Electrochemical spectral induced polarization modeling of artificial sulfide-sand mixtures

Abstract

We examined the sensitivity of the electrochemical spectral induced polarization (SIP) model developed by Wong to the oxidation extent of pyrite and pyrrhotite minerals disseminated in silica sand. The sensitivity of this model to the oxidation of sulfide minerals was mainly related to the model parameters defining the ratio of the active to the inactive passive ions [Formula: see text] dissolved in the pore water, and the variation of the current reaction parameters [Formula: see text] and [Formula: see text]. The increase in these parameters as well as in the associated exchange current densities, [Formula: see text] and [Formula: see text] was consistent with an increase in the activation of the charge transfer at the metal-electrolyte interface, resulting in the decrease in polarization of such an interface, which was reflected by a decrease in the SIP phase response as previously argued by Wong. Under this premise, the model described fairly well measurements below 500 Hz from a laboratory experiment, being consistent with the depletion of the SIP phase response associated with the oxidation degree promoted on the disseminate sulfides analyzed here. This suggested that electrochemical modeling of SIP measurements can provide information to assess the oxidation state of sulfides and also to infer the formation of passivating layers coating the metal minerals during oxidation-dissolution processes. Our results suggested a possible alternative for the monitoring of mine waste deposits producing acid mine drainage and the stability of sequestered harmful metals during remedial treatments by means of the SIP method.

On the pore water chemistry effect on spectral induced polarization measurements in the presence of pyrite

“…Both types of ion can be present in the EDL: those spontaneously adsorbed on the metallic mineral surface by image forces, forming the fixed or Stern layer, and those forming the adjacent diffuse (characterized by concentration gradient) layer. The increase of the active/passive concentration ratio has previously been seen to diminish the SIP magnitude (IP-effect) of metals (Wong, 1979;Placencia-Gómez and Slater, 2014). In the case of pyrite, the most important A-ions (strongest oxidizing agents or electron acceptors) are O 2 and ferric iron Fe 3+ ions (Chandra and Gerson, 2010, for review).…”

“…Such studies mainly focus on the role of the metal content (total weight or volume fraction percentage) and physical (textural) properties such as the metallic particle grain size and surface area on the spectral induced polarization (SIP) response. In contrast, relatively few studies have examined the significance of the physical and chemical characteristics of the metal-electrolyte interface controlling the IP-effect (e.g., Flekkøy, 2013;Gurin et al, 2015;Hubbard et al, 2014;Merriam, 2007;Placencia-Gómez and Slater, 2014) in such systems.…”

“…The leaky-capacitive effect (or "imperfect" surface polarization) and the mineralogical transformations on the external lattice of the metallic mineral surface (e.g., the formation of Fe-oxy-hydroxy-sulphate phases) as part of the oxidative-weathering process, have been found to diminish the magnitude and broaden the peak of the laboratory-measured SIP response for pyrrhotite-sand mixtures (Placencia-Gómez et al, 2013;Placencia-Gómez and Slater, 2014) and mine waste materials (tailings) containing pyrite and pyrrhotite (Campbell and Horton, 2001;Placencia-Gómez et al, 2015). This is likely accompanied by a shift of the polarization peak towards lower frequencies as suggested by the model of Wong (Fig.…”

“…Placencia-Gómez and Slater (2014) found that the Wong model in some cases shows an imperfect fit to experimental data obtained on synthetic mixtures of sand with pyrite or pyrrhotite over the frequency range 0.1-10,000 Hz, although it fits relatively well around the peak relaxation frequencies. Gurin et al (2013Gurin et al ( , 2015 found a quadratic dependence of the relaxation time (τ) on the grain (metallic particles) size, whereas the model of Wong suggests two relationships: quadratic for large particle radii and linear for small radii.…”

Induced Polarization of Rocks Containing Metallic Particles: Evidence of Passivation Effect

“…This is why IP is commonly used in exploration for those deposits where the ore bodies contain disseminated conductive or semiconductive minerals (e.g., Nelson & Van Voorhis, ; Pelton et al, ). In addition, IP can be used for evaluating integrity of permeable reactive barriers made of granular iron (e.g., Slater & Binley, ), for three‐dimensional imaging of slag heaps (e.g., Florsch et al, ) and mining tailings (Placencia‐Gomez et al, , ; Placencia‐Gomez & Slater, ). In these applications, IP often aims to assess the volumetric content of disseminated conductive particles (which we henceforth refer to as”metallic particles”), and can be applied to assess the chemical state of their surface.…”