Sorption of nonpolar and polar organics on dicetyldimethylammonium-bentonite

Abstract

Sorptions of four nonpolar, nonionic organic compounds (ben zene, toluene, ethylbenzene and o-xylene (BTEX)), and four polar, ionizable phenolic compounds (phenol, 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol) on dicetyldim ethylammonium (DCDMA) bentonite were determined in single-, binary-, ternary- and quaternary-solute systems. Uptake onto the DCDMA-bentonite increases in the order: benzene < toluene < ethylbenzene < o-xylene, which corre sponds to the order of increasing hydrophobicity. The sorption isotherms in a single-solute system show that the uptake is highly linear, well correlated with solubility and pH indepen dent, which suggests the sorption mechanism is perhaps due to partitioning. Therefore, the competition seen among other sol utes in the uptake of BTEX is unexpected. By comparison, the uptake of phenolic compounds increases in the order: phenol < 2 chlorophenol < 2,4-dichlorophenol < 2,4,6-trichlorophenol. Moreover, sorption isotherms are nonlinear, pH dependent and competitive, which indicates that the uptake may be a result of both partitioning and site specific adsorption. The impact of solution pH on the sorption of phenolic compounds that can be protonated or deprotonated to various extents depending on their pKa is also observed.