Interaction of aqueous Se(IV)/Se(VI) with FeSe/FeSe2: Implication to Se redox process

► FeSe and FeSe2 can be oxidized to Se(0) by selenite with relatively fast kinetics. ► Oxidation of FeSe and FeSe2 by selenate only occurs under limited conditions with slow kinetics. ► Se(0) is the first reaction product when selenite reduction by Fe(II)-bearing minerals. ► FeSe and FeSe2 have strong reactivity toward Fe3+.