Comparative adsorption studies of cadmium ions on phosphogypsum and natural clay

Cadmium ions pollution and waste resulting from industrial activities are classified as serious environmental problems. In this study, we performed comparative adsorption studies of cadmium (II) on phosphogypsum (PG) and natural clay (NC) from an aqueous solution. The difference in adsorption mechanisms between phosphogypsum and natural clay was inspected using scanning electron micrographs; X-ray diffraction and Fourier transform infrared. The effects of contact time and certain factors such as the adsorbent dosage and the pH of the solution were studied. The comparative study shows that the differences in adsorption behavior come from the chemical and structural differences of the adsorbents studied. It was found that 0.73 mg·g−1 is the maximum adsorption capacity for phosphogypsum, whereas for natural clay it was 5.65 mg·g−1. Cadmium (II) removal was pH-dependent and the optimum adsorptions of phosphogypsum and clay were found at pH basic. It has been confirmed that the pseudo-second order model is best suited to the kinetics of the process studied for the two adsorbents. Overall, natural clay is a better adsorbent than phosphogypsum and this latter can be used as a potential adsorbent candidate for the removal of Cd(II) from aqueous solutions.