Spectral induced polarization and electrodic potential monitoring of microbially mediated iron sulfide transformations

Abstract

[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.

Laboratory study of spectral induced polarization responses of magnetite — Fe2+ redox reactions in porous media

“…They found secondary minerals such as sulfide precipitates produced phase anomalies of up to 60 mrad associated with both abiotic and microbial precipitation of iron and zinc sulfides (Ntarlagiannis et al, , 2010a(Ntarlagiannis et al, , 2010bWilliams et al, 2005;Slater et al, 2007;Personna et al, 2008). Laboratory experiments on sediments from the biostimulation field site at Rifle, CO, agreed with field results suggesting that redox active ions may play an important role in the observed SIP signals (Williams et al, 2009) but highlighted that more controlled experiments were needed (Ntarlagiannis et al, 2010b).…”

“…Non conductive minerals also typically produce small SIP phase responses arising from ion migration within the electrical double layer (EDL) at the mineral water interface (typically <<10 mrad at frequencies <1000 Hz; Vaudelet et al, 2011;Zhang et al, 2012). In contrast, semiconductive minerals dispersed in a matrix of non conducting minerals, including natural authigenic minerals such as magnetite, secondary precipitates and metallic particles may give larger phase responses, typically of the order of several tens to hundreds of mrad Personna et al, 2008;Ntarlagiannis et al, 2010a). These strong polarization responses associated with semiconductive minerals have been interpreted in terms of two phenomena:…”

“…The need for monitoring subsurface geochemistry such as redox conditions at contaminated sites has been recognized, because they play a vital role in controlling the mobility of key redox active contaminants such as Cr, U, Tc and As (Finneran et al, 2002;Islam et al, 2004;Burke et al, 2005;. Thus, remote sensing of redox indicators, such as the presence of Fe (II) in groundwater or the formation of sulfide minerals (Ntarlagiannis et al, , 2010aPersonna et al, 2008), would be a highly valuable complementary approach to conventional sampling and geochemical analysis of groundwater.…”

Spectral induced polarization signatures of abiotic FeS precipitation

“…Traditionally, geophysical methods have been employed to image physical properties of the subsurface, and only recently have geophysical responses been linked indirectly to microbial activity ͑Atekwana et Atekwana and Slater, 2009͒. The need to more precisely correlate the effects of mineral surfaces, microbes, and the products of microbial activity with common geophysical measurements has led to an increasing number of laboratory studies ͑Ntarlagiannis et al, 2005a; Williams et al, 2005;Davis et al, 2006;Slater et al, 2007;Personna et al, 2008;Abdel Aal et al, 2009͒ and initial field studies designed to validate upscaling of the approach ͑Williams et al, 2009͒. One of the most successful methods is the SIP technique.…”

“…The SIP ͑or complex-conductivity͒ method appears to be sensitive to ͑1͒ the presence of microbial cells ͑Ntarlagiannis et al, 2005b͒, ͑2͒ biofilm formation ͑Davis et al, 2006͒, and ͑3͒ microbialinduced sulfide mineral precipitation ͑Ntarlagiannis et al, 2005a; Williams et al, 2005;Slater et al, 2007;Personna et al, 2008͒. In the absence of metallic minerals, the SIP phase responses attributed to microbial cells and biofilm formation are small ͑1.5-mrad phaseshift maximum͒, and they require meticulous instrument calibration and careful measurement protocol ͑Ntarlagiannis et al, 2005b; Davis et al, 2006͒. In contrast, the precipitation of metallic minerals, including metal sulfides, generates significantly larger SIP responses, at least an order of magnitude higher ͑15-mrad phase shift͒, yielding anomalies that are easier to detect and monitor ͑Ntarlagiannis et al, 2005a;Williams et al, 2005;Slater et al, 2007;Personna et al, 2008͒.…”