MICROBIALLY-MEDIATED PYRITE OXIDATION AT CIRCUMNEUTRAL PH IN SANDSTONES OF TREMPEALEAU COUNTY, WI

Metal-sulfide mineral oxidation in circumneutral pH environments is a relevant groundwater quality concern for Wisconsin’s sandstone and carbonate Cambrian-Ordovician aquifer system. The lower Paleozoic units that comprise this aquifer system have been observed to host varying abundances of metal-sulfide minerals, such as pyrite, across Eastern, Western, and South-Central Wisconsin, USA. The oxidation of pyrite present within this aquifer system can generate groundwater contamination, releasing acidity and dissolved metals.

Although pyrite dissolution in the generation of acid mine drainage has been extensively studied, the role of bacteria in mediating pyrite oxidation at circumneutral pH is not well understood. It has recently been shown that chemolithotrophic bacteria can accelerate neutral-pH, aerobic oxidation of both synthetic and specimen pyrite up to 10-fold relative to abiotic controls. However, to our knowledge, no previous studies have documented the influence of biological activity on pyrite oxidation with native groundwater, subsurface materials, and bacterium.

We carried out microcosm experiments with native geologic material of the Tunnel City Group (TCG) glauconitic and dolomitic sandstone, and the Wonewoc Formation (WF) quartz sandstone from Trempealeau County, WI, each containing about 3% by weight or less of nodular or disseminated pyrite, and native groundwater from those geologic units as the aqueous medium and the bacterial inoculum. Preliminary results from our study supports our hypothesis that the oxidation of sulfide minerals in the TCG and WF materials is enhanced in the presence of iron and sulfur oxidizing microorganisms. These findings will shed light on the oxidation kinetics of natural sulfide minerals in sandstone aquifers in Wisconsin and other like-aquifer, geochemical, and geomicrobial subsurface systems.