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[BCG09-10] Selenite sorption on magneaium oxide under the highly alkaline conditions
Keywords:Selenite, Magnesium Oxide, Metastable Phase, Magnesium Hydroxide, Alkaline Conditions
After earthquake disaster, the contribution of the nuclear power generation in the electricity source of supply in Japan decrease, while that the thermal power generation increases. In coal-fired station, the selenium concentrations more than industry waste water regulation (100ppb) in the drainage has been reported to occur in a desulfurization processes of the gases which is generated during burnt coral (Central Research Institute of Electric Power Industry, 2005). The solutions used in the desulfurization processes is kept alkaline in order to facilitate the dissolution gases.
Selenium mainly exists as selenite(HxSeO42-x, Se(Ⅵ)) or selenite(HySeO32-y, Se(Ⅳ)) in solution. Most of selenium exists as selenite in waste water in desulfurization process (Central Research Institute of Electric Power Industry, 2005). A general selenite removal method in the solution includes the adsorption on iron oxide. However, adsorption significantly decrease under the alkali condition because the surface charge of iron oxide become to minus at alkaline conditions (Fukushi, 2008). Therefore, the effective removal of selenite under the alkali condition is expected.
The anions of which oxygens coordinate to the center atom are called oxyanions. There are many oxyanions which cause the water pollutions, e.g., arsenite and bronate. It is reported that magnesium oxide (MgO) has ability for the removals of aresnite and bronate (Liu et al., 2011; Fuente and Eugenio, 2006). It can be expected that MgO has ability for removal for selenite in solution. MgO is metastable phase under the Earth surface environmental, and it transforms to brucite (Mg(OH)2) in solution with time (Yabe et al., 2011). Liu et al., (2011) studied the removal of arsenite from solution by MgO with high sace area. They suggested that the tranformation in solution is related to the uptake of arsenite, i.e., the sorption mechanism of aresenite on MgO under the high arsenite concentration condition is formation of an “arsenite-Mg compound” following transformation to Mg(OH)2. Their study was conducted under the very high sorbate concentration (>1ppm) condition. There were no arguments about the mechanisms under the low concentration condition with sub-ppm order. The water pollution related to selenium mainly becomes problem with low concentration around the waste water satandards (100ppm order). It is thought that understanding the sorption behavior in the low concentration condition is necessary. I conducted bacth sorption experiments of selenite by MgO and magnesium hydroxide which is stable phase in this study to examine the selenite uptake behavior and mechanism on MgO.