Effect of surfactants on the cementation of cadmium

The cementation of cadmium ions (Cd(2+)) from aqueous solution onto zinc was studied in two batch reactors, a batch stirred reactor lined with a cylindrical zinc sheet and another that used a rotating zinc cylinder. The rate of cadmium removal was studied as a function of speed of rotation, initial cadmium concentration, and the addition of certain surfactants and their mixtures. Rotational speed and initial cadmium concentration affect the rate of cadmium cementation. It was found that sodium dodecyl sulfate (SDS) improves the rate of cadmium cementation, while Triton X-100 and cetyltrimethylammonium bromide (CTAB) inhibit it. Thermodynamic parameters were calculated and discussed. Visual observations showed that cadmium deposits on the zinc sheet are in the form of a powder, while cadmium deposits on the zinc cylinder, in the presence of SDS, give porous grains which increases the roughness of the surface, leading to an increase in the cementation rate. The lowest deposit porosity was observed in the presence of CTAB, which corresponds to the highest decrease obtained in the rate of cadmium cementation. The cementation process was successfully applied to recover Cd(2+) spiked into an industrial wastewater sample.