SORPTION OF TANNIC-ACID, PHENOL, AND 2,4,5-TRICHLOROPHENOL ON ORGANOCLAYS

Sorption of the organic pollutants phenol, 2,4,5-trichlorophenol, and tannic acid (Fluka) onto montmorillonite-based sorbents was studied. T he sorbents were homoionic Na- or Ca-montmorillonite, montmorillonite completely exchanged with the cationic organic surfactant dimethyldist earylammonium chloride (or DDA-M), and DDA-M partially re-exchanged wi th Ca2+ (Ca-DDA-M). The influence of pH on sorption of phenol and tric hlorophenol was also investigated. The sorption capacities for phenol, trichlorophenol, and tannic acid were significantly enhanced by surfa ctant treatment of the homoionic clay. Uptake onto the organoclays inc reased in the order phenol < tannic acid < trichlorophenol, which corr esponds to the order of increasing hydrophobicity. The significant rol e played by hydrophobicity was also observed in pH effects which gener ally favored sorption when the pH was low enough to assure that the un charged (protonated) species was predominant. In the case of trichloro phenol, sorption could be shown to be quantitatively attributable to t he neutral species. The results of X-ray diffraction measurements show ed increased d001 spacings when the DDA was intercalated into the inte rlamellar spaces, increasing the available sorbent porosity. This, and the linkage of uptake to solute hydrophobicity, indicates that uptake is by a partitioning mechanism, though non-linear isotherms may be ca used by site limitations. Surprisingly, if a portion of the intercalat ed DDA is removed by exchange with Ca2+, the d001 spacing decreases bu t the sorption capacity of the organoclays is improved. One possible m echanism is improved elementary sheets cohesion due to calcium ions, i mparting molecular sieve characteristics to the solid. The extent and possible selectivity of sorption using these organoclays suggests that they may provide an alternative to activated carbon sorbents in water treatment.