Juana María Rosas

Enhancing p-cresol extraction from soil.

Soil washing is a potential technology for rapid removal of organic hydrocarbons sorbed to soils. In this work, p-cresol desorption with different non-ionic surfactants (Tween 80, Brij 30 and Triton X-100) was compared to cyclodextrine and citrate as solubilizer. A series of batch extraction experiments were conducted at 20°C using the field soil with different extracting solutions at various concentrations to investigate the removal efficiency and to optimize the concentration of the extractant. The use of the different extracting agents was very selective to p-cresol extraction, minimizing soil organic matter releasing and maintaining the natural pH of the soil. The highest asymptotic values of desorption percentages were obtained for Tween 80 and Brij 30 at 48 h. However, Brij 30 ecotoxicity (EC(50)=0.5 mgL(-1)) is in the same order of that obtained for p-cresol, being this surfactant clearly ruled out. Liquid to solid ratio of 2.5 mLg(-1) presented the best extraction results, while concentrations higher than 1 gL(-1) for Tween 80 and Citrate did not produce any significant effect on the desorption efficiency. p-Cresol extraction efficiencies higher than 70% and 60% for Tween 80 and Citrate, respectively.

Soil-Washing Effluent Treatment by Selective Adsorption of Toxic Organic Contaminants on Activated Carbon

The recovery of Tween 80 from a liquid residue, obtained after washing of a contaminated soil with p-Cresol, was studied by selective adsorption of p-Cresol with activated carbons. A modified expression of the Langmuir equation was succesfully used to predict the adsorption isotherms of p-Cresol in the absence and presence of different surfactant concentrations. The presence of surfactant seems to modify the adsorption equilibrium, but it does not produce any significant influence on the adsorption kinetic of p-Cresol. A mathematical model was developed to predict the optimum activated carbon dosage demanded to reduce the p-Cresol concentration as a function of the surfactant concentration, also obtaining the corresponding surfactant loss. The regenerated solution was favorably used as washing solution in a new contaminated soil. These results indicate that this technique can be adequate to recover the surfactant solution, with a relatively minimal loss, for a subsequent application.