Adsorption of dextrin at mineral/water interface

The adsorption mechanism of dextrin on aqueous minerals such as fluorite, apatite, galena, magnetite, gamma-alumina, and graphite was studied by adsorption experiments, zeta potential measurements, and FT-IR studies. Depending on the nature of the mineral surface, dextrin was found to interact in three different ways viz. by chemisorption, physisorption, or hydrophobic-hydrophobic interaction. The adsorption density of dextrin was found to be pH dependent. Maximum adsorption of dextrin was obtained around the pH at which the mineral surface is highly hydroxylated. The mechanism of dextrin interaction with the surface metal hydroxy sites, (=MeOH), was found to proceed via chemical complexation. A linear relationship was observed between the adsorption density of dextrin and the pH of maximum surface hydroxylation. Zeta potential measurements have indicated the possibility of dextrin adsorption by electrostatic interaction under the conditions where mineral surface and dextrin are oppositely charged. Furthermore dextrin was found to adsorb on hydrophobic minerals such as graphite by hydrophobic-hydrophobic interaction. However, the magnitude of adsorption by electrostatic and hydrophobic interaction was found to be very marginal compared to that of chemical complexation. (C) 1997 Academic Press.