挥发性氯代烃在干燥土壤中的平衡吸附研究

Study on Equilibrium Adsorption of Volatile Chlorinated Hydrocarbons on Dry Soils

吸附是挥发性氯代烃(volatile chlorinated hydrocarbons,VCHs)污染土壤的主要机制之一.采集长三角地区3类典型水稻土,用静态平衡吸附实验进行干燥土壤对6种VCHs的平衡吸附研究.结果表明,干燥土壤的平衡吸附等温线难以用Langmuir方程和BET方程描述,但用Dubinin-Astakhov方程拟合良好(R2>0.95).Dubinin-Astakhov方程参数受土壤和VCHs特性的影响.亲和系数β与VCHs分子体积之间没有发现明显的相关性,但β随VCHs分子极性的增大有变大的趋势;参照化合物(四氯乙烯)的吸附能E0与土壤小于平均孔径的孔体积(V<平均孔径)成正相关,但与土壤的平均孔径关系不大;干燥土壤对VCHs的最大吸附体积W0与孔径<10 nm的孔体积(V<10 nm)呈线性关系,但与土壤比表面积相关性较差.干燥土壤的平衡吸附量可以用与V<平均孔径、V<10 nm和β相关的Dubinin-Astakhov方程进行预测.预测值与实测值拟合良好,判定系数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（R20.95）.Parameters of the Dubinin-Astakhov equation were influenced by the characteristics of soils and VCHs.The affinity coefficients（β） 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（Vaverage 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（V10nm）,while poorly correlated to the specific surface area of the soil.The Dubinin-Astakhov equation,a function of Vaverage pore radius,V10nm and β,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）.