Influence of arsenic on iron sulfide transformations |
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| Institution: | 1. Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia;2. University of Bayreuth, Environmental Geochemistry, Universitaetsstrasse 30, 95440 Bayreuth, Germany;1. Department of Hydrology, Universität Bayreuth, Universitätsstraße 30, D-95445 Bayreuth, Germany;2. Department of Earth Sciences, Geochemistry, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands;3. Department of Civil and Environmental Engineering, Northeastern University, 469 Snell Engineering, 360 Huntington Ave, Boston, MA 02115, USA;4. Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstraße 30, D-95445 Bayreuth, Germany;5. Institute of Geosciences, Mineralogy, Friedrich-Schiller-Universität Jena, Carl-Zeiss-Promenade 10, D-07745 Jena, Germany |
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| Abstract: | The association of arsenate, As(V), and arsenite, As(III), with disordered mackinawite, FeS, was studied in sulfide-limited (Fe:S = 1:1) and excess-sulfide (Fe:S = 1:2) batch experiments. In the absence of arsenic, the sulfide-limited experiments produce disordered mackinawite while the excess-sulfide experiments yield pyrite with trace amounts of mackinawite. With increasing initially added As(V) concentrations the transformation of FeS to mackinawite and pyrite is retarded. At S:As = 1:1 and 2:1, elemental sulfur and green rust are the end products. As(V) oxidizes S(-II) in FeS and (or) in solution to S(0), and Fe(II) in the solid phase to Fe(III). Increasing initially added As(III) concentrations inhibit the transformation of FeS to mackinawite and pyrite and no oxidation products of FeS or sulfide, other than pyrite, were observed. At low arsenic concentrations, sorption onto the FeS surface may be the reaction controlling the uptake of arsenic into the solid phase. Inhibition of iron(II) sulfide transformations due to arsenic sorption suggests that the sorption sites are crucial not only as sorption sites, but also in iron(II) sulfide transformation mechanisms. |
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