Method for recovering and preparing high-purity lithium sulfide from electrolytic aluminum overhaul slag and application thereof

Abstract

The application discloses a method for recovering and preparing lithium sulfide from electrolytic aluminum overhaul slag and application thereof. The application aims to solve the problems of electrolytic aluminum overhaul slag storage pollution, high cost of high-purity lithium sulfide raw material preparation and dependence on imports. The method comprises the following steps: selectively leaching electrolytic aluminum overhaul slag to obtain a lithium-containing solution; deeply purifying the lithium-containing solution to remove impurity ions such as aluminum, iron, calcium and sodium, and obtaining a high-purity lithium salt solution; carrying out a sulfuration reaction on the high-purity lithium salt and a sulfuration agent in a specific solvent and under the protection of a specific atmosphere to generate lithium sulfide slurry; and finally, through washing and drying, a high-purity lithium sulfide product is obtained. The core innovation of the application lies in the combination of lithium recovery of large solid waste overhaul slag and the preparation technology of advanced sulfide solid electrolyte raw materials.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of hazardous waste residue from electrolytic aluminum production, specifically, to a method for recovering and preparing high-purity lithium sulfide from the slag of electrolytic aluminum overhaul. Background Technology

[0002] Electrolytic aluminum overhaul slag is a hazardous solid waste generated during the overhaul of aluminum electrolytic cells. Its main components are fluorides, cyanides, aluminum oxides, and small amounts of alkali metal compounds such as lithium, sodium, and potassium. Currently, overhaul slag is mainly disposed of through stockpiling or landfilling, which not only occupies a large amount of land but also causes serious pollution to soil and groundwater due to the fluorides and cyanides present. However, overhaul slag typically contains 0.5% to 3% lithium resources, existing in the form of LiF, etc. If the valuable lithium element can be efficiently recovered, it can not only solve the environmental pollution problem but also achieve resource recycling.

[0003] On the other hand, lithium sulfide (Li2S) is a core raw material for preparing sulfide solid electrolytes, a key material for next-generation all-solid-state lithium batteries. Due to its high ionic conductivity and good machinability, sulfide solid electrolytes are considered one of the most promising solid electrolyte systems. However, the preparation technology of high-purity Li2S is currently mainly monopolized by Japanese and South Korean companies, resulting in high prices. Furthermore, its purity directly determines the ionic conductivity, electrochemical stability, and electrode compatibility of the prepared solid electrolyte. Traditional methods, such as the reaction of lithium carbonate with hydrogen sulfide to prepare Li2S, often suffer from problems such as low purity, excessive oxygen content, and uncontrollable particle morphology, making it difficult to meet the production requirements of high-end solid electrolytes.

[0004] Currently, there are several technologies for recovering lithium from lithium-containing waste or ores, as well as various processes for preparing lithium sulfide. However, existing technologies are mostly isolated: they either focus on recovering lithium from solid waste or on preparing lithium sulfide through refining chemical raw materials. These technologies do not effectively connect solid waste lithium sources with high-end application requirements. Simply using recycled lithium salts of unknown purity to prepare Li2S is highly susceptible to introducing impurities, resulting in substandard products unsuitable for use as sulfide solid electrolytes.

[0005] Therefore, there is an urgent need in this field for an innovative method that can transform low-value, complex-composition lithium slag from overhaul slag into high-purity lithium sulfide raw materials that can meet the stringent requirements of sulfide solid electrolytes through a complete and precise technology chain. Summary of the Invention

[0006] This invention provides a method for recovering and preparing high-purity lithium sulfide from electrolytic aluminum overhaul slag, comprising the following steps:

[0007] Selective leaching of S1 lithium: Electrolytic aluminum overhaul slag is mixed with leaching agent to carry out selective leaching reaction, and lithium-containing leachate is obtained after solid-liquid separation.

[0008] S2 Deep Purification: The lithium-containing leachate obtained in step S1 is subjected to deep purification treatment to remove impurity ions and obtain a high-purity lithium salt solution or high-purity lithium salt solid.

[0009] S3 Directional Sulfation: The high-purity lithium salt obtained in step S2 and the sulfiding agent are subjected to a sulfidation reaction in an organic solvent or under an inert atmosphere at a temperature of 80~300℃. After the reaction is completed, lithium sulfide slurry is obtained.

[0010] S4 Post-processing: The lithium sulfide slurry obtained in step S3 is subjected to solid-liquid separation. The resulting solid is washed and dried to obtain a high-purity lithium sulfide product.

[0011] Further, in step S1, the leaching agent is water, a dilute acid, or an alkaline solution; the selective leaching is carried out under stirring, ultrasonic, or heating conditions, aiming to preferentially dissolve lithium compounds in the overhaul slag while retaining major impurities such as calcium fluoride and alumina in the slag phase, so that the Ca / Al concentration in the leachate is <100 mg·L⁻¹. -1 .

[0012] Further, in step S2, the deep purification treatment includes a combination of one or more of the following methods: chemical precipitation, solvent extraction, ion exchange, adsorption, and membrane separation; the goal of the deep purification is to reduce the total content of impurity elements Al, Fe, Ca, Na, and K to below 100 ppm, and the impurity content is determined by ICP-MS with a detection limit ≤ 0.1 ppm.

[0013] Furthermore, in step S2, the high-purity lithium salt is lithium carbonate, lithium hydroxide, lithium oxalate, or lithium acetate; when a high-purity lithium salt solution is obtained in step S2, it needs to be converted into a solid lithium salt by evaporation crystallization or spray drying.

[0014] Further, in step S3, the sulfiding agent is hydrogen sulfide gas, thiourea, thioacetamide, or a mixture of elemental sulfur and a reducing agent, and the organic solvent is one or more of toluene, xylene, n-hexane, tetrahydrofuran, acetonitrile, and N-methylpyrrolidone.

[0015] Furthermore, when the sulfiding agent is a mixture of elemental sulfur and a reducing agent, the reducing agent is lithium aluminum hydride, sodium borohydride, or hydrogen.

[0016] Furthermore, in step S3, the sulfidation reaction takes 2-12 hours; the inert atmosphere is argon or nitrogen.

[0017] Further, in step S4, the washing is performed using the organic solvent or an inert solvent with a boiling point ≤80°C, and the drying is carried out under vacuum or an inert atmosphere at 60-150°C.

[0018] On the other hand, the present invention provides a high-purity lithium sulfide prepared by any of the methods described above, wherein the purity of the lithium sulfide is ≥99.9% and the impurity oxygen content is ≤1000ppm, wherein the oxygen content is determined by inert gas melting-infrared method (ASTM E1019), and the total content of the impurity elements Al, Fe, Ca, Na and K is ≤100ppm.

[0019] On the other hand, the present invention provides an application of the aforementioned high-purity lithium sulfide product in the preparation of sulfide solid electrolytes, wherein the sulfide solid electrolyte is a sulfide-germanium sulfide type, LGPS type, or Thio-LISICON type solid electrolyte, used to prepare Li... a M b S c A sulfide solid electrolyte (M = Si, Ge, Sn, P, Al, Sb; 2 ≤ a ≤ 12; 0 ≤ b ≤ 2; 3 ≤ c ≤ 12).

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention is the first to systematically couple the disposal of a large volume of hazardous solid waste, such as electrolytic aluminum overhaul slag, with the preparation of a key raw material for a cutting-edge new material, sulfide solid electrolyte.

[0022] The core innovation of this invention lies not in a single leaching, purification, or sulfidation step, but in the precise connection and synergy of two core stages: deep purification and targeted sulfidation. Addressing the high sensitivity of sulfide solid electrolytes to raw material impurities, particularly oxygen and specific metals, the front-end purification stage sets standards far exceeding those of ordinary industrial-grade lithium salts, laying the raw material foundation for the subsequent preparation of high-end Li2S. The subsequent sulfidation process is specifically designed to match the deeply purified specific lithium salts, ensuring optimized reaction pathways and targeted product performance.

[0023] The lithium sulfide prepared by this invention has high purity (≥99%) and low content of key impurities (O≤1000ppm, Al+Fe+Ca+Na+K≤100ppm). Its purity index is comparable to or even better than that of high-end foreign products, which can fully meet the requirements for preparing high-performance sulfide solid electrolytes and reduce the material cost of all-solid-state batteries.

[0024] This method has a clear process flow, key parameters are easy to control, and it has good repeatability and potential for large-scale production. Furthermore, the technical approach of this application can be extended to the high-value utilization of other lithium-containing solid wastes (such as waste lithium batteries, lithium extraction slag from lepidolite, etc.). Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of the present invention for recovering and preparing high-purity lithium sulfide from the slag of electrolytic aluminum overhaul. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments.

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] 1. Selective Leaching: Take 1 kg of electrolytic aluminum overhaul slag (Li content was tested to be 1.5%) and grind it to 100 mesh. Mix it with 5 L of deionized water and leach at 80℃ for 4 hours with stirring. Filter to obtain a lithium-containing leachate.

[0031] 2. Deep purification: Add Ca to the leachate. 2+ CO3 2- Add Na₂CO₃ solution at a ratio of 1:1.2 to precipitate and remove Ca. 2+ Then use 2 mol·L -1 NaOH solution is added slowly dropwise while stirring and monitoring. The final pH is controlled at 10.0 ± 0.2. If localized over-alkalinity causes flocculation, a small amount of the original solution is immediately added to bring the pH back to 9.8, ensuring Al2O3 levels are maintained. 3+ Fe 3+ Complete precipitation without introducing excess OH - H₂S gas is introduced at a rate of 20 mL / min for 30 min to precipitate and remove heavy metal ions. Then, the mixture is passed through a D401 (iminodiacetic acid type) chelating resin ion exchange column for deep adsorption and removal of residual Al. 3+Fe 3+ Finally, the solution was concentrated to 1 / 5 of its original volume by rotary evaporation at 80℃, and then cooled and crystallized at 4℃ for 12 hours to obtain high-purity lithium carbonate solid. The total impurity content was <80ppm according to ICP-MS analysis.

[0032] 3. Directional Sulfidation: In an argon-filled glove box, 10g of the above-mentioned high-purity lithium carbonate was mixed with an excess of 20% thiourea, and 100mL of anhydrous toluene was added as a solvent. The mixture was transferred to a high-pressure reactor and reacted at 150℃ for 8 hours. After natural cooling, a gray slurry was obtained.

[0033] 4. Post-processing: Filter the slurry, wash it three times with anhydrous toluene, and then wash it once with anhydrous diethyl ether. Dry the resulting white solid at 100°C under vacuum for 6 hours to obtain high-purity lithium sulfide product.

[0034] Chemical analysis revealed that the purity of the obtained Li₂S was 99.92%, the oxygen content was 850 ppm, and the total content of Al, Fe, Ca, Na, and K was 65 ppm.

[0035] Weigh 0.60 g of Li₂S, 0.76 g of P₂S₅, and 0.08 g of LiCl, and accurately mix them in a molar ratio of Li₂S:P₂S₅:LiCl = 6:1:1. Place the mixture in a 45 mL zirconia ball mill jar, add 30 Φ10 mm zirconia balls (ball-to-material ratio 25:1), seal the jar in an argon-filled glove box, and then place it in a planetary ball mill. Dry mill at 400 rpm for 20 h, alternating between forward and reverse rotation for 10 min intervals. Loosely pack the resulting glassy powder into a corundum boat with a thickness ≤5 mm, and place it in a tube furnace with an argon flow rate of 100 mL / min. -1 , at 5 ℃ min -1 The temperature was raised to 550 °C and held for 2 h before being cooled in the furnace. The sample was removed and ground through a 100-mesh sieve in a glove box to obtain white Li6PS5Cl electrolyte powder. 0.35 g of the powder was placed into a Φ10 mm hard alloy mold, cold-pressed at 375 MPa for 3 min, and then sputtered onto a 100 nm gold blocking electrode. Electrochemical impedance spectroscopy was used to measure the ionic conductivity at 25 °C, and the conductivity was 2.1 × 10⁻⁶. -3 S cm -1 .

[0036] Example 2

[0037] 1. Selective leaching: Take 1 kg of electrolytic aluminum overhaul slag, grind it to 100 mesh, and mix it with 3 L of 1 mol / L... -1 Mix dilute hydrochloric acid, liquid-to-solid ratio 3L / kg -1 Mechanical stirring at 60℃ and 200 rpm, with an application of 40 kHz and 2W cm⁻¹ heat. -2Ultrasonic leaching for 2 hours; online addition of hydrochloric acid to maintain pH 1.5±0.1; vacuum filtration with 0.45µm PTFE, 0.5L / kg. -1 Wash twice with deionized water at room temperature under countercurrent; residual Li in the residue ≤ 0.12%, lithium leaching rate ≥ 92%.

[0038] 2. Deep purification: Organic phase: 30% v / v TBP + 70% kerosene; Aqueous feed pH 2.0; O / A = 2:1, 3-stage countercurrent extraction, single-stage mixing for 3 min, clarification for 5 min; Lithium extraction rate ≥ 98%; Deionized water O / A = 1:4, 25℃, 2-stage back-extraction, yielding 45 g / L. -1 LiCl solution; diaphragm electrolyzer, DSA-Ti / RuO2 anode, 316L stainless steel cathode, current density 1 kAm. -2 60℃, catholyte endpoint 90g / L -1 LiOH was cooled and crystallized at 5℃ for 8 hours, and the crystals were dried at −0.09MPa and 80℃ for 6 hours to obtain high-purity lithium hydroxide solid. The total impurity content was <50ppm by ICP-MS analysis.

[0039] 3. Directional sulfidation: Weigh 10g of the above-mentioned lithium hydroxide, loosely pack it with a thickness ≤5mm, and place it in a corundum boat; use a tubular furnace with an inner diameter of 50mm, a constant temperature zone of 200mm, and 200mL / min of argon gas. -1 Pre-purge for 30 min; heating rate 5℃ / min -1 At 300℃, switch to drying H2S (purity ≥99.5%) for 100 mL / min. -1 The gas was kept at a constant temperature for 4 hours; the exhaust gas was subjected to two-stage absorption by 5% NaOH and activated carbon; the H2S concentration at the reaction endpoint was ≥95% of the inlet concentration, and UV230nm was used for online monitoring; the theoretical sulfur excess was 10%.

[0040] 4. Post-treatment: After the heat preservation is completed, the furnace is heated to 10℃ for 1 minute. -1 The temperature was lowered to 100℃, then naturally cooled to 25℃ under argon protection; the entire process was carried out in a glove box with water and oxygen levels <1ppm; the product was ball-milled at 200rpm for 10min and passed through a 100-mesh sieve; white lithium sulfide powder was obtained, with Li2S purity ≥99.5%, D50 = 3–5µm, and BET specific surface area 5–8m²g. -1 The residual H2O is less than 0.05%, the residual C is less than 0.02%, the oxygen content is 720 ppm, and the total content of metallic impurities is 42 ppm.

[0041] Used to prepare Li 10 GeP2S 12 Type electrolyte, cold-pressed ionic conductivity 5.1 mS / cm -1 .

[0042] The preparation method is as follows: Li₂S (purity 99.95%, oxygen 720 ppm, D50 3–5 µm) prepared in Example 2 was used as the lithium source and mixed with commercial GeS₂ (99.99%) and P₂S₅ (99.99%) at a target stoichiometric ratio of Li₂S:GeS₂:P₂S₅ = 5:1:2. A zirconia flask was used, containing 30 zirconia balls at a ball-to-material ratio of 25:1. The powder was scraped in an Ar atmosphere, passed through a 100-mesh sieve, and a light gray LGPS precursor powder was obtained. The powder was then placed in a tube furnace under an Ar atmosphere for 5 minutes. -1 The temperature was raised to 300 °C and held for 2 hours. The furnace was then cooled to room temperature and collected under Ar to obtain a crystalline LGPS main phase with a purity > 97% after XRD refinement. The phase was cold-pressed to obtain a dense sheet with a diameter of 10 mm and a thickness of 0.8 mm.

[0043] Example 3

[0044] 1. Alkaline leaching: 1 kg of overhaul residue (Li 1.5%) and 3 L of 2 mol / L solution. -1 Mix with NaOH and stir at 90℃ and 300rpm for 3 hours; solid-liquid ratio 3L / kg. -1 NaOH was added online to maintain pH 13.5 ± 0.2; the solution was filtered through a 0.45 µm filter to obtain a lithium-rich alkaline solution with Ca / Al ratios both < 80 mg / L. -1 .

[0045] 2. Deep purification: CO2 was passed through to pH 11.5 to precipitate Al / Fe; nanofiltration was performed using a DK membrane at 4 MPa and 30 °C for multivalent separation, with Li recovery rate >95%; lithium hydroxide monohydrate was obtained by evaporation and crystallization, and vacuum dried at 80 °C for 6 h; ICP-MS determination showed that the total of Al+Fe+Ca+Na+K was 42 ppm.

[0046] 3. Directional vulcanization: In an argon glove box, 10g LiOH·H2O, 1.8g S8, and 0.4g NaBH4 were placed in a 30mL stainless steel ball mill jar and dry-milled at 400rpm for 2h using a planetary mill; the mixture was then transferred to a tube furnace and milled at 5℃ for 1 minute under argon atmosphere. -1 Heat to 250℃ and hold for 6 hours; then allow to cool naturally.

[0047] 4. Post-processing: The mixture was crushed in argon atmosphere, washed twice with anhydrous diethyl ether, and vacuum dried at 60℃ for 8 hours to obtain white Li₂S powder with a purity of 99.92%, an oxygen content of 820 ppm, and a total Al+Fe+Ca+Na+K content of 38 ppm. It was used as an electrolyte in Li₆PS₅Cl sulfide germanium ore, exhibiting a cold-pressed ionic conductivity of 3.2 mS / cm. -1 .

[0048] Weigh 0.54 g of Li₂S, 0.42 g of P₂S₅, and 0.04 g of GeS₂, and accurately mix them in a molar ratio of Li₂S:P₂S₅:GeS₂ = 70:25:5. Place the mixture in a 45 mL zirconia ball mill jar, add 30 Φ10 mm zirconia balls (ball-to-material ratio 25:1). After sealing in an argon-filled glove box, place the jar into a planetary ball mill and dry-mill at 450 rpm for 24 h, alternating between forward and reverse rotation for 10 min intervals. Loosely pack the resulting glassy powder into a corundum boat with a thickness ≤5 mm, and place it in a tube furnace with an argon flow rate of 100 mL / min. -1 , at 5 ℃ min -1 The temperature was raised to 480 °C and held for 4 h before being cooled in the furnace. The sample was removed and ground through a 100-mesh sieve in a glove box to obtain a white Thio-LISICON electrolyte powder. 0.35 g of the powder was placed into a Φ10 mm hard alloy mold, cold-pressed at 375 MPa for 3 min, and then sputtered onto a 100 nm gold blocking electrode. Electrochemical impedance spectroscopy was used to measure the ionic conductivity at 25 °C, and the conductivity was 1.8 × 10⁻⁶. -3 S cm -1 Activation energy 0.28 eV, electrochemical window 0–4.8 V vs Li + / Li.

[0049] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering and preparing high-purity lithium sulfide from electrolytic aluminum overhaul slag, characterized in that, Includes the following steps: Selective leaching of S1 lithium: Electrolytic aluminum overhaul slag is mixed with leaching agent to carry out selective leaching reaction, and lithium-containing leachate is obtained after solid-liquid separation. S2 Deep Purification: The lithium-containing leachate obtained in step S1 is subjected to deep purification treatment to remove impurity ions and obtain a high-purity lithium salt solution or high-purity lithium salt solid. S3 Directional Sulfation: The high-purity lithium salt obtained in step S2 and the sulfiding agent are subjected to a sulfidation reaction in an organic solvent or under an inert atmosphere at a temperature of 80~300℃. After the reaction is completed, lithium sulfide slurry is obtained. S4 Post-processing: The lithium sulfide slurry obtained in step S3 is subjected to solid-liquid separation. The resulting solid is washed and dried to obtain a high-purity lithium sulfide product.

2. The method according to claim 1, characterized in that, In step S1, the leaching agent is water, dilute acid or alkaline solution; the selective leaching is carried out under stirring, ultrasonic or heating conditions, aiming to preferentially dissolve lithium compounds in the spent refractory, while retaining calcium fluoride, aluminum oxide and other main impurities in the slag phase, so that the Ca / Al concentration in the leaching solution is <100 mg·L -1 .

3. The method according to claim 1, characterized in that, In step S2, the deep purification treatment includes a combination of one or more of the following methods: chemical precipitation, solvent extraction, ion exchange, adsorption, and membrane separation. The goal of the deep purification is to reduce the total content of impurity elements Al, Fe, Ca, Na, and K to below 100 ppm. The impurity content is determined by ICP-MS with a detection limit ≤ 0.1 ppm.

4. The method according to claim 1, characterized in that, In step S2, the high-purity lithium salt is lithium carbonate, lithium hydroxide, lithium oxalate, or lithium acetate. When a high-purity lithium salt solution is obtained in step S2, it needs to be converted into a solid lithium salt by evaporation crystallization or spray drying.

5. The method according to claim 1, characterized in that, In step S3, the sulfiding agent is hydrogen sulfide gas, thiourea, thioacetamide, or a mixture of elemental sulfur and a reducing agent, and the organic solvent is one or more of toluene, xylene, n-hexane, tetrahydrofuran, acetonitrile, and N-methylpyrrolidone.

6. The method according to claim 5, characterized in that, When the sulfiding agent is a mixture of elemental sulfur and a reducing agent, the reducing agent is lithium aluminum hydride, sodium borohydride, or hydrogen.

7. The method according to claim 1, characterized in that, In step S3, the vulcanization reaction takes 2-12 hours; the inert atmosphere is argon or nitrogen.

8. The method according to claim 1, characterized in that, In step S4, the washing is performed using the organic solvent or an inert solvent with a boiling point ≤80℃, and the drying is carried out under vacuum or an inert atmosphere at 60-150℃.

9. A high-purity lithium sulfide prepared by the method according to any one of claims 1-8, characterized in that, The purity of the lithium sulfide is ≥99%, and the oxygen content of the impurities is ≤1000ppm. The oxygen content is determined by inert gas melting-infrared method (ASTM E1019). The total content of the impurity elements Al, Fe, Ca, Na and K is ≤100ppm.

10. The application of the high-purity lithium sulfide product as described in claim 9 in the preparation of sulfide solid electrolytes, characterized in that, The sulfide solid electrolyte is a sulfide-germanium ore type, LGPS type, or Thio-LISICON type solid electrolyte, used to prepare Li a M b S c A sulfide solid electrolyte (M = Si, Ge, Sn, P, Al, Sb; 2 ≤ a ≤ 12; 0 ≤ b ≤ 2; 3 ≤ c ≤ 12).

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