Surface complexation constants describing Pu(IV)/Pu(V) sorption to aluminol and silanol groups were developed from the silica and gibbsite sorption experiments and applied to the montmorillonite dataset, inclusion of the Pu(IV)/Pu(V) redox couple into modelling efforts, Pu(IV)/Pu(V) redox couple based upon the reaction Pu4+ + 0.25 O2 + 1.5 H2O <=> PuO2+ + 3 H+ with logK = 3.439