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[3311-24-11] Mechanism of selenate co-precipitation with ettringite

^○BINGLIN GUO¹, Keiko Sasaki¹, Tsuyoshi Hirajima¹ (1. kyushu university)

司会: 和嶋隆昌（千葉大学）

Keywords:Selenate; , ettringite; , characterization; , hydrocalumite;, immobilization

Ettringite (Ca6Al2(SO4)3(OH)12·26H2O) usually occurs in alkaline environments, which is associated with other minerals, such as portlandite, gypsum or afwillite. In addition, as the general cement compounds, this mineral is formed through hydration of calcium aluminates when sulfate is co-existing during the early hydration process of Portland cement.Because Portland cement is an important matrix for the immobilization or storage of various hazardous materials and ettringite is supposed to play an important role in hazardous waste immobilization process, this gives some environment relevance to ettringite.It is necessary to reveal the mechanisms of selenate removal by ettringite, which is regarded asa crucial mineral in terms of selenateim mobilization under alkaline conditions. In this study, the formation processes of selenate-substituted ettringite (Ca6Al2(SeO4)3(OH)12·26H2O) were systemically elucidated for interpreting the immobilization mechanisms of selenate in aqueous environments. High concentrations of selenate could be immediately co-precipitated with ettringite after adding a Ca source. During co-precipitation process, SeO42−-substituted hydrocalumite was observed as an intermediate, which was characterized by the XRD peak at d110= 2.878 in hydrocalumite. In addition, by combination withscanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and zeta potential measurements, selenate immobilization mechanism was systematically interpreted. The intermediate was proved to affect the formation of selenate–substituted ettringite. Better understanding the immobilization mechanism of selenate by co-precipitation with ettringite is one of the practical issues innuclear waste management