A method for recovering lithium and calcium sulfate from lithium smelting slag

Abstract

The present application provides a method for recovering lithium and calcium sulfate from lithium smelting slag, belonging 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, filtering and separating after the reaction to obtain a primary leaching solution and a primary leaching residue; Step S2, adding the primary leaching solution into the primary leaching system for 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 a second solution to obtain a secondary leaching system, filtering and separating after the reaction to obtain a secondary leaching solution and a purified residue; Step S4, performing crystallization separation on the secondary leaching solution to obtain calcium sulfate dihydrate and a crystallization mother liquor, and adding the crystallization mother liquor into the secondary leaching system for a secondary leaching cycle. The method of the present application can efficiently recover lithium and improve the sulfur-calcium removal rate and calcium sulfate purity in the lithium smelting slag.

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 cascaded recycling of lithium and sulfur-calcium components. There are problems such as insufficient lithium recovery rate, insufficient purity of calcium sulfate, complex process, high cost, and potential environmental impacts.

[0007] Therefore, there is an urgent need to develop a method for recycling lithium and calcium sulfate that can efficiently recover lithium and improve the sulfur-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 recycling 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 soluble impurities such as aluminum, iron, and lithium is achieved through one-time low-acid high-temperature leaching. The primary leaching residue is secondarily leached under high-acid low-temperature conditions to further remove the sulfur-calcium component, realizing the removal of the sulfur-calcium component in the smelting slag and the preparation of high-purity calcium sulfate. This method can efficiently recover lithium and improve the sulfur-calcium removal rate and calcium sulfate purity in lithium smelting slag.

[0009] In the first aspect, the present application provides a method for recycling lithium and calcium sulfate from lithium smelting slag, including the following steps:

[0010] Step S1: Mix the lithium smelting slag and the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leaching solution and a primary leaching residue;

[0011] Step S2: Add the primary leaching solution to the primary leaching system for 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;

[0012] Step S3: Mix the primary leaching residue and the second solution to obtain a secondary leaching system. After the reaction, filter and separate to obtain a secondary leaching solution and a purified residue;

[0013] Step S4: Crystallize and separate the secondary leaching solution to obtain calcium sulfate dihydrate and a crystallization mother liquor. Add the crystallization mother liquor to the secondary leaching system for a secondary leaching cycle.

[0014] By adopting the above technical solution, the method of the present application can efficiently recover lithium and 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 reaches 90% or more.

[0015] According to the leaching characteristic differences 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 preliminarily remove aluminum and iron impurities, and the secondary leaching is mainly used to remove sulfur and calcium. Through a two-step cascade leaching process, lithium is efficiently recovered and the sulfur and calcium components are removed simultaneously to prepare high-purity calcium sulfate. The purified slag is used in cement building materials, fiberglass or plastic additives.

[0016] At low acidity and relatively high temperature, easily 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 treatment. In this application, the primary leaching cycle refers to adding the primary leaching solution into the primary leaching system formed by mixing the subsequent batches of lithium smelting slag and the first solution. Through multiple cycle leaching, lithium ions are enriched and the lithium concentration is increased, thereby realizing the recovery of lithium.

[0017] At high acidity and relatively 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 high-purity calcium sulfate products, realizing the removal of sulfur and calcium components in lithium smelting slag and the preparation of high-purity calcium sulfate.

[0018] The method of this application does not involve complex processes such as sorting, roasting, and evaporation. It is simple to operate, convenient for industrial application, and reduces wastewater and waste gas emissions in traditional methods, which is beneficial to environmental protection.

[0019] Optionally, in the step S1, the lithium smelting slag is selected from at least one of spodumene smelting slag and lepidolite smelting slag.

[0020] By adopting the above technical solution, the method of this application can adapt to the waste slag generated in the process of extracting lithium from lithium ores of different sources, enhancing the universality and flexibility of the technology and reducing the treatment cost. The treatment of these lithium smelting slags can reduce the emission of harmful substances and mitigate environmental pollution.

[0021] Optionally, 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%.

[0022] By adopting the above technical solution, the content composition of the lithium smelting slag of this application can recover multiple valuable elements such as lithium, sulfur, and calcium simultaneously, improving the comprehensive utilization value of resources. The 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.

[0023] Optionally, the first solution in the step S1 is selected from at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid;

[0024] The second solution in the step S3 is a mixed solution prepared from a complexing agent and at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid;

[0025] The complexing 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.

[0026] 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, so as to realize the enrichment of lithium and the pre-removal of aluminum and iron in the primary leaching process.

[0027] 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 solution properties, so by selecting a suitable complexing agent, calcium ions are efficiently extracted in the secondary leaching process, and crystallization occurs efficiently during the crystallization process, providing a basis for realizing the separation of calcium sulfate.

[0028] Optionally, 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-solid ratio is 2 - 10 mL / g.

[0029] By adopting the above technical solution, the present application selects appropriate parameters such as the concentration of the first solution, reaction temperature, and reaction time to achieve the efficient leaching and recovery of elements such as lithium, aluminum, and iron in the lithium smelting slag, while reducing the treatment cost and improving the economy and environmental friendliness of the overall process. A reasonable liquid-solid ratio can ensure the full conversion of solid materials, while reducing the waste of the first solution and the complexity of subsequent treatment.

[0030] Optionally, in the primary leaching solution, the concentration of lithium ions is greater than 0.05 g / L, the concentration of aluminum ions is greater than 1 g / L, the concentration of iron ions is greater than 1 g / L, and the concentration of calcium ions is less than 6 g / L.

[0031] Optionally, in the step S2, the number of cycles of the primary leaching cycle is 3 - 8 times.

[0032] By adopting the above technical solution, through multiple cycles, the present application can increase the concentration of lithium ions from an initial low level to a high level, thereby realizing the recovery of lithium. The number of primary cycle leaching times in the step S2 of the present application can ensure that the concentration of lithium ions reaches a high level, while not increasing unnecessary treatment time and cost due to excessive cycles.

[0033] Optionally, the concentration of lithium ions in the lithium-rich solution is 0.2 - 3 g / L, the concentration of aluminum ions is 2 - 10 g / L, and the concentration of iron ions is 2 - 10 g / L.

[0034] 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 complexing agent is 0.25 - 0.75 mol / L.

[0035] By adopting the above technical solution, the concentration of the second solution in step S3 of the present application directly affects the leaching ability 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 lead to unnecessary solution consumption, increase the treatment cost, and may leach more impurities, affecting the purity of calcium sulfate; if the concentration of the second solution is too low, it may cause the extraction rate to decrease, prolong the reaction time, reduce the leaching efficiency of calcium and sulfur, and affect the yield and purity of calcium sulfate.

[0036] The reaction temperature and reaction time in step S3 of the present application can ensure the full leaching of calcium and sulfur and improve the leaching efficiency of calcium and sulfur. The reaction liquid-solid ratio in step S3 of the present application can ensure that the solid material fully contacts the solution, improve the efficiency, and the complexing agent promotes the leaching of calcium sulfate through the salt effect.

[0037] Optionally, in step S4, the crystallization temperature for crystallization separation is 0 - 50 °C, and the crystallization time is 3 - 24 h.

[0038] By adopting the above technical solution, the specific crystallization temperature and crystallization time in 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, it may lead to a relatively high solubility of calcium sulfate, a slow crystallization rate, and the crystallization particles may be small and uneven, affecting the purity and morphology of the crystals. If the crystallization temperature is too low, it may cause the crystallization rate to be too fast, resulting in an incomplete crystal structure and affecting the purity and morphology of the crystals. If the crystallization time is too long, it may lead to excessive crystal growth, affecting the uniformity and purity of the crystals. If the crystallization time is too short, it may cause insufficient crystal growth, small and uneven crystal particles, and affect the purity and morphology of the crystals. During the crystallization process, through the addition of the complexing agent, when the salt effect and the common ion effect act together, the common ion effect is regulated to dominate, promoting the precipitation of calcium sulfate.

[0039] Optionally, step S4 further includes: adding the crystallization mother liquor replenishing solution into the secondary leaching system for secondary leaching cycle; in step S4, the crystallization mother liquor replenishing solution is adjusted to a concentration of 2 - 8 mol / L; the number of cycles of the secondary leaching cycle is 3 - 5 times.

[0040] By adopting the above technical solution, in step S4 of the present application, the concentration of the crystallization mother liquor is restored by adding a replenishing solution, enabling it to be reused in the leaching process, ensuring the leaching amount of the sulfur-calcium components, and realizing the recycling of the medium.

[0041] Optionally, in step S4, the yield of calcium sulfate ≥ 65%, and the purity of calcium sulfate ≥ 99%.

[0042] By adopting the above technical solution, the method for recycling lithium and calcium sulfate from lithium smelting slag in the present application can achieve a calcium sulfate yield ≥ 65% and a calcium sulfate purity ≥ 99%.

[0043] In summary, the present invention includes at least one of the following beneficial technical effects:

[0044] 1. The method of the present application can efficiently recycle lithium, and improve the removal rate of sulfur-calcium and the purity of calcium sulfate in lithium smelting slag.

[0045] 2. The lithium removal rate of the method of the present application can reach 70% or more, and the sulfur-calcium removal rate reaches 90% or more.

[0046] 3. The method of the present application can achieve a calcium sulfate yield ≥ 65% and a calcium sulfate purity ≥ 99%.

[0047] 4. The method of the present application can obtain calcium sulfate products without evaporation enrichment, realize the recycling of the medium, and reduce the disposal cost of smelting slag.

[0048] 5. The method of the present application does not involve complex processes such as sorting, roasting, and evaporation, is simple to operate, convenient for industrial application, and reduces wastewater and waste gas emissions in traditional methods, which is beneficial to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a process flow chart of a method for recycling lithium and calcium sulfate from lithium smelting slag provided in Embodiment 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0051] The inventors of the present application found in the research on the treatment and recycling of lithium and calcium sulfate from lithium smelting slag that: although the existing lithium smelting slag treatment methods have solved the problem of recycling lithium and other valuable elements to a certain extent, they have not achieved the combined synchronous or cascaded recycling of lithium and sulfur-calcium components, and there are problems such as low lithium recovery rate, insufficient calcium sulfate purity, complex process, high cost, and potential environmental impact.

[0052] 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:

[0053] Step S1: Mix the lithium smelting slag and the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leachate and a primary leaching residue;

[0054] Step S2: Add the primary leachate to the primary leaching system for 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;

[0055] Step S3: Mix the primary leaching residue and the second solution to obtain a secondary leaching system. After the reaction, filter and separate to obtain a secondary leachate and a purified residue;

[0056] Step S4: Crystallize and separate the secondary leachate to obtain calcium sulfate dihydrate and a crystallization mother liquor. Add the crystallization mother liquor to the secondary leaching system for a secondary leaching cycle.

[0057] The following specifically describes the solution of the present application with reference to the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market sales channels. Specific Examples

[0059] Example 1

[0060] This example provides a method for recovering lithium and calcium sulfate from lithium smelting slag, comprising the following steps:

[0061] Step S1: Mix the spodumene smelting slag and the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leachate and a primary leaching residue; 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 180 min, and the reaction liquid-solid ratio is 10 mL / g; the lithium ion concentration in the primary leachate is 0.45 g / L, the aluminum ion concentration is 3 g / L, the iron ion concentration is 3.5 g / L, and the calcium ion concentration is 6 g / L.

[0062] Step S2: Add the primary leachate to the primary leaching system for a primary leaching cycle. The number of cycles of the primary leaching cycle is 3 times to obtain a lithium-enriched solution; 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] Step S3: Mix the primary leaching residue with the second solution to obtain a secondary leaching system. After the reaction, filter and separate to obtain a secondary leachate and a purified residue. Among them, the second solution is a mixed solution of sodium chloride (complexing agent) and hydrochloric acid. The concentration of the second solution is 8 mol / L, the concentration of the complexing 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 leachate is 50 g / L, the aluminum ion concentration is 0.3 g / L, and the iron ion concentration is 0.2 g / L.

[0064] Step S4: Crystallize and separate the secondary leachate at a crystallization temperature of 0 °C for 3 h to obtain calcium sulfate dihydrate and a crystallization mother liquor. Supplement the crystallization mother liquor with the second solution until the solution concentration reaches 8 mol / L, and then add it to the secondary leaching system for secondary leaching circulation. The number of cycles of the secondary leaching circulation is 3 times.

[0065] Example 2

[0066] This example provides a method for recovering lithium and calcium sulfate from lithium smelting slag, including the following steps:

[0067] Step S1: Mix the spodumene smelting slag with the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leachate and a primary leaching residue. Among them, 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 10 min, and the reaction liquid-solid ratio is 2 mL / g. The lithium ion concentration in the primary leachate is 0.17 g / L, the aluminum ion concentration is 1 g / L, the iron ion concentration is 1 g / L, and the calcium ion concentration is 1 g / L.

[0068] Step S2: Add the primary leachate to the primary leaching system for primary leaching circulation. The number of cycles of the primary leaching circulation is 8 times to obtain a lithium-enriched solution. 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.

[0069] Step S3: Mix the primary leaching residue with the second solution to obtain a secondary leaching system. After the reaction, filter and separate to obtain a secondary leachate and a purified residue. Among them, the second solution is a mixed solution of sodium chloride (complexing agent) and hydrochloric acid. The concentration of the second solution is 2 mol / L, the concentration of the complexing 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 leachate is 3.2 g / L, the aluminum ion concentration is 0.3 g / L, and the iron ion concentration is 0.2 g / L.

[0070] Step S4: Crystallize and separate the secondary leaching solution at a crystallization temperature of 50°C and a crystallization time of 24 h to obtain calcium sulfate dihydrate and a crystallization mother liquor. Supplement the crystallization mother liquor with the second solution to a solution concentration of 2 mol / L, and add it to the secondary leaching system for secondary leaching circulation. The number of secondary leaching circulation times is 5 times.

[0071] Example 3

[0072] This example provides a method for recovering lithium and calcium sulfate from lithium smelting slag, including the following steps:

[0073] Step S1: Mix spodumene smelting slag with the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leaching solution and a primary leaching residue. Among them, 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 90 min, and the reaction liquid-solid ratio is 5 mL / g; the lithium ion concentration in the primary leaching solution is 0.3 g / L, the aluminum ion concentration is 2 g / L, the iron ion concentration is 1.8 g / L, and the calcium ion concentration is 3 g / L.

[0074] Step S2: Add the primary leaching solution to the primary leaching system for primary leaching circulation. The number of primary leaching circulation times is 5 times to obtain a lithium-enriched solution; 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.

[0075] Step S3: Mix the primary leaching residue with the second solution to obtain a secondary leaching system. After the reaction, filter and separate to obtain a secondary leaching solution and a purified residue. Among them, the second solution is a mixed solution of potassium chloride (complexing agent) and hydrochloric acid, the concentration of the second solution is 5 mol / L, the concentration of the complexing 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.

[0076] Step S4: Crystallize and separate the secondary leaching solution at a crystallization temperature of 25°C and a crystallization time of 12 h to obtain calcium sulfate dihydrate and a crystallization mother liquor. Supplement the crystallization mother liquor with the second solution to a solution concentration of 5 mol / L, and add it to the secondary leaching system for secondary leaching circulation. The number of secondary leaching circulation times is 4 times.

[0077] Comparative Example 1

[0078] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include Step S1 and Step S2, and one-step leaching and desulfurization of calcium are adopted. The specific steps are as follows:

[0079] Step S1: Mix the spodumene smelting slag and the composite solution to obtain a leaching system. After the reaction, filter and separate to obtain a leachate and a leaching residue. Among them, 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 composite solution is a mixed solution of sodium chloride (complexing agent) and hydrochloric acid. The concentration of the composite solution is 8 mol / L, the concentration of the complexing 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.

[0080] Step S2: Crystallize and separate the leachate at a crystallization temperature of 0 °C and a crystallization time of 3 h to obtain calcium sulfate dihydrate and a crystallization mother liquor. Supplement the composite solution to the crystallization mother liquor until the solution concentration is 8 mol / L, and add it to the leaching system for cyclic leaching. The number of cycles of cyclic leaching is 3 times.

[0081] Comparative Example 2

[0082] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not include Step S3 and Step S4, and uses one-step lithium extraction by leaching. The specific steps are as follows:

[0083] Step S1: Mix the spodumene smelting slag and the first solution to obtain a primary leaching system. After the reaction, filter and separate to obtain a primary leachate and a primary leaching residue. Among them, 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 180 min, and the reaction liquid-solid ratio is 10 mL / g. The lithium ion concentration in the primary leachate is 0.45 g / L, the aluminum ion concentration is 3 g / L, the iron ion concentration is 3.5 g / L, and the calcium ion concentration is 6 g / L.

[0084] Step S2: Add the primary leachate to the primary leaching system for a primary leaching cycle. The number of cycles of the primary leaching cycle is 3 times to obtain a lithium-enriched solution. 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.

[0085] Experimental detection

[0086] Use the alkali fusion method to digest the lithium smelting slag and the primary leaching residue of Examples 1-3 to obtain solution samples, and use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the lithium element concentration in the solution samples to obtain the lithium removal rate.

[0087] The yield of calcium sulfate dihydrate, the purity of calcium sulfate dihydrate, and the sulfur-calcium removal rate were measured by X-ray fluorescence spectrometry.

[0088] The methods for recovering lithium and calcium sulfate from the lithium smelting slag in Examples 1-3 and Comparative Examples 1-2 were tested for lithium removal rate, calcium sulfate dihydrate yield, calcium sulfate dihydrate purity, and sulfur-calcium removal rate. The test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] From the test results in Table 1, it can be seen that the methods for recovering lithium and calcium sulfate from the lithium smelting slag in Examples 1-3 can efficiently recover lithium, improve the sulfur-calcium removal rate and the purity of calcium sulfate in the 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-calcium removal rate can reach 90% or more.

[0092] In Comparative Example 1, no primary leaching for pre-removing impurities was carried out, and only one-step leaching was used to desulfurize the calcium component, resulting in a significant decrease in the yield of calcium sulfate dihydrate. The high contents of aluminum and iron impurities in the leachate affected the crystallization recovery process of calcium sulfate dihydrate, which was not conducive to the crystallization separation of calcium sulfate dihydrate from the leachate, leading to a reduction in the yield of calcium sulfate dihydrate.

[0093] In Comparative Example 2, no secondary leaching was carried out, and only one-step leaching was used for lithium extraction and pre-removing impurities. The lithium removal rate was 85%, but the yield of calcium sulfate dihydrate was 0%. Under the low acidity condition with the first solution concentration of 1.5 mol / L, the sulfur-calcium removal rate was limited, and calcium sulfate dihydrate could not be directly crystallized.

[0094] Examples 4-13

[0095] Example 4

[0096] 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 the same as those in Example 1.

[0097] Example 5

[0098] 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 the same as those in Example 1.

[0099] Example 6

[0100] Example 6 is different from Example 1 in 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 ethylenediaminetetraacetate and ethylenediaminetetraacetic acid, and the remaining process parameters are the same as those in Example 1.

[0101] Example 7

[0102] Example 7 is different from Example 1 in that in step S1 of Example 7, the first solution is hydrochloric acid and nitric acid with 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 with a volume ratio of 1:1, and the remaining process parameters are the same as those in Example 1.

[0103] Example 8

[0104] Example 8 is different from Example 1 in that in step S2 of Example 8, the number of cycles of the primary leaching cycle is 6 times.

[0105] Example 9

[0106] Example 9 is different from Example 1 in that in step S2 of Example 9, the number of cycles of the primary leaching cycle is 8 times.

[0107] Example 10

[0108] Example 10 is different from Example 8 in that in step S3 of Example 10, the concentration of the second solution is 5 mol / L, the concentration of the complexing 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.

[0109] Example 11

[0110] Example 11 is different from Example 8 in that in step S3 of Example 11, the concentration of the second solution is 2 mol / L, the concentration of the complexing 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.

[0111] Example 12

[0112] Example 12 is different from Example 10 in that in step S4 of Example 12, the crystallization temperature for crystallization separation is 25 °C and the crystallization time is 14 h.

[0113] Example 13

[0114] Example 13 is different from Example 10 in that in step S4 of Example 13, the crystallization temperature for crystallization separation is 50 °C and the crystallization time is 24 h.

[0115] The methods for recovering lithium and calcium sulfate from the lithium smelting slag in Examples 4 to 13 were tested for lithium removal rate, yield of calcium sulfate dihydrate, and purity of calcium sulfate dihydrate. The test results are shown in Table 2.

[0116] Table 2

[0117]

[0118] 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 compositions of the first solution in step S1 and the second solution in step S3 are different. Among them, the lithium removal rate and the yield of calcium sulfate dihydrate in Example 1 are the highest.

[0119] The difference between Examples 8 and 9 and Example 1 is that the number of cycles of the leaching cycle in step S2 is different. Among them, the lithium removal rate in Example 8 is relatively high, and at the same time, it will not increase unnecessary processing time and cost due to excessive cycles.

[0120] The difference between Examples 10 and 11 and Example 8 is that the reaction parameters in step S3 are different. Among them, the yield of calcium sulfate dihydrate in Example 10 is the highest.

[0121] The difference between Examples 12 and 13 and Example 10 is that the crystallization parameters in step S4 are different. Among them, the yield of calcium sulfate dihydrate in Example 10 is the highest.

[0122] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the principle of the present application shall 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 reaction to obtain a primary leaching solution and a primary leaching slag; the first solution is selected from at least one of nitric acid, hydrochloric acid, acetic acid, and ethylenediaminetetraacetic acid; the concentration of the first solution is 0.1-1.5 mol / L, and the reaction temperature is 30-160° C.; 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; The second solution 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; the concentration of the second solution is 2-8 mol / L, and the reaction temperature is 50-95°C; 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 secondary leaching circulation.

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 claim 1, characterized in that: In the step S1, the reaction time is 10-180 min, and the reaction liquid-to-solid ratio is 2-10 mL / g.

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

6. The method for recovering lithium and calcium sulfate according to claim 1, characterized in that: In the step S3, 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.

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

8. The method for recovering lithium and calcium sulfate according to any one of claims 1 to 3, characterized in that: 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.

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

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