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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).

Adsorption is one of the principal mechanisms of soil contamination by volatile chlorinated hydrocarbons (VCHs). Three typical paddy soils were collected from Yangtze Delta Region, onto which the equilibrium adsorption of six VCHs was studied under dry conditions using static equilibrium adsorption experiments. Results showed that the equilibrium adsorption isotherms of dry soils did not fit the Langmuir equation or BET equation, but could be well fitted the Dubinin-Astakhov equation (R2 > 0.95). Parameters of the Dubinin-Astakhov equation were influenced by the characteristics of soils and VCHs. The affinity coefficients (beta) were not significant influenced by the molecular volumes of VCHs but tended to increase along with the increase in the molecular polarities. The adsorption energies (E0) of the reference compound (tetrachloroethylene) positively correlated to the pore volume with radius below the average (V(< average pore radius)), while poorly related to the average pore radius of the soil. The maximum adsorption volumes of VCHs onto dry soils (W0) showed linear relationship to the pore volume with radius less than 10 nm (V(< 10nm)), while poorly correlated to the specific surface area of the soil. The Dubinin-Astakhov equation, a function of V < average pore radius), V(<10nm) and beta, could be used to predict the equilibrium adsorbed amounts of VCHs onto the dry soils. The predicted values strongly correlated with the measured values (R2 = 0.98).