Modeling kinetics of copper uptake by inorganic colloids under high surface coverage conditions

Copper uptake by ferric oxide and silica particles is studied through batch kinetic experiments. Copper uptake rates are found to be strongly dependen t on pH and on the sorbate/sorbent molar concentration ratio. Dramatic chan ges to the zeta potential of both colloids from baseline values are observe d. Modeling of copper uptake and zeta potential charge reversals using the surface complexation model (SCM) yields poor descriptions under high surfac e coverage conditions, The conventional SCM, modified in the recent literat ure to (i) the surface polymer model (SPM), which additionally incorporates uptake of dimeric copper species; and (ii) the continuum model (CM), which includes formation of surface precipitates, is extended here to model upta ke kinetics. Both the SPM and the CM are successful in modeling copper upta ke rates as well as zeta potential variations over a wide range of solution conditions. For systems with high surface loadings, copper removal from so lution appears to result from the formation of monomeric and dimeric surfac e complexes, as well as through precipitation mechanisms. It is further con cluded that a kinetic model incorporating diffusion through the surface fil m of sorbed and precipitated copper species as the rate-limiting process, i n association with the SPM and CM, successfully describes the effect of pH and colloid concentration on copper uptake and oxide particle zeta potentia l histories. (C) 2001 Elsevier Science B.V. All rights reserved.