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Pyrite Oxidation by Hexavalent Chromium: Investigation of the Chemical Processes by Monitoring of Aqueous Metal Species
journal contribution
posted on 2005-11-15, 00:00 authored by Frédéric Demoisson, Martine Mullet, Bernard HumbertPyrite, an iron sulfide, occurs in many soils and sediments,
making it an important natural reductant of toxic metal
pollutants. This study investigated the processes leading
to aqueous Cr(VI) reduction by pyrite in a closed thermostated
(25 ± 0.1 °C) system and under an argon atmosphere.
Synthetic pyrite suspensions were reacted with a range
of Cr(VI) solutions from 0 to 7 × 10-4 M and at pH 2−8. Metal
species concentrations were continuously monitored
during a period lasting approximately 20 h. Preliminary
experiments carried out in acidic media without Cr(VI) have
shown that some pyrite dissolution occurred. Then,
metal species concentration changes with time during
pyrite oxidation by Cr(VI) solutions exhibited two distinct
trends depending on the complete or incomplete Cr(VI)
removal. As long as chromate existed in solution, the Cr(III) to Fe(III) ratio was found to be an effective parameter
to investigate the pyrite reaction stoichiometry with Cr(VI). Experimental values close to 2 suggest that sulfur
compounds with oxidation states between 0 and 2 should
be formed during pyrite oxidation by Cr(VI). If Cr(VI)
was completely reduced from solution, then the pyrite
oxidation by Fe(III) ions took place to generate ferrous ions.