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Abstract
A method for coating hydrated iron, cobalt and iron/cobalt oxide on the surface of keramzite sand was developed. The coating parameters (pH, amount of coated metal, molar ratio Co/Fe, temperature of modification and time of treatment) controlling sorption ability of the coated layer were determined. The iron/cobalt coated keramzite thermally activated at 450°C obtained at a molar ratio Co/Fe-0.516 is characterized and use for the removal of metal ions. The effect of contact time, solution pH, sorbate concentration, ionic strength and competing metal concentration on the sorption of copper, lead, zinc and cadmium was studied in batch experiments. The results reveal that the sorption rate of metal ions increases more rapidly in the initial period and reach metastable equilibrium within three hours. The sorption on coated keramzite follows both Langmuir and Freundlich's models. The data on the effect of pH showed that the sorption of all metal ions studied was markedly influenced by the solution pH. According to the concept of surface complexation model the experimental results support the assumption that metal adsorption at oxide coated keramzite sand could be better modeled as an inner-sphere surface reaction. The modified sorbent has a high selectivity towards copper and lead ions. The coated keramzite sand can be recommended as an efficient adsorbent for advanced water treatment of metal-bearing solutions and industrial wastewaters.