Asian Journal of Applied Chemistry Research

Cementation or metal displacement reaction is one of the most effective techniques for removing toxic metals from industrial waste solutions.

Aims: The main purpose of this work is to study the rate of cementation of cadmium by using a rotating bed of Zn Raschig rings packed in a perforated impeller basket for the investigation of the removal of Cd ²⁺ from waste solution.

Study Design: The reactor was tested for Cd²⁺ concentration removed, the diameter of Zinc Raschig rings, and the rotational speed of the basket.

Methodology: The results indicate that there are two rates of cementation for Cd-Zn system, a high rate at the beginning, followed by a lower rate after the initial period. The results also show that percentage removal of Cd²⁺ ions from solution increases by increasing the speed of basket rotation, and as the diameter of Zn Raschig ring packed in the basket reactor, increases the removal of Cd²⁺ decreases. The cadmium deposits on zinc as powder.

Results: The removal of Cd²⁺ is optimum for ring diameter of 0.5 cm, initial concentration of 100 ppm, and basket rotation speed of 500 rpm. The experimental data fit the following equation: Sh=0.041 Sc^0.33Re^0.40.

This equation can be used for the design scale-up and operation of reactors used to remove Cd²⁺ from wastewater by cementation.

Conclusion: Rates of cementation were expressed in terms of the rate of mass transfer, the mass transfer coefficient increases as the rotational speed of the basket increases.