Recovery of zinc from Cd–Ni zinc plant residues

As the scope of the present work, zinc which is engaged in Cd–Ni zinc plant residues has been successfully recovered. While zinc contained in Cd–Ni filtercake has a considerable economic value, cadmium present in the material is one of the major sources of cadmium contamination of the environment. A novel hydrometallurgical technique was utilized for the separation of zinc from cadmium and nickel. Moreover, high purity cadmium and nickel were advantageously separated in successive cementation stages which in turn served as an environmental breakthrough. The process was composed of the collective leaching of the filtercake in order to bring as much metal as possible into the solution followed by selective cementation of cadmium and nickel, respectively. Therefore, a stock solution was provided under the optimum leaching conditions being as t = 150 min, T = 45 °C, stirring speed = 500 rpm, S/L = 1/13, pH = 1.3–1.5 and then cadmium was separated through cementation with zinc plates while nickel was cemented using zinc powder. The optimum working conditions for cadmium cementation were found to be as T = 25 °C, t = 180 min, pH = 2–2.5, stirring speed = 20 rpm and active plate area = 100 cm2/L, while those of nickel were as T = 80 °C, t = 15 min, pH = 3.9–4.1, stirring speed = 50 rpm and zinc powder amount equal to stoichiometric amount needed for the cementation of nickel. Under such conditions, 98.95% of cadmium and 99.98% of nickel were recovered from the solution. Finally, a simple and effective conceptual flow diagram was proposed for the process.