Pyrite−Arsenopyrite Galvanic Interaction and Electrochemical Reactivity

Abstract

Comparative voltammetric studies were performed between high purity pyrite mineral (98.86%) and arsenopyrite mineral (content of 85.96% arsenopyrite, FeAsS; 11.84% pyrite, FeS2; 0.98% galena, PbS; 0.06% chalcopyrite, CuFeS2) in order to analyze the galvanic effect on the electrochemical reactivity of two different mineralogical phases when these are associated in the same mineral, using carbon paste electrodes (CPE) in 0.1 M NaNO3 (pH 6.5) as electrolyte. Theoretical studies were performed for a more detailed analysis on the total energy and energy relative of a total optimization of the species involved in the pyrite and arsenopyrite oxidation as pure mineral. The results indicate that the electrochemical reactivity of pyrite in the arsenopyrite mineral was delayed and displaced to more positive potentials with respect to the high purity pyrite mineral electrochemical response, due to a galvanic effect. On the other hand, the voltammetric studies showed the oxidation stages of arsenopyrite mineral, indicating that arsenopyrite was oxidized in a first stage to Fe2+, realgar (As2S2), H3ASO3, and S0. In a second stage, the arsenopyrite and the pyrite were oxidized to FeOOH(s) and S0, followed by oxidation of H3AsO3 to H2AsO4 − and S0 to SO4 −, besides the scorodite (FeSO4·2H2O) formation. Meanwhile, to more negative potentials the regeneration of FeAsS and the reduction to elemental arsenic do not occur due to the reduction of arsenate (H2AsO4 −) to H3AsO3 and the residual scorodite (FeAsO4·2H2O) that was not dissolved by chemical reaction. The analysis by scanning electron microscopy and energy dispersive spectrometer to surfaces of the electrodes with the mineral (CPE) modified electrochemically was carried out to support the reaction mechanisms.

Formation of surface protective coatings on arsenopyrite using Al-catecholate complex and its mode of inhibition of arsenopyrite oxidation

“…The working electrode was first equilibrated at the OCP and then polarized at 0.0 V for cathodic polarization (without N2 purging) and at +0.8 V for anodic polarization (with N2 purging). These potentials were selected based on the previous studies [7,8]: arsenopyrite was irreversibly oxidized at +0.8V while its reductive dissociation was negligible at 0.0 V.…”

Corrosion Behavior of a Pyrite and Arsenopyrite Galvanic Pair in the Presence of Sulfuric Acid, Ferric Ions and HQ0211 Bacterial Strain

“…Biological pretreatment of gold ores is associated with galvanic effects [14][15][16]. The oxidation potential of pyrite is around 630 mV, while arsenopyrite oxidation is initiated at much lower Eh values, ranging between 390 and 430 mV [5,9].…”

“…In other words, the presence of pyrite accelerates oxidation of arsenopyrite [5][6][7][8][9]. In recent years, the galvanic mechanism of pyrite and arsenopyrite in different media has been discussed [14][15][16][17][18]. Urbano et al [15] stated that the electrochemical reactivity of pyrite in contact with arsenopyrite mineral was delayed and shifted to more positive potentials with respect to the high-purity pyrite mineral electrochemical response due to the galvanic effect.…”

“…In recent years, the galvanic mechanism of pyrite and arsenopyrite in different media has been discussed [14][15][16][17][18]. Urbano et al [15] stated that the electrochemical reactivity of pyrite in contact with arsenopyrite mineral was delayed and shifted to more positive potentials with respect to the high-purity pyrite mineral electrochemical response due to the galvanic effect. This reaction process was described according to the results of scanning electron microscopy (in ferric-free solution with a pH of 6.5).…”

Selective Flotation of Pyrite from Arsenopyrite by Low Temperature Oxygen Plasma Pre-Treatment

“…However, as the physical and chemical properties of arsenopyrite are similar to those of pyrite, arsenopyrite presents a similar hydrophobicity with pyrite in the flotation process when xanthate serves as collector [8,9]. As their hydrophobic surface species are dixanthogen, xanthates are not cation-selective in the case of separation of arsenopyrite and pyrite, which makes it very difficult by 2 of 17 flotation separation [10,11].…”