Temperature‒dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH‒range

2026-06-20T02:13:54Z https://rodare.hzdr.de/oai2d

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true 3.1 HZDR.RODARE 10.14278/rodare.211 Lösch, Henry HZDR Raiwa, Manuel Institute of Radioecology and Radiation Protection, Leibniz Universität Hannover Jordan, Norbert 0000-0002-4625-1580 HZDR Steppert, Michael Institute of Radioecology and Radiation Protection, Leibniz Universität Hannover Steudtner, Robin HZDR Stumpf, Thorsten HZDR Huittinen, Nina Maria HZDR Temperature‒dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH‒range Rodare 2020 luminescence silicates Uranium(VI) complexation thermodynamic constants temperature dependent 2020-01-06 en https://rodare.hzdr.de/record/211 https://www.hzdr.de/publications/Publ-29643 10.14278/rodare.210 https://rodare.hzdr.de/communities/rodare Version_1_2020-01-06 Creative Commons Attribution 4.0 International Open Access In this study the complexation of U(VI) with orthosilicic acid (H4SiO4) between pH 3.5 and 5 with electrospray ionization mass spectrometry (ESI‒MS) and laser‒induced luminescence spectroscopy was comprehensively characterized. The ESI‒MS experiments performed at a total silicon concentration of 5∙10‒5 M (exceeding the solubility of amorphous silica at both pH‒values) revealed the formation of oligomeric sodium‒silicates in addition to the UO2OSi(OH)3+ species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5∙10‒6 M, the silicon concentration was varied between 1.3∙10‒4 ‒ 1.3∙10‒3 M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO4. The results confirmed the formation of the aqueous UO2OSi(OH)3+ complex. The conditional complexation constant at 25 °C, log *β = ‒0.31± 0.24, was extrapolated to infinite dilution using the Davies equation, which led to log *β0 = ‒0.06 ± 0.24. Further experiments at different temperatures (1 – 25 °C) allowed the calculation of the molal enthalpy of reaction ΔrHm0 = 45.8 ± 22.5 kJ∙mol‒1 and molal entropy of reaction ΔrSm0 = 152.5 ± 78.8 J∙K‒1∙mol‒1 using the van’t Hoff equation, corroborating an endothermic and entropy driven complexation process.