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Pressure oxidation is a process for extracting gold from refractory ore. The most common refractory ores are pyrite and arsenopyrite , which are sulfide ores that trap the gold within them. Refractory ores require pre-treatment before the gold can be adequately extracted. [ 1 ]
The chemistry of oxidation of pyrites, the production of ferrous ions and subsequently ferric ions, is very complex, and this complexity has considerably inhibited the design of effective treatment options. [6] Although a host of chemical processes contribute to acid mine drainage, pyrite oxidation is by far the greatest contributor.
Pyrite oxidation is sufficiently exothermic that underground coal mines in high-sulfur coal seams have occasionally had serious problems with spontaneous combustion. [47] The solution is the use of buffer blasting and the use of various sealing or cladding agents to hermetically seal the mined-out areas to exclude oxygen.
In that study, a proposal for the rate at which A.ferrooxidans can oxidise pyrite is the ability to use ferrous iron to generate a ferric iron catalyst : Fe 2+ + 1 ⁄ 4 O 2 + H + → Fe 3+ + 1 ⁄ 2 H 2 O. Under the above acidic conditions, ferric iron (Fe 3+) is a more potent oxidant than oxygen, resulting in faster pyrite oxidation rates.
The strong acidification of the medium caused by pyrite oxidation releases bicarbonate ions (HCO − 3) or carbon dioxide (CO 2) along with calcium (Ca 2+) and sulfate ions (SO 2− 4). Full pyrite oxidation can be schematized as: 2 FeS 2 + 7.5 O 2 + 4 H 2 O → Fe 2 O 3 + 4 H 2 SO 4. The sulfuric acid released by pyrite oxidation then reacts ...
Acid sulfate soils are naturally occurring soils, sediments or organic substrates (e.g. peat) that are formed under waterlogged conditions.These soils contain iron sulfide minerals (predominantly as the mineral pyrite) and/or their oxidation products.
Metal sulfides (e.g., pyrite FeS 2, arsenopyrite FeAsS, chalcopyrite CuFeS 2) are normally processed by chemical oxidation either in aqueous media or at high temperatures. In fact, most base metals, e.g., aluminium, chromium, must be (electro)chemically reduced at high temperatures by which the process entails a high energy demand, and ...
In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering.