Multinuclear Complex Formation between Ca(II) and Gluconate Ions in Hyperalkaline Solutions

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• 作者：Attila Pallagi ; 脡va G. Bajn贸czi ; Sophie E. Canton ; Trudy Bolin ; G谩bor Peintler ; Bence Kutus ; Zolt谩n Kele ; Istv谩n P谩link贸 ; P谩l Sipos
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：June 17, 2014
• 年：2014
• 卷：48
• 期：12
• 页码：6604-6611
• 全文大小：405K
• 年卷期：v.48,no.12(June 17, 2014)
• ISSN：1520-5851

文摘

Alkaline solutions containing polyhydroxy carboxylates and Ca(II) are typical in cementitious radioactive waste repositories. Gluconate (Gluc^{鈥?/sup>) is a structural and functional representative of these sugar carboxylates. In the current study, the structure and equilibria of complexes forming in such strongly alkaline solutions containing Ca2+ and gluconate have been studied. It was found that Gluc鈥?/sup> significantly increases the solubility of portlandite (Ca(OH)₂(s)) under these conditions and Ca2+ complexes of unexpectedly high stability are formed. The mononuclear (CaGluc+ and [CaGlucOH]0) complexes were found to be minor species, and predominant multinuclear complexes were identified. The formation of the neutral [Ca₂Gluc(OH)₃]0 (log 尾₂₁₃ = 8.03) and [Ca₃Gluc₂(OH)₄]0 (log 尾₃₂₄ = 12.39) has been proven via H₂/Pt-electrode potentiometric measurements and was confirmed via XAS, 1H NMR, ESI-MS, conductometry, and freezing-point depression experiments. The binding sites of Gluc鈥?/sup> were identified from multinuclear NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms were proved to be the most probable sites for Ca2+ binding. The suggested structure of the trinuclear complex was deduced from ab initio calculations. These observations are of relevance in the thermodynamic modeling of radioactive waste repositories, where the predominance of the binuclear Ca2+ complex, which is a precursor of various high-stability ternary complexes with actinides, is demonstrated.}