INTERACTION OF CARBOXYLIC ACIDS WITH FRESH AND AGED FERRIHYDRITE, GOETHITE AND HEMATITE: ZWITTERION EFFECTS

The state in which non-amino carboxylic acids and amino acids exist in the natural environment varies. The non-amino carboxylic acids are usually in their anionic states whereas the amino acids exist as zwitterions. These variations influence the interaction of peptide-rich and peptide-deficient organic matter with minerals in the environment. To interpret these variations, the research explored the sorption of non-amino and amino carboxylic acids to fresh ferrihydrite (FFh) and aged ferrihydrite (AFh), goethite, and hematite using UV-Vis Spectrophotometry and flow adsorption microcalorimetry. So far, we have analyzed the sorption of the non-amino carboxylic acid, acetate (C₂H₃O₂Na.3H₂O), and its amino analog, glycine (C₂H₄NNaO₂), at pH 5 on FFh and AFh. The results indicate very different behaviors in the quantity sorbed and evolution of the sorption process. On the FFh, for example, the quantity of acetate sorbed (3.5 mmol g^-1) was about twice that of glycine (1.5 mmol g^-1) while on the AFh the amount of acetate (1.3 mmol g^-1) sorbed was approximately six times less than that of glycine (6.0 mmol g^-1). Although the amount of glycine sorbed to FFh was lower, results from flow adsorption calorimetry indicate far more complex evolutionary patterns in its sorption compared to acetate. For example, while only three sequential sorption steps were discernible with acetate, a total of 8 was discernible with glycine. The variation in the amount sorbed and the sorption dynamics is attributable to differences in surface properties of the ferrihydrite and the potential for ionic polymerization of the glycine zwitterion. In the next phase of the presentation, we will further explore the sorption behaviors of acetate and glycine on goethite and hematite. Additionally, the presentation will further cover the energy exchange as non-amino carboxylic acids and amino acids interact with ferrihydrite, goethite, and hematite.