Corrosion and Electrochemical Oxidation of a Pyrite by Thiobacillus ferrooxidans

Abstract

The oxidation of a pure pyrite by Thiobacillus ferrooxidans is not really a constant phenomenon; it must be considered to be more like a succession of different steps which need characterization. Electrochemical studies using a combination of a platinum electrode and a specific pyrite electrode (packed-ground-pyrite electrode) revealed four steps in the bioleaching process. Each step can be identified by the electrochemical behavior (redox potentials) of pyrite, which in turn can be related to chemical (leachate content), bacterial (growth), and physical (corrosion patterns) parameters of the leaching process. A comparison of the oxidation rates of iron and sulfur indicated the nonstoichiometric bacterial oxidation of a pure pyrite in which superficial phenomena, aqueous oxidation, and deep crystal dissolution are successively involved.

A critical stage in the formation of acid mine drainage: Colonization of pyrite by Acidithiobacillus ferrooxidans under pH‐neutral conditions

“…Pyrite is essentially insoluble in water, even under acidic conditions [reaction (1); Morse et al ., 1987;Lizama & Suzuki, 1989b) demonstrating that water-mineral geochemistry alone (Buckley & Woods, 1987;Lizama & Suzuki, 1989b) cannot explain the establishment of favourable conditions for growth of thiobacilli. Pyrite oxidation is also controlled by electrochemical and geochemical constraints where the redox reaction between ferric iron and the pyrite surface ultimately produces acid byproducts [reaction (2); Dutrizac & MacDonald, 1974;Wiersma & Rimstidt, 1984;Holmes & Crundwell, 2000;Lawrence et al ., 1997;Mustin et al ., 1992). However, at circumneutral pH, the residence time of soluble ferric iron is short-lived due to hydrolysis [reaction (3); Kirby et al ., 1999), which would limit the contribution of reaction (2) in establishing favourable conditions for bacterial growth.…”

Pyrite oxidation mechanism in aqueous medium

“…The mechanism of bacterial leaching of sulfide minerals has been reported by many researchers. [63][64][65][66] Bacterial secretion is a more reactive oxidant than other oxidants, such as Fe 3+ and O 2 . According to Rojaschapana et al, [67] the oxidizability of Leptospirillum ferrooxidans went beyond that of Fe 3+ alone.…”

Antioxidant plant metabolites affect leaching of mineral elements from Callovo‐Oxfordian clays

“…In our experiment, the addition of antioxidant increased alteration with S and P leaching, but only leaching processes were considered. Antioxidants might limit physicochemical and also biological mineral weathering (Mustin et al, 1992;Kraus et al, 2003). They can inhibit microbial activity and therefore microbial weathering (Meline et al, 1996).…”

“…Bio-produced or excreted metabolites such as protons, organic acids, quinones or siderophores modify pH and redox potential and promote element mobility (Hinsinger, 1998;Marschner, 2012). Conversely, aromatic or terpenic substances such as humic acids or essential oils produced by plants (thymol) might limit sulphide oxidation and acidification processes by decreasing the electrochemical reactivity of mineral surfaces (Mustin et al, 1992;Meline et al, 1996;Perdicakis et al, 2001).…”

“…They have been used to reduce soil erosion (Durán Zuazo et al, 2008) and could be considered as a vegetation cover for excavated COx heaps. A few publications have shown that pyrite oxidation was reduced in the presence of thymol (Mustin et al, 1992;Meline et al, 1996;Perdicakis et al, 2001). However, there is a general lack of knowledge on the effects of antioxidants on mineral weathering.…”