Inlab redox electrode

The pyrite electrode was immersed in a cell (50 mL) containing an oxidant (bacteria or pH 1.8 acidified water as a control). Pyrite oxidation without permanent electrode polarization was investigated over a period of 100 days using exchange current density as a direct measure of the reaction rate. The exchange current was represented by the current passing across the mineral-solution interface due to the redox reaction alone. The redox potential (Eh) was measured with a combined InLab Redox electrode (Mettler-Toledo AG, Greifensee, Switzerland) using a pH-mV meter PHM 93 (Radiometer, Copenhagen). The rest potential of the pyrite electrode (Es) was measured against a saturated calomel electrode using the pH-mV meter. The pyrite electrode was used as a working electrode, the saturated calomel electrode as a reference electrode, and the platinum net electrode as a counter electrode (Figure 1). Polarization of the working electrode was carried out using the potentiostatic unit of a polarographic analyzer (PA3, Laboratory Devices, Prague). The polarization curve used to determine the exchange current was obtained by briefly polarizing the pyrite electrode within 1 min of each observation. The linear potential sweep rate was 1 mV/s in both cathodic and anodic directions from the rest potential of working electrode, i.e., to -100 and 100 mV overpotentials, respectively.

The red-ox potential was determined using a SevenCompactTM S220 with an InLab Redox electrode (Mettler-Toledo, Greifensee, Switzerland) according to the methodology of Okoń et al. [33 (link)]. The results are given in mV. TBARS index was determined by measuring the absorbance value of the solution and 2-thiobarbituric acid according to Pikul et al. [34 (link)]. The intensity of the colour from the reaction of 2-thiobarbituric acid with malonic dialdehyde (MDA) was measured using a U-2900 spectrophotometer (Hitachi, Tokyo, Japan) at a wavelength of 532 nm. The values are expressed in mg MDA/kg of product.