Reductive Dissolution of Tl(I)–Jarosite by <i>Shewanella putrefaciens</i>: Providing New Insights into Tl Biogeochemistry

Thallium (Tl) is emerging as a metal of concern in countries such as China due to its release during the natural weathering of Tl-bearing ore deposits and mining activities. Despite the high toxicity of Tl, few studies have examined the reductive dissolution of Tl mineral phases by microbial populations. In this study we examined the dissolution of synthetic Tl­(I)–jarosite, (H₃O)_0.29Tl_0.71Fe_2.74(SO₄)₂(OH)_5.22(H₂O)_0.78, by <i>Shewanella putrefaciens</i> CN32 using batch experiments under anaerobic circumneutral conditions. Fe­(II) concentrations were measured over time and showed Fe­(II) production (4.6 mM) in inoculated samples by 893 h not seen in mineral and dead cell controls. Release of aqueous Tl was enhanced in inoculated samples whereby maximum concentrations in inoculated and cell-free samples reached 3.2 and 2.1 mM, respectively, by termination of the experiment. Complementary batch Tl/<i>S. putrefaciens</i> sorption experiments were conducted under experimentally relevant pH (5 and 6.3) at a Tl concentration of 35 μM and did not show significant Tl accumulation by either live or dead cells. Therefore, in contrast to many metals such as Pb and Cd, <i>S. putrefaciens</i> does not represent a sink for Tl in the environment and Tl is readily released from Tl–jarosite during both abiotic and biotic dissolution

Simultaneous Release of Fe and As during the Reductive Dissolution of Pb–As Jarosite by <i>Shewanella putrefaciens</i> CN32

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 (PbFe₃(SO₄,AsO₄)₂(OH)₆) 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