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Published in Anthony Peter Gordon Shaw, Thermitic Thermodynamics, 2020
Most of the compounds in Table 5.22 occur naturally as minerals. Some are more common than others. Some of the most common are pyrite (FeS2), chalcopyrite (CuFeS2), chalcocite (Cu2S), sphalerite (ZnS), and galena (PbS). Chalcocite and covellite (CuS) are less common than chalcopyrite, the primary ore of copper. Sphalerite and galena are the primary ores of zinc and lead, respectively. Cinnabar (HgS) is the only important ore of mercury. Even though cinnabar is not especially rare, the overall concentrations of mercury and silver within the earth’s crust are thought to be similar [1]. Troilite (FeS), the stoichiometric end-member of the pyrrhotite group, is a common constituent of meteorites. Pyrrhotites usually contain significantly less iron than sulfur, as indicated by the general formula Fe(1 − x)S in which x may be as great as about 0.17. They are commonly associated with pyrite, chalcopyrite, and other sulfides in terrestrial ore deposits [109].
Formation of pyrite in the process of fine coal desulfurization by microwave enhanced magnetic separation
Published in International Journal of Coal Preparation and Utilization, 2023
Zhenxing Zhang, Xinyu Wei, Guanghui Yan, Junwei Guo, Pengfei Zhao, Fan Yang, Hongyu Zhao, Bo Zhang
The specific magnetic susceptibility was used to thoroughly characterize the phase change as a result of microwave treatment and reveal the law of phase formation. Pulverized coal with different particle sizes was treated by microwave with a power of 1000 W, a frequency of 2.45 GHz, and the processing times of 1, 2, 3, 4, and 5 min. The changes in the magnetic properties of the pulverized coal with different particle sizes in different times were analyzed using a Gouy-II magnetic balance. Figures 9(a-b) show the variation in specific magnetic susceptibility of −0.047 mm, 0.074–0.15 mm, 0.15–0.3 mm, 0.3–0.5 mm, and −0.5 mm pulverized coal at different microwave treatment times. The specific magnetic susceptibility of each particle size pulverized coal first shows an increasing and then a decreasing trend. Pyrite is the most prominent component of coal, responding to microwave energy and also simultaneously exhibited significant changes in the magnetic properties of coal. The XRD analysis shown in Figures. 2, 3, 4, and 5 shows that the coal series pyrite in the fine coal gradually transformed from pyrite to pyrrhotite and then to troilite under microwave treatment. Among the three, pyrrhotite is the most magnetic, followed by troilite, and then pyrite.
Magnetic sorbents biomineralization on the basis of iron sulphides
Published in Environmental Technology, 2018
Jana Jencarova, Alena Luptakova, Nikola Vitkovska, Dalibor Matysek, Petr Jandacka
The composition of iron sulphides produced by SRB is often not exactly known. In such cases, when identification of mineral phases is difficult, the creation of amorphous non-stoichiometric ‘mixture’ of iron sulphides is assumed. The structural factors in precipitates are clearly reflected in the magnetic properties which are quite variable depending on the exact nature of the Fe/S ratio. Simple magnetic measurements can rapidly and non-destructively characterize the concentration, mineralogy and magnetic grain size of magnetic minerals present in samples. These properties are strongly sensitive to the abundance and type of iron-bearing minerals. All iron sulphides exhibit a response to an externally applied magnetic field. Ferrimagnetic minerals produce the strongest reactions, antiferromagnetic and paramagnetic minerals weaker. For example, troilite (FeS) is antiferromagnetic, greigite (Fe3S4) strongly ferrimagnetic, mackinawite (Fe(1+x)S) and pyrite (FeS2) are paramagnetic, monoclinic pyrrhotite (Fe7S8) is ferrimagnetic, but pyrrhotite (Fe(1−x)S) with hexagonal structure is antiferromagnetic. Variation in environmental conditions can alter the reactive iron species within the mineral, potentially modifying their magnetic properties. Organic matter, biogenic activity, pH, Eh, sediment and porewater geochemistry are important factors that can promote reductive and/or oxidative diagenesis and authigenic (re)precipitation of magnetic mineral species that may differ significantly from those originally deposited [41].
Recent Advances in Magnetization Roasting of Refractory Iron Ores: A Technological Review in the Past Decade
Published in Mineral Processing and Extractive Metallurgy Review, 2020
Jianwen Yu, Yuexin Han, Yanjun Li, Peng Gao
Several researchers have investigated the effect of microwave heating on phase change and magnetic separation of pyrite (Uslu et al. 2003; Waters et al. 2007; Xing et al. 2017). According to the reported results, the microwave treated pyrite was firstly converted to ferromagnetic pyrrhotite, and then to troilite under a nitrogen atmosphere. With the prolonging of microwave radiation time, the pyrite was initially transformed to ferromagnetic pyrrhotite, then to anti-ferromagnetic hematite (α-Fe2O3), and finally to ferromagnetic maghemite (γ-Fe2O3) in air. Thus, the performance of magnetic separation in removing mineral pyrite from coal was improved due to the magnetic enhancement of pyrite induced by microwave radiation.