Comment on “FeS colloids – formation and mobilization pathways in natural waters” by Noël et al., Environ. Sci. Nano, 2020, 7, 2102–2116
In this comment, I am critically discussing observations made in the study by Noël et al. (2020) on the formation of FeS colloids (passing through 0.02 μm filters) during sulfidation of ferrihydrite at different S(−II)/Fe(III) ratios. The authors argue that at low ratios remarkably stable colloidal FeS clusters are forming that may be of paramount environmental relevance. Since the authors did only study the iron side of these colloids and not the sulfur side, I am proposing that there is quite some evidence from a series of studies performed in our group that these clusters may be precursors of pyrite (FeSx) or even nanopyrite (FeS2) but not FeS.