Mobilization of colloidal particulate matter (most important, clay particles) from a soil matrix in the subsurface environment is an important environmental process. As many contaminants tend to adsorb onto various colloidal mineral particles, co-transport of contaminants in association with mobilized particles could contribute significantly to the migration of these contaminants in the environment. Numerous studies have observed the effects of pH on colloid mobilization but have overlooked the possible direct role of acidity. This study looked at the role of acidity with H+ as a chemical agent. Through cyclic elution of a natural sand column with a weak acid and base solution, there was an increase in mobilized clay colloids. It was found that low concentrations of organic acids could assist in detaching surface clays through lysing of labile Ca2+ and Mg2+ ions. The H+ ions sever the chemical bonds between the grain surface and the colloidal surface by being substituted for the interstitial Ca and Mg ions. This substitution has been found to release over 1 kg of surface clay per 1 mole of H+ consumed. It was postulated that pH oscillation addition to proton dynamics could play a major role in subsurface colloid transport. The results from this study could help improve predicting of subsurface contaminant fronts and aid in managing contaminant transport in the soil water environments.
