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Pyrometallurgical Process for Recycling of Valuable Materials and Waste Management: Valorisation Applications of Blast Furnace Slags
Published in Hossain Md Anawar, Vladimir Strezov, Abhilash, Sustainable and Economic Waste Management, 2019
Sara Yasipourtehrani, Vladimir Strezov, Tim Evans, Hossain Md Anawar
There are different crystalline phases for BFS after heat treatment, such as merwinite, melilite, larnite, gehlenite, and åkermanite (Fredericci et al., 2000). Merwinite (Ca3 Mg (SiO4)2) is a metastable phase of BFS and it forms at 1000°C. Through further heating, merwinite irreversibly disappears to the thermodynamically stable phase. Melilite, which is another crystalline phase, includes all principal components of BFS and 10wt% Al2O3. Larnite (Ca2SiO4) is a slag with more SiO2 and CaO than is needed to form åkermanite (2CaO.MgO.2SiO2) and gehlenite (2CaO.Al2O3.SiO2), which are known as the melilite series. Melilite is a solid solution between gehlenite and akermanite. The excess CaO and SiO2 is sufficient to form calcium silicate (Fredericci et al., 2000). Eisenhuttenleute (1995) produced a slag atlas and discussed presented different characteristic compositions of BFS in two systems of CaO-SiO2-Al2O3 and CaO-SiO2-MgO. Melilite is a solid solution of åkermanite (Ca2MgSi2O7) and gehlenite (Ca2Al2SiO7) (Mendybaev et al., 2006). Melilite consists of åkermanite and gehlenite and produces interrupted solid solution. When the amount of Al2O3 increases the gehlenite phase will be obtained, but when the amount of MgO is increased the åkermanite phase will be obtained.
The role of SiO2 and silica-rich amorphous materials in understanding the origin of uncommon archeological finds
Published in Materials and Manufacturing Processes, 2020
Although these equations are too simple, the first balance shows that the SiO2 content of the charge is inexpedient, since all Fe at the end is bound in the slag and lost. The third scenario is the most realistic one and probably rather common.[36] An inverse proportion can be observed between the SiO2 content of the roasted ore and the yield of metal. However, the basic slag composition in all cases is the same (wüstite and fayalite), and corresponds to the lowest melting point in the FeO-SiO2 system and, rather well, to the composition of most slags found on ancient iron smelting sites. Therefore, we need more information on the chemical and mineralogical compositions of the slags in order to calculate the yield of an ancient furnace. In practice, these reactions and processes are much more difficult, because of the other chemical components of the system, like Ca and Mg contributing to clinker phase crystallization, e.g. gehlenite-akermanite, larnite, monticellite, etc.[16] Another problem is the technologically different kind of slags mixed, which has to be categorized correctly to apply the composition in yield calculation. Because of this, recognizing fused clay residue and glassy slags is of key importance,[15] as they have high SiO2 content, but are not related to smelting. Based on our investigations, it seems that generally early ironmakers had at disposal bog ores with 5-10% SiO2.
Study of physical and dielectric properties of bio-waste-derived synthetic wollastonite
Published in Journal of Asian Ceramic Societies, 2018
The results of this study demonstrate that chicken eggshells and RHA can be used for the production of sustainable, high-purity synthetic wollastonite as an ingredient for ceramics and other industrial products. The physical and dielectric properties of wollastonite were investigated and the following results were obtained: It was found that the peak of β-wollastonite, a small quantity of larnite (Ca2SiO4) and unreacted cristobalite (SiO2) are detected at 1000°C and that only β-wollastonite is observed after calcination at 1100°C.Powder calcined at 1150 and 1200°C contains mainly α-wollastonite and a slight portion of unconverted β-wollastonite.The average particle and grain sizes increase with increases in the calcined and densification temperatures of wollastonite.The density and mechanical strength are also improved with increases in the sintering temperature.The dielectric properties of wollastonite are not affected significantly, however, by the transformation of β to the α phase.The wide range of temperatures (30–480°C) does not alter the dielectric behavior of wollastonite.
Assessment of crystalline phase change and porosity by Rietveld refinement on lightweight cullet and paper ash glass-ceramic
Published in Journal of Asian Ceramic Societies, 2020
K. Abu-Samah, M.R. Sahar, M. Yusop, F. Mohd-Noor, M.F. Omar, R. Zainal, D.N. F. Abdul Halim
The evolutions of crystallinity from Rietveld refinement against the cullet content at different sintering temperature are presented in Figure 4. Figure 4(a–c) represents the β-Wollastonite, Larnite and quartz phase, respectively. The result delineates that the composition of cullet/paper ash and sintering temperature have greatly influenced in the formation of β-Wollastonite. The graph illustrated in Figure 4(a) shows that the β-Wollastonite phase increases progressively with the increasing of sintering temperature.