Characteristics of the sorption of humic acid by soil minerals

Abstract

The interaction of a humic acid with the minerals goethite, α-alumina, kaolinite, and silica was studied with respect to the solubility of the humic acid in the absence and presence of each of the minerals. The proton consumption associated with the interaction process was also determined for each mineral–humic acid system. The sorption of humic acid was found to be related to the nature of charge on the mineral surfaces, with positively charged surfaces sorbing the humic acid to a greater extent than negatively charged surfaces. The sorption process involving positively charged mineral surfaces was found to be associated with a consumption of protons as a consequence of the interaction, whereas that involving negatively charged mineral surfaces does not consume protons. The interaction between α-alumina and humic acid appears to involve aggregation of the mineral for the conditions used in this study. The pH at which the aggregated particles are dispersed decreased with increase in concentration of the background electrolyte.