Copper uptake by inorganic particles - Equilibrium, kinetics, and particle interactions: Experimental

Copper uptake by ferric oxide and silica particles is studied through batch equilibrium and kinetic experiments under different conditions of pH and ionic strength. Acid-base titrations of the oxide particles indicate that the point of zero charge is 3.0 for the ferric oxide and 4.7 for the silica particles used in this study. For the same particles, electrokinetic measurements show an isoelectric point of 2.2 for ferric oxide and 2.7 for silica. The extent of metal removal is found to strongly depend on solution conditions and to increase with an increase in pH. Changes in ionic strength cause little or no significant change in the pH dependence of ion uptake. From control experiments, as well as from copper hydrolysis and speciation calculations, copper precipitation (as CuO) is evident above pH 6. In the acidic and neutral pH ranges, a marked increase in the ζ potential of both sorbents from baseline values is found during equilibrium copper uptake. Size distribution measurements show an increase in the number of flocculated sorbent particles at pH values corresponding to the steep increase in copper uptake. Further, at highly acidic pH ranges silica particles are found to be well stabilized and non-flocculating in equilibrium uptake studies. Similar findings are observed with ferric oxide particles at highly alkaline pH values. Kinetic studies indicate that copper uptake by ferric oxide is a much slower process as compared with uptake by silica under the conditions studied here. Also, the lower the sorbate/sorbent molar concentration ratio, the faster is the rate of copper uptake. With both particles, a rapid increase in ζ potential is observed within the first few minutes. Floc formation and breakage are evident from size distribution measurements. These findings indicate a possible role of metal ion uptake in particle flocculation kinetics through alteration of the ζ potential of sorbent particles. Copyright (C) 2000 Elsevier Science B.V.