SYNERGISTIC EFFECT OF MINERAL SURFACE CONSTITUENTS IN DEXTRIN ADSORPTION

The present work is a part of a systematic research on the interaction mechanism between polysaccharides and mineral surfaces, and deals with the adsorption of dextrin onto oxide and salt-type minerals. The minerals tested include hematite, rutile, fluorite, calcite, apatite, etc. It is observed that dextrin adsorption on these minerals is strongly pH-dependent, with high adsorption densities at pH values around the isoelectric points of the minerals, which indicates interactions with surface metal hydroxide species. X-ray photoelectron spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements reveal chemical shifts of binding energies of core electrons, or chemical shifts of modified Auger parameters of mineral surface elements after dextrin adsorption, pointing to a chemical mechanism of interaction. Furthermore, it is observed that the reaction of minearls with moderate amounts of fatty acids prior to dextrin addition results in an increase in dextrin adsorption, whereas reaction with excessive fatty acids prior to dextrin addition results in a decrease in dextrin adsorption. In the light of the results of our previous studies, and also from the experimental observations of the present work, it is concluded that although surface hydrophobic species alone do not have any significant effect on dextrin adsorption, they synergistically enhance dextrin adsorption when present together with surface metallic sites.