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    Kinetics of hydrochloric acid leaching of smithsonite
    (Pleiades Publishing Inc, 2011) Dhawan, Nikhil; Safarzadeh, M. Sadegh; Birinci, Mustafa
    The dissolution kinetics of smithsonite ore in hydrochloric acid solution has been investigated. As such, the effects of particle size (-180 + 150, -250 + 180, -320 + 250, -450 + 320 mu m), reaction temperature (25, 30, 35, 40, and 45A degrees C), solid to liquid ratio (25, 50, 100, and 150 g/L) and hydrochloric acid concentration (0.25, 0.5, 1, and 1.5 M) on the dissolution rate of zinc were determined. The experimental data conformed well to the shrinking core model, and the dissolution rate was found to be controlled by surface chemical reaction. From the leaching kinetics analysis it can be demonstrated that hydrochloric acid can easily and readily dissolve zinc present in the smithsonite ore, without any filtration problems. The activation energy of the process was calculated as 59.58 kJ/mol. The order of the reaction with respect to HCl concentration, solid to liquid ratio, and particle size were found to be 0.70, -0.76 and -0.95, respectively. The optimum leaching conditions determined for the smithsonite concentrate in this work were found to be 1.5 M HCl, 45A degrees C, -180 + 150 mu m, and 25 g/L solid to liquid (S/L) ratio at 500 rpm, which correspond to more than 95% zinc extraction. The rate of the reaction based on shrinking core model can be expressed by a semi-empirical equation as: [GRAPHICS] .
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    Reductive leaching of cobalt from zinc plant purification residues
    (Elsevier Science Bv, 2011) Safarzadeh, Mohammad Sadegh; Dhawan, Nikhil; Birinci, Mustafa; Moradkhani, Davood
    The leaching kinetics of the cobalt present in zinc plant purification residues (cobalt filtercakes) was investigated in the presence of the aromatic reducing agent - phenol - without any pretreatments. As such, the effects of particle size (- 75 + 53 to -180 + 150 mu m), reaction temperature (25 to 85 degrees C), phenol dosage (2 to 15%) and sulfuric acid concentration (0.5 to 2.0 M) on the dissolution rate of cobalt and manganese were investigated. The experimental data conformed well to the shrinking core model, and the dissolution rate of cobalt was found to be controlled by diffusion through the product layer. Due to the low percentage of cobalt (< 1%) in the filtercake, SEM and XRD studies did not show any cobalt-containing phases. It was demonstrated that sulfuric acid with phenol addition can effectively dissolve cobalt and manganese present in the filtercake. The activation energy of the reaction was calculated as 22.92 kJ/mol. The order of the reaction with respect to H(2)SO(4) concentration, particle size, and phenol dosage was found to be 0.61, - 1.88 and 0.70, respectively. The optimum conditions for the leaching of cobalt and manganese were found to be as 2.0 M H(2)SO(4), 85 degrees C, -75 + 53 mu m, and 10% phenol at the stirring speed of 600 rpm, which correspond to more than 97% cobalt and similar to 100% manganese recoveries. The rate of cobalt leaching based on shrinking core model can be expressed by a semiempirical equation as: 1-2/3X-(1-X)(2/3) = k(0).[H(2)SO(4)](0.61).r(0)(-188).[phenol%](0.70).exp(-22.92/RT).t (C) 2010 Elsevier B.V. All rights reserved.