Measurement of streaming current and calculation of zeta potential for beds of wide-dispersion microparticulate solids interacting with water

Abstract

If water or an aqueous solution is replaced by an organic liquid of low polarity and permittivity, e.g. an n-heptane—acetone 9 : 1 (v/v) mixture, a reproducible and time-independent streaming current is generated in the bed of a water-soluble solid, e.g. calcite. In the case where the residual water content in the organic liquid is sufficiently low, a reproducible and time-independent streaming current is obtained from the bed of a water-reactive solid, e.g. cement, also. Chromatographic experimental techniques and commercial instrumentation allow us both to handle dry organic liquids and to overcome experimental difficulties caused by the polydispersion of a microparticulate solid even if dust particles are contained in the sample. The combination of chromatographic and electrokinetic measurements in one experiment enables the simultaneous observation both of streaming current changes, induced by concentration pulses of probes injected into the liquid stream entering the column, and of the sorption interactions of probes with the solid column packing. This represents a new approach to the investigation both of solid surfaces and of the processes taking place in the solid—liquid interface. An equation for the calculation of the zeta potential from the streaming current generated in a bed of unknown geometry and characteristized by a strong overlap of electric double layers on the bed particles is proposed and briefly tested.