The removal of antimony from copper electrolytes using amino-phosphonic resins: Improving the elution of pentavalent antimony

An effective method is presented to elute Sb(V) from the amino-phosphonic resins that are used industrially to control the antimony concentration in copper electrolytes. Unlike Sb(III), which is amenable to elution with HCl and other reagents, Sb(V) is extremely difficult to elute from amino-phosphonic resins. Consequently, in industrial practice, a gradual build-up of Sb(V) often takes place on the resin beads, and this reduces the resin capacity and useful life. In this project, it was found that solutions containing 0.5–1.0 g/L of thiourea in 5–7 M HCl are effective eluting agents for Sb(V). It is postulated that thiourea reduces Sb(V) to Sb(III), a reaction that can only take place in concentrated HCl. The main parameters influencing the elution of Sb(V) with thiourea and HCl are presented and discussed.

Research Highlights
► The elution of Sb(V) from amino-phosphonic resins with HCl is extremely slow. In an industrial operation, this may lead to a build-up of Sb(V) on the resin, decreasing the resin capacity and its useful life and, hence, increasing the operation cost of the ion exchange process.
► It was found experimentally that a solution containing HCl and thiourea is an effective eluting agent for Sb(V). The HCl/thiourea solution elutes Sb(V) at a rate that is similar to that of the conventional HCl elution of Sb(III). The mechanism apparently involves a redox reaction, i.e., thiourea reduces Sb(V) to Sb(III).
► The efficiency of the HCl/thiourea elution Sb(V) depends on the temperature and the concentration of both thiourea and HCl. The Sb(V) elution rate increases proportionally with increasing temperature in the range of 30–60 °C and with increasing HCl concentrations in the range of 5–7 M. The elution rate increases with increasing thiourea concentration in the range of 0.1–0.8 g/L. Higher thiourea concentrations cause a slight decrease in the elution efficiency.
► The beneficial effect of thiourea on the HCl elution of Sb(V) was confirmed using three other commercial amino-phosphonic resins.
► The presence of thiourea does not interfere with the HCl elution of Sb(III).