Soil washing for remediation of soils contaminated with petroleum hydrocarbons and/or metals

Two industries which have caused constant contamination problems in Mexico are the petrochemical and the mining industries. In both cases, industrial activity has lead to the contamination of a number of sites in the national territory (more than 76 sites are contaminated with metals and more than 103 with petroleum derivatives) (SEMARNAT 2000).Surfactant enhanced soil washing (SESW) has become a very important option for the remediation of soils contaminated with a variety of compounds and elements, i.e., petroleum hydrocarbons, pesticides, dense nonaqueus-phase liquids, metals, and others. Soil washing enhanced by surfactants is a feasible remediation technique when there is no chance for biodegradation-based methodologies. In the case of soils contaminated with metals, there are no degradation process, since metals cannot be destroyed, but isolated, removed or stabilized, among other physical process.When time and/or space are scarce, soil washing is an excellent cost/benefit option. This chapter reviews the state of the art for surfactant enhanced soil washing developments. Aspects such as the selection of the best surfactant and doses and the use of natural surfactants, alone or in combination with synthetic ones, are discussed. The specific issues when washing soils contaminated with metals are also discussed. Finally, aspects related with the design of an industrial washing process and estimation of costs are reviewed and discussed.