DISPERSION AND ZETA-POTENTIAL OF PURE CLAYS AS RELATED TO NET PARTICLE CHARGE UNDER VARYING PH, ELECTROLYTE CONCENTRATION AND CATION TYPE

The effect of changing pH and electrolyte concentration on the dispers ion and zeta potential of Na-and Ca-forms of kaolinite, illite and sme ctite was investigated in relation to changes in their net negative ch arge. The percentage of dispersible Na-clay and the percentage increas e in net negative charge was positively correlated with pH, but the sl opes varied from clay to clay. In general, the net negative charge was the primary factor in clay dispersion, and the pH affected clay dispe rsion by changing the net charge on clay particles. Na-smectite had la rger net charge at all pHs than Na-illite and Nakaolinite, and it alwa ys had larger flocculation values. The role of electrolyte concentrati on could be due to its effect both on flocculation and variable charge component of the clay minerals. The zeta potential at different pHs a lso reflected the same trend of clay dispersion with net particle char ge. In Ca-clays the trends were similar to Na-clays up to pH 7.0. In m ore alkaline solution CaCO3 formation led to charge reduction on clay particles, resulting in flocculation and reduction of zeta potential. At similar pHs the electrophoretic mobilities of all the clays showed constant potential behaviour. However, the zeta potentials of Ca-clays were always smaller than those of sodic clays because the clays were more aggregated. Net particle charge was the most important factor in controlling clay dispersion for the whole range of pH and ionic streng th and for all types of cations.