Zinc (Zn) leaching yields and kinetics from three different zinc plant leach residues (ZLR) generated in different periods (ZLR1>30 years, ZLR2 5-30 years and ZLR3<2 years) were investigated. The factors affecting the Zn leaching rate such as solid to liquid ratio, temperature, acid concentration and agitation were optimized. Under optimum conditions, 46.2 (±4.3), 23.3 (±2.7) and 17.6 (±1.2) mg of Zn can be extracted per gram of ZLR1, ZLR2 and ZLR3, respectively. The Zn leaching kinetics of ZLRs follow the shrinking core diffusion model. The activation energy required to leach Zn from ZLR1, ZLR2 and ZLR3 were estimated to be 2.24kcal/mol, 6.63kcal/mol and 11.7kcal/mol, respectively, by the Arrhenius equation. The order of the reaction with respect to the sulfuric acid concentration was also determined as 0.20, 0.56, and 0.87 for ZLR1, ZLR2 and ZLR3, respectively. Zn was selectively recovered from the leachates by adjusting the initial pH and by the addition of sodium hydroxide and sodium sulfide. More than 90% of Zn was selectively recovered as sphalerite from the ZLR polymetallic leachates by chemical sulfide precipitation.
Keywords: Leaching kinetics; Metal sulfide precipitation; Metallurgical wastes; Selective recovery; Shrinking core model.
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