Pathways of ferrous iron mineral formation upon sulfidation of lepidocrocite surfaces

Reductive Dissolution and Reactivity of Ferric (Hydr)oxides: New Insights and Implications for Environmental Redox Processes

“…We therefore propose that the occurrence of excess Fe(II) matches in fact the process of electron injection into the bulk structure of the ferric (hydr)oxides [22]. As was discussed earlier electron injection into a semiconductor's conduction band requires the occurrence of adsorbed Fe(II).…”

“…Hellige et al [22] reported a sequence of redox reactions at the surface of lepidocrocite for more than 2 weeks following complete consumption of ∼10 mM dissolved sulfide within the first 2 h. Handler et al [23] observed near-complete exchange of Fe atoms between the aqueous phase and goethite over a 30-day time period following equilibration with aqueous Fe(II).…”

“…The system stays stable for a while but after 1 day a consumption of solid-phase Fe(II) and MES starts, accompanied by a release of dissolved Fe(II) and the formation of pyrite (as detected by Mössbauer spectroscopy). Figure 3.4 illustrates these dynamics based on TEM images obtained from a comparable study with lepidocrocite [22].…”

“…Hellige et al [22] and Wan [62] have therefore measured total Fe(II) as being extractable with 1N HCl. If FeS matches the concentration of extractable Fe(II), then the mass balance according to Eq.…”

“…The observation is in line with the study by Poulton et al [19] in which they discovered a fraction of solid-phase Fe(II) that can be extracted with 1N HCl and which is neither FeS nor sorbed Fe(II). Interestingly, experiments performed with lepidocrocite with positive mass balances were subject to rapid pyrite formation, while experiments with zero or negative mass balances showed a strong delay or even no pyrite formation [22,65].…”