The redox activity of minerals can be characterized electrochemically in a variety of ways, ranging from working electrodes made with single crystals of a mineral to solutions of mineral nanoparticles. Each variation on this approach has pros and cons, one of which concerns the ability to utilize intact particles without disruption of their native surface coatings. For this purpose, we have been using “powder disk electrodes” (PDEs) made with a variety of Fe(II) and S(-II) containing minerals, especially magnetite. Many magnetite samples have been studied, representing a range of sources, purities, particle sizes, and surface coatings. Electrochemical methods including chronopotentiometry (CP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) have been applied to magnetite PDEs and the results are compared within each sample analysis, among different samples of magnetite, and to results obtained with other characterization methods. In general, the results obtained are consistent with prior work on magnetite suspensions (e.g., E(OCP) ≈ 280 mV vs. SHE) or by other methods (e.g., polarization resistance). Of particular interest is the correlation of electrochemically-determined properties of magnetite and its reactivity with solutes, as measured by the kinetics of reaction with various probe compounds. The chemical redox probes (CRPs) that we have used in recent studies of iron oxides (e.g., resazurin), as well as the nitro aromatic compounds (NACs) that often are used as model contaminants, show high variable rates of reduction by magnetite.

Electrochemical characterization of minerals and their redox reactions with solutes

253rd National Meeting (2017)

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