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Researchers from Italy investigated the effects of humic acid on U(VI) reduction in aqueous solutions using laser induced fluorescence.

Irradiation-induced uranium(VI) reduction to uranium(IV) in a titanium dioxide solution has been found to involve only adsorbed uranium species. Time-resolved laser-induced fluorescence was used both as a monitor and an energy source for the reaction experiments and results also show that uranium reduction is possible even in an oxygenated medium and that the mechanisms in play may also have counterparts in oxic-photic zone of surface waters.

Synchronous and time-resolved fluorescence techniques proved useful in the investigation of low concentration metal ion-humic acid (HA) interactions. Comparable values of intrinsic binding constants for Tl(III) and Cr(III), regardless of pH, metal:ligand ratio and fluorescence method used, were obtained with the use of an electrostatic discrete site approach. Tl(III) and Cr(III) complexation results also revealed that other species may also bind to humic acids beside the aquo ion and the first hydroxo complex.

Synchronous and time-resolved techniques proved useful in the investigation of low concentration metal ion-humic acid (HA) interactions. Comparable values of intrinsic binding constants for Tl(III) and Cr(III) can be obtained by modeling the experimental data with an electrostatic discrete site approach. Results from the complexation of the two metals with groundwater HA indicated that other species may also bind to HA aside from the aquo ion and the first hydroxo complex.

The ability of humic acid to function as a sensitizer during photoinduced reduction of Cr(VI) to Cr(III) in suspensions containing ZnO particles was investigated using equilibrium sorption studies. The results showed that Cr(VI) adsorption on ZnO was very low while Cr(III) was completely adsorbed on ZnO. Cr(VI) photoreduction was induced by solar irradiation and it led to a substantial increase in the volume of Cr adsorbed on the mineral oxide.