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Huo Q, Li R, Chen M, Zhou R, Li B, Chen C, Liu X, Xiao Z, Qin G, Huang J, Long T. Mechanism for leaching of fluoride ions from carbon dross generated in high-temperature and low-lithium aluminum electrolytic systems. JOURNAL OF HAZARDOUS MATERIALS 2024; 469:133838. [PMID: 38430589 DOI: 10.1016/j.jhazmat.2024.133838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 02/05/2024] [Accepted: 02/18/2024] [Indexed: 03/05/2024]
Abstract
Carbon dross, a hazardous solid waste generated during aluminum electrolysis, contains large amounts of soluble fluoride ions for the main components of the electrolyte (such as Na3AlF6 and NaF). Response surface methodology (RSM) was used to investigate the mechanism for fluoride ion leaching from carbon dross via water leaching, acid leaching and alkali leaching, and the kinetic and thermodynamic principles of the leaching process were revealed. The RSM predicted the optimum conditions of water leaching, alkali leaching and acid leaching, and the conditions are as follows: temperature, 50 °C; shaking speed, 213 r·min-1; particle size, 0.075 mm; shaking speed, 194 r·min-1; liquid-solid ratio, 12.6 mg·L-1; sodium hydroxide concentration, 1.53 mol·L-1; liquid-solid ratio, 25.0 mg·L-1; sulfuric acid concentration, 2.00 mol·L-1; and temperature, 60 °C,and actual results which were almost consistent with the predicted results were gained. The fluoride ions in the alkaline and acid leaching solutions were mainly the dissociation products of fluorides such as Na3AlF6, Na5Al3F14 and CaF2, as indicated by thermodynamics calculations. In particular, the fluoride compounds dissolved in alkali solution were Na3AlF6, Na5Al3F14, AlF3, ZrF4, K3AlF6, while the acid solution could dissolve only Na3AlF6 and CaF2. The leaching kinetics experiments showed that the leaching rate fit the unreacted shrinking core model [1-2/3α-(1-α)2/3 =kt] and that the leaching process was controlled by internal diffusion. This study provides theoretical guidance for the removal of soluble fluoride ions from carbon dross and will also assist in the separation of electrolytes from carbon dross. ENVIRONMENTAL IMPLICATION: Carbon dross, a hazardous waste generated during the aluminum electrolysis production process, contains a large amount of soluble fluoride. Improper storage will lead the fluoride ions pollution in soil, surface water or groundwater under the direct contact between carbon dross and rainfall, snow or surface runoff. The influence of wind will cause carbon dross dust to pollute further areas. With the human body long-term contact with fluoride ion contaminated soil or water, human health will be seriously harmed.
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Affiliation(s)
- Qiang Huo
- Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education - Guangxi Key Laboratory of Landscape Resources Conservation and Sustainable Utilisation in Lijiang River Basin, Guilin, Guangxi 541006, China; Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guilin, Guangxi 541006, China; College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Ruoyang Li
- Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guilin, Guangxi 541006, China; College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Mingyan Chen
- Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guilin, Guangxi 541006, China; College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Runyou Zhou
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Bin Li
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Chunqiang Chen
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Xi Liu
- Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education - Guangxi Key Laboratory of Landscape Resources Conservation and Sustainable Utilisation in Lijiang River Basin, Guilin, Guangxi 541006, China; School of Economics and Management, Guangxi Normal University, Guilin 541006, China
| | - Zeqi Xiao
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Guozhao Qin
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Jianghui Huang
- College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China
| | - Tengfa Long
- Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education - Guangxi Key Laboratory of Landscape Resources Conservation and Sustainable Utilisation in Lijiang River Basin, Guilin, Guangxi 541006, China; Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guilin, Guangxi 541006, China; College of Environment and Resources, Guangxi Normal University, Guilin, Guangxi 541006, China.
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Yang K, Li J, Huang W, Zhu C, Tian Z, Zhu X, Fang Z. A closed-circuit cycle process for recovery of carbon and valuable components from spent carbon cathode by hydrothermal acid-leaching method. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2022; 318:115503. [PMID: 35752004 DOI: 10.1016/j.jenvman.2022.115503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 05/16/2022] [Accepted: 06/07/2022] [Indexed: 06/15/2023]
Abstract
Spent carbon cathode (SCC) as a hazardous solid waste produced in aluminum electrolysis industry, contains plenty valuable components but generate a seriously threat to the environment. This paper focus on a closed-circuit cycle process for direct treatment of SCC based on the hydrothermal acid-leaching method. Thermodynamic calculation, single factor experiment, orthogonal experiment and kinetic study are utilized to obtain the leaching properties of impurities, optimize the leaching conditions, study the influence of conditions on leaching, and capture the restriction factors of leaching. The results indicate that the carbon content of the treated SCC can reach 97.3% when the leaching condition attach the optimal (liquid-solid ratio of 25 mL/g, temperature of 413 K, time of 270 min and acid concentration of 4 mol/L), and liquid-solid ratio is regarded as the crucial factor influencing on that. In addition, the activation energy of impurities reaches 6.25 kJ/mol and the whole leaching process is controlled by the diffusion extent. Finally, the filtrate after the hydrothermal acid leaching is treated, and calcium fluoride, cryolite and sodium chloride are successfully separated. The proposed process eliminates the harm of SCC to the environment, and completes a closed-circuit cycle for the treatment of SCC and recovery of valuable components. It enriches the hydrometallurgical processes of SCC, and provides an attractive scheme for the treatment of SCC.
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Affiliation(s)
- Kai Yang
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China
| | - Jie Li
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China
| | - Wenlong Huang
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China
| | - Chengping Zhu
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China
| | - Zhongliang Tian
- School of Metallurgy and Environment, Central South University, 410083, Changsha, China
| | - Xinye Zhu
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China
| | - Zhao Fang
- School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, Shaanxi, China.
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Leaching Kinetics of Aluminum from Alkali-Fused Spent Cathode Carbon Using Hydrochloric Acid and Sodium Fluoride. Processes (Basel) 2022. [DOI: 10.3390/pr10050849] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Abundant carbon resides in spent cathode carbon (SCC) of aluminum electrolysis and its high-purity carbon powder is conducive to high-value recycling. The alkali-fused SCC was separated and effectively purified using an HCl/NaF solution. Effects of particle size, leaching temperature, time, initial acid concentration, and sodium fluoride dosage, on the purity of carbon powder and aluminum removal rate, were investigated. Using aluminum as the research object, kinetics of aluminum acid leaching were examined by single-factor experiments. Results showed that under an initial 4 M HCl concentration, particle size D(50) = 67.49 μm, liquid-solid ratio of 15:1, 333 K, 120 min, 0.3 M NaF, carbon powder with ash level below 1% were obtained in subsequent purification of SCC. The leaching process was described by Avram equation, the model characteristic parameter was 0.75147 and the apparent activation energy was 22.056 kJ/mol, which indicated a mixed control mechanism between chemical reactivity and diffusion. The kinetic reaction equation of leaching aluminum from alkali-fused SCC in a mixed HCl/NaF system was established.
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Yao Z, Zhong Q, Xiao J, Ye S, Tang L, Zhang Z. An environmental-friendly process for dissociating toxic substances and recovering valuable components from spent carbon cathode. JOURNAL OF HAZARDOUS MATERIALS 2021; 404:124120. [PMID: 33068991 DOI: 10.1016/j.jhazmat.2020.124120] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 08/29/2020] [Accepted: 09/25/2020] [Indexed: 06/11/2023]
Abstract
Spent carbon cathode (SCC), a hazardous solid waste discharged from the aluminum electrolysis industry, has a serious environmental pollution risk. This study aims to explore an environmental friendly process for dissociating toxic substances and recovering valuable components from SCC. Parameters of molten salt-assisted roasting and water leaching were optimized. A possible dissociation mechanism of toxic substances was proposed. Results showed that 99.12% of cyanide was decomposed and 96.63% of fluoride was leached under optimal conditions. The recovery route of fluoride was designed according to the solution equilibrium chemical calculation and the difference in solubility and particle size between the recovered products. Exhaust gas with a high concentration of CO and CO2 was used for the carbonation of the leaching solution to recover cryolite. Effects of reaction conditions on precipitation mass and phase composition of recovered cryolite were investigated in detail. Characterization results indicated that the crystallinity and particle size of cryolite recovered under optimal conditions were extremely similar to those of commercial products. Finally, NaF and Na2CO3 were separated and recovered via evaporative crystallization combined with selective filtration. This proposed process with circular economy and green chemistry characteristics is expected to recover valuable components while minimizing environmental hazards of SCC.
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Affiliation(s)
- Zhen Yao
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China; School of Materials and Architectural Engineering, Guizhou Normal University, Guiyang 550001, PR China
| | - Qifan Zhong
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China; National Engineering Laboratory for Efficient Utilization of Refractory Nonferrous Metal Resources, Central South University, Changsha 410083, PR China.
| | - Jin Xiao
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China; National Engineering Laboratory for Efficient Utilization of Refractory Nonferrous Metal Resources, Central South University, Changsha 410083, PR China.
| | - Shengchao Ye
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China
| | - Lei Tang
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China
| | - Zhenhua Zhang
- School of Metallurgy and Environment, Central South University, Changsha 410083, PR China
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