ELECTROPHORETIC MOBILITY AND PARTICLE-SIZE OF CLAYS USING LASER-DOPPLER VELOCIMETRY PHOTON-CORRELATION SPECTROSCOPY

Laser Doppler velocimetry-photon correlation spectroscopy (LDV-PCS) was evaluated for the characterization of clay minerals. Electrophoretic mobility and particle size of pure and mixed suspensions of KGa-2 kaolinite and SWy-1 bentonite were determined as a function of pH, ionic strength, and suspension concentration ratios. Kaolinite mobility changed from significant positive values at low pH to negative values at high pH, consistent with the variable-charge nature of kaolinite. Evidence for a contribution of positive charge originating at bentonite edges at Low pH (<4) was also found. Tonic strength also affected mobility of kaolinite and, at low pH, bentonite. Mixtures of kaolinite and bentonite at low pH yielded mobility distribution spectra intermediate to those of the component clays. The two populations were not resolved, which suggests that the kaolinite and bentonite formed mixed particle associations. Particle-size analyses supported inferences from mobility data that significant particle-particle association occurred under neutral to Low pH and moderate ionic strength conditions.