Feasibility study of the use of different extractant agents in the remediation of a mercury contaminated soil from Almaden

The soil of Almaden mining district in Spain has a high concentration of mercury (1000 mg kg(-1)), therefore decontamination activities are necessary. This paper studies the effectiveness of some chelant agents (thiosulfate, EDTA, iodide and HNO(3)) for the remediation of this soil which has been polluted for several millennia. The risk assessment of the contamination and the feasibility study (RA-FS) of the remediation were based on a standard sequential extraction procedure (SEP) together with lixiviation tests. Results obtained from these RA-FSs allow the prediction of the mercury removal reached in bench scale tests of the flushing technique. In addition the SEP was performed before and after treatments, and it was found that in some cases the remaining mercury concentration after treatment is associated to the more mobile fractions, indicating that additional treatments would be required. It also indicates that an important additional removal would be obtained if acid extraction is carried out after the first treatment. Finally, the reliability of the standard SEP used was tested to determine if the very high total metal concentration of this contaminated site affects the fractionation results. This was done by the repetition of each sequential extraction step before moving to the next one. Results indicate that both procedures give almost identical results for mercury but some important differences can be observed for iron. (C) 2011 Elsevier B.V. All rights reserved.