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

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).