Cadmium Removal from Cadmium‐Containing Apatites by Ion‐Exchange Reactions

The exchange reaction of cadmium by non‐toxic metallic cation ions in a cadmium‐containing apatite was studied. A cadmium‐containing apatite with characteristics close to those of natural phosphate ore was synthesized. Copper and then zinc ions have been found to be the most effective elements for the exchange reaction. After 4 h of treatment at room temperature, 25 % and 14 % of cadmium were removed using 0.1 m solutions of copper and zinc ions, respectively. At 60 °C, cadmium removal efficiency improved considerably. For copper ions, the efficiency reached 53 %, while it arrived at 25 % for zinc ions. The equilibrium study shows that the two reactions are thermodynamically feasible but balanced reactions with little reaction progress for small cadmium content. The reaction can be well modeled by the shrinking‐core model and is found to be controlled by the diffusion through the reacted layer. This study focuses on the extraction of cadmium from cadmium‐containing apatite by ion exchange reactions with non‐toxic metal cations. By adjusting the reaction operating conditions, interesting extraction efficiencies can be achieved with the advantage of no phosphate losses compared to other decadmiation techniques.