An integrated method incorporating sulfur-oxidizing bacteria and electrokinetics to enhance removal of copper from contaminated soil

The combination of bioleaching and electrokinetics for the remediation of m etal contaminated land has been investigated, in bioleaching, bacteria conv ert reduced sulfur compounds to sulfuric acid, acidifying soil and mobilizi ng metal ions. In electrokinetics, DC current acidifies soil, and mobilized metals are transported to the cathode by electromigration. When bioleachin g was applied to silt soil artificially contaminated with seven metals and amended with sulfur, bacterial activity was partially inhibited and limited acidification occurred. Electrokinetic treatment of silt soil contaminated solely with 1000 mg/kg copper nitrate showed 89% removal of copper from th e soil within 15 days. To combine bioleaching and electrokinetics sequentia lly, preliminary partial acidification was performed by amending copper-con taminated soil with sulfur (to 5% w/w) and incubating at constant moisture (30% w/w) and temperature (20 degrees C) for 90 days. Indigenous sulfur-oxi dizing bacteria partially acidified the soil from pH 8.1 to 5.4. This soil was then treated by electrokinetics yielding 86% copper removal in 16 days, in the combined process, electrokinetics stimulated sulfur oxidation, by r emoving inhibitory factors, yielding a 5.1-fold increase in soil sulfate co ncentration. Preacidification by sulfur-oxidizing bacteria increased the co st-effectiveness of the electrokinetic treatment by reducing the power requ irement by 66%.