Pilot-scale electrokinetic cleanup of lead-contaminated soils

The results of two pilot-scale experiments on enhanced electrokinetic extraction of lead from contaminated soil samples collected from a military Small Arms Training Facility are presented. The tests were conducted using two boxes with electrode spacing of 87 cm (Box 1) and 174 cut (Box 2). The soil was formed of a sandy layer on top of a clayey sand layer. The soil contained bullet fragments and the mean initial lead concentration in the minus 2.00 mm soil fraction was 3041 mg/kg and 1187 mg/kg in the sand and clayey sand layers, respectively. A Current density of 1.3A/m(2) was used in both tests and was doubled after 112 days of processing. organic acid was used to maintain the catholyte pH between 4 and 5. Box 1 and Box 2 were processed for 9 months and 11 months, respectively. The results showed that organic acid amendment at the cathode reduced the voltage and energy requirement by 70% and enhanced lead extraction. Lead transport showed a delay of about 14 days in the initial transport front development. For the conditions described in this study. the reactive rate of lead transport by ion migration and electroosmosis was 0.4 cm/day under 1 V/cm, which is less than 10% of the theoretical nonreactive value. There was a minimum limit for lead extraction from the soil by electrokinetics. Final lead concentrations in the treated sections were around 500 mg/kg in the sand and 400 mg/kg in the clayey sand. The results represent a reduced lead concentration by 85% in the sand and by 70% in the clayey sand. Complete breakthrough of lead did not occur due to accumulation near the cathode. even though catholyte pH was 4 to 5. A transverse upward transport and accumulation of lead at the soil surface was observed in both tests. Treatment duration of 9 months was adequate for Box 1, while 11 months of processing was not enough for Box 2 to bring the total lead concentration to below 500 mg/kg across the soil. Electrical energy cost for the process was between $14 and $18 per cubic meter per month.