SYNTHESIS AND CHARACTERIZATION OF MODEL AQUATIC PARTICULATES FOR USE IN SORPTION STUDIES

The synthesis and characterization of single- and multi-component model aquatic particulars is the object of this dissertation. Particulates were synthesized from illite, humic and fulvic acids, and iron, aluminum, and manganese hydrous oxides. Characterization included measurement of cation exchange capacity (CEC), and attempts to determine surface area and the pH of zero point of charge. Each of these methods was tested to determine their applicability to aquatic particulates, and attempts were made to improve the methodology. CEC varied with composition and time of aging. Pure hydrous oxides exhibited decreases in CEC over time. Aging effects were also shown by aluminum hydrous oxide-clay mixtures. The CEC of iron hydrous oxide-clay particulates increased with iron content on the clay. Similar trends in CEC with composition were observed for organic matter-containing particulates. CEC data, in conjunction with compositional data, suggested that hydrous oxide-clay particulates had a limited adsorption capacity for organic matter. Attempts to measure surface area through adsorption of cationic dyes were unsuccessful. Dye adsorption on illite varied with the square root of the ionic strength of the dye solution. This trend was interpreted in terms of a simple model of charge density at the solid-solution interface and Gouy-Chapman theory. For metal hydrous oxide-containing particulates, the apparent surface area also depended on pH. This was indicative of a greater proportion of pH-dependent charged surfaces than with illite. In addition, a fluorescence method for determining the solution concentration of dye is presented. This method eliminates errors due to colloidal scattering and absorption by dye bound to colloids. The presence of colloids in supernatant solutions in a common problem in absorbance measurements. Zero point of charge measurements for pure metal hydrous oxides agreed with values reported in the literature. However, attempts to measure the zero point of charge using acid-base titration were unsuccessful for clay-containing particulates. This failure was attributed to the non-specific adsorption of hydronium ions and the presence of a permanent exchange capacity