Studies On Interactions Of Lou Soil - PAHs - Surfactant

Polycyclic aromatic hydrocarbons (PAHs) are a group of hard-degradation pollutants which exist widely in the environment. Surfactant-enhanced remediation is a promising remediation technology of the soils polluted by PAHs. Surfactants are used to move the organic pollutants absorbed on the soil by the solubilization and mobilization resulted from surfactant characteristics. Considering the soil characteristics and the structure of surfactants in selecting surfactants that will be the most appropriate for application in remediation technologies for soils or water polluted by hydrophobic organic compounds is important, to avoid excessive use of surfactant. Therefore, in the selection of a surfactant, as well as its capacity to solubilize the contaminant, it is very important to consider its tendency to be adsorbed by the decontaminated soil. Phenanthrene and naphthalene as a target pollutant and four kinds of surfactants (anionic SDS: sodium dodecylbenzenesulfonate; nonionic Tween 80: polyoxyethylene sorbitan monostearate; nonionic Brij-35:polyoxyethylene lauryl ether, nonionic Triton X-100 :octylphenoxypolyethoxyethanol ) are used in this study. Batch adsorption experiments were done with four surfactants concentration under CMC respectively and Brij35,Tween80 concentration above their CMC. Based on the adsorbed mechanisms of four single surfactant, their mixture on calcareous soil and the adsorption behavior of phenanthrene and naphthalene on the soil particles though batch adsorption experiments, the optimal surfactant concentration were chosen for elution experiment of phenanthrene and naphthalene, the effect of mixing ratio of mixed surfactants on the adsorption of phenanthrene and naphthalene on the soil particles is clarified and the remediation effect of mixed surfactants to phenanthrene and naphthalene -contaminated soils is also discussed. These results are quite helpful to give the academic basis to the protection and remediation of calcareous soil environment.(1) Batch adsorption experiments were employed to evaluate the adsorption of phenanthrene and naphthalene on Lou soil.The results showed that the adsorption of phenanthrene and naphthalene on Lou soil is approximately non-linear, Freundlich equation is best fitted their adsorption behavior. The adsorption of phenanthrene and naphthalene on Lou soil decrease with increasing temperature, the adsorption is an exothermic process, the adsorption free energy change is less than zero, indicating that the adsorption process is spontaneous; entropy values less than zero, indicating that Lou soil for phenanthrene and naphthalene has a strong fixation capacity. The increase of solution pH decreased the adsorption of phenanthrene and naphthalene on Lou soil; and with ionic strength increases, the adsorption of phenanthrene and naphthalene on Lou soil increase. The adsorption of phenanthrene and naphthalene on CaCO₃ are also nonlinear, and CaCO₃ shows a greater contribution to adsorption of phenanthrene and naphthalene on Lou soil.(2) Batch adsorption experiments were employed to evaluate the adsorption of surfactants on Lou soil, and the factors affected its adsorption, i.e. surfactant mixing ratio and pH were also studied. Results showed that the adsorption of nonionic surfactant, i.e. Triton X-100, Tween-80 and Brij-35 on Lou soil was L type isotherm that can be described with both Langmuir and Freundlich models, while LS type isotherm, which can be fitted by Freundlich isotherm, was the best model for simulating the SDS adsorption. The adsorption amount of SDS on soil was lower than that of Tween80, but was higher than that of both Triton X-100 and Brij35.(3) For mixing adsorption of anionic–nonionic surfactant on Lou soil, there was little interaction between SDS and Brij35, while greater interaction was between TritonX-100 and SDS, the mixture of 2 kinds of surfactants could increase the adsorption of TritonX-100 but decrease adsorption of SDS. The interaction was the strongest between SDS and Tween80 which resulted in decreasing the adsorption of both SDS and Tween80 simultaneously, although the adsorption amount of Tween80 decreased sharply. The increase of solution pH decreased the adsorption of SDS and Tween80 on Lou soil, but affected the adsorption of Brij35, TritonX100 slightly. The adsorption percentage of nonionic surfactants on Lou soil was above 80% at pH 8.0. The results above indicated that the soil characteristics and the structure of surfactants are important factors in selecting the appropriate surfactants for recovering organic contaminated soil.(4) The single surfactant-enhanced remediation showed that while the dosages of surfactants under their respective critical micelle concentration (CMC), the increase of surfactant concentration increased the elution of phenanthrene and naphthalene on Lou soil, enhanced solubilization of phenanthrene and naphthalene. The sequence of water solubility enhancements is SDS>Tween80> TritonX-100>Brij35. The mixed surfactant-enhanced remediation enhancements is attributed to the increase of solubility of solute in aqueous phase and changes of soil surface structure. The higher the NaCl concentration was, the higher the elution percentage of phenanthrene and naphthalene by SDS, the elution percentage of phenanthrene and naphthaleneby Triton X-100, Tween-80 and Brij35 reduced with the increase of ionic strength. (5) The mixed surfactant-enhanced remediation showed better performance on elution of phenanthrene and naphthalene from soil than single surfactant due to its stable mixed micelles in solution. While the mixing quality ratio of SDS and Tween80 was 3:5, SDS and TritonX-100 was 1:8 and Brij35: SDS was 21:200, phenanthrene and naphthalene were eluted completely according to the experimental results.