Influence of current density and pH on electrokinetics

Two series of electrokinetic experiments have been conducted on kaolinite to study the effects of current density and influent pH on electrokinetic processing. In the first series, eleven tests were conducted at different current densities ranging from 0.123 mA/cm(2) (10 mA) to 0.615 mA/cm(2) (50 mA) using distilled water as the influent. In the second series, ten tests were conducted with constant current densities of 0.123 mA/cm(2) (10 mA) and at different influent pH of 2, 4, 8, 10 and 12. In all cases, the soil was initially mixed with the influent. Results from the first series showed that the flow rate increases as the current density increases. On the other hand, increasing the current density reduced the time needed for the acid front generated at the anode to reach the cathode. In tests with different influent pH, results indicated a gradual increase in electro-osmotic flow between pH of 2 to 10 and a sharp increase from 10 to 12. We also noticed that pH of the cathode compartment increased at the early stage of testing and then started to decrease with time for tests with influent pH ranging from 2 to 10. At the same time, the flow rate started to decrease with time. However, this was not the case for tests with influent pH of 12. The pH of the cathode compartment remained high and the flow rate was constant throughout the testing period. Increasing current density resulted in a slight increase in the energy expenditure for the same number of pore volume. However, increasing the influent pH resulted in a large reduction of the energy expenditure for the same number of pore volume. All tests have been duplicated and similar results were achieved. (C) 1997 Elsevier Science B.V.