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Isaak Lapides, Shmuel Yariv - Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel

Sorption of organic compounds on natural and modified soil sorbents may be significantly influenced by the sorbent hydration. Considerable work was performed on the effect of hydration on sorption of organic compounds by soils, soil minerals, soil organic matter and humic materials. Less is known about the way hydration affects the thermodynamics of sorption of organic compounds on modified, organic cation-exchanged clays. Thus, the present paper examines sorption of selected probe organic compounds on different HDTMA (hexadecyl-trimethylammonium)-exchanged bentonites from water (i.e., on a "wet" sorbent) and from an inert solvent, n-hexadecane (i.e. on a "dry" sorbent). The probe compounds were chosen to form a series of sorbates with an increasing ability to undergo molecular interactions as demonstrated by sorption measurements in an inert solvent. Hydration effect on sorbate interactions in the sorbent phase is extracted from aqueous and n-hexadecane-based sorption isotherms, using a solute activity scale. Organoclay hydration significantly suppresses the interactions of a "less polar" organic compound. A similar observation was previously reported for water-competitive sorption of non-polar organic compounds by small organic cation-based organoclays. In contrast, organoclay hydration may have no distinct reducing effect on sorption (or even enhance sorption) of organic sorbates capable of stronger specific interactions. Basal spacing of organoclays loaded with the probe organic compounds from different liquid media was determined to reveal possible mechanisms that may result in an apparent decrease of the hydration-induced sorption suppression. It appears that the diminishing (or disappearance) of the hydration-induced suppressive effect on sorption correlates with an increasing potential of a sorbate to undergo molecular interactions (and hence to compete effectively with water for sorption sites). Hydration-induced change of the organoclay polarity and hydration-enhanced breaking of sorbent aggregates which exposes new sorption sites may also contribute to the lessening of the hydration-induced suppression of organic compound sorption.

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Hydration Effect on Interactions of Organic Compounds with Organoclays.

Isaak Lapides, Shmuel Yariv - Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel

Sorption of organic compounds on natural and modified soil sorbents may be significantly influenced by the sorbent hydration. Considerable work was performed on the effect of hydration on sorption of organic compounds by soils, soil minerals, soil organic matter and humic materials. Less is known about the way hydration affects the thermodynamics of sorption of organic compounds on modified, organic cation-exchanged clays. Thus, the present paper examines sorption of selected probe organic compounds on different HDTMA (hexadecyl-trimethylammonium)-exchanged bentonites from water (i.e., on a "wet" sorbent) and from an inert solvent, n-hexadecane (i.e. on a "dry" sorbent). The probe compounds were chosen to form a series of sorbates with an increasing ability to undergo molecular interactions as demonstrated by sorption measurements in an inert solvent. Hydration effect on sorbate interactions in the sorbent phase is extracted from aqueous and n-hexadecane-based sorption isotherms, using a solute activity scale. Organoclay hydration significantly suppresses the interactions of a "less polar" organic compound. A similar observation was previously reported for water-competitive sorption of non-polar organic compounds by small organic cation-based organoclays. In contrast, organoclay hydration may have no distinct reducing effect on sorption (or even enhance sorption) of organic sorbates capable of stronger specific interactions. Basal spacing of organoclays loaded with the probe organic compounds from different liquid media was determined to reveal possible mechanisms that may result in an apparent decrease of the hydration-induced sorption suppression. It appears that the diminishing (or disappearance) of the hydration-induced suppressive effect on sorption correlates with an increasing potential of a sorbate to undergo molecular interactions (and hence to compete effectively with water for sorption sites). Hydration-induced change of the organoclay polarity and hydration-enhanced breaking of sorbent aggregates which exposes new sorption sites may also contribute to the lessening of the hydration-induced suppression of organic compound sorption.

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