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- Ferrow, Embaie, et al.
(författare)
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Pyrite: Linking Mossbauer spectroscopy to mineral magnetism
- 2003
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Ingår i: Material Research in Atomic Scale by Mössbauer Spectroscopy. - 1402011962 ; 94, s. 251-259
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Konferensbidrag (refereegranskat)abstract
- Gold-bearing pyrite ores are refractory and must be pre-treated to break down the sulphides by oxidation. This is done usually by roasting, bacterial oxidation and smelting. Moreover, ores with high sulphur content require pre-treatment to prevent excessive chlorine consumption, an important source of pollution. The pyrite waste created in mining operation presents serious problems on the environmental impact of acid mine drainage. In order to improve separation of pyrite from other metals as well as for the development of new strategies to inhibit oxidation of pyrite, it is necessary to understand the thermal, chemical, magnetic and biological implications during alteration of pyrite. The oxidation of pyrite in air was studied using Mossbauer spectroscopy and mineral magnetic methods. A pyrite concretion from biogenic limestone shows a very weak natural remanent magnetization. Heating of the pyrite produced alpha-hematite as the end product. Intermediate mineral phases created during heating depend mainly on temperature, heating rate, grain size and the atmosphere in the oven. The most magnetic phases occur about 500 T as determined from magnetic susceptibility and hysteresis measurements. The components of the compound hysteresis were iron sulphates and polymorphs of hematite as determined by Mossbauer spectroscopy. Heating of powder of pyrite produced higher concentration of pyrrhotite than grains of mm size as a result of more thorough oxidation as a result of increased ratio of iron to sulphur produced by degassing during heating. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mossbauer spectroscopy with rock magnetic methods provides information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters.
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| 2. |
- Ferrow, Embaie, et al.
(författare)
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Reaction kinetics and oxidation mechanisms of the conversion of pyrite to ferrous sulphate: A Mossbauer spectroscopy study
- 2005
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 1572-9540 .- 0304-3843. ; 163:1-4, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 degrees C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S-S and Fe-S bonds in pyrite.
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| 3. |
- Mannerstrand, Maria, et al.
(författare)
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Garnet chemistry from the Sloinge excavation, Halland and additional Swedish and Danish excavations - Comparisons with garnet, occurring in a rock context
- 2003
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Ingår i: Journal of Archaeological Science. - : Elsevier BV. - 1095-9238 .- 0305-4403. ; 30:2, s. 169-183
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Tidskriftsartikel (refereegranskat)abstract
- Information on the geological origin of raw garnet is a pre-requisite for the better understanding of garnet production and trade in ancient societies. The presented study is a first attempt to determine possible source rocks for the garnets found in the Sloinge excavation in southwest Sweden. It includes analyses of garnets from other excavations in Sweden and Denmark. It is also an attempt to demonstrate the strength and shortcomings of a mineralogical-chemical approach to test hypotheses concerning trade and mining in ancient societies. The chemical composition of garnets from both the excavations and from possible source rocks in southwest Sweden have been analysed with a scanning electron microscope equipped with an EDS-detector. In addition, literature data on garnet compositions in east-central Sweden are used for comparative purposes. The analyses show that the archaeological garnets all are almandine-rich and remarkably similar in composition, irrespective of their origin. This result indicates that an important trade with garnet from a few mines occurred during the late Iron Age. Possible and probable source rocks are garnet-amphibolites/mafic granulites which are common in southwest Sweden. (C) 2002 Published by Elsevier Science Ltd.
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