Characteristics and mechanism of uranium photocatalytic removal enhanced by chelating hole scavenger citric acid in a TiO.sub.2 suspension system

Polycarboxylic acid acts as hole scavenger and chelating agent, which is essential for the photocatalytic removal of multivalent metal ions. The photocatalytic uranium removal, role of chelating hole scavenger citric acid (CA), and removal mechanism were investigated in a TiO.sub.2 suspension system. The results show that chelating agent CA is an efficient hole scavenger. The maximum removal efficiency of U(VI) reaches up to 98.6%. The uranium-bearing precipitates contains Na[(UO.sub.2)(Cit)], UO.sub.2, or UO.sub.4·2H.sub.2O. The mechanisms for the photocatalytic removal of U(VI) and the role of CA are discussed. These results suggest that proper chelating hole scavengers can promote and regulate the photocatalytic removal of multivalent metal ions.