A total site density of 6.6 sites nm−2 (2.5 for each normal site and 0.8 for each subsurface site) was used by Hiemstra et al. A surface site density of 7 sites nm−2, close to the total surface site density used by Hiemstra et al., was chosen in this study.
Potentiometric titrations (pH range 5 to 9.5) were performed at 25 °C at different ionic strengths of NaCl (0.1, 0.05 and 0.01 mol L−1) with a Metrohm 736 GP Titrino titrator, at a mass to volume ratio of 30 g L−1 under Ar atmosphere.
≡AlOH0.5− + H+ ↔ ≡AlOH20.5+ log K° = 9.3
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