ABSTRACT
Solid particles that appear in the natural environment as a result of weathering phenomena and human activity play a critical role in determining the fate of both airborne and waterborne pollutants. Solid particle surfaces develop electrical charge in two principal ways: either permanently, from isomorphic substitutions of component ions in the bulk structure of the solid, or conditionally, from the reactions of surface functional groups with adsorptive ions in aqueous solution. The steady migration of charged particles through a dilute suspension to which a uniform, constant electric field is applied has long been investigated as a method to infer the behavior of the net total particle surface charge density. A classical technique for measuring the intrinsic surface charge density on a particle is the Schofield method. Surface-reactive particles comprising layer-type aluminosilicates are almost the only ones that bear net structural surface charge among the natural colloids.
