We measured spectral induced polarization (SIP) signatures in sand columns during (1) FeS biomineralization produced by sulfate reducing bacteria (Desulfovibrio vulgaris) under anaerobic conditions, and (2) subsequent biomineral dissolution upon return to an aerobic state. The low‐frequency (0.1–10 Hz peak) relaxations produced during biomineralization can be modeled with a Cole‐Cole formulation, from which the evolution of the polarization magnitude and relaxation length scale can be estimated. We find that the modeled time constant is consistent with the polarizable elements being biomineral encrusted pores. Evolution of the model parameters is consistent with FeS surface area increases and pore‐size reduction during biomineral growth, and subsequent biomineral dissolution (FeS surface area decreases and pore expansion) upon return to the aerobic state. We conclude that SIP signatures are diagnostic of pore‐scale geometrical changes associated with FeS biomineralization by sulfate reducing bacteria.
[1] Stimulated sulfate-reduction is a bioremediation technique utilized for the sequestration of heavy metals in the subsurface. We performed laboratory column experiments to investigate the geoelectrical response of iron sulfide transformations by Desulfovibrio vulgaris. Two geoelectrical methods, (1) spectral induced polarization (SIP), and (2) electrodic potential measurements, were investigated. Aqueous geochemistry (sulfate, lactate, sulfide, and acetate), observations of precipitates (identified from electron microscopy as iron sulfide), and electrodic potentials on bisulfide ion (HS À ) sensitive silver-silver chloride (Ag-AgCl) electrodes ($À630 mV) were diagnostic of induced transitions between anaerobic iron sulfide forming conditions and aerobic conditions promoting iron sulfide dissolution. The SIP data showed $10 mrad anomalies during iron sulfide mineralization accompanying microbial activity under an anaerobic transition. These anomalies disappeared during iron sulfide dissolution under the subsequent aerobic transition. SIP model parameters based on a Cole-Cole relaxation model of the polarization at the mineral-fluid interface were converted to (1) estimated biomineral surface area to pore volume (S p ), and (2) an equivalent polarizable sphere diameter (d) controlling the relaxation time. The temporal variation in these model parameters is consistent with filling and emptying of pores by iron sulfide biofilms, as the system transitions between anaerobic (pore filling) and aerobic (pore emptying) conditions. The results suggest that combined SIP and electrodic potential measurements might be used to monitor spatiotemporal variability in microbial iron sulfide transformations in the field.
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