A method for collaborative lithium extraction using aluminum electrolytic cell overhaul slag

Abstract

The present invention discloses a method for synergistically extracting lithium from aluminum electrolytic cell overhaul slag. The method comprises mixing raw materials comprising aluminum electrolytic cell overhaul slag, spodumene concentrate, a fluorine-fixing agent, and a binder to form pellets, followed by a calcination reaction to obtain activated spodumene; and subjecting the activated spodumene to an acid leaching reaction to obtain a lithium-containing leachate. This method achieves high lithium extraction efficiency, effectively recovers lithium from the overhaul slag, achieves harmless treatment of the overhaul slag, and significantly reduces the energy consumption of spodumene activation and transformation. It offers both economic and environmental benefits and broad prospects for industrial application.

Description

Technical Field

[0001] The present invention relates to a method for treating aluminum electrolytic cell overhaul slag, and in particular to a method for collaboratively extracting lithium from aluminum electrolytic cell overhaul slag, belonging to the technical field of comprehensive utilization of hazardous waste and deep extraction of lithium resources. Background Art

[0002] Electrolytic cells are essential equipment in the aluminum electrolysis industry, with a typical service life of 3-5 years. The waste generated by replacing electrolytic cells during maintenance is collectively known as overhaul slag. Typically, 20-30 kg of overhaul slag is generated for every ton of aluminum produced. This slag, which can be divided into spent refractory materials, spent cathode carbon materials, and mixed materials, contains valuable elements such as lithium and aluminum, as well as highly toxic fluorides and cyanides. According to the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB5085.3-2007), the levels of fluoride and cyanide in the leachate from overhaul slag can reach approximately 2500 and 5 mg / L, respectively, far exceeding the safety limits stipulated in the standard. Consequently, overhaul slag was listed on the National List of Hazardous Wastes in 2016. The resource utilization and harmless treatment of overhaul slag urgently need to be addressed.

[0003] Currently, the primary method for disposing overhaul slag in China is harmless treatment. Patent CN 115846377 A proposes using non-strongly alkaline calcium-containing materials to solidify the fluorine in overhaul slag, but this method does not address how to reduce the toxicity of cyanide in the overhaul slag. Patent CN 115591927 A relates to a method for harmlessly treating overhaul slag using microbial agents, but this method has a long treatment cycle, an insufficient cyanide degradation rate, and does not address the removal of fluoride. Industrially, a harmless treatment method for overhaul slag has been developed in China, using calcium hypochlorite to decompose cyanide into nitrogen and carbon dioxide, and calcium hydroxide and fluoride ions to form a calcium fluoride precipitate. This method was put into operation at Zhongfu Aluminum in Henan Province and has now been adopted by numerous aluminum electrolysis companies. Although these methods have achieved some results in harmless treatment of overhaul slag, they overlook the resource utilization of overhaul slag and fail to fully recover the high-value element lithium in the slag.

[0004] The lithium in overhaul slag comes from lithium salts, typically lithium carbonate, added to the electrolyte. The addition of lithium salts effectively improves the performance of aluminum electrolysis, a method adopted by numerous aluminum electrolysis companies both domestically and internationally. Lithium was designated a strategic metal in the 2016 National Mineral Resources Plan. Recovering lithium from overhaul slag meets my country's strategic needs and is crucial for the sustainable development of the lithium industry. The lithium salts added to the aluminum electrolysis process typically come from brine or lithium ore extraction products. Currently, lithium extraction from spodumene is attracting significant attention in China due to its high production efficiency and high lithium recovery rates. Methods for extracting lithium from spodumene can be categorized as the sulfuric acid method, limestone method, sulfate roasting method, chloride roasting method, and alkaline autoclave method. The sulfuric acid method is widely used industrially due to its simplicity and high lithium recovery rate, but it also suffers from high energy consumption. Natural α-spodumene must be calcined at 1000-1100°C for 1-2 hours to convert to easily leached β-spodumene. This energy-intensive conversion process is incompatible with my country's "dual carbon" development strategy, and a solution is urgently needed. Patent CN 114477241A discloses a method for extracting lithium from spodumene by low-temperature conversion roasting assisted by sulfate and alkali compounds. However, this method achieves high lithium extraction rates only through autoclaving, making it difficult to commercialize. Patent CN 109517981 A discloses a method for extracting lithium from spodumene by milling leaching assisted by calcium-containing substances, replacing milling roasting. However, this milling process also requires high energy consumption, resulting in an excessively fine particle size of the milled product and high milling media loss. Furthermore, this method also requires autoclaving of the milled product to achieve a high lithium extraction rate, making it difficult to commercialize. Summary of the Invention

[0005] To address the shortcomings of existing overhaul slag, such as insufficient resource utilization and high energy consumption for lithium extraction from spodumene, the present invention aims to provide a method for synergistically extracting lithium from aluminum electrolytic cell overhaul slag. This method offers a high overall lithium extraction rate, simple operation, low cost, energy conservation, and environmental protection, achieving efficient resource utilization.

[0006] In order to achieve the above technical objectives, the present invention provides a method for synergistically extracting lithium using aluminum electrolytic cell overhaul slag, wherein raw materials comprising aluminum electrolytic cell overhaul slag, spodumene concentrate, a fluorine-fixing agent and a binder are mixed to form pellets, which are then subjected to a roasting reaction to obtain activated spodumene; and the activated spodumene is subjected to an acid leaching reaction to obtain a lithium-containing leachate.

[0007] The present invention utilizes the fluorine in the overhaul slag to help break the aluminum-oxygen and silicon-oxygen bonds in the spodumene structure during the roasting process, thereby reducing the temperature of the spodumene activation and transformation roasting to a certain extent, saving energy consumption, and the resulting activated spodumene is more conducive to the leaching and extraction of lithium; the lithium in the overhaul slag can also be extracted into the leachate during the acid leaching process, realizing the resource utilization of the overhaul slag. In addition, the cyanide in the overhaul slag can be decomposed into nitrogen and carbon oxides under high-temperature roasting, and the fluorine that does not participate in the activation and transformation of spodumene forms a stable compound (such as calcium fluoride) with a fluorine-fixing agent, realizing the harmless treatment of the overhaul slag.

[0008] Among them, the principle of reducing the energy consumption of spodumene transition roasting is to use the fluorine in the overhaul slag to release negative one-valent F during the roasting process. - Substitute the negative divalent O in the aluminosilicate structure 2- , which causes the aluminum-oxygen bond and silicon-oxygen bond in the mineral structure to be destroyed, thereby activating the spodumene even under low-temperature roasting. In addition, in order to maintain the electrical neutrality of the mineral, the excess positive monovalent Li + It will be "expelled" from the spodumene lattice structure, making the lithium easily leached by sulfuric acid.

[0009] The principle of lithium extraction from overhaul slag is as follows: since the lithium salt added in the aluminum electrolysis process will react with fluorides such as Na3AlF6 or NaF in the molten electrolyte to generate LiF, the main target of lithium extraction from overhaul slag is LiF. LiF can react with H2SO4 to generate Li2SO4 and HF, and the generated HF can be leached by Ca in the leachate. 2+ Fixed as CaF2, Ca in the leachate 2+ The calcium ions mainly come from the reaction between the remaining CaO and H2O in the roasting material. The main reactions are as follows:

[0010] 2LiF+H2SO4=Li2SO4+2HF↑

[0011] CaO+H2O=Ca(OH)2

[0012] 2HF+Ca(OH)2=CaF2+2H2O

[0013] The principle of harmless treatment of overhaul slag is as follows: a portion of the fluorine in the overhaul slag participates in the activation and transformation of spodumene, while the remaining fluorine forms a stable compound with the fluorine-fixing agent in the form of fluoride. When the fluorine-fixing agent is calcium oxide or calcium hydroxide (which can be decomposed to obtain calcium oxide), the stable compound is calcium fluoride. The cyanide in the overhaul slag is decomposed into non-toxic substances during the roasting process. The main reactions involved are as follows:

[0014] 2AlF3+3CaO=3CaF2+Al2O3

[0015] 2NaF+CaO=CaF2+Na2O

[0016] 4NaCN+9O2=2Na2O+4CO2↑+4NO2↑

[0017] 4Na4[Fe(CN)6]+55O2=2Fe2O3+8Na2O+24CO2↑+24NO2↑

[0018] As a preferred solution, the amount of the aluminum electrolysis cell overhaul slag is 20 to 50 wt% of the spodumene concentrate.

[0019] Controlling the amount of aluminum electrolytic cell overhaul slag within an appropriate range is beneficial for improving lithium extraction efficiency. If the overhaul slag dosage is too low, it will not provide sufficient fluorine to promote the low-temperature transformation of spodumene. If the overhaul slag dosage is too high, the amount of spodumene lithium extraction tailings will be too large, making it uneconomical.

[0020] As a preferred solution, the particle size of the aluminum electrolytic cell overhaul slag is -200 mesh to +400 mesh. Controlling the particle size of the overhaul slag within a reasonable range is beneficial to promoting the activation and transformation of pyroxene concentrate.

[0021] As a preferred solution, the fluorine-fixing agent includes calcium oxide and / or calcium hydroxide.

[0022] As a preferred solution, the amount of the fluorine-fixing agent is 5 to 20 wt% of the spodumene concentrate. Controlling the amount of the fluorine-fixing agent within an appropriate range is beneficial for improving resource utilization. Too low an amount of the fluorine-fixing agent will fail to effectively stabilize the fluorine in the overhaul slag, potentially causing fluorine to enter the atmosphere as HF during the roasting process, polluting the environment. Too high an amount of the fluorine-fixing agent will result in an excessive amount of spodumene lithium extraction tailings, making it uneconomical.

[0023] As a preferred solution, the binder is a clay-type mineral, wherein the clay-type mineral includes montmorillonite, bentonite, kaolin, etc.

[0024] As a preferred solution, the amount of the binder is 2 to 3 wt% of the spodumene concentrate.

[0025] As a preferred solution, the raw materials also include a fluorine-containing additive. To ensure sufficient fluorine to promote the low-temperature activation and transformation of spodumene, when the fluorine content of the overhaul slag within the addition amount range cannot provide sufficient fluorine to promote the low-temperature activation and transformation of spodumene, an appropriate amount of fluorine-containing additive can be added to ensure that the spodumene can be activated and transformed at low temperatures.

[0026] As a preferred solution, the fluorine-containing auxiliary agent includes at least one of sodium fluoride, boron trifluoride, and sodium fluorosilicate.

[0027] As a preferred solution, the amount of the fluorine-containing auxiliary agent is 0-10wt% of the spodumene concentrate. Controlling the amount of the fluorine-containing auxiliary agent within a reasonable range is conducive to promoting the synergistic lithium extraction efficiency. Excessive use of the fluorine-containing auxiliary agent will lead to excessively high fluoride concentration in the leachate, increasing the toxicity of the leachate.

[0028] As a preferred solution, the pellets have a particle size of 5 to 10 mm. Controlling the pellet size within an appropriate range can improve roasting efficiency and promote the activation and transformation of spodumene. Too small a pellet size can lead to melting and sticking of the material during roasting, while too large a pellet size will require a longer roasting time to achieve activation and transformation of the spodumene within each pellet.

[0029] As a preferred embodiment, the calcination reaction conditions are: a temperature of 750-950°C, more preferably 800-900°C, and a time of 60-90 minutes. Controlling the calcination reaction temperature and time within a reasonable range is conducive to improving the calcination efficiency. A calcination temperature that is too low or a calcination time that is too short is not conducive to the full activation and transformation of α-spodumene. A calcination temperature that is too high or a calcination time that is too long will cause the spodumene concentrate to melt and stick, increasing the energy consumption of the spodumene transformation.

[0030] As a preferred solution, the activated spodumene is ground to a particle size of -100 mesh to +325 mesh before acid leaching. Controlling the particle size of the activated transformed spodumene within a reasonable range is beneficial to improving leaching efficiency, ensuring the purity of the leachate, and reducing energy consumption.

[0031] As a preferred solution, during the acid leaching reaction, sulfuric acid is used as the leaching agent, the sulfuric acid concentration is 2-8 mol / L, the liquid-to-solid ratio is 5-10 mL:1 g, the temperature is 70-90°C, and the time is 60-120 min. Controlling the leaching agent concentration, liquid-to-solid ratio, leaching temperature, and leaching time during the acid leaching process within a reasonable range can improve the leaching efficiency and facilitate obtaining a lithium extraction solution with higher purity. Too low a leaching agent concentration, too low a liquid-to-solid ratio, too low a leaching temperature, or too short a leaching time will relatively reduce the lithium extraction rate; while too high a sulfuric acid concentration, too high a liquid-to-solid ratio, too high a temperature, or too long a leaching time will lead to an increase in the content of impurity elements in the lithium extraction leachate, and is also not economical.

[0032] As a preferred solution, activated spodumene is subjected to an acid leaching reaction to produce lithium-extraction tailings. The leaching concentrations of fluoride and cyanide in the tailings are both below 5 mg / L. These concentrations are determined according to the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007). The leaching concentrations of fluoride and cyanide in the tailings are within safety standards, making them non-hazardous waste.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] (1) Utilizing the fluorine in the aluminum electrolytic cell overhaul slag to achieve low-temperature activation and transformation of spodumene, the efficiency of lithium extraction from spodumene is improved, while saving energy consumption, making the development of the lithium mining industry more compatible with my country's "dual carbon" strategic plan;

[0035] (2) The lithium in the aluminum electrolytic cell overhaul slag is extracted into the leachate in the form of Li2SO4 during the acid leaching process, realizing the resource utilization of the overhaul slag;

[0036] (3) The main harmful substances fluoride and cyanide in the overhaul slag of aluminum electrolytic cells are converted or decomposed into harmless substances during the roasting process, thus achieving harmless treatment of the overhaul slag;

[0037] (4) The method is simple, easy to operate, low-cost, energy-saving and environmentally friendly, and can “turn waste into treasure”. It has both economic and environmental benefits and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the process flow of the method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag according to the present invention. DETAILED DESCRIPTION

[0039] The specific embodiments of the present invention are further described below by way of examples, but the specific embodiments of the present invention are not limited to the following examples.

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with Examples and Comparative Examples. It should be understood that the specific Examples and Comparative Examples described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] The scheme of the present invention is suitable for processing overhaul slag with a fluoride content of 3.0-25.0wt%, a cyanide content of 0.03-1.0wt%, and a lithium content of not less than 0.2wt%, and spodumene concentrate with a Li2O content of not less than 3.0wt%.

[0042] The average primary fluoride composition of the overhaul slag used in all examples and comparative examples was: 6.28% NaF1, 1.89% CaF2, and 1.66% Na3AlF6. The primary cyanide, NaCN, was 0.56%, and the lithium content was 0.44%. According to the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), the fluoride and cyanide levels in the overhaul slag leachate reached 2387.92 and 8.97 mg / L, respectively, making it classified as hazardous waste. Furthermore, the Li2O content of the spodumene concentrate used in all examples and comparative examples was 5.97%.

[0043] Example 1

[0044] Get spodumene concentrate 100g, with respect to spodumene concentrate, add 35wt% overhaul slag (35g) of granularity between 200-400 order, the calcium hydroxide (15g) of 15wt% and the bentonite (2g) of 2wt% and be mixed with the spodumene concentrate and be prepared into the pellet that particle size is 5-10mm.This pellet is dried under 100 ℃ for 120min and removed moisture, and then is placed in a muffle furnace and carries out transition roasting, and the roasting temperature is set at 900 ℃, and the roasting time is 60min.After roasting is completed, treat that roasting material is cooled to 100 ℃ of ball mills to-100 order~+325 order, then placing the ball-milled fine material in concentration is that 4mol / L, volume are 1.5L, temperature are 90 ℃ sulfuric acid solution, uniformly stirred 90min, and then obtained after filtration contains lithium leachate and carries out lithium tailings.

[0045] Testing and analysis revealed that the lithium leaching rate in the leachate obtained from Example 1 (relative to the spodumene concentrate and overhaul slag used) was 97.22%. The lithium-extraction tailings, identified in accordance with the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), contained only 2.16 and 0.85 mg / L of fluoride and cyanide, respectively, significantly lower than the original overhaul slag, making it a non-hazardous waste. Overall, these results demonstrate that this technical solution can achieve resource utilization and harmless treatment of overhaul slag, while also enabling efficient lithium extraction from spodumene at low energy consumption.

[0046] Example 2

[0047] Lithium was extracted using the method of Example 1, except that the amount of overhaul slag added was changed to 50 g (50 wt % relative to the spodumene concentrate) and the transition roasting temperature was set to 800°C.

[0048] Testing and analysis revealed that the lithium extraction rate in the leachate obtained from Example 2 (relative to the spodumene concentrate and overhaul slag used) was 98.31%. The lithium extraction tailings, identified in accordance with the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), showed fluoride and cyanide leaching concentrations of only 2.03 and 0.57 mg / L, respectively. Compared to Example 1, Example 2 achieved similar lithium extraction rates, demonstrating that, under certain conditions, increasing the amount of overhaul slag to provide a more sufficient fluorine source can further lower the spodumene transition temperature.

[0049] Example 3

[0050] Lithium was extracted using the method of Example 1, except that the amount of overhaul slag added was changed to 5 g (5 wt % relative to the spodumene concentrate).

[0051] After testing and analysis, the lithium extraction rate in the leachate obtained in Example 3 (relative to the spodumene concentrate and overhaul slag used) was 68.57%. According to the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), the fluoride and cyanide leaching concentrations in the lithium extraction tailings were only 0.89 and 0.11 mg / L, respectively. Compared with Example 1, the lithium extraction rate in Example 3 decreased by 28.65 percentage points. This is mainly attributed to the low amount of overhaul slag added under these implementation conditions, resulting in an insufficient fluorine source, which prevented the complete transformation of α-type spodumene during the low-temperature roasting process, thereby affecting lithium extraction.

[0052] Example 4

[0053] Lithium was extracted using the method of Example 1, except that 10 g of sodium fluoride (10 wt % relative to the spodumene concentrate) was added and the transition roasting temperature was set at 800°C.

[0054] Testing and analysis revealed that the lithium extraction rate in the leachate obtained in Example 4 (relative to the spodumene concentrate and overhaul slag used) was 97.98%. The fluoride and cyanide leaching concentrations of the lithium extraction tailings, as determined in accordance with the "Hazardous Waste Identification Standards for Leaching Toxicity Identification" (GB 5085.3-2007), were only 2.34 and 0.68 mg / L, respectively. Compared to Examples 1 and 2, Example 4 achieved similar lithium extraction rates, demonstrating that the addition of a certain amount of sodium fluoride to compensate for the fluorine source not provided by the overhaul slag can further lower the spodumene transition temperature.

[0055] Example 5

[0056] Lithium was extracted using the method of Example 1, except that the transition calcination temperature was set at 700°C.

[0057] Analysis revealed that the lithium extraction rate in the leachate obtained from Example 5 (relative to the spodumene concentrate and overhaul slag used) was 46.38%. The lithium extraction tailings, identified in accordance with the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), showed fluoride and cyanide leaching concentrations of only 1.88 and 0.94 mg / L, respectively. Compared to Example 1, the lithium extraction rate in Example 5 decreased by 50.84 percentage points. This is primarily due to the lower temperature of the spodumene transformation roasting in this example, which prevented the α-type spodumene from fully transforming during the low-temperature roasting process, thus affecting lithium extraction.

[0058] Comparative Example 1

[0059] Lithium is extracted using the method of Example 1, except that no overhaul slag is added.

[0060] After testing and analysis, the lithium leaching rate in the leachate obtained in Comparative Example 1 (relative to the spodumene concentrate used) was 36.12%. Compared with Example 1, the lithium extraction rate of Comparative Example 1 decreased by 61.10 percentage points. This is mainly due to the low temperature of the spodumene transformation roasting in this embodiment and the lack of the introduction of fluorine-containing overhaul slag, while spodumene cannot achieve low-temperature activation transformation without assistance. Therefore, the lithium extraction rate of Comparative Example 1 is significantly lower than that of Example 1. The lithium extraction tailings of Comparative Example 1 were identified in accordance with the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007) standard, and the fluoride and cyanide contents were below the detection limit. The lithium extraction tailings met the requirements for safe stacking.

Claims

1. A method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag, characterized by: Mixing raw materials including aluminum electrolytic cell overhaul slag, spodumene concentrate, a fluorine-fixing agent, and a binder to form pellets, and then performing a roasting reaction to obtain activated spodumene; subjecting the activated spodumene to an acid leaching reaction to obtain a lithium-containing leachate; The amount of the aluminum electrolytic cell overhaul slag is 20-50wt% of the spodumene concentrate; The amount of the fluorine-fixing agent is 5-20 wt% of the spodumene concentrate.

2. The method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag according to claim 1, characterized in that: The particle size of the aluminum electrolytic cell overhaul slag is -200 mesh to +400 mesh.

3. The method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag according to claim 1, characterized in that: The fluorine-fixing agent includes calcium oxide and / or calcium hydroxide.

4. The method for collaboratively extracting lithium from aluminum electrolysis cell overhaul slag according to claim 1, characterized in that: The binder is a clay-type mineral; The amount of the binder is 2-3 wt% of the spodumene concentrate.

5. The method for extracting lithium from aluminum electrolysis cell overhaul slag according to claim 1, 3 or 4, characterized in that: The raw materials also include fluorine-containing auxiliary agents.

6. The method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag according to claim 5, characterized in that: The fluorine-containing auxiliary agent includes at least one of sodium fluoride, boron trifluoride, and sodium fluorosilicate; The amount of the fluorine-containing auxiliary agent is 0-10 wt% of the spodumene concentrate.

7. The method for collaboratively extracting lithium from aluminum electrolysis cell overhaul slag according to claim 1, characterized in that: The particle size of the pellets is 5-10 mm.

8. The method for extracting lithium from aluminum electrolysis cell overhaul slag according to claim 1 or 7, characterized in that: The calcination reaction conditions are: temperature of 750-950° C. and time of 60-90 min.

9. The method for collaborative lithium extraction using aluminum electrolysis cell overhaul slag according to claim 1, characterized in that: During the acid leaching reaction, sulfuric acid is used as a leaching agent, the sulfuric acid concentration is 2-8 mol / L, the liquid-solid ratio is 5-10 mL:1 g, the temperature is 70-90° C., and the time is 60-120 min.

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