SSurface Thermodynamics and Some Engineering Properties of an Organoclay by Muniram Budhu, Rossman Giese

ABSTRACT

The interaction between organic substances and clay mineral surfaces in the presence of water and air controls important subsurface processes such as contaminant release, migration, re-adsorption and decay pattern. Clay mineral surfaces modified by exchanging inorganic cations from their surfaces with various organic ammonium cations have the ability to adsorb toxic organic compounds. The modified clays called organoclays are touted as potential clients for clean up of sites contaminated with organic fluids and as a solution for preventing plumes of organic contaminants from spreading into the environment from containment sites. In this paper, a theoretical analysis of surface thermodynamics that allows one to determine whether a given organic compound will be adsorbed on a specific substrate, and the strength of the adsorption is presented. This theory gives one the ability to modify the surface properties of clay minerals so as to make them more hydrophobic (and more able to adsorb organic liquids) or more hydrophilic (and more able to repel organic fluids). Test results from a smectite clay converted to an organoclay by treating it with hexadedyltrimethylammonium (HDTMA) reveals a change in soil fabric from a platelike fabric to a granular fabric. The granular fabric results in rapid initial consolidation of the organoclay and much larger permeability eith water as the permeating fluid than the unmodified clay. The permeability of the organoclay reduces significantly when organic fluids were used as the permeants.