Fig. 1:Surface proton density of kaolinite obtained by surface titration. (a) Comparison of titration curves at 25°C. (b) Recalculation of the titration curves so the proton surface concentrations would be zero at pH=5 (see text). (c) An enlargement of the pH range of 3 to 5 of Fig. ý1b. Source data: W&S 1992 - Wieland and Stumm (2); BCN 1996 - Brady et al. (4); HCW 1998 - Huertas et al. (11); W&B 1998 - Ward and Brady (8); S&S 1997 - Schroth and Sposito (5).