Mechanism(s) Controlling Sorption of Neutral Organic Contaminants by Surfactant-Derived and Natural Organic Matter

Abstract

Layer silicate clays modified with cationic surfactants (organoclays) such as hexadecyltrimethylammonium (HDTMA) are effective sorbents for neutral organic contaminants (NOCs) and may be useful for in-situ and ex-situ remediation of contaminated soils and waters. In this study, the sorptive characteristics of organoclays were compared in terms of magnitude and mechanism to those of natural soil organic matter. The data presented here support multiple mechanisms controlling the sorption of aqueous-phase NOCs on organoclays including solvation of the cationic ammonium centers, the alkyl chains of HDTMA, and the mineral surfaces and solute partitioning. In contrast, solute partitioning appears to be the singular mechanism for the sorption of aqueous-phase NOCs by natural soil organic matter. Organic contaminant sorption by the surfactant-derived organic matter of organoclays is substantially higher than by natural soil organic matter due to the existence of multiple sorptive mechanisms for organoclays and the greater solvency of their organic phases.

Effect of lead on the sorption of phenol onto montmorillonites and organo-montmorillonites

“…This caused the solvency (i.e., the solubilization capability) of HDTMA phase for phenol to increase, so that the isotherms became convex to the abscissa. A similar phenomenon was observed for the partition of trichloroethylene and chlorobenzene by HDTMA-clays [43]. On the other hand, phenol sorption by homoionic montmorillonites is due to specific sorption to the negatively charged surface of clays and the sorption capacity is much lower than that by partition to HDTMAmontmorillonites.…”

New insights into surface-functionalized swelling high charged micas: Their adsorption performance for non-ionic organic pollutants

“…6a) show a nonlinear behavior. This behavior was previously observed on HDTMA-smectite and it was attributed to that in addition to solute partitioning into de organoclay, solvation of the alkylammonium and the mineral surfaces occur [33]. The percentage of NOCs removed relative to the initial concentration (Fig.…”

“…Smith et al [32] demonstrated that small organic cations create a relatively rigid, nonpolar surface amenable to NOC uptake by sorption and, hence, a surface characterized by a relatively high NOC uptake; in contrast, large organic cations create an organic partition medium for NOC uptake that provokes a relatively low NOC uptake. Moreover, Sheng et al [33] indicated that organoclays have multiple sorptive mechanisms and the sorption of aqueous-phase NOCs is controlled by solvation of cationic ammonium centers, the alkyl chain of organic cation, the clay surfaces and solute partitioning. Table 2 shows the distribution coefficient, Kd, and the normalized coefficient to the organic content, Kom.…”

“…After phenol sorption, the main reflection, 001, shows minor changes in the width and moves slightly, however, the organomica remains highly expanded and ordered. Sheng et al [33], have found that aromatic compounds, due to their flat shape and presence of π-bond, interact strongly with the organic cation in the organoclay, causing a reorientation of the alkyl chains when alkylammonium cations lie parallel to the sheets of silicate and the alkylammonium adopted a vertical position. In Cm-Mica-4 the organization of the alkylammonium cations corresponds to inclined bilayers [19] and thus, phenol sorption do not affect to the arrangement of alkylammonium cations.…”

Surfactant Modified Zeolite from Cyclone Ash as Adsorbent for Removal of Reactive Orange 16 from Aqueous Solution

“…The aromat ic and sulfonate groups of organic co mpounds and their planar shape and delocalized -bonds interact strongly with ammon iu m centers of HDTMA [33,34,35].…”