ELECTROKINETIC PROPERTIES OF OXIDE PARTICLES IN NATURAL-WATERS

Microelectrophoresis measurements have been made on haematite and on q uartz particles equilibrated with and dispersed in two different river waters; a basic hard water obtained from the Sherston Avon (SA) and a n acidic soft water obtained from Whitray Beck (WE). Information conce rning the reversibility of surface-modifying adsorption processes has been obtained from studies of the effects of extensive washing of rive r-water-equilibrated particles with distilled water and with indiffere nt electrolyte solutions. Additional information concerning the influe nces of specific river water constituents on the oxide surface propert ies has been obtained from electrokinetic studies of particles dispers ed in synthetic electrolyte solutions. The results obtained indicate t hat in the case of haematite, the surface electrical properties are co ntrolled by a combination of inorganic cation and organic anion intera ctions 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. Th is evidence suggests that the combined effects of cation and anion spe cies on the surface electrical properties of haematite dispersed in th ese river waters arises either by the adsorption of these species at d ifferent surface sites or by adsorbed anions providing surface sites f or 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 approxim ate to 8.4 for SA pH approximate to 5.5 for WE) and humic concentratio ns (3 mg dm(-3) for SA, 7 mg dm(-3) for WE) of the two waters. In the case of quartz particles, surface interactions with organic anion spec ies present in the river waters are of negligible importance with rega rd to modification of the surface electrical properties. The quartz su rface properties appear to be determined essentially by interactions w ith inorganic cations, principally Ca2+ and Mg2+ in the basic SA water , and additionally, Al species in the acidic WB water.