Surface thermodynamics and some engineering properties of an organo-clay

Organo-clay minerals, in which surface inorganic cations have been exchanged by various organic ammonium cations, have the ability to adsorb many organic compounds. Organo-clays are of interest as potential substrates for the decontamination of sites containing organic fluids and as a barrier for plumes of organic contaminants. A factor that has not been examined in detail is the possible change in the fabric of a clay when converted to an organo-clay. A theoretical analysis of the interparticle forces, based on electrostatic and surface thermodynamic theory, indicates that the conversion of a normally hydrophilic swelling clay to an-organo-clay should radically alter these forces, resulting in a change in fabric. To examine this, a smectite clay was converted to an organo-clay by treating it with hexadecyl trimethyl ammonium (HDTMA) cations. Scanning electron microscopy revealed a dramatic change in soil fabric, from an initial dense plate-like fabric to a more open granular fabric for the organo-clay. The granular fabric resulted in a rapid initial consolidation of the organoclay and exhibited a much larger permeability, with water as the permeating fluid, than the unmodified clay. The permeability of the organo-clay decreases significantly when organic fluids are used as permeants.