Details

Autor(en) / Beteiligte

• Renock, Devon
• Voorhis, James

Titel

Electrochemical Investigation of Arsenic Redox Processes on Pyrite

Ist Teil von

• Environmental science & technology, 2017-04, Vol.51 (7), p.3733-3741

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2017

Quelle

MEDLINE

Beschreibungen/Notizen

• The specific Eh–pH conditions and mechanism(s) for the reduction of arsenite, As­(III), by pyrite are incompletely understood. A fundamental question is what role the pyrite surface plays in the reduction process. We used electrochemical methods to evaluate the reduction of As­(III) under controlled redox conditions. As­(III) reduction to elemental As(0) occurs on the pyrite surface under suboxic-reducing conditions and is promoted at low pH. Remarkably, As­(III) reduction on pyrite occurs at similar potentials to those for reduction on platinum metal, suggesting a similar mechanism and kinetics for these surfaces. The onset for As­(III) reduction at pH ≤ 3.5 coincides with the potential for hydrogen electroadsorption on pyrite, E ≈ +0.1 V (versus RHE). Batch reactions show that As­(III) is reduced on pyrite at the Eh–pH predicted by the electrochemical study. X-ray photoelectron spectroscopy reveals that, at pH ≤ 3.5, a significant fraction of the surface arsenic (30–60%) has an oxidation state consistent with As(0). Here, we propose a mechanism whereby atomic hydrogen that forms on ferric (hydr)­oxide surface layers promotes As­(III) reduction at low Eh and pH. Insights provided by this study will have implications for understanding the controls on dissolved As­(III) concentrations in suboxic–anoxic environments.