Enhanced soil-washing treatment for soils which are highly contaminated with crude oil

Soil and water contamination due to hydrocarbon spills is a frequent problem worldwide. In the case of Mexico, even when programs oriented to the diminution of these undesirable events are in progress, in the year 2000 a total of 1,518 hydrocarbon spills (6,250 tons) were reported. Surfactant enhanced washing of soils is a remediation technology, which has been shown to be a high cost-effective process. The first step in the washing process development is the selection of suitable surfactants and doses. In this work, twelve anionic and nonionic surfactants and their mixtures were assessed in the remediation of highly contaminated crude oil soils. Moreover, the use of different amounts of NaCl and Na-silicate (10%), due to the high amount of Ca, Mg and Mn in the soils is shown and discussed. The studied soil was artificially contaminated with crude oil from the El Batab (Campeche, Mexico) perforation well in a concentration of 108,980 mgTPH/kg soil. SDS and E-600 surfactants at 1% concentration achieved higher TPH removal rates (20.4 and 32.9%, respectively). The surfactant-salt mixture that showed a TPH removal rate higher than those obtained with the best single surfactants was SDS+ EW600+Na2SiO3 10% (30.2%). Using a tensiometric technique, the SDS critical micelle concentration (CMC) was measured without any salt present and with 0.5, 1 and 2% of NaCl. These data were employed together with other surfactants CMC and HLB (hydrophilic-lypophilic balance) reported values in order to explain the surfactants performance during the soil washing assessments. In general, TPH removal values were higher when high HLB values-surfactants were employed.