Humic acid-modified silica as a model aquifer material

The sorption behavior of nonionic organic chemicals on humic acid-modified silica was examined to assess its possible use as a simplified model of natural low organic carbon aquifer materials. Column and batch sorption experiments were conducted on humic acid-coated silica (0.073% organic carbon), using tetrachloroethylene (PCE) and 1-methylnaphthalene (MN). Batch kinetic experiments showed that equilibrium was attained rapidly for PCE (˜1 d), whereas several tens of days were required for MN. Batch experiment results indicated Freundlich (nonlinear) isotherm behavior when a wide concentration range was examined. Sorption coefficients derived from the column experiments were consistent with the batch-derived Freundlich isotherms, illustrating the importance of isotherm type on breakthrough curves and solute transport in ground water. Similarities exist between the sorption behavior observed in this study and that of a number of natural aquifer materials. Humic acid-modified silica serves as a simplified model for aquifer materials, which tend to be more complex and difficult to characterize and can be used to examine organic solute transport processes in ground water.