Macroscopic and spectroscopic characterization of uranium(VI) sorption onto orthoclase and muscovite and the influence of competing Ca²⁺

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• 作者：Constanze Richter ^{constanze.richter@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Katharina Mü ; ller ^{k.mueller@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Bjö ; rn Drobot ^{b.drobot@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Robin Steudtner ^{r.steudtner@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Kay Groß ; mann ^{k.grossmann@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Madlen Stockmann ^{m.stockmann@hzdr.de" class="auth_mail" title="E-mail the corresponding author} ; Vinzenz Brendler ; ^{v.brendler@hzdr.de" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Sorption ; Uranium ; Orthoclase ; Muscovite ; Calcium ; TRLFS ; ATR FT-IR ; PARAFAC ; SCM
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2016
• 出版时间：15 September 2016
• 年：2016
• 卷：189
• 期：Complete
• 页码：143-157
• 全文大小：726 K

文摘

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 Ca²⁺ 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 Ca²⁺ at pH ⩾ 8 up to 30% due to the formation of the neutral aqueous Ca₂UO₂(CO₃)₃ (aq) complex. TRLFS measurements on the supernatant confirmed the predominance of this Ca₂UO₂(CO₃)₃ (aq) complex in accordance with thermodynamic calculations. Furthermore, TRLFS measurements on the mineral suspension as a function of pH (4–9) and Ca²⁺ revealed the existence of several species. Parallel factor analysis (PARAFAC) indicated the formation of three surface species totally. In the absence of Ca²⁺, the XOUO₂⁺ and XOUO₂CO₃⁻ surface complexes were formed, whereas the presence of Ca²⁺ leads to the formation of XOUO₂⁺ and XOUO₂OH as the formation of the aqueous Ca₂UO₂(CO₃)₃ (aq) complex reduces the free UO₂²⁺ concentration in the solution. In addition, ATR FT-IR spectroscopy confirmed an outer-sphere surface species in the absence of Ca²⁺. 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 Ca²⁺. Namely, $\log K_{\text{<glyph name="tbnd"></glyph>XO<glyph name="sbnd"></glyph>}{\text{UO}}_2^{+}}=1.69$ and $\log K_{\text{<glyph name="tbnd"></glyph>XO<glyph name="sbnd"></glyph>}{\text{UO}}_2{\text{CO}}_3^{-}}=8.96$ were determined for sorption onto orthoclase, whereas $\log K_{\text{<glyph name="tbnd"></glyph>XO<glyph name="sbnd"></glyph>}{\text{UO}}_2^{+}}=0.41$ and $\log K_{\text{<glyph name="tbnd"></glyph>XO<glyph name="sbnd"></glyph>}{\text{UO}}_2{\text{CO}}_3^{-}}=8.71$ best describe sorption onto muscovite in the absence of Ca²⁺.