title: Adsorption of aspartic acid on kaolinite.
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 degrees C, 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; 10-18% of 100 microM aspartic acid adsorbed to kaolinite at 100 m(2)L(-1) between pH 3 and 10. Data from the titrations and adsorption experiments were fitted closely by an extended constant-capacitance surface complexation model, in which monodentate outer-sphere complexes formed between deprotonated 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.
authors.affiliation: Colloid and Environmental Chemistry Laboratory, La Trobe University, P.O. Box 199, Bendigo, Victoria 3552, Australia.
authors.forename: Jaslin
authors.initials: J
authors.lastname: Ikhsan
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Johnson
authors.forename: John D
authors.initials: JD
authors.lastname: Wells
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Angove