The Synergistic Effect of Cu²⁺–Fe²⁺–Fe³⁺ Acidic System on the Oxidation Kinetics of Ag-Doped Pyrite

Abstract

The impurities contained in the structure of natural pyrite have been reported to introduce variation in its semiconducting properties and oxidation behavior. However, there is no direct study about the effect of specific impurities on the pyrite electrodissolution process kinetics. Among the impurity elements, silver is of particular interest and is often found in natural pyrite. Silver is shown to be capable of catalysis of sulfide mineral dissolution in an acidic environment. In the present study, Ag-doped pyrite was fabricated by a hydrothermal method. X-ray powder diffraction and X-ray photoelectron spectroscopy analyses of the pyrite showed a homogeneous silver distribution in the pyrite. The electrochemical dissolution kinetics of the Ag-doped pyrite were studied in different sulfuric acid electrolytes, with or without the addition of Fe and Cu cations. A variety of electrochemical techniques, including linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and impedance analysis were applied to evaluate the electrochemical response of the pyrite minerals. The experimental results showed a reduced pyrite electrochemical reactivity with increasing Ag content of the Ag-doped pyrites. The exchange current density of the pyrite electrodes in the sulfuric acid electrolytes decreased from 4.0 × 10–6 to 1.0 × 10–6 A/cm2 by increasing the silver content of the pyrites from 138 to 3820 ppm. However, the anodic dissolution of the Ag-doped pyrite electrode showed a substantial increase in the Cu–Fe-containing sulfuric acid solution. For instance, i 0 of a pyrite electrode with 138 ppm Ag increased from 9.6 × 10–6 A/cm2 in the Fe-containing sulfuric acid solution to 2.3 × 10–5 A/cm2 in the Fe–Cu-containing sulfuric acid solution. In the electrochemical impedance spectroscopy analysis, the Ag-doped pyrite with a higher concentration of Ag showed smaller charge-transfer resistances.

The effect of tartrate on the mild leaching of low-grade polymetallic complex chalcopyrite ore in acidic ferric chloride solution

“…7b) showed a peak at 169.0 eV in the case of LPCCO, which is attributed to SO x 2− generated by the oxidation of the LPCCO surface during air exposure. 33 In the cases without and with tartrate, the height of this peak at 169.0 eV decreases possibly due to the coverage of passive film. Fig.…”

“…7d shows the Fe 2p spectra of three cases, in which the doublet peaks at 712.4 eV and 726.2 eV are attributed to Fe 2p 3/2 and Fe 2p 1/2 of Fe( ii ) and Fe( iii ) sulfide/oxide, respectively. 33…”

Hydrothermal Monodisperse Microspherulite Pyrite: Novel Synthesis Process and Electrochemical Study of Its Oxidation

“…Pyrite oxidation behavior relative to synthesis time was studied by a series of electrochemical tests on a fabricated (see ref ( 63 ) for details) pyrite-carbon paste electrode (PCPE). This working electrode had an active area of 0.2 cm 2 .…”

Effect of salinity on the kinetics of pyrite dissolution in oxygenated fluids at 60 °C and implications for hydraulic fracturing

“…Impurities in pyrite can slightly accelerate the rate of pyrite oxidation; pyrite with As has higher oxidation rates than pyrite with Ni or Co, and pyrite without impurities has the lowest rates (Lehner and Savage, 2008;Lehner et al, 2007). However, a study on Ag-doped pyrite indicated that a higher Ag content in pyrite decreases the pyrite electrochemical reactivity (Li and Ghahreman, 2018). These studies on impurities were conducted mainly on synthetic impurity-doped and undoped pyrite, which could introduce different findings in comparison with natural pyrite.…”