Simultaneous Release of Fe and As during the Reductive
Dissolution of Pb–As Jarosite by <i>Shewanella putrefaciens</i> CN32
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Abstract
Jarosites
are produced during metallurgical processing, on oxidized
sulfide deposits, and in acid mine drainage environments. Despite
the environmental relevance of jarosites, few studies have examined
their biogeochemical stability. This study demonstrates the simultaneous
reduction of structural Fe(III) and aqueous As(V) during the dissolution
of synthetic Pb–As jarosite (PbFe<sub>3</sub>(SO<sub>4</sub>,AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>) by <i>Shewanella
putrefaciens</i> using batch experiments under anaerobic circumneutral
conditions. Fe(III) reduction occurred immediately in inoculated samples
while As(V) reduction was observed after 72 h. XANES spectra showed
As(III) (14.7%) in the solid phase at 168 h coincident with decreased
aqueous As(V). At 336 h, XANES spectra and aqueous speciation analysis
demonstrated 20.2% and 3.0% of total As was present as As(III) in
the solid and aqueous phase, respectively. In contrast, 12.4% of total
Fe was present as aqueous Fe(II) and was below the detection limits
of XANES in the solid phase. TEM-EDS analysis at 336 h showed secondary
precipitates enriched in Fe and O with minor amounts of As and Pb.
Based on experimental data and thermodynamic modeling, we suggest
that structural Fe(III) reduction was thermodynamically driven while
aqueous As(V) reduction was triggered by detoxification induced to
offset the high As(V) (328 μM) concentrations released during
dissolution