Design of Multistage Extraction System for Simultaneous Separation of Silver and Gold from Thiourea Solutions

Abstract

This study is focused on the extraction and recovery of gold and silver from thiourea acid leaching ore liquors. In a first step, extraction is performed using di(2-ethylhexyl)dithiophosphoric acid (D2EHDTPA). The extraction of gold and silver takes place simultaneously, allowing the removal of both metals in a single equipment under the same operational conditions. Each metal is then recovered by selective stripping, using NH4SCN/H2SO4 solutions to separate the silver from the D2EHDTPA. Such treatment is followed by a second stripping system, where a (NH4)2S2O3 solution is used to recover gold. A mathematical model is developed to represent all the operations in the process flowsheet. Through this model, it is predicted that, for properly selected operating conditions, recoveries higher than 99.9% for silver, gold and thiourea (to be recycled) can be obtained. The data predicted by the model has a good fit with previously reported experimental data. The proposed process is a more sustainable approach, in comparison with the traditional process involving cyanide, and has potential to be economically feasible.