chloride (compounding agent) and hydrochloric acid, the concentration of the second solution is 2 mol / L, the concentration of the compounding agent is 0.25 mol / L, the reaction temperature is 95°C, the reaction time is 180 min, and the reaction liquid-solid ratio is 10 mL / g; the calcium ion concentration in the secondary leaching solution is 3.2 g / L, the aluminum ion concentration is 0.3 g / L, and the iron ion concentration is 0.2 g / L.

[0054] Step S4, the secondary leachate is crystallized and separated, the crystallization temperature is 50°C, the crystallization time is 24h, calcium sulfate dihydrate and crystallization mother liquor are obtained, the crystallization mother liquor is supplemented with the second solution to a solution concentration of 2mol / L, and added to the secondary leaching system for secondary leaching cycle, and the number of cycles of the secondary leaching cycle is 5 times.

[0055] Example 3 This embodiment provides a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps: Step S1, mixing spodumene smelting slag and the first solution to obtain a primary leaching system, filtering and separating after the reaction to obtain a primary leaching solution and a primary leaching slag; wherein the content of SO3 in the spodumene smelting slag is 10%, the content of CaO is 16%, and the content of lithium element is 0.1%; the first solution is hydrochloric acid, the concentration of the first solution is 1 mol / L, the reaction temperature is 90°C, the reaction time is 90min, and the reaction liquid-solid ratio is 5mL / g; the lithium ion concentration in the primary leaching solution is 0.3g / L, the aluminum ion concentration is 2g / L, the iron ion concentration is 1.8g / L, and the calcium ion concentration is 3g / L.

[0056] Step S2, adding the primary leaching solution into the primary leaching system to carry out a leaching cycle, the number of cycles of the primary leaching cycle is 5 times, and a lithium-enriched solution is obtained; the lithium ion concentration in the lithium-enriched solution is 0.52 g / L, the aluminum ion concentration is 7.8 g / L, and the iron ion concentration is 7 g / L.

[0057] Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; wherein the second solution is a mixed solution of potassium chloride (compounding agent) and hydrochloric acid, the concentration of the second solution is 5 mol / L, the concentration of the compounding agent is 0.75 mol / L, the reaction temperature is 70°C, the reaction time is 60 min, and the reaction liquid-solid ratio is 5 mL / g; the calcium ion concentration in the secondary leaching solution is 12 g / L, the aluminum ion concentration is 0.15 g / L, and the iron ion concentration is 0.12 g / L.

[0058] Step S4, the secondary leachate is crystallized and separated, the crystallization temperature is 25° C., the crystallization time is 12 h, calcium sulfate dihydrate and a crystallization mother liquor are obtained, the crystallization mother liquor is supplemented with the second solution to a solution concentration of 5 mol / L, and is added to the secondary leaching system for secondary leaching cycle, and the number of cycles of the secondary leaching cycle is 4 times.

[0059] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain step S1 and step S2, and adopts one-step leaching desulfurization calcium, and the specific steps are: Step S1, mixing spodumene smelting slag and a composite solution to obtain a leaching system, filtering and separating after the reaction to obtain a leachate and a leaching slag; wherein the content of SO3 in the spodumene smelting slag is 30%, the content of CaO is 33%, and the content of lithium is 0.5%; the composite solution is a mixed solution of sodium chloride (compounding agent) and hydrochloric acid, the concentration of the composite solution is 8 mol / L, the concentration of the compounding agent is 0.25 mol / L, the reaction temperature is 50°C, the reaction time is 10 min, and the reaction liquid-solid ratio is 3 mL / g; the calcium ion concentration in the leachate is 15 g / L, the aluminum ion concentration is 1.9 g / L, and the iron ion concentration is 1.4 g / L.

[0060] Step S2, the leachate is crystallized and separated, the crystallization temperature is 0°C, the crystallization time is 3h, calcium sulfate dihydrate and crystallization mother liquor are obtained, the crystallization mother liquor is supplemented with a composite solution to a solution concentration of 8 mol / L, and added to the leaching system for cyclic leaching, and the number of cycles of the cyclic leaching is 3 times.

[0061] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain step S3 and step S4, and adopts one-step leaching to extract lithium, and the specific steps are: Step S1, mixing spodumene smelting slag and the first solution to obtain a primary leaching system, filtering and separating after the reaction, to obtain a primary leaching solution and a primary leaching slag; wherein the content of SO3 in the spodumene smelting slag is 30%, the content of CaO is 33%, and the content of lithium element is 0.5%; the first solution is hydrochloric acid, the concentration of the first solution is 1.5 mol / L, the reaction temperature is 160°C, the reaction time is 180min, and the reaction liquid-solid ratio is 10mL / g; the lithium ion concentration in the primary leaching solution is 0.45g / L, the aluminum ion concentration is 3g / L, the iron ion concentration is 3.5g / L, and the calcium ion concentration is 6g / L.

[0062] Step S2, adding the primary leaching solution into the primary leaching system to carry out a leaching cycle, the number of cycles of the primary leaching cycle is 3 times, and a lithium-enriched solution is obtained; the lithium ion concentration in the lithium-enriched solution is 1.25 g / L, the aluminum ion concentration is 10 g / L, and the iron ion concentration is 10 g / L.

[0063] Experimental testing The lithium smelting slag and the primary leaching slag of Examples 1 to 3 were digested by an alkali fusion method to obtain a solution sample, and the lithium element concentration in the solution sample was measured by an inductively coupled plasma optical emission spectrometer (ICP-OES) to obtain a lithium removal rate; The calcium sulfate dihydrate yield, calcium sulfate dihydrate purity and calcium sulfate removal rate were measured by X-ray fluorescence spectroscopy.

[0064] The methods for recovering lithium and calcium sulfate from lithium smelting slag of Examples 1 to 3 and Comparative Examples 1 to 2 were tested for lithium removal rate, calcium sulfate dihydrate yield, calcium sulfate dihydrate purity, and sulfur and calcium removal rate. The test results are shown in Table 1.

[0065] Table 1

[0066] From the test results in Table 1, it can be seen that the method for recovering lithium and calcium sulfate from lithium smelting slag of Examples 1 to 3 can efficiently recover lithium, improve the sulfur and calcium removal rate and calcium sulfate purity in lithium smelting slag, the lithium removal rate can reach 70% or more, the calcium sulfate dihydrate yield can reach 65% or more, the calcium sulfate purity can reach 99.0% or more, and the sulfur and calcium removal rate can reach 90% or more.

[0067] Comparative Example 1 did not perform a leaching pre-impurity removal, but only used a one-step leaching desulfurization calcium component, and the yield of calcium sulfate dihydrate decreased significantly. The high content of aluminum and iron impurities in the leachate affected the crystallization recovery process of calcium sulfate dihydrate, was not conducive to the crystallization and separation of calcium sulfate dihydrate from the leachate, and resulted in a decrease in the yield of calcium sulfate dihydrate.

[0068] Comparative Example 2 did not perform secondary leaching, but only used one-step leaching to extract lithium and pre-impurity removal, with a lithium removal rate of 85%, but a calcium sulfate dihydrate yield of 0%. Under low acidity conditions with a first solution concentration of 1.5 mol / L, the calcium sulfate removal rate was limited, and calcium sulfate dihydrate could not be directly crystallized.

[0069] Embodiments 4 to 13 Example 4 The difference between Example 4 and Example 1 is that in step S1 of Example 4, the first solution is nitric acid; in step S3, the second solution is a mixed solution of sodium nitrate and nitric acid, and the other process parameters are consistent with those of Example 1.

[0070] Example 5 The difference between Example 5 and Example 1 is that in step S1 of Example 5, the first solution is acetic acid; in step S3, the second solution is a mixed solution of sodium acetate and acetic acid, and the other process parameters are consistent with those of Example 1.

[0071] Example 6 The difference between Example 6 and Example 1 is that in step S1 of Example 6, the first solution is ethylenediaminetetraacetic acid; in step S3, the second solution is a mixed solution of disodium ethylenediaminetetraacetic acid and ethylenediaminetetraacetic acid, and the other process parameters are consistent with those of Example 1.

[0072] Example 7 The difference between Example 7 and Example 1 is that in step S1 of Example 7, the first solution is hydrochloric acid and nitric acid in a volume ratio of 1:1; in step S3, the second solution is a mixed solution of sodium chloride and hydrochloric acid and nitric acid in a volume ratio of 1:1, and the other process parameters are consistent with those of Example 1.

[0073] Example 8 The difference between Example 8 and Example 1 is that in step S2 of Example 8, the number of cycles of one leaching cycle is 6 times.

[0074] Example 9 The difference between Example 9 and Example 1 is that in step S2 of Example 9, the number of cycles of one leaching cycle is 8 times.

[0075] Example 10 The difference between Example 10 and Example 8 is that in step S3 of Example 10, the concentration of the second solution is 5 mol / L, the concentration of the compounding agent is 0.50 mol / L, the reaction temperature is 73° C., the reaction time is 95 min, and the reaction liquid-solid ratio is 6 mL / g.

[0076] Embodiment 11 The difference between Example 11 and Example 8 is that in step S3 of Example 11, the concentration of the second solution is 2 mol / L, the concentration of the compounding agent is 0.75 mol / L, the reaction temperature is 95° C., the reaction time is 180 min, and the reaction liquid-solid ratio is 10 mL / g.

[0077] Example 12 The difference between Example 12 and Example 10 is that in step S4 of Example 12, the crystallization temperature of the crystallization separation is 25° C. and the crystallization time is 14 h.

[0078] Embodiment 13 The difference between Example 13 and Example 10 is that in step S4 of Example 13, the crystallization temperature of crystallization separation is 50° C. and the crystallization time is 24 h.

[0079] The methods for recovering lithium and calcium sulfate from lithium smelting slag in Examples 4 to 13 were tested for lithium removal rate, calcium sulfate dihydrate yield, and calcium sulfate dihydrate purity. The test results are shown in Table 2.

[0080] Table 2

[0081] From the test results in Table 2, it can be seen that the difference between Examples 4 to 7 and Example 1 is that the first solution in step S1 and the second solution in step S3 have different components. Among them, the lithium removal rate and calcium sulfate dihydrate yield of Example 1 are both the highest.

[0082] The difference between Example 8 and Example 9 and Example 1 is that the number of cycles of the leaching cycle in step S2 is different, wherein the lithium removal rate of Example 8 is higher, and unnecessary processing time and cost will not be increased due to excessive cycles.

[0083] The difference between Example 10 and Example 11 and Example 8 is that the reaction parameters in step S3 are different, among which the yield of calcium sulfate dihydrate in Example 10 is the highest.

[0084] The difference between Example 12 and Example 13 and Example 10 is that the crystallization parameters in step S4 are different, among which the yield of calcium sulfate dihydrate in Example 10 is the highest.

[0085] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for recovering lithium and calcium sulfate from lithium smelting slag, characterized in that: The following steps are involved: Step S1, mixing lithium smelting slag and a first solution to obtain a primary leaching system, filtering and separating after the reaction to obtain a primary leaching solution and a primary leaching slag; Step S2, adding the primary leaching solution into a primary leaching system to perform a primary leaching cycle to obtain a lithium-enriched solution; the lithium ion concentration in the lithium-enriched solution is 0.2-3 g / L; Step S3, mixing the primary leaching residue and the second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and purified residue; Step S4, subjecting the secondary leachate to crystallization separation to obtain calcium sulfate dihydrate and a crystallization mother liquor, and adding the crystallization mother liquor to a secondary leaching system for a secondary leaching cycle.

2. The method for recovering lithium and calcium sulfate according to claim 1, characterized in that: In the step S1, the lithium smelting slag is selected from at least one of spodumene smelting slag and lepidolite smelting slag.

3. The method for recovering lithium and calcium sulfate according to claim 2, characterized in that: In the step S1, the content of SO3 in the lithium smelting slag is 2-30%, the content of CaO is 5-33%, and the content of lithium element is 0.05-0.5%.

4. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, wherein: The first solution in step S1 is selected from at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid; The second solution in step S3 is a mixed solution prepared by a compounding agent and at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid; The compounding agent is selected from at least one of potassium nitrate, sodium nitrate, sodium chloride, potassium chloride, sodium acetate, potassium acetate, disodium ethylenediaminetetraacetate, and tetrasodium ethylenediaminetetraacetate.

5. The method for recovering lithium and calcium sulfate according to claim 4, characterized in that: In the step S1, the concentration of the first solution is 0.1-1.5 mol / L, the reaction temperature is 30-160° C., the reaction time is 10-180 min, and the reaction liquid-to-solid ratio is 2-10 mL / g.

6. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, characterized in that: In step S2, the number of cycles of one leaching cycle is 3 to 8 times.

7. The method for recovering lithium and calcium sulfate according to claim 4, characterized in that: In step S3, the concentration of the second solution is 2-8 mol / L, the reaction temperature is 50-95° C., the reaction time is 10-180 min, the reaction liquid-solid ratio is 3-10 mL / g, and the concentration of the compounding agent is 0.25-0.75 mol / L.

8. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, characterized in that: In the step S4, the crystallization temperature of the crystallization separation is 0-50° C., and the crystallization time is 3-24 hours.

9. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, wherein: The step S4 further comprises: adding the crystallization mother liquor replenishment solution into the secondary leaching system for secondary leaching cycle; in the step S4, the crystallization mother liquor replenishment solution is adjusted to a concentration of 2-8 mol / L; and the number of cycles of the secondary leaching cycle is 3-5 times.

10. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, characterized in that: In step S4, the calcium sulfate yield is ≥65%, and the calcium sulfate purity is ≥99%.

Images