Highly selective dissolution and synchronous extraction of zinc from zinc-cobalt slag by an ionic liquid [Hbet][Tf2N]–H2O system: A novel method for separating zinc and cobalt

Abstract

Zinc-cobalt slag produced from zinc hydrometallurgical process is a hazardous solid waste containing heavy metal ions; it is a secondary source of cobalt. Separating zinc and cobalt is the key problem in the comprehensive recovery. Here, a novel clean method for separating zinc and cobalt using a carboxyl-functionalized ionic liquid, ([Hbet][Tf2N]), is proposed. This innovative method provides a dual separation mode with selective dissolution and extraction during the heating and cooling of the [Hbet][Tf2N]–H2O system, and a higher separation effect on zinc and cobalt is obtained. The dissolution ratio of zinc oxide is 92.6% at 90 °C and 60 min, whereas the dissolution of cobalt and manganese is negligible (5.37% and 0.05%, respectively). The selective dissolution of metal oxide MxOy in [Hbet][Tf2N]–H2O is explained using a U/x value that correlates with the lattice energy, U, of metal oxide. In addition, the recovery of Zn and regeneration of the ionic liquid is implemented by back extraction of Zn-loaded [Hbet][Tf2N] using an oxalic acid solution. This study presents an efficient method for separating of zinc and cobalt using a dual-mode selective dissolution and synchronous extraction, which is a promising technique for separating similar metallic elements.