Influence of calcite on the electrokinetic treatment of a natural clay

Abstract

After presenting a geochemical model for the interaction between calcite and varying environmental conditions, the paper discusses the experimental results of long duration electrokinetic tests, run on a natural clayey soil in unbuffered conditions. Local measurements of electrical potential, temperature and water flow were performed during the tests, while pH and fluid conductivity were measured locally once the tests had been dismantled. Sharp change of pH and reduction of the soil electrical conductivity, that in pure clays usually occur in the proximity of the cathode, were observed in the region close to the anode. As well, the soil in the anode area systematically tended to develop fractures, that mostly persisted until the end of the experiments. The features observed, that are not adequately taken into account by existing models, are interpreted in the light of the proposed calcite–water interaction. The onset of fractures, soil desaturation and electrical conductivity drop seem to be justified as a consequence of severe CO2 pressures arising in the anode area. Calcite dissolution and precipitation is held responsible for the changes of void ratio along the samples.