J. Ikhsan, B. B. Johnson, John D. Wells, M. J. Angove. (2004), 'Adsorption of Aspartic Acid on Kaolinite', Journal of Colloid and Interface Science, 273: 1-5.

ABSTRACT

The interaction of aspartic acid with kaolinite was studied by potentiometric titrations and by adsorption measurements both at constant aspartate concentration (but varying pH) and at a constant pH of 5.5. The temperature was 25 oC, and the ionic medium 5 mM KNO3. Aspartic acid dissociation constants estimated from titrations agreed with those from the literature. The adsorption of aspartic acid to kaolinite was weak, and varied only slightly with pH; 10 to 18% of 100 µM aspartic acid adsorbed to kaolinite at 100 m2 L-1 between pH 3 and pH 10. Data from the titrations and adsorption experiments were fitted closely by an extended constant-capacitance surface complexation model, in which monodentate outersphere complexes formed between deprontonated aspartic acid molecules and protonated sites on the variable-charge edges of the kaolinite crystals. There appeared to be no adsorption to the permanently-charged crystal faces.

Keywords: Aspartic acid, amino acid, dissociation constants, adsorption, kaolinite, surface, complexation, modeling, ECCM.