Wf. Jaynes et Gf. Vance, BTEX SORPTION BY ORGANO-CLAYS - COSORPTIVE ENHANCEMENT AND EQUIVALENCE OF INTERLAYER COMPLEXES, Soil Science Society of America journal, 60(6), 1996, pp. 1742-1749
Aqueous organic contaminants, such as gasoline-derived aromatics, are
effectively sorbed by organo-clays. Organo-clays were prepared from mo
ntmorillonite (SWy-1, SAz-1) and vermiculite (VSC) clay minerals by ex
changing quaternary, alkylammonium cations for the inorganic exchange
cations; thus, a variety of clay-charge/organiccation combinations wer
e formed. Dodecyltrimethylammonium (DTMA), hexadecyltrimethylammonium
(HDTMA), didodecyldimethylammonium (DDDMA), and dioctadecyldimethylamm
onium (DODMA) organic cations were used. An aqueous mixture of BTEX (b
enzene, toluene, ethylbenzene, xylenes) consistent with unleaded gasol
ine was used to relate organo-clay sorptivity to structure. Greater so
rption of the BTEX mixture constituents than the pure compounds occurr
ed when total sorbed BTEX loadings on the organo-clays exceeded 10 g/k
g. A cosorption effect caused curvilinear isotherms and enhanced BTEX
mixture sorption; BTEX sorption increased the organo-clay organic matt
er content, which promoted additional BTEX sorption. The sorptivities
of the organo-clays were generally proportional to the organic C conte
nts; although SAz-DDDMA and VSC-HDTMA, with 20 to 30% less C, had twic
e the BTEX sorptivity of SAz-DODMA and VSC-DDDMA. No relationship was
found between surface area and BTEX sorption. A straight-chain alkyl c
ation conferred five times greater BTEX sorption to an organo-clay tha
n did a comparable cyclic alkyl cation. This suggests that rearrangeme
nts in the alkyl groups may facilitate sorption in a manner analogous
to solvation. Organo-clay BTEX sorptivity was governed by the type of
alkylammonium complex; a paraffin complex with a 25.4 to 27.6 Angstrom
basal spacing was optimal. Organo-clays of similar basal spacing prep
ared using different clays and alkylammonium cations had equivalent so
rptive phases. Selection of an appropriate combination of clay and org
anic cation can optimize contaminant sorption by organo-clays.