Selenium can be found in several oxidation states and its solubility and mobility in the environment largely depends on its oxidation state. Batch reactor experiments were performed adding selenite or selenate to a nanosized pyrite-greigite suspension at different pH, with and without the addition of extra Fe2+, with the aim to observe the reduction of Se. X-ray absorption spectroscopy was used to unravel the Se speciation, and revealed, for the first time, the formation of the thermodynamically stable ferroselite (FeSe2) as a predominant product along with elemental Se. The nucleation and growth of FeSe2 is believed to occur at the nano-pyrite/greigite mixture surface via several steps, and reaction kinetics and aging time may play a significant role. The results are supported by thermodynamic calculations and aqueous phase analyses. The present study demonstrates that in Fe2+-sulfide-bearing environment, Se can be immobilized in its most insoluble form (FeSe2).

Nanosized pyrite-greigite reactivity towards selenite and selenate

243rd National Meeting (2012)

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