Rocks containing high-pressure mineral assemblages derived from the mantle transition zone between depths of about 400 and 670 kilometers occur as xenoliths and megacrysts on the island of Malaita in the southwest Pacific on the Ontong Java Plateau. Observed ultrahigh pressure mineral chemistries include majorite, calcium- and magnesium-perovskite, aluminous silicate phases, and microdiamond. Based on an empirical barometer, majoritic garnets in these xenoliths record pressures of up to 22 gigapascal. The occurrence of material with perovskite chemistry and several enigmatic aluminous phases indicates pressures of up to 27 gigapascal. Samples were brought to the surface at about 34 million years ago by potassic ultramafic magmas, which evidently originated in the lower mantle.
The substitution of charcoal as an alternative fuel to coke breeze in a simulated Japanese Steel Mills (JSM) sinter blend was investigated. Compared with coke breeze, higher mix moisture contents were required for the sinter mixture containing charcoal to achieve optimum granulation. The green granules formed from the sinter mixture containing charcoal were clearly less dense and formed a less compacted green bed as evidenced by the packing density. To achieve return fines balance, fuel addition had to be increased from 3.62 to 4.17% (on a dry mixture basis) as the substitution of charcoal increased from 0 to 50%. However, at 100% subsitution, the sinter mixture failed to achieve balance even at a very high fuel addition level of 4.7%. Compared with the sinter fired with coke breeze, the sinter from the mixtures containing up to 50% charcoal was marginally weaker in terms of sinter yield, tumble strength (TI) and reduction disintegration (RDI). The reasons for weaker sinter are discussed. Fuel rate increased considerably with charcoal substitution due to increased fuel addition and decreased sinter yield. However, increasing fuel rate did not lead to a reduction of sintering productivity. In contrast, the sintering speed and productivity were maintained as the charcoal substitution rate increased from 0 to 25% and then increased considerably with further increase in charcoal substitution rate. The emission mechanisms of the CO, CO2, SO2 and NOX and H2O gases during sintering are clearly quite different. CO, CO2 and NOx emission was observed over the entire sintering process and varied slightly as the sintering process progressed. However, the SO2 and H2O emissions were observed only towards the completion of the sintering process. Both the CO and CO2 concentrations in the waste gas increased with the increasing substitution of charcoal for coke breeze; however the concentrations of SO2 and NOX in the waste gas decreased.
In order to develop downstream processing routines for iron ore and to understand the behaviour of the ore during processing, extensive mineralogical characterisation is required. Microscopic analysis of polished sections is effective to determine mineral associations, mineral liberation and grain size distribution. There are two main imaging techniques used for the characterisation of iron ore, i.e. optical image analysis (OIA) and scanning electron microscopy (SEM). In this article, a QEMSCAN system is used as an example of SEM methodology and results obtained from it are compared against results obtained by the CSIRO Recognition3/Mineral3 OIA system. Both OIA and SEM systems have advantages and drawbacks. Even though the latest SEM systems can distinguish between major iron oxides and oxyhydroxides, it is still problematic for SEM systems to distinguish between iron ore minerals very close in oxygen content, e.g. hematite and hydrohematite, or between different types of goethite. Scanning electron microscopy systems also can misidentify minerals with close chemical composition, i.e. hematite as magnetite and vitreous goethite as hematite. In OIA, iron minerals with slight differences in their oxidation or hydration state are more easily and directly recognisable by correlation with their reflectivity. In both methods, the presence of microporosity can result in some misidentification, but in SEM methods misidentifications due to microporosity can be critical. Low resolution during QEMSCAN analysis can significantly affect the textural classification of particle sections. The main conclusion of this study is that, for low iron content ores or tailings, SEM systems can provide much more detailed information on the gangue minerals than OIA. However, for routine characterisation of iron ores with high iron content and containing a variety of iron oxides and oxyhydroxides, OIA is a faster, more cost effective and more reliable method of iron ore characterisation. A combined approach using both techniques will provide the most detailed understanding of iron ore samples being characterised.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.