Chemodynamic behavior of complex mixtures: Liquid-liquid partitioning and sorption of organic contaminants from mixed solvents

Contamination of soils and water at waste disposal sites commonly involves various combinations of nonpolar or hydrophobic organic chemicals (HOCs) and hydrophobic ionogenic organic chemicals (HIOCs), as well as mixtures of water and one or more organic cosolvents (either completely or partially miscible in water). Emphasis of this work was on understanding the chemodynamics of such complex mixtures, specifically solubility and sorption. Experimental and theoretical analysis presented has focused on (i) liquid-liquid partitioning behavior of aromatic hydrocarbons between environmentally-relevant organic immiscible liquids (OILs) and water and (2) the solubility and sorption of HIOCs by soils from completely miscible organic solvent/water mixtures.; Partition coefficients for several HOCs were either measured or compiled from the literature for a wide range of OILs (e.g., gasoline, diesel fuel, motor oil, and coal tar). The use of the UNIFAC (UNIQUAC Functional Group Activity Coefficient) model to estimate the likely nonidealities resulting from interactions between components in these complex OILs is also presented. Both the UNIFAC simulations and the observed OIL-water partition coefficients suggest that nonideality is sufficiently small. Thus, the use of Raoult's law convention for activity coefficients in conjunction with super-cooled liquid solubilities was considered adequate in assessing the partitioning of HOCs between several OILs and water.; The role of solute hydrophobicity and acidity, solvent type, and pH on the sorption of organic acids by a surface soil from mixed solvents was investigated. Predictions of a model that incorporated effects of cosolvent-enhanced solubility and cosolvent-suppressed speciation were compared to measured data. Sorption of neutral benzoic acid was observed to decrease with increasing methanol content, while benzoate sorption increased. Effects of specific solvent and solute properties were investigated by measuring (1) benzoic acid sorption from additional binary mixtures of water and cosolvents with a wide range in solvent properties and (2) sorption of several substituted carboxylic acids from methanol/water solutions. Of the different solute-solvent combinations investigated, enhanced sorption by soils was only observed with carboxylic acids in the presence of methanol or dimethylsulfoxide (DMSO). It was postulated that enhanced sorption resulted from hydrogen-bonding interactions combined with the formation of heterogeneous solvation shells about the solute and the sorbent.