Selenite and selenate uptaken in ettringite: Immobilization mechanisms, coordination chemistry, and insights from structure

Journal Article · Sun Oct 15 04:00:00 EDT 2017 · Cement and Concrete Research

DOI:https://doi.org/10.1016/J.CEMCONRES.2017.07.004· OSTI ID:22701575

Guo, Binglin; Sasaki, Keiko; Hirajima, Tsuyoshi

Although ettringite is a crucial material in terms of Se immobilization, the immobilization mechanisms, atomic configuration, and intercolumn structure of Se sorbed in ettringite are unclear. The immobilization mechanism of Se oxoanions was evaluated through structural insight into ettringite. It is contrasting between SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} in chemical property of the solid residues after immobilization. The oxoanion exchange with structural SO{sub 4}{sup 2−} is the main mechanism for immobilization of SeO{sub 4}{sup 2−}. In contrast, SeO{sub 3}{sup 2−} is easily immobilized to form inner-sphere complexes in ettringite. In addition, it is necessary to reveal the SeO{sub 3}{sup 2−} complexation sites for understanding the mechanisms in immobilization of SeO{sub 3}{sup 2−}. Based on the characterization results with the bond valence theory, the location sites of sorbed SeO{sub 3}{sup 2−} in ettringite structure were proposed. The results obtained in this work are relevant to the understanding of Se and its isotopes immobilized in cement or alkaline environments, especially for nuclear waste management. - Highlights: • The immobilization mechanisms of SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} in ettringite are different. • Sorption of SeO{sub 3}{sup 2−} will remove structural water molecules in ettringite. • SeO{sub 3}{sup 2−} could form some inner-sphere complexes in the ettringite structure. • The EXAFS and bond valence theory was applied to determine the sorption mechanism. • The atomic configuration of ettringite surface was proposed after sorption of SeO{sub 3}{sup 2−}.

• OSTI ID: 22701575
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Vol. 100; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
CHEMICAL PROPERTIES
COORDINATION NUMBER
COORDINATION VALENCES
FINE STRUCTURE
HEAVY METALS
ISOTOPES
RADIOACTIVE WASTE MANAGEMENT
SORPTION
X-RAY SPECTROSCOPY