EFFECT OF AL AND ORGANIC-ACIDS ON THE SURFACE-CHEMISTRY OF KAOLINITE

The cause of pH and ionic strength-dependent proton and hydroxyl adsor ption onto kaolinite is specific binding at edge Al and Si sites, and it can be modeled as a function of temperature with a triple layer mod el (TLM) of the mineral-solution interface. Exchange of Al for protons and hydroxyls is observed at low pH, with a stoichiometry approaching 1:3 (Al:H+). Adsorption of organic acids from dilute solutions depend s on: 1) solution pH; 2) the functionality of the acid; and, to a less er extent, 3) temperature. Such adsorption may occur primarily at Al s ites exposed on kaolinite edges, as indicated by sorption experiments on the constituent oxides, where negligible sorption was observed on S iO2 (quartz), but was significant on Al2O3 (corundum) surfaces. Under similar conditions, oxalate adsorbs more strongly than acetate or form ate to aluminol sites.