THE EFFECT OF PB(II) SPECIES, PH AND DISSOLVED CARBONATE ON THE ZETA-POTENTIAL AT THE QUARTZ/AQUEOUS SOLUTION INTERFACE

The zeta potential of quartz has been measured in CO2-free and air-saturated aqueous lead solutions to delineate the effect of pH and atmospheric CO2 on the adsorption of Pb(II) at the oxide/solution interface. Under CO2-free conditions, an addition of 10(-4) M total lead causes the zeta potential of quartz to reverse its sign from negative to positive in the pH range from 7 to 11. If lead solutions are prepared with air-saturated water, this zeta potential reversal is not observed. Computations of thermodynamic equilibria for the systems Pt(II)-H2O and Pb(II)-H2O-CO2 indicate the predominance of lead hydroxo complexes in the pH range of positive zeta potentials under CO2-free conditions, and the precipitation of lead carbonate in suspensions prepared with air-saturated water. The charge reversal of lead-activated quartz in CO2-free dispersions seems to be related to the adsorption of lead hydroxo complexes. In the presence of air or carbonate additives, the negative zeta potentials of lead-activated quartz in the pH range from 7 to 10 may be due to specific adsorption of the bicarbonate anion.