Mercury transport and speciation during electrokinetic soil remediation

Abstract

A 30 V direct electric field was applied to a contaminated soilfrom a chlor-alkali plant for 182 days. The principal soilcontaminats were mercury, polchlorinated dibenzofurans, andlead. When chloride was added to the soil, mercury moved towardsthe cathode, showing that anionic mercury chloride complexes didnot dominate. When iodide was added to the soil solution,mercury moved towards the anode, illustrating the predominanceof an anionic mercury iodide complex. The iodide mobilisedmercury from the soil and transported it rapidly into the anodesolution, so that mercury was removed from the soil. When theexperiment was continued, mercury returned to a cationic formand electromigration transported the mercury back into the soil.This was probably due to the lower iodide concntrations that mayresult from the oxidation of iodide to iodine near the anode.Sequential extraction showed that mercury was strongly bound tothe soil, both before and after the electrokinetic treatment.The heavy metals were found in the `acidic and oxidising', andthe residual fraction of the leaching procedure. Mercury wasmore available after the treatment with iodide.