A method for preparing battery grade graphite using aluminum electrolytic spent cathodes

Abstract

The application provides a method for preparing battery-grade graphite by using aluminum electrolysis waste cathode, which comprises the following steps: I. mixing crushed and ground waste cathode carbon powder with an alkaline solution to prepare a mixed slurry, and after a hydrothermal reaction, filtering to obtain an alkali-leached waste cathode and an alkaline filtrate; II. mixing the dried alkali-leached waste cathode with an acidic solution to prepare a mixed slurry, heating and reacting, and after filtering, obtaining an acid-leached waste cathode and an acidic filtrate; III. obtaining purified graphite carbon powder by calcining and graphitizing the dried acid-leached waste cathode. The method can effectively improve the economic value of aluminum electrolysis waste cathode calcined carbon blocks, and after reasonable removal of remaining impurities and graphitization, graphite carbon powder meeting the I-grade standard of artificial graphite for lithium ion battery graphite negative electrode materials can be obtained, and the alkaline solution and the acidic solution can be recycled in the reaction process, so that a new green and environmentally friendly and high economic benefit process technology is provided, and the problem that the waste cathode in the current aluminum electrolysis industry is difficult to utilize can be effectively solved and a new artificial graphite approach for lithium ion batteries is provided.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment, specifically involving a method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis. The waste cathode carbon blocks after calcination are reacted with alkaline and acidic solutions to remove impurities, and then graphitized by calcination to recycle and prepare battery-grade graphite. Background Technology

[0002] During operation, the cathodes of aluminum electrolysis cells are continuously corroded by high-temperature molten salt, molten aluminum, and metallic sodium. The resulting cathode cracks and changes in conductivity damage the electrolysis cells, requiring major overhauls every 3-10 years. The solid waste generated is known as aluminum electrolysis waste cathode. The high-value utilization of the valuable carbonaceous materials in these waste cathodes and the environmental pollution caused by large amounts of toxic substances such as fluorides and cyanides have become bottlenecks restricting the rapid development of my country's aluminum electrolysis industry.

[0003] Existing treatment processes for waste cathodes mainly include wet processing and pyrometallurgical processing. Chinese patent CN200810231562.1 discloses a harmless treatment and recovery process for cyanide and fluoride in aluminum electrolysis overhaul slag. The waste cathode is mixed with soluble calcium / magnesium salts, which can be dissolved in water as calcium / magnesium / sodium hypochlorite, respectively. After solid-liquid separation, the filtrate is recycled, and the solid can be used as an additive in building materials or third-party production processes. However, this technology suffers from low economic value and is difficult to promote. Chinese patent CN202211690488.6 discloses a method for the comprehensive recycling and reuse of waste cathodes from aluminum electrolysis through water leaching and pressure purification. The waste cathode, water, and hydrogen peroxide are heated and leached. The filtered solid is then subjected to high-pressure acid leaching with concentrated sulfuric acid. Finally, the residue from the solid-liquid separation is mixed with concentrated sulfuric acid, concentrated hydrochloric acid, hydrogen peroxide, and an aqueous solution for a second high-pressure acid leaching. The solid-liquid separation yields artificial graphite with a fixed carbon content of 97%, but this does not meet the requirement of 99.7% fixed carbon content for battery-grade graphite and requires further purification for utilization. Chinese patent CN202211734447.2 discloses an ultra-high temperature reducing atmosphere medium-frequency roasting furnace, graphite material, and its preparation method. This method involves placing waste cathode material into the medium-frequency roasting furnace and roasting it at ultra-high temperature under an inert atmosphere. After multiple stages of processing—including a first furnace front chamber, a second furnace front chamber, a preheating section, a high-temperature section, a cooling section, a water-cooling section, and a discharge device—crude graphite is produced. This is then purified and magnetically separated to obtain the graphite material. However, this method involves a complex process flow, and the fixed carbon content during graphitization remains only around 97%. CN200610086890.8 discloses a method for processing waste refractory material from aluminum electrolysis cells. This method involves mixing and grinding waste cathode, sand, lime, and fly ash, sintering at 1000-1250℃ for 30-60 minutes, cooling, adding magnesia, and grinding again to obtain a powdery, impermeable refractory material containing calcium fluoride, calcium aluminosilicate, etc. This method makes full use of the carbon sites in the waste cathode, but the resulting refractory material has low added value.

[0004] The industry's treatment of waste cathodes from aluminum electrolysis began in 1946. Various countries, especially the United States, have conducted extensive research and development, developing various processes for treating waste cathode carbon blocks. Related research in my country started later, around the 1990s, and is currently mainly in the laboratory research stage, with few industrialized or semi-industrialized treatment processes. In 2016, the State Environmental Protection Administration listed waste cathodes from aluminum electrolysis as hazardous waste in the "National Hazardous Waste List." The concept of green mining development is an important part of the healthy and sustainable development of my country's industry, which requires the rational utilization of valuable tailings waste during mineral processing. Therefore, developing a new method for the harmless and high-value utilization of waste cathodes from aluminum electrolysis is of great significance. Summary of the Invention

[0005] This invention provides a method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis. The method involves first reacting the anaerobic-roasted waste cathode carbon blocks with an alkaline solution via hydrothermal reaction to remove residual silicon and aluminum components from the waste cathode. After solid-liquid separation, the alkaline-leached waste cathode is further reacted with an acidic solution to remove valuable metal impurities such as Fe. After solid-liquid separation, the solid acid-leached waste cathode is then graphitized at high temperature to prepare battery-grade graphite. Both the alkaline and acidic solutions obtained after solid-liquid separation can be recycled.

[0006] This method, through rational design, fully utilizes the graphite carbon in waste cathodes to ultimately generate battery-grade graphite, a high-value-added product, resulting in significant economic benefits. It can completely solve the problems of high cost and low added value in the harmless treatment of waste cathodes from aluminum electrolysis, thus achieving sustainable development in the aluminum electrolysis industry.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis includes the following steps:

[0009] I. The crushed and ground waste cathode carbon powder is mixed with an alkaline solution to prepare a mixed slurry. After hydrothermal reaction, it is filtered to obtain alkaline-leached waste cathode and alkaline filtrate.

[0010] II. The dried alkaline leaching waste cathode is mixed with an acidic solution to prepare a mixed slurry. The mixture is heated to react, and after filtration, acid leaching waste cathode and acidic filtrate are obtained.

[0011] III. The dried acid-leached waste cathode is calcined and graphitized to obtain purified graphite carbon powder.

[0012] Preferably, the waste cathode carbon powder in step I is the product of waste cathode carbon blocks after anaerobic roasting and defluorination treatment at 1500℃ or above, with a carbon content ≥85wt% and a fluorine content ≤0.3wt%.

[0013] Preferably, the alkaline solution in step I is one or a mixture of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0014] Preferably, in step I, the alkaline solution and waste cathode carbon powder in the slurry are mixed in a mass ratio of 3~12 (preferably 8, 10, 12):1, and the concentration of the alkaline solution is 1~12 mol / L (preferably 2 mol / L, 3 mol / L, 4 mol / L).

[0015] Preferably, the hydrothermal temperature in step I is 160~260℃ and the reaction time is 1~6h.

[0016] Preferably, the acid in the acidic solution in step II is one or a mixture of hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, and phosphoric acid.

[0017] Preferably, in step II, the acidic solution and waste cathode carbon powder in the slurry are mixed in a mass ratio of 3~20 (preferably 6, 8, 10):1, and the concentration of the acid solution is 1~6 mol / L (preferably 2 mol / L, 3 mol / L, 4 mol / L).

[0018] Preferably, the reaction temperature in step II is 30~90℃ and the reaction time is 1~6h.

[0019] Preferably, the calcination temperature in step III is 1500~3000℃ (preferably 1900℃, 2300℃, 2800℃), and the calcination time is 20~600min (preferably 30 min, 120 min, 300 min).

[0020] As a preferred embodiment, the purified graphite carbon powder in step III has a graphitization degree of ≥90% (preferably ≥91.3wt%, ≥92.6wt%, ≥94.7wt%) and a solid carbon content of ≥99.7wt% (preferably ≥99.95wt%, ≥99.96wt%, ≥99.98wt%).

[0021] Preferably, the waste cathode carbon powder contains the following components: C 86~91 w B %, Al 0.2~0.9 w B %, Fe 0.1~0.95 w B %, Si 3.7~5.1 w B %, O 4.9~7.0 w B %, the above ingredients, together with other ingredients, make up 100%. w B %.

[0022] Compared with existing technologies, the beneficial technical effect of this invention lies in the fact that this method achieves complete removal of impurities from waste cathodes. The graphitization degree and fixed carbon content of the graphite carbon powder can reach the standard of Class I lithium-ion battery graphite anode materials (GB / T23943-2009). Against the backdrop of the rapid development of my country's new energy industry, this method not only effectively solves the problem of high costs for the harmless treatment of aluminum electrolysis waste cathodes and low added value of processed products, thus limiting its sustainable development, but also allows the generated battery-grade graphite carbon to be supplied to the new energy lithium battery industry, demonstrating significant economic benefits and promising application prospects. Attached Figure Description

[0023] Figure 1This is a process flow diagram of the preparation of battery-grade graphite from aluminum electrolysis waste cathodes according to the present invention.

[0024] Figure 2 This is a scanning electron microscope image of the waste cathode carbon powder used to prepare battery-grade graphite from aluminum electrolysis waste cathodes according to the present invention.

[0025] Figure 3 Scanning electron microscope image of purified graphite carbon powder prepared from waste cathode of aluminum electrolysis according to the present invention. Implementation

[0026] The specific technical solutions of the present invention will be described with reference to the embodiments. Example

[0027] according to Figure 1 The process shown in this embodiment uses aluminum electrolysis waste cathodes taken from blocky carbonaceous waste stored in the warehouse of an aluminum plant in Lanzhou. The elemental analysis results of the waste cathode carbon powder after anaerobic roasting and defluorination treatment are shown in Table 1.

[0028] Table 1. Elemental analysis results of waste cathode carbon powder ( w B %)

[0029] C Al Fe F Cr Ni Cu Li Si O 90.7 0.26 0.11 0.27 0.0042 0.0061 0.0012 0.0085 3.73 4.91

[0030] 300g of waste cathode carbon powder, crushed and ground to 200 mesh, was weighed and added to a 3mol / L mixed solution of sodium hydroxide and sodium carbonate, maintaining a liquid-to-solid mass ratio of 8. The uniformly mixed slurry was then subjected to a hydrothermal reaction at 230℃ for 6 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an alkaline-leached waste cathode. The filtrate could be recycled. The alkaline-leached waste cathode was then ground through a 200-mesh sieve and added to a 2mol / L mixed solution of hydrochloric acid and carbonic acid, maintaining a liquid-to-solid mass ratio of 10. The uniformly mixed slurry was then reacted at 60℃ for 3 hours. The cooled solid-liquid mixture was then filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an acid-leached waste cathode. The filtrate could be recycled. The acid-leached waste cathode was then calcined at 2300℃ for 120 minutes to graphitize it. The degree of graphitization was measured to be 91.3%, and the fixed carbon content was 99.95%, meeting the Class II standard for artificial graphite in lithium-ion battery graphite anode materials. Example

[0031] according to Figure 1 The process shown in this embodiment uses aluminum electrolysis waste cathodes taken from blocky carbonaceous waste stored in the warehouse of an aluminum plant in Shanxi Province. The elemental analysis results of the waste cathode carbon powder after anaerobic roasting and defluorination treatment are shown in Table 2.

[0032] Table 2 Elemental analysis results of waste cathode carbon powder ( w B %)

[0033] C Al Fe F Cr Ni Cu Li Si O 89.2 0.32 0.21 0.09 0.0043 0.0064 0.0022 0.0071 4.54 5.62

[0034] 500g of waste cathode carbon powder, crushed and ground to 200 mesh, was weighed and added to a 2mol / L potassium hydroxide and potassium carbonate mixed solution, maintaining a liquid-to-solid mass ratio of 10. The uniformly mixed slurry was hydrothermally reacted at 250℃ for 4 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an alkaline-leached waste cathode. The filtrate could be recycled. The alkaline-leached waste cathode was then ground through a 200-mesh sieve and added to a 2mol / L sulfuric acid and phosphoric acid mixed solution, maintaining a liquid-to-solid mass ratio of 8. The uniformly mixed slurry was reacted at 80℃ for 2 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an acid-leached waste cathode. The filtrate could be recycled. The acid-leached waste cathode was calcined at 1900℃ for 300 minutes to graphitize it. The degree of graphitization was measured to be 92.6%, and the fixed carbon content was 99.96%, meeting the Class II standard for artificial graphite in lithium-ion battery graphite anode materials. Example

[0035] according to Figure 1 The process shown in this embodiment uses aluminum electrolysis waste cathodes taken from blocky carbonaceous waste stored in the warehouse of an aluminum plant in Shandong. The elemental analysis results of the waste cathode carbon powder after anaerobic roasting and defluorination treatment are shown in Table 3.

[0036] Table 3 Elemental analysis results of waste cathodes ( w B %)

[0037] C Al Fe F Cr Ni Cu Li Si O 86.2 0.82 0.91 0.03 0.003 0.017 0.0083 0.0062 5.05 6.96

[0038] 200g of waste cathode carbon powder, crushed and ground to 200 mesh, was weighed and added to a 4mol / L sodium hydroxide solution. The liquid-to-solid mass ratio was controlled at 1:2. The uniformly mixed slurry was hydrothermally reacted at 200℃ for 8 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an alkaline-leached waste cathode. The filtrate could be recycled. The alkaline-leached waste cathode was then ground through a 200-mesh sieve and added to a 4mol / L nitric acid solution. The liquid-to-solid mass ratio was controlled at 6. The uniformly mixed slurry was reacted at 40℃ for 6 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an acid-leached waste cathode. The filtrate could be recycled. The acid-leached waste cathode was calcined at 2800℃ for 30 minutes to graphitize it. The graphitization degree was measured to be 94.7%, and the fixed carbon content was 99.98%, meeting the Class I standard for artificial graphite in lithium-ion battery graphite anode materials.

[0039] Comparative Example 1

[0040] Similarly, the waste cathode carbon powder obtained from the anaerobic roasting and defluorination treatment of the blocky carbonaceous waste stockpiled in the warehouse of an aluminum plant in Shandong, as described in Example 3, was used according to... Figure 1 The process shown is illustrated, but without alkali treatment for comparison. The specific implementation steps are as follows:

[0041] 200g of waste cathode carbon powder, crushed and ground to 200 mesh, was weighed and added to a 4mol / L nitric acid solution, maintaining a liquid-to-solid mass ratio of 6. The mixed slurry was reacted at 40℃ for 6 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain the product, acid-leached waste cathode. The filtrate can be recycled. The acid-leached waste cathode was calcined at 2800℃ for 30 minutes to graphitize it. The degree of graphitization was measured to be 81.4%, and the fixed carbon content was 90.12%, which does not meet the Class III standard for artificial graphite in graphite-based anode materials for lithium-ion batteries.

[0042] Comparative Example 2

[0043] Similarly, the waste cathode carbon powder obtained from the anaerobic roasting and defluorination treatment of the blocky carbonaceous waste stockpiled in the warehouse of an aluminum plant in Shanxi Province, as described in Example 2, was used according to... Figure 1 The process shown is illustrated, but without acid treatment for comparison. The specific implementation steps are as follows:

[0044] 200g of waste cathode carbon powder, crushed and ground to 200 mesh, was weighed and added to a 4mol / L sodium hydroxide solution, maintaining a liquid-to-solid mass ratio of 1:2. The uniformly mixed slurry was subjected to a hydrothermal reaction at 200℃ for 8 hours. The cooled solid-liquid mixture was filtered, and the filter cake was dried at 105℃ for 12 hours to obtain an alkaline-leached waste cathode. The filtrate could be recycled. The alkaline-leached waste cathode was calcined at 2800℃ for 30 minutes to graphitize it. The degree of graphitization was measured to be 90.8%, and the fixed carbon content was 98.03%, which did not meet the Class III standard for artificial graphite in graphite-based anode materials for lithium-ion batteries.

[0045] In summary, through the synergistic effect of alkaline and acid leaching treatments, the purified graphite carbon powders prepared in Examples 1, 2, and 3 all meet the Class I standard for artificial graphite in graphite-based anode materials for lithium-ion batteries. In particular, under the specific conditions of Example 3, the degree of graphitization of the obtained purified graphite carbon powder was 94.7%, and the fixed carbon content was 99.98%. However, the purified graphite carbon powders obtained by using only alkaline or acid treatments do not meet the Class III standard for artificial graphite in graphite-based anode materials for lithium-ion batteries.

Claims

1. A method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis, characterized in that, The method includes the following steps: I. Mixing crushed and ground waste cathode carbon powder with an alkaline solution to prepare a mixed slurry, and after hydrothermal reaction, filtering to obtain alkaline-leached waste cathode and alkaline filtrate; II. The dried alkaline leaching waste cathode is mixed with an acidic solution to prepare a mixed slurry. The mixture is heated to react, and after filtration, acid leaching waste cathode and acidic filtrate are obtained. III. The dried acid-leached waste cathode was calcined and graphitized to obtain purified graphite carbon powder; The waste cathode carbon powder is the product of waste cathode carbon blocks after anaerobic roasting and defluorination treatment at 1500℃ or above, with a carbon content ≥85wt% and a fluorine content ≤0.3wt%. In step I, the hydrothermal reaction temperature is 160–260℃, and the reaction time is 1–6 h. In step II, the acid in the acidic solution is one or a mixture of hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, and phosphoric acid. In step II, the reaction temperature is 30–90°C and the reaction time is 1–6 hours. In step III, the calcination temperature is 1900–3000℃ and the calcination time is 30–300 min; In step III, the purified graphite carbon powder has a graphitization degree of ≥90% and a fixed carbon content of ≥99.7wt%.

2. The method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step I, the alkaline substance in the alkaline solution is one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

3. The method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step I, the alkaline solution and waste cathode carbon powder in the slurry are mixed in a mass ratio of (3-12):1, and the concentration of the alkaline solution is 1-12 mol / L.

4. The method for preparing battery-grade graphite using waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step II, the acidic solution and waste cathode carbon powder in the slurry are mixed in a mass ratio of (3-20):1, and the concentration of the acid solution is 1-6 mol / L.

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