A LABORATORY-SCALE STUDY OF APPLIED VOLTAGE ON THE ELECTROKINETIC SEPARATION OF LEAD FROM SOILS

The application of electrokinetic (EK) soil-flushing technology to the separation of lead from a nonsynthetic, fine-grained, low permeabilit y soil was examined. In these laboratory-scale experiments the effects of applied voltage (30 and 60 V DC) on cumulative electroosmotic (EO) flow, charge-input, and lead removal were investigated. To develop a more generalized cause-effect relationship, these parameters were stud ied using three anode/cathode reservoir conditioning schemes: NaNO3/Na NO3, NaNO3/HAc (acetic acid), and HCl/HAc. Charge-input and cumulative EO flow generally increased when the applied voltage was raised. When reservoir pH controls were used, results were more consistent with th eoretically predicted outcomes. Increasing the applied voltage increas ed the electrolysis of water, which increased the fluid conductivity a nd charge-input. Although cumulative EO flow increased in proportion t o the voltage, the advantage of operating at a higher applied voltage diminished as the amount of lead remaining in the soil decreased. The highest lead removal rates for both the 30 and 60 V tests were achieve d using the 0.1 M HCl/1.0 M HAc reservoir conditioning scheme. The add ition of HCl to the anode reservoir solution enhanced the impact of th e acid front, especially during the initial pore volumes of flow which occurred before the oxidation of water could produce significant amou nts of H+ at the anode. Additionally, HAc in the cathode reservoir pre vented the formation of a base front and the subsequent Pb readsorptio n/precipitation onto soil. The greater cumulative EO flow and charge-i nput in the experiments conducted with the HCl/HAc reservoir condition ing scheme resulted in faster Pb removal via advection and electrolyti c migration. In contrast, the lowest remediation and removal values we re obtained with the NaNO3/NaNO3 reservoir treatment scheme, which had a low cumulative EO flow, relative to the other tests, and lacked res ervoir fluid pH control. To demonstrate the impact of soil pH oh Ph re moval, soil-bound Pb concentrations as a function of soil pH were also examined, The ''critical pH'' range necessary to ensure effective Pb removal was between 4 and 4.5.