Competitive Interactions among Components of Humic Acids in Granular Activated Carbon Adsorption Systems:  Effects of Solution Chemistry

The adsorption by activated carbon of a humic acid extracted from Laurentian soil and polystyrene sulfonate, a synthetic polymer, was investigated. Size-exclusion chromatography was used to study competitive interactions among humic components by measuring the changes in molecular weight distributions of molecules remaining in solution after adsorption. The adsorption of humic substances was governed, in large part, by molecular size distribution in relation to adsorbent pore sizes. We demonstrate that the extent of adsorption increases with increasing ionic strength and calcium content. Increases in the extent of adsorption are due, in part, to a decrease in macromolecule size; our data suggest that these changes occur in solution prior to adsorption. The results of analyses employing size-exclusion chromatography demonstrate that low molecular weight fractions of humic material are preferentially removed from solution. Increases in the extent of adsorption correspond to shifts in the adsorbed molecular weight distribution to values.