[Study on equilibrium adsorption of volatile chlorinated hydrocarbons on humid soils]

Adsorption is one of the principal mechanisms for soil contamination by volatile chlorinated hydrocarbons (VCHs). Dynamic adsorption experiments were carried out to study the equilibrium adsorption of four common VCHs pollutants onto eight typical soils in China. Results showed that dry soils had far greater adsorption capacity than humid soils. The soil adsorption capacity sharply decreased with the increase in the soil water content, and then reached a plateau as the water content rose to 10% or above. The adsorption isotherms of trichloroethylene (TCE), tetrachloroethylene (PCE) and 1,1,1-trichloroethane (MC) could be fitted with Henry's equation, while the adsorption isotherms of 1,1,2-trichloroethane (1,1,2-TCA) could be fitted with Freundlich model. The adsorption capacities of VCHs on humid soils were principally influenced by the content of soil organic carbon (SOC), but sometimes also impacted by the composition of SOC and the polarities of the VCHs molecules. Low polar molecules such as TCE and PCE showed adsorption capacities positively dependent on the SOC content. High polar molecules such as MC and 1,1,2-TCA displayed adsorption behavior not only influenced by SOC content but also by the SOC composition of high SOC content soils such as black soil. An adsorption equilibrium simulation model was developed for TCE and PCE on humid soils, the predicted values correlating well with the measured values (n = 80, R2 = 0.98).