Removal of copper and cadmium ions from diluted aqueous solutions by low cost and waste material adsorbents

The sorption of copper and cadmium ions using activated carbon, kaolin, bentonite, diatomite and waste materials such as compost, cellulose pulp waste and anaerobic sludge as sorbents is reported. Equilibrium isotherms were obtained for the adsorption of these metals in single and binary solutions. Bentonite presented the highest adsorption capacities for both copper and cadmium. A competitive uptake was observed when both metals are present; copper being preferentially adsorbed by all materials with the exception of anaerobic sludge. Equilibrium data were fitted to Langmuir and Freundlich models, with satisfactory results for most of the adsorbent-metal systems studied. Of all the adsorbents studied, bentonite and compost presented the highest removal efficiencies, reaching 99% for copper when cadmium is also present, for initial solution concentrations of up to 100 mg L-1. Anaerobic sludge has a greater preference for cadmium, even in the presence of copper, with removal efficiencies of 98% for similar concentrations to those mentioned above.