Method for treating overhaul slag by alkaline process and recycling

Abstract

The invention discloses a method for treating overhaul slag by an alkaline process and recycling the overhaul slag. The method comprises the following steps: crushing and grinding the overhaul slag until the particle size is not greater than 0.18 mm; uniformly mixing the obtained crushed and ground overhaul slag with sodium hydroxide and sodium carbonate according to a preset mass ratio to obtain a mixture, and carrying out alkali fusion sintering on the mixture under the conditions that the heating rate is 5-8 DEG C / min, the sintering temperature is 850-950 DEG C and the heat preservation time is 2-3 hours to obtain a sintered material; mixing the sintered material with water according to a preset mass ratio, heating, stirring and leaching, and then carrying out solid-liquid separation to obtain alkaline leachate containing fluorine, aluminum and lithium and carbon residues; introducing carbon dioxide gas into the alkaline leaching solution to adjust the pH value of the system to 6.5-7.0, carrying out stirring reaction, and carrying out solid-liquid separation to obtain cryolite and a first filtrate; adjusting the pH value of the first filtrate to 9.0-9.5 by using alkali liquor, carrying out stirring reaction, and carrying out solid-liquid separation to obtain an aluminum hydroxide precipitate and a second filtrate; and evaporating and concentrating the second filtrate, then adding a sodium carbonate solution to carry out precipitation reaction, and carrying out solid-liquid separation to obtain lithium carbonate.

Description

Technical Field

[0001] This invention relates to the field of metallurgical solid waste resource utilization, specifically to a method for treating overhaul slag using an alkaline process and utilizing it as a resource. Background Technology

[0002] Electrolytic aluminum overhaul slag is a major hazardous solid waste generated during the overhaul of electrolytic cells in the electrolytic aluminum production process. It mainly consists of waste lining materials such as cathode carbon blocks, refractory bricks, insulating bricks, and impermeable castables. Due to prolonged contact with high-temperature electrolyte solutions (containing aluminum fluoride, cryolite, lithium fluoride, etc.), the overhaul slag is enriched with valuable elements such as soluble fluorides, cyanides, and lithium. Fluorine accounts for approximately 5%-8%, and lithium accounts for approximately 2%. According to the 2023 National Hazardous Waste List, overhaul slag is classified as HW48 hazardous waste. If directly landfilled or openly dumped, soluble fluorides will seep into the ground through rainwater runoff, polluting the soil and groundwater. Cyanide hydrolysis will also release toxic gases, posing a significant environmental hazard.

[0003] Currently, the disposal and utilization of electrolytic aluminum overhaul slag mainly relies on landfilling or partial refractory material recycling. Most enterprises, lacking efficient resource recovery technologies, simply stockpile the remaining waste, posing a serious risk of secondary pollution. Although the industry has explored processes such as rotary kiln roasting, flotation, and acid / alkali leaching, it still faces problems of inadequate hazardous waste disposal and low resource recovery efficiency. For example, acid leaching, currently the mainstream lithium extraction technology, involves drying and grinding pretreatment followed by leaching of lithium elements with sulfuric or hydrochloric acid, followed by evaporation and crystallization to extract oxides or lithium carbonate, achieving partial recovery of lithium resources. However, the acid process only targets lithium, failing to effectively utilize the more abundant fluorine, leading to a waste of high-value fluorine resources. Furthermore, the leaching residue still contains untreated fluorides, posing a risk of secondary pollution.

[0004] Therefore, a method for treating overhaul slag using an alkaline process and utilizing it as a resource is needed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for treating and utilizing overhaul slag using an alkaline process. By using a specific high-temperature alkaline sintering process, the occurrence form of substances in the overhaul slag is changed. Then, through wet leaching and stepwise precipitation, efficient separation and recovery of fluorine as cryolite, aluminum as aluminum hydroxide, and lithium as lithium carbonate are achieved, thus achieving the dual goals of waste harmlessness and maximizing resource value.

[0006] To achieve the above objectives, the present invention provides a method for treating and utilizing overhaul slag using an alkaline process, comprising:

[0007] The overhaul slag is crushed and ground to a particle size of no more than 0.18 mm;

[0008] The crushed and fined overhaul slag is mixed with sodium hydroxide and sodium carbonate in a preset mass ratio to obtain a mixture. The mixture is then subjected to alkaline melting sintering at a heating rate of 5-8℃ / min, a sintering temperature of 850-950℃, and a holding time of 2-3h to obtain a sintered material.

[0009] The sintered material is mixed with water at a preset mass ratio and then heated and stirred for leaching. Subsequently, solid-liquid separation is performed to obtain an alkaline leachate containing fluorine, aluminum, and lithium, and carbonaceous residue.

[0010] Carbon dioxide gas is introduced into the alkaline leachate to adjust the pH of the system to 6.5-7.0. After stirring and reacting, solid and liquid are separated to obtain cryolite and a first filtrate. The pH of the first filtrate is adjusted to 9.0-9.5 with alkaline solution. After stirring and reacting, solid and liquid are separated to obtain aluminum hydroxide precipitate and a second filtrate. The second filtrate is evaporated and concentrated, and then sodium carbonate solution is added to carry out a precipitation reaction. After solid and liquid separation, lithium carbonate is obtained.

[0011] Preferably, the mass ratio of the crushed and ground overhaul slag to sodium hydroxide and sodium carbonate is 100:20:5.

[0012] Specifically, the sintering material is mixed with water at a preset mass ratio and then heated and stirred for leaching, including: mixing the sintering material with water at a preset mass ratio of 4:1, and stirring and leaching at a stirring rate of 300-400 r / min and a temperature of 80-90°C for 1.5-2 hours.

[0013] Specifically, the process of introducing carbon dioxide gas into the alkaline leachate to adjust the pH value of the system to 6.5-7.0, stirring the reaction, and then separating the solid and liquid components includes: introducing carbon dioxide gas into the alkaline leachate to adjust the pH value of the system to 6.5-7.0, stirring the reaction at a temperature of 60-70°C for 30 minutes, and then separating the solid and liquid components.

[0014] Specifically, the first filtrate is adjusted to pH 9.0-9.5 with an alkaline solution, and then solid-liquid separation is performed after stirring. This includes adding a 10% sodium hydroxide solution to the first filtrate, adjusting the pH to 9.0-9.5, and then stirring the reaction at 80°C for 1 hour before solid-liquid separation.

[0015] Specifically, the second filtrate is evaporated and concentrated, then sodium carbonate solution is added to carry out a precipitation reaction, and lithium carbonate is obtained after solid-liquid separation. The process includes: evaporating and concentrating the second filtrate until the lithium ion concentration is greater than or equal to 5 g / L, then adding saturated sodium carbonate solution and stirring the reaction at 60°C for 2 hours, and finally filtering and drying to obtain lithium carbonate. Attached Figure Description

[0016] Figure 1This is a schematic diagram of a method for treating and utilizing overhaul slag using an alkaline process, as provided in an embodiment of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0019] In the description of the embodiments of the present invention, the words "exemplary," "for example," or "for instance" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary," "for example," or "for instance" in the embodiments of the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Rather, the use of the words "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a specific manner.

[0020] Electrolytic aluminum overhaul slag is a hazardous solid waste generated during the overhaul of electrolytic cells, rich in valuable elements such as fluorides, cyanides, and lithium. Due to its easily leached soluble fluorine, which pollutes the environment, and the presence of highly toxic cyanides, it has been listed in the "National Hazardous Waste List." Current disposal methods primarily involve landfilling or simple recycling into refractory materials, which poses risks of resource waste and secondary pollution. Existing technologies, such as acid leaching, can recover some lithium, but fail to effectively utilize the higher content of fluorine and aluminum, and the treated slag still poses environmental risks. Other alkaline treatment processes focus primarily on lithium extraction and fluorine solidification and stabilization, failing to achieve high-value product recovery of fluorine and aluminum.

[0021] To overcome the shortcomings of existing technologies, a method for treating overhaul slag using an alkaline process and utilizing it for resource recovery is proposed. By using a specific high-temperature alkaline sintering process, the occurrence form of substances in the overhaul slag is changed. Then, through wet leaching and stepwise precipitation, efficient separation and recovery of fluorine as cryolite, aluminum as aluminum hydroxide, and lithium as lithium carbonate are achieved, thus achieving the dual goals of waste harmlessness and maximizing resource value.

[0022] Figure 1 A schematic diagram of a method for treating and utilizing overhaul slag using an alkaline process, as provided in an embodiment of the present invention, is shown in the figure. The method includes:

[0023] Step S101: Crush and grind the overhaul slag to a particle size of no more than 0.18 mm.

[0024] For example, the overhaul slag can be crushed to a particle size of ≤20mm using a jaw crusher, and then ground to 80 mesh (particle size ≤0.18mm) using a ball mill to increase the reaction contact area.

[0025] Step S102: The crushed and ground overhaul slag is mixed with sodium hydroxide and sodium carbonate in a preset mass ratio to obtain a mixture. The mixture is then subjected to alkali melting sintering at a heating rate of 5-8℃ / min, a sintering temperature of 850-950℃, and a holding time of 2-3h to obtain a sintered material.

[0026] In different embodiments, the mass ratio of the crushed and ground overhaul residue to sodium hydroxide and sodium carbonate varies. In one specific embodiment, the predetermined mass ratio of the crushed and ground overhaul residue to sodium hydroxide and sodium carbonate is 100:20:5.

[0027] For example, finely ground overhaul slag, sodium hydroxide (analytical grade), and sodium carbonate (flux) are mixed evenly at a mass ratio of 100:20:5 to obtain a mixture. The mixture is then fed into a rotary kiln and sintered using process parameters of a heating rate of 5–8 °C / min, a sintering temperature of 850–950 °C, and a holding time of 2–3 h.

[0028] Step S103: The sintered material is mixed with water at a preset mass ratio and then heated and stirred for leaching. Subsequently, solid-liquid separation is performed to obtain an alkaline leachate containing fluorine, aluminum, and lithium and carbonaceous residue.

[0029] For example, the sintered material is mixed with water at a preset mass ratio of 4:1, and stirred and leached at a stirring rate of 300-400 r / min and a temperature of 80-90°C for 1.5-2 hours. Then, solid-liquid separation is performed to obtain an alkaline leachate containing fluorine, aluminum, and lithium and carbonaceous residue.

[0030] For example, using industrial water as a solvent, the sintered material after rotary kiln sintering is mixed with industrial water at a liquid-to-solid ratio of 4:1, and leached at 80-90℃ with stirring for 1.5-2 hours at a stirring rate of 300-400 r / min. The leached mixture is then subjected to solid-liquid separation using plate and frame filtration (filter cloth pore size 0.22 μm) to obtain a Na-containing... + AlO2 - F - Li + The leachate (pH=12-13) and carbonaceous residue.

[0031] Step S104: Carbon dioxide gas is introduced into the alkaline leachate to adjust the pH of the system to 6.5-7.0. After stirring and reacting, solid and liquid are separated to obtain cryolite and a first filtrate. The pH of the first filtrate is adjusted to 9.0-9.5 with alkaline solution. After stirring and reacting, solid and liquid are separated to obtain aluminum hydroxide precipitate and a second filtrate. The second filtrate is evaporated and concentrated, and then sodium carbonate solution is added to carry out a precipitation reaction. After solid and liquid separation, lithium carbonate is obtained.

[0032] For example, carbon dioxide gas is introduced into the alkaline leachate to adjust the pH of the system to 6.5-7.0, and the reaction is stirred at 60-70°C for 30 minutes before solid-liquid separation to obtain cryolite and the first filtrate.

[0033] Add 10% sodium hydroxide solution to the first filtrate, adjust the pH to 9.0-9.5, stir and react at 80°C for 1 hour, then separate the solid and liquid to obtain aluminum hydroxide precipitate and a second filtrate.

[0034] The second filtrate was evaporated and concentrated until the lithium ion concentration was greater than or equal to 5 g / L. Then, a saturated sodium carbonate solution was added and the mixture was stirred and reacted at 60°C for 2 hours. The mixture was then filtered and dried to obtain lithium carbonate.

[0035] For example, CO2 gas (purity ≥99%) is introduced into the leachate, the pH is adjusted to 6.5-7.0, the reaction temperature is 60-70℃, and the mixture is stirred for 30 minutes; the resulting precipitate is filtered and separated, and the dried Na3AlF6 (cryolite) is reused as a flux for electrolytic aluminum.

[0036] Add 10% NaOH solution to the above filtrate to adjust the pH to 9.0-9.5, stir at 80℃ for 1 hour; filter to obtain aluminum hydroxide, and calcine to obtain aluminum oxide.

[0037] Concentration and Crystallization: The filtrate after aluminum removal is evaporated and concentrated to Li. + Concentration ≥ 5 g / L, add saturated Na₂CO₃ solution (molar ratio Li) + CO3 2- =2:1), stir at 60℃ for 2 hours; Reaction formula: 2Li + +CO3 2- →Li2CO3↓, filtered and dried to obtain lithium carbonate (purity ≥99.2%).

[0038] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for treating and utilizing overhaul slag using an alkaline process, comprising: The overhaul slag is crushed and ground to a particle size of no more than 0.18 mm; The crushed and fined overhaul slag is mixed with sodium hydroxide and sodium carbonate in a preset mass ratio to obtain a mixture. The mixture is then subjected to alkaline melting sintering at a heating rate of 5-8℃ / min, a sintering temperature of 850-950℃, and a holding time of 2-3h to obtain a sintered material. The sintered material is mixed with water at a preset mass ratio and then heated and stirred for leaching. Subsequently, solid-liquid separation is performed to obtain an alkaline leachate containing fluorine, aluminum, and lithium, and carbonaceous residue. Carbon dioxide gas is introduced into the alkaline leachate to adjust the pH of the system to 6.5-7.

0. After stirring and reacting, solid and liquid are separated to obtain cryolite and a first filtrate. The pH of the first filtrate is adjusted to 9.0-9.5 with alkaline solution. After stirring and reacting, solid and liquid are separated to obtain aluminum hydroxide precipitate and a second filtrate. The second filtrate is evaporated and concentrated, and then sodium carbonate solution is added to carry out a precipitation reaction. After solid and liquid separation, lithium carbonate is obtained.

2. The method according to claim 1, wherein, The mass ratio of the crushed and ground overhaul slag to sodium hydroxide and sodium carbonate is preset to 100:20:

5.

3. The method according to claim 1, wherein, The sintered material is mixed with water at a preset mass ratio and then heated and stirred for leaching, including: mixing the sintered material with water at a preset mass ratio of 4:1, and stirring and leaching at a stirring rate of 300-400 r / min and a temperature of 80-90°C for 1.5-2 hours.

4. The method according to claim 1, wherein, The process of introducing carbon dioxide gas into the alkaline leachate to adjust the pH value of the system to 6.5-7.0, stirring the reaction, and then separating the solid and liquid components includes: introducing carbon dioxide gas into the alkaline leachate to adjust the pH value of the system to 6.5-7.0, stirring the reaction at a temperature of 60-70°C for 30 minutes, and then separating the solid and liquid components.

5. The method according to claim 1, wherein, The first filtrate is adjusted to pH 9.0-9.5 with alkaline solution, and then solid-liquid separation is performed after stirring. This includes: adding 10% sodium hydroxide solution to the first filtrate, adjusting the pH to 9.0-9.5, stirring at 80°C for 1 hour, and then separating the solid and liquid.

6. The method according to claim 1, wherein, The second filtrate is evaporated and concentrated, and then sodium carbonate solution is added to carry out a precipitation reaction. After solid-liquid separation, lithium carbonate is obtained. The process includes: evaporating and concentrating the second filtrate until the lithium ion concentration is greater than or equal to 5 g / L, then adding saturated sodium carbonate solution and stirring the reaction at 60°C for 2 hours, and finally filtering and drying to obtain lithium carbonate.

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