title: Rare earth element recycling from waste nickel-metal hydride batteries.
abstract: With an increase in number of waste nickel-metal hydride batteries, and because of the importance of rare earth elements, the recycling of rare earth elements is becoming increasingly important. In this paper, we investigate the effects of temperature, hydrochloric acid concentration, and leaching time to optimize leaching conditions and determine leach kinetics. The results indicate that an increase in temperature, hydrochloric acid concentration, and leaching time enhance the leaching rate of rare earth elements. A maximum rare earth elements recovery of 95.16% was achieved at optimal leaching conditions of 70°C, solid/liquid ratio of 1:10, 20% hydrochloric acid concentration, -74μm particle size, and 100min leaching time. The experimental data were best fitted by a chemical reaction-controlled model. The activation energy was 43.98kJ/mol and the reaction order for hydrochloric acid concentration was 0.64. The kinetic equation for the leaching process was found to be: 1-(1-x)(1/3)=A/ρr0[HCl](0.64)exp-439,8008.314Tt. After leaching and filtration, by adding saturated oxalic solution to the filtrate, rare earth element oxalates were obtained. After removing impurities by adding ammonia, filtering, washing with dilute hydrochloric acid, and calcining at 810°C, a final product of 99% pure rare earth oxides was obtained.
authors.affiliation: Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Jiangxi 341000, China; Faculty of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Jiangxi 341000, China. Electronic address: yangxiuli21@126.com.
authors.forename: Xiuli
authors.initials: X
authors.lastname: Yang
authors.affiliation: Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Jiangxi 341000, China.
authors.forename: Junwei
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Jiangxi 341000, China.
authors.forename: Xihui
authors.initials: X
authors.lastname: Fang
mesh_terms: D011211:Electric Power Supplies; D004785:Environmental Pollutants / Q000032:analysis*; D006851:Hydrochloric Acid / Q000737:chemistry; D007220:Industrial Waste / Q000032:analysis*; D008674:Metals, Rare Earth / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D059027:Recycling / Q000379:methods*; D012995:Solubility; D013696:Temperature
chemical_list: D004785:Environmental Pollutants; D007220:Industrial Waste; D008674:Metals, Rare Earth; D010087:Oxides; D009532:Nickel; D006851:Hydrochloric Acid
keywords: Hydrochloric acid; Oxalic acid; Rare earth element; Recycling; Waste nickel-metal hydride battery