COSOLVENT EFFECTS ON SORPTION OF ORGANIC-ACIDS BY SOILS FROM MIXED-SOLVENTS

Sorption of substituted phenols and carboxylic acids by soils was measured from methanol/water solutions. These data were used to assess a cosolvency model thal incorporated changes in organic acid speciation as a function of soil-solution pH and the conditional pK(a) values observed in mixed solvents. For the chlorophenols, the cosolvency model with speciation adequately described the log-linear decrease in sorption with increasing volume fraction cosolvent (f(c)). For the carboxylic acids, the magnitude of sorption observed in methanol/water solutions could not be predicted by incorporating speciation effects into the cosolvency model. The contribution of other mechanisms, involving various solute/solvent and solvent/sorbent interactions, to the observed deviations from model predictions is discussed.