Copper uptake by inorganic particles - equilibrium, kinetics, and particleinteractions: experimental

Copper uptake by ferric oxide and silica particles is studied through batch equilibrium and kinetic experiments under different conditions of pH and i onic strength. Acid-base titrations of the oxide particles indicate that th e point of zero charge is 3.0 for the ferric oxide and 4.7 for the silica p articles used in this study. For the same particles, electrokinetic measure ments 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 condit ions and to increase with an increase in pH. Changes in ionic strength caus e little or no significant change in the pH dependence of ion uptake. From control experiments, as well as from copper hydrolysis and speciation calcu lations, copper precipitation (as CuO) is evident above pH 6. In the acidic and neutral pH ranges, a marked increase in the zeta potential of both sor bents from baseline values is found during equilibrium copper uptake. Size distribution measurements show an increase in the number of flocculated sor bent particles at pH values corresponding to the steep increase in copper u ptake. Further, at highly acidic pH ranges, silica particles are found to b e well stabilized and non-flocculating in equilibrium uptake studies. Simil ar findings are observed with ferric oxide particles at highly alkaline pH values. Kinetic studies indicate that copper uptake by ferric oxide is a mu ch slower process as compared with uptake by silica under the conditions st udied here. Also, the lower the sorbate/sorbent molar concentration ratio, the faster is the rate of copper uptake. With both particles, a rapid incre ase in zeta potential is observed within the first few minutes. Flee format ion and breakage are evident from size distribution measurements. These fin dings indicate a possible role of metal ion uptake in particle flocculation kinetics through alteration of the zeta potential of sorbent particles. (C ) 2001 Elsevier Science B.V. All rights reserved.