Electrokinetic properties of oxide particles in natural waters

Abstract

Microelectrophoresis measurements have been made on haematite and on quartz particles equilibrated with and dispersed in two different river waters; a basic hard water obtained from the Sherston Avon (SA) and an acidic soft water obtained from Whitray Beck (WB). Information concerning the reversibility of surface-modifying adsorption processes has been obtained from studies of the effects of extensive washing of river-water-equilibrated particles with distilled water and with indifferent electrolyte solutions. Additional information concerning the influences of specific river water constituents on the oxide surface properties has been obtained from electrokinetic studies of particles dispersed in synthetic electrolyte solutions. The results obtained indicate that in the case of haematite, the surface electrical properties are controlled by a combination of inorganic cation and organic anion interactions with the particle surfaces. Whilst adsorbed cation species were found to be readily and completely removed from the particle surfaces by washing the particles with simple electrolyte solutions, adsorbed organic anion materials were found to be held far more tenaciously. This evidence suggests that the combined effects of cation and anion species on the surface electrical properties of haematite dispersed in these river waters arises either by the adsorption of these species at different surface sites or by adsorbed anions providing surface sites for cation species. Organic anion interactions with haematite particles appear to occur to essentially the same extent in the different river waters in spite of the significantly different pH values (pH ≈ 8.4 for SA pH ≈ 5.5 for WB) and humic concentrations (3 mg dm −3 for SA, 7 mg dm −3 for WB) of the two waters. In the case of quartz particles, surface interactions with organic anion species present in the river waters are of negligible importance with regard to modification of the surface electrical properties. The quartz surface properties appear to be determined essentially by interactions with inorganic cations, principally Ca 2+ and Mg 2+ in the basic SA water, and additionally, Al species in the acidic WB water.