Effect of copper and cadmium binding on flocculation of ferric oxide particles

The sorption of copper and cadmium ions from aqueous solutions by ferric ox ide particles was studied using batch equilibrium and kinetic experiments. The sorption process was found to be pH dependent, with the uptake increasi ng at high pH values. An increase in equilibrium pH was observed when the i nitial pH was in the acidic range, and a decrease from initial values was o bserved in the basic range, in the case of both copper and cadmium sorption . The former phenomenon is due to competition between metal and proton bind ing, and the latter is due to precipitation mechanisms at high initial pH v alues. A large increase in the zeta potential of the particles from baselin e values was observed during equilibrium sorption. This increase occurs as a result of surface charge neutralization due to metal ion uptake. Particle destabilization appears to occur as a result of metal ion sorption. Kineti c experiments indicate that the uptake of copper by Ferric oxide particles is a slow process. The pH histories were similar to those obtained in the s orption equilibrium experiments. Changes in the size distribution of the fe rric oxide particles due to aggregate formation during uptake of ions were observed in the kinetic studies. These findings indicate a potential role o f metal ion uptake in particle flocculation kinetics through alteration of the surface electrostatic potential.