Electrochemical oxidation of arsenopyrite in chloride solutions

Oxidation of arsenopyrite and deposition of gold on the oxidized surfaces: A scanning probe microscopy, tunneling spectroscopy and XPS study

“…Two weak cathodic maxima at approximately 0.15 and À0.25 V, and a current surge at potentials more negative than À0.3 V are observed on the negative-going sweep; the charge associated with the reduction is much less than that passed in the electrooxidation processes. Similar data have previously been acquired at different arsenopyrite electrodes (Kostina and Chernyak, 1976;Cruz et al, 1997;Lázaro et al, 1997;Lin and Zheng, 1997;Costa et al, 2002); they are consistent with the idea that a passivating layer decomposes at high enough overpotentials, thereby accelerating the oxidation of underlying mineral. In the second cycle, the surges of cathodic and anodic currents are shifted to more negative and more positive potentials, respectively, extending the passivity region; the cathodic maximum arising at about +0.4 V is due to the reduction of Fe(III) species.…”

“…The mechanisms of relevant reactions are still insufficiently understood, particularly because the processes in aqueous media, usually electrochemical in nature, are deeply complicated by semiconducting properties of sulfide minerals, so the interfacial transfer of electrons and the transport of charge carriers between different sites at which the various reactions occur are critically dependent upon the precise composition and local characteristics of the appropriate spatial regions (Rimstidt and Vaughan, 2003). The electrochemical oxidation of arsenopyrite occurs in two steps associated with passivation at moderate positive potentials and ''transpassive'' behavior at higher ones (Kostina and Chernyak, 1976;Cruz et al, 1997;Lázaro et al, 1997;Lin and Zheng, 1997;Costa et al, 2002). Lin and Zheng (1997) proposed that the dissolution of arsenopyrite in acidic chloride solutions is retarded by elemental sulfur that is oxidized to sulfate at the second step.…”

“…The electrochemical oxidation of arsenopyrite occurs in two steps associated with passivation at moderate positive potentials and ''transpassive'' behavior at higher ones (Kostina and Chernyak, 1976;Cruz et al, 1997;Lázaro et al, 1997;Lin and Zheng, 1997;Costa et al, 2002). Lin and Zheng (1997) proposed that the dissolution of arsenopyrite in acidic chloride solutions is retarded by elemental sulfur that is oxidized to sulfate at the second step. However, although the elemental sulfur is the predominant surface product of the electrochemical, bacterial and abiotic ferric iron oxidation of arsenopyrite, it does not seem to form a continuous film and scarcely passivates the mineral surfaces since its removal produces no significant change in the dissolution rate of the underlying mineral (McGuire et al, 2001a,b,c;Costa et al, 2002).…”

Pretreatment of a refractory arsenopyritic gold ore using hydroxyl ion

“…The NaOHpretreated arsenopyrite shows a significant increase in reactivity. Because the arsenopyrite oxidation process is associated with realgar (As 2 S 2 ) and orpiment (As 2 S 3 ) (Lin and Zheng, 1996;Lázaro et al, 1997), the increased reactivity observed can possibly be associated with the formation of an arsenic ionic species during the oxidative process of As 2 S 3 (Darban et al, 2011).…”

Alkali and alkaline earth metal chloride solutions influence sulfide mineral dissolution

“…The reported increases in dissolution were attributed to a change in H + ion activity, and not determined to be an effect of the electrolyte itself (Awakura et al, 1980;Barrett and Anderson, 1982;Nunez et al, 1990). Limited studies have been conducted on the dissolution of pyrite (FeS 2 (s)) in the presence of sodium chloride in solution (Ohmoto et al, 1994), and on oxidative dissolution of pyrite and arsenopyrite (FeAsS(s)) in electrolyte solutions (Lin and Zheng, 1996;Walker et al, 2006). These studies assume the only reactants in dissolution to be H + or the oxidant species, namely O 2 and Fe 3+ , but the potential interaction of the mineral surfaces with cations in solution, which could affect dissolution, has not been investigated.…”