Sinegistic extraction of cobalt and nickel by solvent extraction

Cobalt and its compounds have found wide range of applications in a number of industrial and technological fields. In addition to their unique magnetic properties, these compounds show great resistance against oxidation and corrosion under extremely high temperatures. However, one of the main drawbacks that these compounds have is the separation of cobalt from nickel. These two elements are usually found together, and they have very similar physical and chemical properties, making them very hard to be purified. Moreover, The supply-demand gap for nickel and other valuable ores have been increasing with limited supply and increasing demand. With this in mind, one of the practical solutions to the problem would be recycling of solid and liquid waste containing trace amounts of precious metals, which lately has drawn very much attention. Furthermore, the separation of nickel and cobalt from aqueous solutions by solvent extraction, a method that depends on the selective dissolving of metal ions in aqueous solution, has been overstudied, and found many applications in various industries.In this study, we investigated the selective cobalt extraction from aqueous acidic solutions by solvent extraction. Tri-iso-octylamine (TIOA) and tri-n-octyl phosphine oxide (TOPO) were used as synergistic extractants. After several trials, the optimum extraction conditions (the solvent type, the pH of the feedstock, the concentration of the extractant, the stirring speed, the rate of the reactants (V0/Va), the concentration of thiocyanate, and the extraction time) were found. Under the optimum conditions, the cobalt extraction from the Co/Ni solutions in various concentrations was performed. The extracted cobalt was transferred back to the aqueous phase by washing with ammonia solution.Keywords: Cobalt Nickel Separations, Tri-iso-octylamine, Tri-n-octyl phosphine oxide, Solvent Extraction