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Colloidal hematite (α-Fe₂O₃) is used as model solid to investigate the kinetic effect of specific adsorption interactions on the chemical reduction of uranyl (U^VIO₂²⁺) by ferrous iron. Acid–base titrations and Fe(II) and uranyl adsorption experiments are performed on hematite suspensions, under O₂- and CO₂-free conditions. The results are explained in terms of a constant capacitance surface complexation model of the hematite–aqueous solution interface. Two distinct Fe(II) surface complexes are required to reproduce the data: (≡Fe^IIIOFe^II)⁺ (or ≡Fe^IIIOFe^II(OH₂)_n⁺) and ≡Fe^IIIOFe^IIOH⁰ (or ≡Fe^IIIOFe^II(OH₂)_n−1OH⁰). The latter complex represents a significant fraction of total adsorbed Fe(II) at pH > 6.5. Uranyl binding to the hematite particles is characterized by a sharp adsorption edge between pH 4 and pH 5.5. Because of the absence of competing aqueous carbonate complexes, uranyl remains completely …