Thermodynamical and catalytic aspects of zinc separation from aqueous solution

Abstract

Abstract The present research work examines extraction mechanism of zinc by D2EHPA (Di-2-ethyl hexyl phosphoric acid) and comprehensively studies the main effective parameters on the process. Results of thermodynamic experiments showed that zinc extraction by D2EHPA was endothermic and spontaneous, and thermodynamic parameters including entropy and enthalpy were + 27.37 J·mol−1·K−1 and 25.21 kJ·mol−1, respectively. Gibbs free energy was varied between − 7.21 kJ·mol−1 and − 8.41 kJ·mol−1 with the variation of temperature from 20 °C to 70 °C. Solution ionic strength was increased by addition of potassium and lithium sulfate solution while addition of calcium sulfate decreased ionic strength whereby zinc extraction efficiency was also decreased. TBP showed positive synergism at concentration of 5% (v/v) and negative synergism effect at concentrations of 2% and 10%. Simultaneous addition of both TBP and salt caused extraction efficiency to drop significantly and lower both TBP and ionic strength efficiency. Results showed that a continuous addition of TBP tends to effectively improve the zinc extraction efficiency. Experiments in the presence of catalyst Ni-Raney demonstrated that zinc extraction kinetic increases remarkably and due to easy recycling of the catalyst, we can propose a novel idea in solvent extraction field.