Study On Mixed Surfactant-Enhanced Remediation Of Nitrobenzene-Contaminated Soils

Surfactant-enhanced remediation is a newly emerging remediation technology of the soils polluted by organics. Surfactants are used to remove the organic pollutants absorbed on the soil particles by the solubilization and mobilization resulted from surfactant characteristics. Nitrobenzene (NB) as a target pollutant and three kinds of surfactants (cationic CTAB: cetyltrimethylammonium bromide, anionic SDBS: sodium dodecylbenzenesulfonate; nonionic Tween 80: polyoxyethylene sorbitan monostearate) are used in this study. Base on the adsorbed mechanisms of three single surfactants on soils and their effect on the adsorption behavior of NB on the soil particles, the effect of mixing ratio of mixed surfactants on the adsorption of NB on the soil particles is clarified and the remediation effect of mixed surfactants to NB-contaminated soils is also discussed. These results are quite helpful to give the academic basis to the protection and remediation of soil environment.1) Adsorption behavior of single surfactants showed that all three surfactants reached saturation absorption on the soil particles at the CMC (critical micelle concentration). The saturated adsorption amount was CTAB >> SDBS > Tween80. At lower surfactant concentrations, the three surfactants could form surface hemimicelles on the soil particles by the electrostatic attraction (CTAB), the hydrogen-bond (Tween80), and the hydrophobic and electrostatic interactions (SDBS), respectively. With the increase of surfactant concentrations, the three surfactants could form surface micelles on the soil particles by the hydrophobic interactions. When NB was added, the adsorption amount of surfactants increased. While SDBS and Tween80 were added at the same time, the adsorption amounts both decreased.2) Adsorption behavior of NB showed that the relationship between the adsorption amount of NB on the soil particles and the equilibrium concentration in solution was well linear within the concentration ranging from 0 to 25 mg/L. The main way of adsorption of NB on soil particles was partition process. The adsorption amount of NB increased at lower surfactant concentrations, and then decreased at higher surfactant concentrations due to the adsorption of monomer, dimer and trimer of surfactants and the solubilization of micelles in solution. Among three surfactants, SDBS had the best decreased effect on the adsorption amount of NB on the soil particles. The mixed surfactants showed the best decrease effect while the mixing ratio of SDBS and Tween80 was 0.4:0.6 and 0.6:0.4. 3) The single surfactant-enhanced remediation showed that while using the three surfactants to flush the NB-contaminated soils, the efficiency was SDBS >> Tween80 > CTAB. SDBS showed the best effect due to its least adsorption amount on soils and the highest stability and solubilization of micelles in solution.4) The mixed surfactant-enhanced remediation showed that the mixture of SDBS and Tween80 could well remove NB from the soils due to its stable mixed micelles in solution. While the mixing ratio of SDBS and Tween80 was 0.6:0.4, the remediation effect was the best according to the experimental results.