Electroosmotic pump: Rate controlling mechanism for unusually fast electroremediation kinetics of Cr(VI) in basic Kanpur soil

Electroremediation of Cr(VI) from a wet-sieved, basic (pH = 10.5) Kanpur soil showed unusually fast kinetics. 75% Cr(VI) was removed from Kanpur soil in 40 h, in contrast to 34% Cr(VI) from kaolin in 144 h. Moreover, in contrast to published studies, the predominant transport mechanism of Cr(VI) was electroosmosis and not electromigration. The unusually high kinetics of electroremediation has been attributed to the formation of an electroosmotic pump near the anodic end of the soil. The buffering capacity of the soil and the rate of generation of H+ in the anode chamber appear to be the dominant factors for the formation of the electroosmotic pump. In addition to maintaining a high electroosmotic flow rate, the pump also increases the degree of saturation of the soil in the initial period itself, thereby increasing the effective cross-sectional area for the removal of Cr(VI). This study also shows that depending on the nature of the soil, acid–base neutralisation could either enhance or retard electroremediation kinetics.