Electrochemical spectral induced polarization modeling of artificial sulfide-sand mixtures

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 (c₂/c_o) dissolved in the pore water, and the variation of the current reaction parameters α and β The increase in these parameters as well as in the associated exchange current densities, i_o(α) and i_o(β) 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.