Separation and concentration of cobalt from aqueous thiocyanate solutions containing cobalt–nickel by emulsion liquid membranes using TBP as extractant

In this work, the zinc plant copper cake (CINKUR Co., Turkey) was leached with hydrochloric 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 the 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 kerosene as diluent, tributyl phosphate as extractant, sorbitan monooleate (SPAN 80) as surfactant, 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 was performed. The important parameters governing the extraction behavior of cobalt have been investigated. These parameters were mixing speed, surfactant concentration, extractant concentration, phase ratio, treatment ratio, stripping solution base concentration, initial cobalt concentration in feed solution, thiocyanate concentration in the feed solution, and the feed solution pH. The results obtained showed that by appropriate selection of the extraction and stability conditions, nearly all of the cobalt ions present in the feed solution were extracted within 10 min. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 310 for non-equimolar Co–Ni feed solutions.