Relationship of Surface Area of pH-Dependent Suspensions and Water Retention

Abstract

The equilibrium water retention, M_W/M_S, of suspensions having a pH-dependent surface charge (carbonate-containing aluminum hydroxide and fumed silica) appears to be due to water adsorbed by the surface as well as water retained in pores. The water retained in pores has a lower limit determined by the closest packing porosity. Maximal water retention occurred when the pH was equal to the point of zero charge and attractive particle interactions predominated. The contribution of pore water to M_W/M_S can be minimized by selecting a pH significantly different from the point of zero charge. The water retention properties of the suspension under these conditions are believed to be due to adsorption and the closest packing porosity. Preliminary results indicate that this M_W/M_S can be related to the surface area of the suspended solid.