In recent years there has been a considerable amount of research work done relative to the effect of pretreatment and aging in water on the surface properties of both simple metal oxides and more complex oxides such as the silicate minerals.
The present paper investigates the change of point of zero charge (PZC) of a number of simple oxides and several complex oxides as a function of aging time in water. In some cases acid pretreatment of minerals was performed. However, in most cases the minerals were not acid pretreated. In several systems pH change as a function of aging time in water was monitored.
Pure mineral specimens were prepared for study by first hand-picking best appearing specimens and reducing them in particle size in either an agate mortar and pestle or, in the case of asbestiform minerals, in a tungsten carbide pica mill. Next, the minerals were separated into plus and minus 325 mesh fractions. The latter were retained for experimentation. In addition to naturally occurring minerals, synthetic Al2O3 (Linde A) was also studied. In all cases minerals without further treatment were stored in plastic vials.
Electrophoretic mobility studies were performed with a commercially available microelectrophoresis apparatus, the zeta meter.