The determination of the thermodynamic constants of MgUO(CO) complex in NaClO and NaCl media by time-resolved luminescence spectroscopy, and applications in different geochemical contexts.

The formation constants and specific ion interaction coefficients of MgUO(CO) complex were determined in 0.1 to 1.0 mol kg NaCl and 0.10 to 2.21 mol kg NaClO media in the framework of the specific ion interaction theory (SIT), by time-resolved laser-induced luminescence spectroscopy. The upper limits of ionic strength were chosen in order to limit luminescence quenching effects generated by high concentrations of Cl and ClO already observed during our earlier studies on CaUO(CO) complexes (Shang & Reiller, Dalton Trans., 49, 466; Shang et al., Dalton Trans., 49, 15443). The cumulative formation constant determined is , and the specific ion interaction coefficients are ε(MgUO(CO), Na) = 0.19 ± 0.11 kg mol in NaClO and ε(MgUO(CO), Na) = 0.09 ± 0.16 kg mol in NaCl. Two gratings of 300 and 1800 lines per mm were used to acquire MgUO(CO) luminescence spectra, where the high-resolution 1800 lines per mm grating detected slight spectral shifts for the principal luminescent bands relative to CaUO(CO). The applications of the consistent set of thermodynamic constants and ε values for MUO(CO) (M = Mg and Ca) were examined in different geochemical contexts, where Mg over Ca concentration ratio varies to help defining the relative importance of these species.