CHARACTERIZATION OF MULTIPLE FUNCTIONAL-GROUPS ON KAOLINITE

Multiple proton functional group conditional binding constants (K'(t) and their concentrations (C'1) are determined from detailed acid/base titration data. The C-K' information is obtained for kaolinite by assuming that the distribution can be approximated by cumulative independent mono protic groups, Linear programming optimization techniques are used to fit the data. In addition, the electrode calibration is optimized in the data fit. This adjustment is important for high and low pHs. Discrete concentration dependent pKs of about 3.4, 4.5, 6.7 and 9.8 are determined for a reference kaolinite. These correspond reasonably well to designations made by Wehrli et al. (1990, Aquatic Sciences, Vol. 52, pp. 1-31) to AlOH2 and AlOH proton reactions at edge and surface sites and to silanol exchange. There is an ionic strength effect for one site. Long and short reaction times and reversibility affect the results.