| Popis: |
Ten small halogenated hydrocarbons were adsorbed from aqueous solutions by montmorillonite clay and fumed silica, at halocarbon concentrations from 0.05–10 mg/liter. The compounds studied were bromodichloromethane; carbon tetrachloride; 1,1,2-trichloroethane; 1,1,2,2-tetrachloroethane; trichloroethene; tetrachloroethene; 1,2-dibromoethane; 1,2-dichlorobenzene; 2-bromotoluene; and 4-bromotoluene. The affinity of the adsorbents for the halocarbons was in the order citrate-bicarbonate-dithionite (CBD)-treated montmorillonite > silica > untreated montmorillonite. Of the compounds tested, tetrachloroethane and trichloroethene were adsorbed to the greatest extent by CBD-treated montmorillonite. The quantity of trichloroethene and tetrachloroethane adsorbed by CBD-treated montmorillonite was about an order of magnitude higher than the quantity of saturated or aromatic halocarbons adsorbed. The untreated montmorillonite adsorbed aromatic halocarbons and the two chloroethenes but not the saturated halocarbons. Silica adsorbed all the halocarbons tested. However, there was no apparent correlation between halocarbon molecular properties and adsorption to silica. Adsorption of tetrachloroethane and 1,2-dichlorobenzene by CBD-treated montmorillonite was irreversible, whereas adsorption of these two compounds by fumed silica was reversible. These results suggest that the adsorption of halocarbons from water by montmorillonite is a chemisorption and that by silica is a physisorption. |
