Mercury-Contaminated Soil Remediation by Iodide and Electroreclamation

Electroremediation was applied to contaminated soils in order to study the transport of metals and organic compounds by the external electric field. The electric field caused acidic conditions near the anode, so that copper, zinc, lead, nickel, cadmium, calcium and manganese were released from soil from a chlor-alkali site. The metals were transported towards and immobilised near the cathode, where pH was high. The metals were very strongly attached to the soil, which was shown by selective extraction. Mercury was removed through the electromigration of a mercury-iodide complex. 89 % of the mercury was removed from the soil near the cathode, and 46 % had arrived in the anode solution after 3 days. Chloride mobilised less than 50 %. Clay had an over-all larger influence (retardation) then peat or goethite on the migration behaviour of metals in an artificial soil with sand base. The influence of clay on polyaromatic hydrocarbons (PAH) was the opposite. The presence of clay or fulvic acid increased the apparent solubility of pyrene and phenanthrene. However, when solid organic matter was added, pyrene and phenanthrene were sorbed to the soil, and the organic matter that was released into the soil solution could not compete for the PAH. Fulvic, citric, oxalic and gluconic acids, and phosphate were transported towards the cathode, while chloride, nitrate and sulphate moved towards the anode, as expected. The results from an in-situ pilot scale experiment on mercury-contaminated soil are presented as well as a discussion on the Swedish method of surveying contaminated sites (MIFO).

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