Binary and ternary uranium(vi) humate complexes studied by attenuated total reflection Fourier-transform infrared spectroscopy

Abstract

The complexation of U(VI) with humic acid (HA) in aqueous solution has been investigated at an ionic strength of 0.1 M (NaCl) in the pH range between pH 2 and 10 at different carbonate concentrations by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. For the first time, the formation of binary and ternary U(VI) humate complexes was directly verified by in situ spectroscopic measurements. The complex formation constants for the binary U(VI) humate complex (UO₂HA(II)) and for the ternary U(VI) mono hydroxo humate complex (UO₂(OH)HA(I)) as well as the ternary U(VI) dicarbonato humate complex (UO₂(CO₃)₂HA(II)⁴⁻) determined from the spectroscopic data amount to log β_0.1 M = 6.70 ± 0.25, log β_0.1 M = 15.14 ± 0.25 and log β_0.1 M = 24.47 ± 0.70, respectively, and verify literature data.