Solvent Extraction of Zinc from a Bioleaching Solution by Modification of D۲EHPA: Optimization and Thermodynamic Studies

In this work, zinc extraction from an industrial leach solution was investigated by saponified di(۲-ethylhexyl)phosphoric acid (D۲EHPA). The solution obtained was from a bioleaching process of a low-grade lead-zinc sulfide ore that contained ۵۰ g/L of zinc and ۶.۳ g/L of iron. The selective and high Zn(II) extraction yield were obtained by modification of D۲EHPA in a proposed two-step process. Firstly, a significant amount of iron (۸۷%) was removed as sodium-jarosite via precipitation from the pregnant leaching solution (PLS) prior to zinc extraction, and secondly, the effective parameters involved in zinc extraction including the contact time, saponification degree, type of saponifier, stirring speed, pH, temperature, D۲EHPA concentration, and phase ratio (A:O) were investigated. The results obtained showed that ۹۸.۴% of zinc could be extracted under the optimum conditions, i.e. ۲۰% D۲EHPA, ۱۵% saponification degree, ۶۵۰ rpm, pH ۲, and an A:O ratio of ۱:۱ at the ambient temperature (۲۵ ± ۲ °C) during ۹۰ s; it was ۲۵% higher than using non-saponified D۲EHPA under the same conditions. Moreover, while one theoretical step was required for the complete extraction of zinc by saponified D۲EHPA, the required number of steps using D۲EHPA was about three. Therefore, the advantages of the process would be two-fold: reducing the number of extraction stages and no need for neutralizing the raffinate in every extraction stage.

Keywords:

Zinc extraction , D۲EHPA , Saponification , Thermodynamic