Ad. Findlay et al., ELECTROKINETIC PROPERTIES OF OXIDE PARTICLES IN NATURAL-WATERS, Colloids and surfaces. A, Physicochemical and engineering aspects, 111(3), 1996, pp. 203-212
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.