Aqueous Surface Chemistry of Oxides and Complex Oxide Minerals

The isoelectric point (IEP(s)) and the zero point of charge (ZPC) are convenient references for predicting the charge-dependent behavior of oxide minerals and their suspensions. The ZPC is the pH at which the solid surface charge from all sources is zero. The IEP(s) is a ZPC arising from interaction of H+, OH-, the solid, and water alone. The IEP(s) of a simple oxide is related to the appropriate cationic charge and radius. The ZPC of a complex oxide is approximately the weighted average of the IEP(s)'s of its components. Predictable shifts in ZPC occur in response to specific adsorption and to changes in cation coordination, crystallinity, hydration state, cleavage habit, surface composition, and structural charge or ion exchange capacity.