Abstract
Abstract The influence of pH and reaction time on the formation of FeSe2 by reductive precipitation of Se(IV) with nano-sized pyrite-greigite was investigated. Reductive precipitation is an effective method of attenuating the mobility of 79Se, which is foreseen to be a dangerous radioisotope for the geological disposal of high-level radioactive waste (HLW). The results indicated that Se(0)was formed at pH <4.05, whereas, at pH > 6.07, considerable amount of FeSe2 was formed along with Se(0). These observations are in agreement with the thermodynamic predictions reported in this work. Furthermore, the formation of FeSe2 was found to continue by increasing the reaction time, indicating that the Se(0) formed in the early reaction stage is gradually transformed to FeSe2 upon the depletion of aqueous Se(IV). Since FeSe2 has a stronger reactivity than pyrite, it was proposed that greigite, rather than pyrite, was responsible for the formation of FeSe2. The findings in this study are of interest for key geochemical processes governing the mobility of toxic 79Se in the environment in presence of iron sulfides.
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