Electrokinetic remediation of a soil contaminated by the pyritic sludge spill of Aznalcollar (SW, Spain)

The electrokinetic remediation (EKR) of a soil sample contaminated with a sludge spill of pyritic mining origin is studied. The initial total metal content of the soil indicates that there is a very large concentration of Fe (about 100 g/kg), whereas other metals of environmental relevance are Zn (2390 mg/kg), Pb (1740 mg/kg), Cu (459 mg/kg) and Cd (7 mg/kg). A speciation procedure is performed for each of these metals, indicating that their mobility is quite different. Results indicate that EKR allows only the remediation of those fractions of the contaminants which are associated to the exchangeable and weak acid soluble fractions. These speciation results were used to obtain the values of the parameters that were introduced in a newly developed mathematical model which allows the prediction of the extent of the removal, the rate of recovery, and chemicals requirements. The experiments performed indicate that reversed electroosmosis (towards the anode) occurs and decreases the system performance.