Macroscopic and spectroscopic characterization of uranium(VI) sorption onto orthoclase and muscovite and the influence of competing Ca2+. (15th September 2016)

• Record Type: Journal Article
• Authors: Richter, Constanze; Müller, Katharina; Drobot, Björn; Steudtner, Robin; Großmann, Kay; Stockmann, Madlen; Brendler, Vinzenz
• Is Part Of: Geochimica et cosmochimica acta. Volume 189(2016:Sep. 15)
• Page Start: 143
• Page End: 157
• Publication Date: 2016-09-15
• Subjects: Sorption -- Uranium -- Orthoclase -- Muscovite -- Calcium -- TRLFS -- ATR FT-IR -- PARAFAC -- SCM; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2016.05.045
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The uranium(VI) sorption onto orthoclase and muscovite, representing the mineral groups of feldspars and micas as important components of the earth crust, was investigated in the presence and absence of Ca 2+ under aerobic conditions. Batch experiments were accompanied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) as well as in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. The results indicate that the U(VI) sorption is reduced by Ca 2+ at pH ⩾ 8 up to 30% due to the formation of the neutral aqueous Ca2 UO2 (CO3 )3 (aq) complex. TRLFS measurements on the supernatant confirmed the predominance of this Ca2 UO2 (CO3 )3 (aq) complex in accordance with thermodynamic calculations. Furthermore, TRLFS measurements on the mineral suspension as a function of pH (4–9) and Ca 2+ revealed the existence of several species. Parallel factor analysis (PARAFAC) indicated the formation of three surface species totally. In the absence of Ca 2+, the XOUO2 + and XOUO2 CO3 − surface complexes were formed, whereas the presence of Ca 2+ leads to the formation of XOUO2 + and XOUO2 OH as the formation of the aqueous Ca2 UO2 (CO3 )3 (aq) complex reduces the free UO2 2+ concentration in the solution. In addition, ATR FT-IR spectroscopy confirmed an outer-sphere surface species in the absence of Ca 2+ . These experimental results were used for the assessment of surface complexation parameters to improve the basis for a mechanistic modeling of the sorption processes of U(VI) onto orthoclase and muscovite including the influence of Ca 2+ . Namely, log K XO UO 2 + = 1.69 and log K XO UO 2 CO 3 - = 8.96 were determined for sorption onto orthoclase, whereas log K XO UO 2 + = 0.41 and log K XO UO 2 CO 3 - = 8.71 best describe sorption onto muscovite in the absence of Ca 2+ .