Electrokinetic Soil Remediation: Effects of  pH, temperature and chemical reactions

Madeleine Lisa Mary Penn, Cambridge University, Geotechnical Engineering Group

Abstract

This thesis investigated electrokinetic remediation of contaminated soil with particular reference to the influence of pH, temperature and chemical reactions on the efficiency of the process. This topic was researched through laboratory experiments₁ geotechnical centrifuge modelling and numerical modelling.

The laboratory tests examined the migration of ionic species through porous media due to electric and concentration gradients. Equipment and instrumentation were developed and experiments were performed using kaolin clay saturated with either sodium sulphate or copper sulphate. The results highlighted the limiting effect of the pH fronts, which reduce the efficiency as chemical reactions involving the soil, the migrating ions and the pH fronts cause a reduction in the voltage gradient. A further test series was undertaken at elevated temperatures and revealed the beneficial effect of reducing the required remediation time, as the fundamental transport processes of electrokinetics are accelerated by high temperatures.

Geotechnical centrifuge model testing was performed on the Cambridge balanced arm centrifuge using new equipment. The models were prepared using kaolin clay saturated with copper sulphate pore fluid. The tests determined the pattern of the voltage, concentration and temperature fields generated by a two-electrode configuration within a three-dimensional model.

Two numerical models were employed to examine the influence of pH, temperature and chemical reactions on electrokinetic ion migration. On the basis of experimental observations in this thesis, one of the models was modified to include transient electro-osmotic flows and cation hydroxide precipitation. Comparisons between experimental data and numerical simulations emphasised the need to incorporate chemical equilibrium reactions, and the resultant spatial and temporal variations in the voltage field, in order to correctly predict electrokinetic ion migration.

Keywords:

electrokinetic, remediation, kaolin, pH, temperature, reactive pollutant migration, geotechnical centrifuge