Method for preparing lithium sulfide and byproduct sodium chloride from lithium-containing sodium sulfate waste residue

Abstract

A method for preparing lithium sulfide and coproducing sodium chloride by using lithium-containing sodium sulfate waste residues comprises the following steps: S1, uniformly mixing the lithium-containing sodium sulfate waste residues with a carbonaceous reducing agent, and calcining under an oxygen isolation condition to obtain calcined clinker; s2, stirring and leaching the calcined clinker by using a polar organic solvent in an inert atmosphere, and carrying out solid-liquid separation to obtain an organic solvent leaching solution containing lithium sulfide and sodium sulfide; s3, adding lithium chloride into the organic solvent leaching solution to carry out double decomposition reaction, carrying out solid-liquid separation after the reaction, and washing and drying the obtained solid slag to obtain a byproduct sodium chloride; and S4, carrying out purification treatment on the solution obtained by solid-liquid separation in S3, and separating to obtain a lithium sulfide product. Sodium sulfate is converted into high-purity anhydrous sodium sulfide which is a raw material necessary for a double decomposition method in one step, so that high-purity lithium sulfide and a byproduct sodium chloride are produced; and meanwhile, the lithium component in the waste residue is synchronously and efficiently converted into a main product lithium sulfide, so that the resource value is remarkably improved.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium sulfide, and more particularly to a method for preparing lithium sulfide from lithium-containing sodium sulfate waste residue and producing sodium chloride as a byproduct. Background Technology

[0002] With the rapid development of the new energy industry, the demand for lithium resources continues to grow. During lithium product production, especially when using the spodumene sulfuric acid process, a large amount of lithium-containing sodium sulfate waste residue is generated. This waste residue contains 0.5%-3.5% lithium resources (in the form of lithium sulfate). Traditional disposal methods mainly involve stockpiling or landfilling, which not only occupies a large amount of land resources but also poses serious environmental pollution risks (such as dust pollution and groundwater salinization), while also resulting in a significant waste of lithium resources. Currently, the global accumulated stockpiles of this type of waste residue have reached millions of tons, and this number continues to grow at a rate of tens of thousands of tons per year. Its resource utilization has become one of the key challenges restricting the sustainable development of the lithium battery industry.

[0003] The efficient extraction of lithium resources from lithium-containing sodium sulfate waste residue faces significant technical challenges. Existing technologies, such as the CN109354044A patent, propose a method for recovering lithium by mixing and roasting lithium-containing sodium sulfate with coal powder, achieving a lithium recovery rate of over 95%. However, this method still suffers from problems such as complex processes (requiring multiple steps including roasting, water extraction, acid extraction, and evaporation crystallization), high risk of secondary pollution (due to the use of dilute sulfuric acid for extraction), and poor economic feasibility. Other methods, such as the recovery technology involved in the CN114573006A patent, are also difficult to apply on a large scale due to similar complexities. Ultimately, the physicochemical properties of sodium sulfate and lithium sulfate in the waste residue are extremely similar, making separation extremely difficult. This results in high recovery costs for traditional processes and makes it difficult to obtain high-value-added products.

[0004] On the other hand, lithium sulfide (Li2S), as a key cathode material precursor for sulfide-based all-solid-state batteries, has seen its market demand grow rapidly with the development of battery technology. However, traditional lithium sulfide preparation methods, such as lithium metal sulfidation (which consumes expensive lithium metal), hydrogen sulfide gas-phase method (which involves the treatment of highly toxic gases), and carbothermal reduction method (which has high energy consumption and carbon residue issues), generally suffer from high raw material costs, complex processes, huge energy consumption, and serious environmental pollution, severely restricting its large-scale application. It is worth noting that even some newly developed patented technologies (such as CN120440841A), although attempting to prepare lithium sulfide through reduction methods, still involve multi-step calcination and complex purification processes, and require the use of specific reagents (such as iron powder). Their economic viability and scalability potential still need to be verified. The high cost of lithium sulfide also directly drives up the manufacturing cost of all-solid-state batteries, becoming one of the key bottlenecks in their industrialization process.

[0005] Therefore, developing a green new method that can efficiently and economically extract lithium from lithium-containing sodium sulfate waste and directly convert it into high-value-added lithium sulfide products, while realizing the resource utilization of all components of the waste (such as converting sodium into sodium chloride byproducts), is not only of great practical significance and application value, but also of strategic significance for promoting the sustainable development of the lithium battery industry and the construction of a circular economy. Summary of the Invention

[0006] This invention addresses the problems of severe accumulation of lithium-containing sodium sulfate waste residue, difficulty in extracting lithium resources from the waste residue, high cost of lithium sulfide preparation, and significant environmental pollution associated with traditional treatment methods. It provides a method for the co-production of high-purity lithium sulfide and sodium chloride using lithium-containing sodium sulfate waste residue. This method not only achieves resource utilization of the waste residue but also produces high-value-added battery materials, resulting in significant economic and environmental benefits.

[0007] The technical solution of the present invention is as follows: A method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue, characterized by comprising the following steps: S1. The lithium-containing sodium sulfate waste residue is uniformly mixed with a carbonaceous reducing agent and calcined under oxygen-free conditions to obtain calcined clinker. S2. Under an inert atmosphere, the calcined clinker is stirred, leached, and separated into solid and liquid components using a polar organic solvent to obtain an organic solvent leachate containing lithium sulfide and sodium sulfide. S3. Lithium chloride is added to the organic solvent leaching solution to carry out a metathesis reaction. After the reaction, solid-liquid separation is performed. The resulting solid residue is washed and dried to obtain sodium chloride as a byproduct. S4. The solution obtained from the solid-liquid separation in S3 is purified to obtain lithium sulfide product.

[0008] Furthermore, in step S1, the calcination temperature is 800-1000℃ and the calcination time is 1-3h.

[0009] Furthermore, in step S1, the oxygen isolation condition is to introduce nitrogen or argon gas at a flow rate of 0.5-2.0 L / min, or to evacuate the system.

[0010] Furthermore, the specific steps of stirring and immersion in step S2 include immersion at 50-70°C for 1-4 hours with a stirring speed of 300-800 rpm under an inert atmosphere.

[0011] Furthermore, the inert atmosphere is specifically nitrogen or argon, wherein the oxygen content is less than 10 ppm and the water content is less than 15 ppm.

[0012] Furthermore, in step S3, lithium chloride is added in solid form or in the form of a saturated organic solution, and the amount added is 1.0-1.5 times the theoretical amount.

[0013] Furthermore, in step S3, the reaction conditions for the metathesis reaction are a reaction temperature of 40-80℃, a reaction time of 2-6 hours, and a stirring speed of 200-600 rpm.

[0014] Furthermore, the purification process in step S4 includes evaporation and crystallization of the obtained solution, followed by washing with an organic solvent to obtain a lithium sulfide product.

[0015] Furthermore, the specific purification steps in step S4 include evaporating and crystallizing the obtained solution to obtain crude lithium sulfide, washing the crude lithium sulfide with N,N-dimethylformamide under the following conditions: stirring and washing at 20-40°C with a solid-liquid ratio of 1:3-1:5 for 10-30 minutes, repeating the washing 2-3 times, followed by filtration.

[0016] Furthermore, after step S4, the obtained lithium sulfide product is further processed: the washed product is vacuum dried at 80-100℃ and -0.09 to -0.10 MPa for 4-8 hours, and the dried product is passed through a 100-200 mesh sieve to obtain the final lithium sulfide product.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves efficient synergistic conversion and high-value utilization of lithium and sodium components in lithium-containing sodium sulfate waste residue, simultaneously generating battery-grade lithium sulfide and industrial-grade sodium chloride products, significantly improving the level of comprehensive resource utilization; 2. This invention effectively avoids the problem of impurity introduction caused by relying on commercially available industrial-grade sodium sulfide by providing high-purity sodium sulfide as a key reaction intermediate within the system. It overcomes the difficulties of product contamination and high purification costs caused by insufficient raw material purity in the traditional metathesis method for preparing lithium sulfide, thereby significantly reducing the preparation cost of high-purity lithium sulfide.

[0018] This invention effectively alleviates the problem of lithium-containing sodium sulfate waste accumulation, while reducing environmental pollution in the traditional lithium sulfide production process, and has significant environmental benefits. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the steps of a method for preparing lithium sulfide and producing sodium chloride as a byproduct using lithium-containing sodium sulfate waste residue according to the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Example 1 Please see Figure 1 The first embodiment of the present invention provides a method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue, comprising the following steps: S1. Take 10.0 kg of lithium-containing sodium sulfate waste residue (analyzed to contain 2.8 wt% Li₂SO₄ and 92.5 wt% Na₂SO₄) and mix it evenly with 2.5 kg of pulverized coal. Place the mixture in a tube furnace, introduce argon gas (flow rate 1.2 L / min), and heat it to 800℃ at a rate of 5℃ / min. Hold the temperature for calcination for 1 hour. After natural cooling, 11.5 kg of black calcined clinker is obtained. (After sampling and ion chromatography and elemental analysis, the conversion rate of sodium sulfate was found to be 75.0%, the Na₂S content was 48.84 mol, the conversion rate of lithium sulfate was 78.4%, and the Li₂S content was 1.98 mol, i.e., 0.091 kg Li₂S).

[0023] The carbothermic reduction reaction involved in step S1: Li2SO4 + 2C → Li2S + 2CO2↑ Na₂SO₄ + 2C → Na₂S + 2CO₂↑ Understandably, in the carbothermic reduction reaction, in addition to pulverized coal, lithium-containing sodium sulfate waste residue can also be mixed with carbonaceous reducing agents such as coke, activated carbon, or carbon powder. The mass ratio of the lithium-containing sodium sulfate waste residue to the carbonaceous reducing agent is 100:20-100:30, which does not affect the implementation of this patent.

[0024] Understandably, in addition to argon, inert gases such as nitrogen (flow rate of 0.5-2.0 L / min) or vacuuming can also be used to achieve oxygen isolation conditions, without affecting the implementation of this patent.

[0025] S2. Transfer the calcined clinker to an argon-protected reactor ([O2] < 10 ppm, [H2O] < 15 ppm), add 25 L of anhydrous ethanol, and leach for 2 hours at 60°C and 500 rpm with stirring. Filter using a pressure filter, and wash the filter residue twice with 5 L of anhydrous ethanol, combining the results to obtain 28.5 L of ethanol leachate containing lithium sulfide and sodium sulfide.

[0026] Understandably, in addition to ethanol, other polar organic solvents such as methanol, n-propanol, isopropanol, glycerol, ethylene glycol, ethylene dithiol, ethylenediamine, n-butylamine, acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetone can also be used; the stirring and leaching conditions are 300-800 rpm and leaching at 50-70°C for 1-4 hours, which will not affect the implementation of this patent.

[0027] S3. Add 4.14 kg of anhydrous lithium chloride (97.68 mol, 1.0 times the theoretical amount) to the leaching solution, stir the mixture at 80℃ and 400 rpm for 3 hours, cool to 25℃, filter, wash the filter cake three times with 3 L of cold anhydrous ethanol, and dry the filter cake at 105℃ for 4 hours to obtain 5.00 kg of white sodium chloride product with a yield of 87.5% and a purity of 99.2%.

[0028] The metathesis reaction involved in step S3: Na2S + 2LiCl → 2NaCl↓ +Li2S Understandably, the lithium chloride can be in solid form or saturated organic solution form, the reaction temperature is 40-80℃, the reaction time is 2-6 hours, and the stirring speed is 200-600 rpm, which does not affect the implementation of this patent.

[0029] S4. The filtrate was evaporated and crystallized under reduced pressure at 60℃ and -0.1MPa to obtain crude lithium sulfide product. The crude product was washed with 1.2L of N,N-dimethylformamide for 20 minutes (solid-liquid ratio 1:3), and the washing was repeated twice. Then it was washed once with 0.8L of anhydrous diethyl ether. The solid product was dried in a vacuum drying oven (-0.1MPa, 200℃) for 6 hours and passed through a 150-mesh sieve to obtain 2.03kg of white powdered lithium sulfide product, with a yield of 87.0% and a main content of 99.3%. The content of key impurities was: Na 49ppm, Fe 15ppm, and Ca 24ppm.

[0030] Understandably, the washing conditions can be: at 20-40℃, stirring and washing at a solid-liquid ratio of 1:3-1:5 for 10-30 minutes, with 2-3 washing cycles; the drying conditions can be: vacuum drying at 80-200℃ and -0.09 to -0.10 MPa for 4-8 hours; after drying, the product can pass through a 100-200 mesh sieve without affecting the implementation of this patent.

[0031] Example 2 The difference from Example 1 is as follows: Calcination conditions in S1: The holding time is extended to 3 hours.

[0032] The amount of lithium chloride added in S3 is increased to 1.3 times the theoretical amount.

[0033] Analysis results: After calcination, the conversion rate of sodium sulfate was increased to 85.5% (Na2S 55.70mol) and the conversion rate of lithium sulfate was increased to 86.0% (Li2S 0.101kg).

[0034] Experimental results: Adding 6.14 kg of anhydrous lithium chloride to the reaction yielded 5.70 kg of sodium chloride (89.2% yield, 98.8% purity) and 2.20 kg of lithium sulfide (82.7% yield, 99.6% main product content).

[0035] Example 3 The difference from Example 1 is as follows: Calcination conditions in S1: Calcination temperature is raised to 900℃ and held for 2 hours.

[0036] The amount of lithium chloride added in S3 is 1.3 times the theoretical amount.

[0037] Analysis results: After calcination, the conversion rate of sodium sulfate was significantly increased to 95.2% (Na2S 62.01 mol), and the conversion rate of lithium sulfate was increased to 96.5% (Li2S 0.113 kg).

[0038] Experimental results: Adding 6.84 kg of anhydrous lithium chloride to the reaction yielded 6.35 kg of sodium chloride (92.8% yield, 99.0% purity) and 2.52 kg of lithium sulfide (85.1% yield, 99.8% main product content).

[0039] Example 4 The difference from Example 1 is as follows: Calcination conditions in S1: Calcination temperature is raised to 1000℃ and held for 1 hour.

[0040] The amount of lithium chloride added in S3 is 1.3 times the theoretical amount.

[0041] Analysis results: After calcination, the conversion rate of sodium sulfate was 90.1% (Na2S 58.69mol) and the conversion rate of lithium sulfate was 92.0% (Li2S 0.108kg).

[0042] Experimental results: The reaction was carried out with 6.47 kg of anhydrous lithium chloride. 6.02 kg of sodium chloride was obtained, with a yield of 90.9% and a purity of 98.5%. 2.38 kg of lithium sulfide was obtained, with a yield of 84.8% and a main product content of 99.4%.

[0043] Example 5 The difference from Example 1 is as follows: Calcination conditions in S1: Calcination temperature is increased to 1000℃, and holding time is extended to 3 hours.

[0044] The amount of lithium chloride added in S3 is increased to 1.5 times the theoretical amount.

[0045] Analysis results: After calcination, the conversion rate of sodium sulfate was as high as 98.5% (Na2S 64.16mol) and the conversion rate of lithium sulfate was as high as 98.8% (Li2S 0.116kg).

[0046] Experimental results: Adding 8.16 kg of anhydrous lithium chloride to the reaction yielded 6.53 kg of sodium chloride (91.9% yield, 97.9% purity) and 2.65 kg of lithium sulfide (86.5% yield, 99.5% main product content).

[0047] Comparative Example 1 The difference from Example 1 is as follows: Calcination conditions in S1: Calcination temperature reduced to 750℃, held for 2 hours.

[0048] The amount of lithium chloride added in S3 is 1.3 times the theoretical amount.

[0049] Analysis results: After calcination, the conversion rate of sodium sulfate was only 70.5% (Na2S 45.92mol), and the conversion rate of lithium sulfate was 72.0% (Li2S 0.085kg).

[0050] Experimental results: Adding 5.06 kg of anhydrous lithium chloride to the reaction yielded 4.51 kg of sodium chloride (87.3% yield, 98.9% purity) and 1.75 kg of lithium sulfide (79.7% yield, 98.5% main product content).

[0051] Comparative Example 2 The difference from Example 1 is as follows: Calcination conditions in S1: Calcination temperature is raised to 1050℃ and held for 2 hours.

[0052] The amount of lithium chloride added in S3 is 1.3 times the theoretical amount.

[0053] Analysis results: After calcination, the conversion rate of sodium sulfate was measured to be 88.2% (Na2S 57.45mol) and the conversion rate of lithium sulfate was 85.0% (Li2S 0.100kg).

[0054] Experimental results: Adding 6.33 kg of anhydrous lithium chloride to the reaction yielded 5.89 kg of sodium chloride (91.2% yield, 95.1% purity) and 2.15 kg of lithium sulfide (78.5% yield, 98.8% main product content).

[0055] Comparative Example 3 The difference from Example 3 is as follows: The amount of lithium chloride added in S3 is reduced to 0.8 times the theoretical amount.

[0056] Experimental results: Adding 4.20 kg of anhydrous lithium chloride to the reaction yielded 5.45 kg of sodium chloride (79.5% yield, 99.4% purity) and 2.18 kg of lithium sulfide (73.6% yield, 98.9% main product content).

[0057] Comparative Example 4 The difference from Example 3 is as follows: Lithium chloride (S3) addition amount: increased to 1.8 times the theoretical amount. Experimental results: 9.47 kg of anhydrous lithium chloride was added for reaction. 6.72 kg of sodium chloride was obtained, with a yield of 98.1% and a purity of 95.8%. 2.48 kg of lithium sulfide was obtained, with a yield of 83.7% and a main product content of 98.2%.

[0058] The results of each embodiment and comparative example are shown in Table 1. Table 1: Results of each embodiment and comparative example

[0059] The results from Examples 1-5 and Comparative Examples 1-2 show that calcination temperature and time are key factors affecting the conversion rate of sodium sulfate and the final yield of lithium sulfide. Within the temperature range of 800℃ to 1000℃, appropriately increasing the temperature and extending the holding time can significantly improve the conversion rate and yield. However, when the temperature is too low, the reaction kinetics are insufficient, resulting in the lowest conversion rate and yield; when the temperature is too high, the conversion rate and yield may decrease due to increased side reactions or material volatilization.

[0060] The results of Example 3 and Comparative Examples 3 and 4 show that the excess ratio of lithium chloride is a key parameter for balancing the yield and purity of lithium sulfide. When the excess lithium chloride is insufficient, the metathesis reaction is incomplete, leading to a significant decrease in the lithium sulfide yield. When the excess lithium chloride is excessive, although the yield is still acceptable, the excess lithium salt introduces more sodium impurities, resulting in a significant decrease in the purity of the lithium sulfide product. Therefore, controlling the excess ratio of lithium chloride to around 1.3 times can simultaneously achieve a high yield and optimal purity.

[0061] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue, characterized in that: Includes the following steps: S1. The lithium-containing sodium sulfate waste residue is uniformly mixed with a carbonaceous reducing agent and calcined under oxygen-free conditions to obtain calcined clinker. S2. Under an inert atmosphere, the calcined clinker is stirred, leached, and separated into solid and liquid components using a polar organic solvent to obtain an organic solvent leachate containing lithium sulfide and sodium sulfide. S3. Lithium chloride is added to the organic solvent leaching solution to carry out a metathesis reaction. After the reaction, solid-liquid separation is performed. The resulting solid residue is washed and dried to obtain sodium chloride as a byproduct. S4. The solution obtained from the solid-liquid separation in S3 is purified to obtain lithium sulfide product.

2. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 1, characterized in that: In step S1, the calcination temperature is 800-1000℃ and the calcination time is 1-3h.

3. A method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 2, characterized in that: In step S1, the oxygen isolation conditions are achieved by introducing nitrogen or argon gas at a flow rate of 0.5-2.0 L / min, or by evacuating the system.

4. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 1, characterized in that: The specific steps of stirring and immersion in step S2 include immersion at 50-70°C for 1-4 hours with a stirring speed of 300-800 rpm under an inert atmosphere.

5. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 4, characterized in that: The inert atmosphere is specifically nitrogen or argon, with an oxygen content of less than 10 ppm and a water content of less than 15 ppm.

6. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 1, characterized in that: In step S3, lithium chloride is added in solid form or in the form of a saturated organic solution, and the amount added is 1.0-1.5 times the theoretical amount.

7. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 6, characterized in that: The reaction conditions for the metathesis reaction in step S3 are a reaction temperature of 40-80℃, a reaction time of 2-6 hours, and a stirring speed of 200-600 rpm.

8. The method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 1, characterized in that: The purification process in step S4 includes evaporation and crystallization of the obtained solution, followed by washing with an organic solvent to obtain lithium sulfide product.

9. A method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 8, characterized in that: The specific steps of purification in step S4 include evaporating and crystallizing the obtained solution to obtain crude lithium sulfide, washing the crude lithium sulfide with N,N-dimethylformamide under the following conditions: stirring and washing at 20-40°C with a solid-liquid ratio of 1:3-1:5 for 10-30 minutes, repeating the washing 2-3 times, followed by filtration.

10. A method for preparing lithium sulfide and producing sodium chloride as a byproduct from lithium-containing sodium sulfate waste residue according to claim 1, characterized in that: The step S4 is followed by further processing of the obtained lithium sulfide product: the washed product is vacuum dried at 80-200℃ and -0.09 to -0.10 MPa for 4-8 hours, and the dried product is passed through a 100-200 mesh sieve to obtain the final lithium sulfide product.

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