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Crucible Materials
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
Mag–chrome or MgO–Cr2O3 refractories find predominant use in copper smelting, converting and refining furnaces (Schlesinger 1996). Widespread use of mag–chrome began in the 1950s and 1960s and continues to date. Chromite ore contains CrO and MgO and also Al2O3, Fe2O3 and SiO2 in significant amounts. The first mag–chrome refractories produced, and which still remain in use, are the silicate-based (“burned”) materials. They are obtained when the chromite ore is fired at temperatures <1500°C with or without added magnesia. Their microstructure shows grains of a spinel-based structure, (Mg,Fe)(Al,Fe,Cr)2O4, surrounded by a rim of fosterite Mg2SiO4 (m.p. ~1900°C) and silicates. The silicate phases are low melting (~1200°C for fayalite), and the usefulness of such refractories is thus limited.
Selected Case Studies of Ternary Systems
Published in D. R. F. West, N. Saunders, Ternary Phase Diagrams in Materials Science, 2020
Note the saddle-points on the magnetite–fayalite section at 1150°C corresponding to the eutectic formation of fayalite and magnetite and at a higher, but unspecified temperature, associated with the incongruent melting of fayalite, which involves γ-iron. The arrows on the liquidus isotherm also indicate a saddle-point on the tridymite-magnetite eutectic curve near to the silica-magnetite-haematite invariant eutectic.
Minerals
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Minerals such as quartz (SiO2), halite (NaCl), or fluorite (CaF2) are generally close to the pure composition described by their formulas. They have compositions that vary little in nature, and only very minor amounts of other elements substitute for those in the ideal formula. Their formulas tell us the ratios of the constituent elements. Other minerals are solid solutions, and commas in formulas indicate elements that can substitute for each other (Fig. 3.19). Olivine, for example, may have any composition between Mg2SiO4 and Fe2SiO4, but the atomic ratio Mg+Fe:Si:O is always 2:1:4. So, olivine forms a solid solution and is a binary mineral series between two end members: Mg2SiO4 (called forsterite) and Fe2SiO4 (called fayalite). A general formula for olivine is (Mg,Fe)2SiO4 if it contains more Mg than Fe, and (Fe,Mg)2SiO4 if it contains more Fe than Mg. Subscripts may be used in the formula to reflect the ratio of Mg:Fe, if it is known. (e.g., Mg1.82Fe0.18SiO4 describes olivine that is 1.81/2 = 81% forsterite and 9% fayalite.)
Evaluation of carbothermal reduction for processing of banded hematite quartzite iron ore
Published in Canadian Metallurgical Quarterly, 2020
Veeranjaneyulu Rayapudi, Nikhil Dhawan
In this study, the processing of low-grade BHQ iron ore (Fe∼34%) was investigated for the recovery of iron values. The conventional carbothermal reduction yielded limited iron enrichment (FeG 40–50%, FeR 90–95% at 800 °C for 1 h). The reduction kinetics was not delineated due to heterogeneous ore character and low process response. Microwave carbothermal reduction at the varying charcoal dosage (6–11%) yielded better iron grade, however, at higher charcoal dosage (11%) the ferrite ball formation was observed. Taguchi statistical design revealed the conditions of formation of ferrite ball higher charcoal dosage (9–12%) and higher power (720–900 W). The products formed include fayalite, wustite and ferrite and the magnetic fraction can be used in alternative iron making. Ferrite ball can be used as a cast-iron product and non-magnetic fraction can be blended with high grade or reduced ore. It is strongly believed that the results can provide some key insights for researchers for application of microwaves in the enrichment of low-grade iron ores.
Potential utilization of hazardous mining wastes in the production of lightweight aggregates
Published in Mineral Processing and Extractive Metallurgy, 2018
Hyunsik Park, Minchul Ha, Doyun Shin, Minseok Kim, Il Sohn
Using characteristic XRD patterns of quenched samples, the dominant phases present at each temperature were determined. The changes in the four major constituents at the various temperatures can be seen in Figure 5. The un-heated green pellets at 25°C consist mainly of the quartz, hematite and calcite, which corresponds to a simple mixture of three mining wastes used. Because calcite decomposes at 897°C, it is no longer observed in samples heated above 1050°C but is present as CaO (Gaskell 2003). At 1050 and 1100°C, quartz, alumina, hematite and lime are the main phases present. The raw materials are physically present until 1100°C, and new complex phases are not apparent from the XRD patterns. However, fayalite (Fe2SiO4) is formed for samples heated at 1150°C. Some hematite phases and quartz phases are observed within the XRD patterns, but a wüstite-based compound is formed due to the redox equilibrium of the iron oxides within the molten phase. Fayalite, a well-known phase having the olivine structure, is a common mineral observed in nature and is widely used to form low-temperature liquid slags at 1177–1205°C in the copper smelting and is dependent on the FeO/SiO2 ratio (Park et al. 2011a). The formation of fayalite in the pellet changes the sintering mechanism from a solid-state sintering to a partial liquid-state sintering process and allows improved sintering kinetics at lower temperature processing. By increasing the contact between the solid particles, the pathway for diffusion is significantly increased, resulting in higher kinetics and also greater amounts of diffusion. When the specimen is heated to 1200°C and higher, a significant amount of liquid phase is present within the sample and when the sample is quenched an amorphous phase can be formed which is evident from the hump above the baseline of the XRD pattern near 2θ of 27°. As the amount of liquid phase increases, the intensity of the crystalline quartz peak will be reduced and the glass forming Si–O bonding within the liquid melt will likely become increasingly dominant. This glass forming Si–O bonding characteristic can be qualitatively identified through FT-IR analysis.