Separation and concentration of cobalt from zinc plant acidic thiocyanate leach solutions containing cobalt and nickel by an emulsion liquid membrane using triisooctylamine as carrier

Abstract

In this study, the zinc plant purification cake (CINKUR Co., Turkey) was leached with sulphuric acid and main acidic leach solution containing Zn(II), Fe(II), Pb(II), Al(III), Cu(II), Co(II) and Ni(II) ions was obtained. Except for cadmium, cobalt and nickel, the other metals were precipitated by adding various reagents and adjusting the pH of solution. Then, cadmium was separated by solvent extraction process. After these separation processes, ammonium thiocyanate and water were added to remaining leach solution. Thus, acidic thiocyanate leach solutions used in ELM process were obtained. ELM consists of a diluent (kerosene), a surfactant (ECA 4360J), an extractant (TIOA), and 6 M ammonia solution as the stripping solution. Separation and concentration of cobalt by ELM from acidic thiocyanate leach solution containing cobalt and nickel were studied. The important parameters governing the extraction behaviour of cobalt have been investigated. These parameters were mixing speed, surfactant concentration, extractant concentration, phase ratio, treatment ratio, stripping solution base concentration, thiocyanate concentration in the feed solution, and the feed solution pH. The results obtained at the optimum conditions showed that nearly all of cobalt ions present in the feed solution were extracted within 5 min. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 108 for equimolar Co–Ni feed solutions.