Response to the Comment by G. Druschel and M. Borda on “Pyrite dissolution in acidic media”

Abstract

Most of the seven sections developed in the Comment are actually generalities which, when related to our study, support our interpretations and conclusions. The Comment essentially accepts our experimental data but proposes a more consistent representation that redefines our results in the context of more complex pathways for pyrite oxidation. Only four sections (3, 5, 6 and 7) criticize explicitly our interpretations or conclusions. We will focus on these criticisms. The authors of the Comment first challenge the set of reactions through which we proposed to interpret our experimental results. Our set of reactions would be poorly consistent with the chemical reactivity of thiosulfate (S2O3 2 ) and tetrathionate (S4O6 2 ), the two intermediary species we proposed. Previous studies on pyrite oxidation at acid pH failed to detect or to measure quantitatively elemental S or metastable sulfoxyanions in solution, as has been noted by the Comment’s authors. This implies that electron transfer is very rapid at low pH. However, the non-congruence of the dissolution reaction observed in our study, among others, suggests that intermediary species must be removed from the solution as precipitates or as gases. That means that the lifetime of intermediary species, or their occurrence in solution, remain as key questions, despite the generalization that some species, such as S4O6 2 , can be considered relatively stable in solution (but only in absence of pyrite or at higher concentrations).This was extensively discussed in our paper. The authors of the Comment assert that if tetrathionate ion was an actual intermediary species in our study, we should have detected it, since they studied its stability.