Transformation of selenium solid phase in the presence of iron under reducing conditions

Doi, Reisuke ; Tachikawa, Hirokazu*; Yui, Mikazu

Se solubility and its solubility-limiting solid phase were investigated in a simulated geological repository environment. Experiments in bentonite equilibrated waters and the simple condition experiment without bentonite were performed. With bentonite approximately 10 mol/dm Se concentration was obtained. The experiment without bentonite was conducted to confirm the solubility-limiting solid phase. This experiment was carried out at a higher temperature (80C) to accelerate the solid transformation of Se. The Se concentration decreased with increasing time. Several Se solid phases were identified. Though Se(cr) was dominant at first, this solid phase gradually transformed with time and Fe-Se solids began to form. It is suggested that FeSe, which is the most thermodynamically stable phase, is likely to be the Se solubility-limiting solid phase under a geological repository environment in the long-term.