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For the cobalt ‐ bearing copper oxide concentrate from Congo, experiment of coke reduction smelting with fayalite slag was conducted. The effects of CaO ‐ to ‐ SiO2 mass ratio, FeO ‐ to ‐ SiO2 mass ratio and coke rate on the reduction rates of copper and cobalt were investigated. The reduction sequence and conditions of copper, cobalt, iron and silicon oxides were analyzed by thermodynamics. The reduction process of copper, cobalt and iron oxides was quantitatively analyzed by means of metal oxide reduction thermodynamics and coke gasification kinetics. The results show that the reduction of copper, cobalt and iron in the copper oxide concentrate can be divided into the competitive fast reduction period in the early stage and the slow reduction period of copper and cobalt in the later stage. The reduced metal iron in the slow reduction period will undergo reoxidation. The large amount of competitive iron reduction in the early stage and its reoxidation in the later stage will reduce the reduction rate of copper, cobalt and iron and the effective utilization rate of coke. The formation mechanism of ferroalloy layer on the surface of crude copper is revealed. [ABSTRACT FROM AUTHOR]

Water-quenched copper-nickel metallurgical slag enriched with olivine minerals exhibits promising potential for the production of CO2-mineralized cementitious materials. In this work, copper-nickel slag-based cementitious material (CNCM) was synthesized by using different chemical activation methods to enhance its hydration reactivity and CO2 mineralization capacity. Different water curing ages and carbonation conditions were explored related to their carbonation and mechanical properties development. Meanwhile, thermogravimetry differential scanning calorimetry and X-ray diffraction methods were applied to evaluate the CO2 adsorption amount and carbonation products of CNCM. Microstructure development of carbonated CNCM blocks was examined by backscattered electron imaging (BSE) with energy-dispersive X-ray spectrometry. Results showed that among the studied samples, the CNCM sample that was subjected to water curing for 3 d exhibited the highest CO2 sequestration amount of 8.51wt% at 80°C and 72 h while presenting the compressive strength of 39.07 MPa. This result indicated that 1 t of this CNCM can sequester 85.1 kg of CO2 and exhibit high compressive strength. Although the addition of citric acid did not improve strength development, it was beneficial to increase the CO2 diffusion and adsorption amount under the same carbonation conditions from BSE results. This work provides guidance for synthesizing CO2-mineralized cementitious materials using large amounts of metallurgical slags containing olivine minerals. [ABSTRACT FROM AUTHOR]

The primary intent of the research is to comprehensively assess the environmental benefits and cost dynamics associated with the adsorption process of CS–RHA (Copper Slag and Rice Husk Ash) to produce a novel geopolymer adsorbent material for application in wastewater treatment. The geopolymer forms a polyiron sialate network under alkali activation by dissolving fayalite, and aluminium silicate to ferro-ferri silicate hydrate gel. The mechanical strength, leaching characteristics, and microstructure of the geopolymer were determined using XRD and FTIR, and magnetic properties by VSM as well surface properties were derived from BET surface area and zeta potential. Recognizing the critical role of sodium iron silicate hydrate (NFS) in the sorption of methylene blue (MB) dyestuff, batch experiments were carried out using different adsorbents. The results indicated that the dye removal efficiency increased from 60% in control samples (FS) to 98% for the blend (FS1) under different pH values. The data was found to fit with the nonlinear form of Freundlich isotherm and follow pseudo-second-order kinetics. The active adsorption sites were deduced as –O–Fe–O–Si–O–Na and Si–OH groups. The addition of RHA increases the adsorption capacity of the geopolymer in a short time through chemical adsorption. The significant negative surface charge promotes MB adsorption via improved electrostatic attraction. The spent adsorbents were recovered through magnetic separation with a retrieval rate of 80–85% and active sites were rejuvenated by calcination. Consequently, waste copper slag emerges as a promising adsorbent with minimum potential ecological risk and high effective recycling capacity. [ABSTRACT FROM AUTHOR]

Iron (Fe) accounts for the highest-content of valuable metal recoverable from copper slag, which is most effectively recycled using pyrometallurgical high-temperature treatment. It is believed that the roasting temperature significantly affects the physical structure of copper slag. Therefore, this paper used thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM) to examine the Fe phase transformation in water-quenched copper slag (WQCS) and naturally cooled copper slag (NCCS) after high-temperature treatment (700–1100 °C). The main Fe-containing phases in the WQCS were represented by fayalite (Fe2SiO4) and magnetite (Fe3O4). As the temperature increased, the Fe2SiO4 underwent oxidative decomposition and re-formation, with a phase transition law of Fe2SiO4→Fe2O3+Fe3O4→FeSiO3+Fe2SiO4, while that of the Fe3O4 was Fe3O4→Fe2O3→Fe3O4. The phase transition processes were more complex in the NCCS, where the main Fe-containing phases were Fe2SiO4, Fe3O4 and chalcopyrite (CuFeS2). The oxidative decomposition temperatures of the Fe2SiO4 ranged from 700 °C to 850 °C. As the temperature increased, the phase transition law of Fe3O4 was Fe3O4→Fe2O3→Fe3O4→Fe2O3. Lastly, at 700 °C, the CuFeS2 began to oxidize and decompose, with a phase transition law of CuFeS2→FeS + Fe2O3→Fe3O4.

For powder magnetic cores, a spinel ferrite insulating layer offers the advantages of high magnetic flux density and low iron loss. However, FeO is generated in the insulting layer after annealing at 873 K, which causes a decrease in electrical resistivity. To overcome this problem, we focused on fayalite (Fe2SiO4), which exhibits a high electrical resistivity and is stable even at temperatures above 1273 K. Fe2SiO4 can be formed by a reaction between FeO and SiO2. Therefore, if Fe powder particles mixed with both spinel ferrite and SiO2 are heated at a temperature that is sufficiently high to form FeO, Fe2SiO4 is expected to be produced, and the resulting particles are likely to exhibit high electrical and thermal resistance. To examine this possibility, a mixture of Fe3O4 of spinel-type ferrite, SiO2, and Fe powder was heated at 1023 K, and the structure and composition of the resulting material were investigated. Analyses using X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the formation of Fe2SiO4, which showed a high electrical resistivity. These results indicate that Fe2SiO4 can be used as an insulating layer for powder magnetic cores. [ABSTRACT FROM AUTHOR]

The lattice parameters and the crystal and magnetic structures of Fe2SiO4 have been determined from 10 K to 1453 K by high-resolution time-of-flight neutron powder diffraction. Fe2SiO4 undergoes two antiferromagnetic phase transformations on cooling from room temperature: the first, at 65.4 K, is to a collinear antiferromagnet with moments on two symmetry-independent Fe ions; the second transition, at ~23 K, is to a structure in which the moments on one of the sets of Fe ions (those on the 'M1 site') become canted. The magnetic unit cell is identical to the crystallographic (chemical) unit cell and the space group remains Pbnm throughout. The magnetic structures have been refined and the results found to be in good agreement with previous studies; however, we have determined the spontaneous magnetostrictive strains, which have not been reported previously. In the paramagnetic phase of Fe2SiO4, at temperatures of 70 K and above, we find that the temperature dependence of the linear thermal expansion coefficient of the b axis takes an unusual form. In contrast to the behaviour of the expansion coefficients of the unit-cell volume and of the a and c axes, which show the expected reduction in magnitude below ~300 K, that of the b axis remains almost constant between ~70 K and 1000 K. [ABSTRACT FROM AUTHOR]

In this study, we present new evidence for changes in magma storage conditions that preceded the 1232 ka caldera-forming eruption of the Bandelier magmatic system in the Jemez Mountains Volcanic Field. Using high precision 40Ar/39Ar sanidine dating we determine that at least eight rhyolites erupted within 8.6 ± 3.4 kyr of the ~400 km3 eruption that formed Valles caldera. Some of those rhyolites contain fayalite with or without biotite, others contain only biotite. An eruption of fayalite-bearing rhyolite at 1240.5 ± 2.1 ka ended an eruption hiatus of at least 100 kyr. Following that first post-hiatus episode of volcanism, at least four more eruptions of fayalite-bearing rhyolite and three eruptions of biotite-bearing rhyolite occurred prior to the caldera-forming eruption. We use phase equilibrium experiments and geothermobarometry to infer the storage conditions and processes that led to these differing crystal cargos and ultimately generated ~400 km3 of predominantly fayalite rhyolite ignimbrite (Tshirege Member of the Bandelier Tuff). We find that biotite-bearing rhyolites were stored at 695–750°C, 75–160 MPa, and at an oxygen fugacity more oxidizing than the quartz-fayalite-magnetite (QFM) buffer reaction. Fayalite-bearing rhyolites were similarly stored at 695–745°C and 70–190 MPa, but at more reducing conditions (⁠|${f}_{O_2}$| ≤ QFM). We suggest that the reduced, fayalite-bearing rhyolite was most likely produced via interaction of crystal-poor rhyolitic magma with a reducing, potentially Cl-bearing, and H2O-rich supercritical fluid phase. This fluid flux event was a key component of the substantial magmatic rejuvenation that enabled the mobilization of ~400 km3 of mostly fayalite-bearing rhyolite prior to not only the Tshirege event, but the older Otowi event as well. [ABSTRACT FROM AUTHOR]

In general, phosphate cements have a very rapid setting reaction at room temperature. The same holds for copper slag-based phosphate cements. This means that using them as a binder, for instance as mortar, is always possible on a small scale, but very difficult on a large scale. In this paper, the heat treatment of the copper slag was shown to be an effective way to increase the setting time and keep the mix workable for an adequate period. The main objective of this research was to examine the changes in the phase composition of quenched copper slag after exposure to 500 °C and to evaluate the impact of these changes on the reactivity of the material in an acidic environment, as well as on the mechanical properties, microstructure, and structure of the produced phosphate cement materials. Various experimental methods were utilized to characterize the raw materials and the obtained phosphate cementitious materials, including isothermal microcalorimetry (TAM Air), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as the determination of the chemical composition using X-ray fluorescence (XRF) and the particle size distribution. Furthermore, compressive strength tests were conducted to gauge the mechanical resistance of the materials. The main findings of this work revealed that subjecting the copper slag to a thermal treatment of 500 °C induced a partial transformation in its structure. The high temperature caused the oxidation of some of the divalent iron oxide in the slag, leading to the formation of hematite. This treatment increased the setting time and reduced the reactivity of the copper slag with phosphoric acid, ultimately enabling the production of a dense phosphate-based cementitious material with outstanding mechanical properties. The compressive strength of the newly developed cement was recorded to be greater than 78.9 MPa after 7 days, and this strength continued to increase, reaching 82.5 MPa after 28 days. [ABSTRACT FROM AUTHOR]

Fayalite (Fe2SiO4 is a major component of olivine and is often formed in the surface oxide layer (oxide scale) on steel plates owing to its high temperature oxidation. The thermal conductivity of the oxide scale and its constituents, including fayalite, is essential for controlling the cooling rate of hot steel plates. Therefore, this study uses modulated thermoreflectance microscopy to determine the thermal effusivity/conductivity of fayalite particles with diameters smaller than 180 μm because the sample coinmercially available is such a small size. This thermal optical microscopy enables the measurement of thermal effusivity for small areas, such as 10 μm. The thermal effusivity and conductivity were found to be 4.1 ± 0.2 kJs-0.5 K-1m-2 and 6.0 ± 0.5 Wm-1K-1, respectively. These values are representative of the bulk value. Additionally. the thermal conductivity of fayalite is shown to be higher than that of wüstite (Fe1-xO), which is the main component of the oxide scale. The oxide scale formed on the thick steel plate comprises a Si-rich layer, a wüstite layer, and a magnetite layer. Furthermore. the Si-rich layer comprises fayalite, wüstite. and pores. The effective thermal conductivity of the Si-rich layer was calculated by observing the oxide scale formed on the steel plate. The low thermal conductivity of the Si-rich layer indicates that the thermal conductivity of the layer is strongly affected by the porosity of the oxide scale. Furthermore, although the Si-rich layer is thin, it significantly contributes to the heat resistance of' the oxide scale. [ABSTRACT FROM AUTHOR]

The presence of olivine and its geochemical composition (forsterite/fayalite ratio) are relevant factors for the study of Mars. The use of Raman spectrometers in the Mars 2020 and future missions opens new possibilities to assess the Mg/Fe ratios in the analyzed olivine bearing rocks. On the one hand, its presence indicates approximately where and when Mars had volcanic activity, due to the partial weathering of this mineral into other secondary minerals. On the other hand, the forsterite and fayalite content of olivine can be used to study the origin and evolution of its parent magma, since this mineral is one of the first to crystallize from it. In order to properly study the forsterite and fayalite ratio of olivines, this work proposes a new calibration model using Raman spectroscopy, doing a thorough literature review of previous studies in order to improve the calibration quality. The proposed model improves greatly the accuracy and uncertainty associated with the final result of forsterite and fayalite (around 2%) compared to those published earlier in the literature (around or above 10%). Using the new model, it will be possible to assess the forsterite and fayalite ratios of Martian olivines properly, providing relevant information about their parent magma. [ABSTRACT FROM AUTHOR]

A piece of iron slag was found on an archaeological site near Boršice on the SE margin of the Chřiby Mts., Czech Republic, which is known by occurrence of artifacts from the Early Neolithic (5700 - 5000 BC), Bronze and Early Medieval Ages. We present results of laboratory investigation of this slag. It is composed mainly of fayalite laths, which belong to two generations, less occur glass phase, wüstite and leucite, exceptionally also metallic iron. The composition of fayalite displays unified chemical trend and ranges in rather narrow span (Fa93.7-96.3DCS1.1-5.8Fo0.0-5.0Te0.0-0.2). The glass phase contains in addition to common compounds (Si, Fe, Al, alkalis) also elevated contents of P and Ca. The microstructure of the studied slag as well as chemistry of individual phases are very homogeneous across the whole sample. We interpret this slag as an iron smelting slag, originated during production of iron from ores using the direct method. The used ore was in all probability a limonite bog ore, whereas the use of local fresh and/or weathered pelosiderites is not probable on the basis of the recorded phase composition and chemical compositions of individual phases. [ABSTRACT FROM AUTHOR]

Copyright of Acta Petrologica et Mineralogica / Yanshi Kuangwuxue Zazhi is the property of Acta Petrologica et Mineralogica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Calcium-aluminum-rich inclusions (CAIs) commonly observed in chondritic meteorites are the oldest dated solids formed in the Solar System. Short-lived isotope chronologies (26Al-26Mg, 182Hf-182W) suggest a ∼2 Ma gap between the formation of CAIs and the accretion of the final chondrite parent bodies. One thin section, 3.27 cm2 in size, of an ordinary chondrite NWA 3358 (H3.1) studied contains 52 refractory inclusions (CAIs and amoeboid olivine aggregates (AOAs)) comprising 0.14 % of its area, which is the highest abundance of refractory inclusions among non-carbonaceous chondrites containing on average ∼0.009 area % of CAIs and AOAs. In combination with a low chondrule/matrix ratio of ∼1.5, this makes NWA 3358 a unique ordinary chondrite. The aqueously-formed fayalites (Fa >99) in NWA 3358 have the inferred initial 53Mn/55Mn ratio of (5.56 ± 0.44) × 10−6 which is the highest measured value for secondary minerals in chondrites and corresponds to the formation time of ∼1.0–1.5 Ma after CAIs. Based on the 53Mn-53Cr chronology of fayalite formation and the thermal modeling, we infer that the first-generation of an H chondrite parent body, ∼6–12 km in diameter, accreted within 1.0 Ma after formation of CAIs, filling the gap of ∼2 Ma between CAIs and the earliest chondrite parent bodies. This early accretion provides a possible mechanism of CAIs/AOAs storage in the inner solar nebula and could explain the high amount of refractory inclusions in NWA 3358. A later destruction of these first-generation bodies may also explain the presence of CAIs and chondrules of different ages within later formed chondrite parent bodies. [ABSTRACT FROM AUTHOR]

Copper slag is usually a mixture of iron oxide and silicon dioxide, which exist in the form of fayalite (2FeO·SiO2), and contains ceramic components as the SiO2, Al2O3 and CaO depending on the initial ore quality and the furnace type. Our present study was focused on manufacture of foundry pig iron with Cu content from copper slag using high-temperature reduction smelting and investigate utilization of by-products as a reformed slag, which is giving additional value to the recycling in a replacement of raw material of Portland cement. Changes of the chemical and mineralogical composition of the reformed slag are highly dependent on the CaO concentration in the slag. The chemical and mineralogical properties and microstructural analysis of the reformed slag samples were determined through X-ray Fluorescence spectroscopy, X-Ray diffractometer and Scanning Electron Microscopy connected to the dispersive spectrometer studies.

The structure, elasticity and conductivity of hydrous fayalite (Fe2SiO4Hx (x= 0.25, 0.5, 0.75)) are discussed based on the First-principles. Fe2SiO4Hx (x= 0.25, 0.5, 0.75) models are established by hydrogen atoms occupying the interstice space of the fayalite (Fe2SiO4) unit cell. The optimized results show that hydrogen atoms form hydroxyl (OH−) with the surrounding oxygen atoms in the modeling course, which is consistent with the experimental conclusion that water exists in fayalite in the form of OH−. The calculated results of the elastic constants for Fe2SiO4Hx (x= 0.25, 0.5, 0.75) show that the elastic constants increase as the pressure increases and decrease as the water content increases at 0 ∼ 30 GPa. Compared to Fe2SiO4, the ranges of compression wave velocity (Vp) of Fe2SiO4Hx (x= 0.25, 0.5, 0.75) are 1.02 ∼ 3.52%, 3.06 ∼ 4.30%, 3.63 ∼ 6.93%; in the meanwhile, the ranges of shear wave velocity (Vs) are 0.01 ∼ 7.01%, 0.40 ∼ 8.85%, and 2.50 ∼ 3.13%; this is in line with the wave velocity, which was observed to experimentally reduce to 2 ∼ 5% in the low-velocity layer of the mantle. The decrease of wave velocity due to water may be the formation mechanism of low velocity layer. When analyzing the conductivity, the conductivity per relaxation time σ/τ gradually increases with the rise of temperature, while different pressures have little influence on σ/τ. At the same temperature, σ/τ increases with the water content of fayalite. The result theoretically explains why the upper mantle transition zone has the phenomenon of high conductivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetite and fayalite were effectively separated by novel combined collector. • AT enhanced the selectivity of flotation and reduced the dosage of collector. • Co-adsorption of AT and PAE on fayalite surface improves its hydrophobicity. • Synergistic mechanism of AT and PAE was revealed from multiple perspectives. As an iron-bearing silicate mineral, fayalite has similar surface properties to magnetite, which makes it challenging to efficiently separate fayalite from magnetite by flotation. In this study, magnetite and fayalite were separated using novel combined collector polyoxyethylene alkyl amine (PAE) and terpinol (AT) through reverse flotation. Combined with a variety of characterization analysis and molecular dynamics (MD) simulation, the synergistic adsorption mechanism of the combined collector on mineral surface was revealed from multiple perspectives. The optimum scheme and pH response range of the combined collector were determined by micro-flotation test. Compared with PAE alone, the difference value of flotation recovery between fayalite and magnetite using combined collector was increased by 10.16%, and the dosage was reduced by 20%. Additionally, an effectively adsorption of combined collector onto fayalite surface to improve its surface hydrophobicity. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and MD simulations results showed synergistic adsorption was produced onto fayalite surface using combined collector mainly through non-polar interaction, hydrogen bond association and bridge adsorption. Furthermore, the spatial distribution and diffusion behavior of water molecules provide microscopic evidence for the enhancement of surface hydrophobicity of fayalite by combined collector. [ABSTRACT FROM AUTHOR]

The North American Mid-Continent rift (MCR) is a 1.1 Ga aborted rift, which has recently become an area of intense focus for energy resource exploration following the report of H 2 emissions. To document the nature of the producing rocks, we conducted a multi-scale study on preserved drill-core samples from the DR1-A well located in the same area as the H 2 -producing wells in Kansas. We showed that this well reaches an unmapped part of the MRS composed of fayalite-bearing monzo-diorites in which we identified atypical veins of iddingsite, a complex mixing of Fe-rich phyllosilicates. Combining scanning and transmission electron microscopy (SEM and TEM) with scanning transmission X-ray microscopy (STXM) allowed us to differentiate at least two types of sub-micro-meter Fe-rich veins. A central reduced vein cutting the fayalite, other mafic minerals, the plagioclase, and to a lesser extent the alkali feldspar, contains a complex mix of serpentine, chlorite, and mica. Furthermore, a border vein, with a higher degree of Fe-oxidation, is found to be contained only within the fayalite. This external vein mainly contains iron and silicon, together with a few percent of potassium and calcium, and can be divided into two sub-veins composed of Fe3+-rich interstratified chlorite-smectite and Fe3+-rich serpentine in direct contact with the fayalite. Textures and microstructures of these phyllosilicates suggest that they have crystallized from a late magmatic and differentiated fluid, which precipitation produced the central vein together with the exsolution of an H 2 O-enriched fluid phase. This exsolved fluid, chemically far from equilibrium with the fayalite, appears to have induced a deuteric alteration of the fayalite, leading to the crystallization of the external veins enriched in ferric iron. These observations bring new perspectives on the history of formation of iron-rich clay minerals, which may, somehow, be related to H 2 production. • The igneous rock from the Kansas basement is a fayalite-bearing monzo-diorite. • Two generations of iron-rich clay minerals are described within the monzo-diorite. • Reduced‑iron-rich clay minerals are formed by precipitation of a late magmatic fluid. • Oxidized‑iron-rich clay minerals are formed by deuteric alteration of the fayalite. • Late magmatic alteration could be prone to produce hydrogen by iron oxidation. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present study, thermal properties of geopolymer paste, based on fayalite waste from copper producing plants and metakaolin, were analyzed. The used activator solution was a mixture of sodium water glass, potassium hydroxide and water with the following molar ratio: SiO2/M2O = 1.08, H2O/M2O = 15.0 and K2O/Na2O = 1.75. High strength geopolymers pastes were evaluated after exposure to 400, 800 and 1150 °C. The physical properties (absolute and apparent density, water absorption) and compressive strength were determined on the initial and the heat treated samples. The phase composition, microstructure and spectroscopic characteristics were examined by XRD, SEM-EDS, FTIR and Mössbauer spectroscopy, respectively. The structure of the heat-treated geopolymers differs in the outer and inner layers of the specimens due to variation in the phase composition. The outer layer was characterized by a reddish color and more rigidity, while the inner core was black and less viscous at elevated temperatures. The results showed that geopolymer pastes based on fayalite are fire-resistant up to 1150 °C. Moreover, after heat treatment at this temperature, the compressive strength increased by 75% to 139 MPa, while water absorption reduced by about 9 times to 1.2%. These improvements are explained with the crystallization of the geopolymer gel to leucite and K,Na-sanidine, and substitutions of Al/Fe in the geopolymer gel and iron phases. [ABSTRACT FROM AUTHOR]

An effective strategy to achieve separation and recovery of iron and nickel from low-grade laterite ore via microwave carbothermic reduction roasting is reported. In this work, we determined the underlying reason for the poor separation of iron and nickel during the magnetic separation process. The effect of operating variables on the recovery and separation of nickel and iron from low-grade laterite ore was initially investigated during microwave carbothermic reduction roasting to reveal the underlying reason for their poor separation. Then, the phase transformation and interfacial reduction of fayalite Fe2SiO4 and hortonolite Fe2−xMgxSiO4 in the mineral composition of laterite were systemically investigated via SEM/EDS and XRD analysis to determine the influence of CaO and MgO on the stepwise reduction behavior of Fe2SiO4. Phase transformation during the microwave carbothermic reduction roasting process by microwave irradiation heating occurred according to the following steps: (Fe,Ni)2SiO4 (x = 0) and Mgx(Fe,Ni)2−xSiO4 (0 ≤ x ≤ 2) → MgxCay(Fe,Ni)2−x−ySiO4 (0 ≤ x + y ≤ 2) → MgxCa2−xSiO4. Finally, the substituted iron and nickel ions were found to reduce to ferronickel alloy under a reductive atmosphere. The ferronickel alloy with a nickel grade of 7.05 wt.% and an iron grade of 71.70 wt.% was produced successfully from low-grade laterite ores in which the recovery ratios of nickel and iron were 92.44% and 91.17%, respectively. Furthermore, these methods could be extended to the reduction behavior and interfacial reaction of silicates in other ores.

Direct reduction-magnetic separation process (DRMSP) is a highly effective and clean method to upgrade the complex resources, which has been widely used to recovery the value metals in copper slag (CS) and nickel laterite (NL) in recent years. Adequate growth of the alloy particles is a key parameter influencing the complete extraction of alloys from CS and NL in this process. Therefore, the liquid phase formation mechanism, growth kinetics of the alloy particles, and the correlation between the alloy particle growth and liquid phase formation were studied to reveal the synergistic effect of the co-reduction of CS and NL. The results indicated that fayalite in the copper slag reacted with forsterite in nickel laterite to form augite group minerals with low melting points, resulting in more liquid phase formation in the reductive roasting process. A comparison with the reduction kinetic parameters of the single nickel laterite showed that the growth index and activation energy decreased significantly from 2.85 and 272.98 KJ/mol to 2.08 and 171.99 KJ/mol, respectively, after the addition of 40% copper slag, which confirmed that copper slag promoted the particle growth. Moreover, the liquid phase increased the total cohesive force between the alloy particles, revealing the correlation between alloy particle growth and liquid phase.

In view of deterioration of the raw material base it is necessary to optimize autogenous smelting of copper sulphide raw materials, to intensify the heating regime, and to increase Vanyukov furnace (VF) productivity, which is possible when additional fuel is supplied to the process also acting as a reducing agent. Physicochemical investigation of the properties of slags obtained during copper sulfide concentrate smelting from the Balkhash Copper Smelting Plant (BMZ) are conducted with and without intr oduction of a reducing agent. It is found that presence of a reducing agent (activated charcoal) within a melt promotes formation of fayalite in the slag whose content reaches 73–77%. Without supplying a reducing agent the amount is 40–50%. In the presence of a reducing agent the slag copper content is at the level of 0.55%, and in its absence it is 0.84%. Thermal studies determine the temperature for complete melting of slag samples. Introduction of a reducing agent into a molten copper sulphide charge makes it possible to obtain slags with melting points not above 1120.4°C, while in its absence a slag sample melting temperature reaches 1220.4°C. Creation of a reducing condition during copper sulfide concentrate smelting makes it possible to reduce the slag melting point by 100–150°C due to a reduction of trivalent into bivalent iron and formation of an additional amount of fayalite. [ABSTRACT FROM AUTHOR]

Copper slag is usually a mixture of iron oxide and silicon dioxide, which exist in the form of fayalite (2FeO·SiO2), and contains ceramic components as the SiO2, Al2O3 and CaO depending on the initial ore quality and the furnace type. Our present study was focused on manufacture of foundry pig iron with Cu content from copper slag using high-temperature reduction smelting and investigate utilization of by-products as a reformed slag, which is giving additional value to the recycling in a replacement of raw material of Portland cement. Changes of the chemical and mineralogical composition of the reformed slag are highly dependent on the CaO concentration in the slag. The chemical and mineralogical properties and microstructural analysis of the reformed slag samples were determined through X-ray Fluorescence spectroscopy, X-Ray diffractometer and Scanning Electron Microscopy connected to the dispersive spectrometer studies. [ABSTRACT FROM AUTHOR]

Hydrogen-induced decomposition of fayalite (Fe2SiO4) at high pressure is of considerable interest for a better understanding of the chemical processes occurring in the cores and mantles of icy satellites. At pressures up to 10 GPa and temperatures 250-300 °C (typical of the cores and mantles of Jupiter's and Saturn's satellites), a variable amount of hydrogen can react with fayalite contained in their rocks. Volatile compounds that can form via these reactions are usually identified by mass spectroscopy. In our experiments, we used compressed deuterium gas instead of hydrogen to ensure that the volatiles analyzed by mass spectroscopy could only result from the decomposition of fayalite. To study the effect of the amount of deuterium present in the system, the fayalite (Fa) samples were deuterated at P = 7.5 GPa and T = 280 °C with the preset molar ratios D2/Fa = 1, 1.5, 2.2, and 5 in the reaction cell. The deuterated samples were further quenched to the liquid N2 temperature and, after releasing the pressure, removed from the reaction cell and studied by quadrupole mass-spectroscopy, X-ray diffraction, and Raman spectroscopy. Our results showed that the high-pressure deuteration invariably led to the chemical decomposition of fayalite. The solid products of the reaction varied from a mixture of ferrosilite (FeSiO3) and iron at D2/Fa = 1 to a mixture of silica and iron at D2/Fa = 2.2. The decomposition occurred via breaking the Fe-O bonds and was always accompanied by the formation of water. Applying the observed reactions to the natural conditions of, e.g., the center of Titan or Ganymede, one may infer that fayalite can be dissolved in the hydrogen fluid or replaced by iron, ferrosilite, or silica depending on the molar ratio H2/Fa. [ABSTRACT FROM AUTHOR]

Chondrites are the most common meteorites in the world. However, the carbonaceous chondrites represent only a small fraction of those. Among them, Allende meteorite is one of the most studied carbonaceous chondrites. The main objective of this paper is to use the Raman spectral peak positions of olivine as a parameter to chondrite classification, here, specifically, Allende meteorite. Although these correlations are not new in the literature, this approach has not been used to classify carbonaceous chondrites yet. To develop the olivine calibration, only the peak positions of the doublet in the 700–1100 cm−1 region were analyzed in this study. The typical Raman spectrum of olivine displays two major peaks, here called Peak A, with Raman shifting in the 814–824 cm−1 range, and Peak B, in the 836–857 cm−1 range. The results of measurements found were perfectly matched to a linear correlation between Peak A and Peak B. The peak position versus composition plot shows a good correlation between the samples used as reference. The correlation curve obtained from the reference olivines is consistent with the data found in literature, as well as the peak versus peak plot. Finally, from the analysis of the olivine Raman spectral peak positions present in Allende meteorite, it is possible to conclude that there is little Fe in its matrix. Actually, the proportion of metallic Fe is less than 3% when the range of fayalite content is between Fa26–32.Thus, although the exact amount of iron present in the sample is not entirely clear, this kind of methodology quickly and effectively provides a response regarding the Fa ratio in the meteorite. [ABSTRACT FROM AUTHOR]

Copper slag is a by-product obtained during smelting and refining of copper. Copper smelting slag typically contains about 1 wt.% copper and 40 wt.% iron depending upon the initial ore quality and the furnace type. Main components of copper slag are iron oxide and silica. These exist in copper slag mainly in the form of fayalite (2FeO ·SiO2). This study was intended to recover pig iron from the copper smelting slag by reduction smelting method. At the reaction temperature of below 1400°С the whole copper smelting slag was not smelted, and some agglomerated, showing a mass in a sponge form. The recovery behavior of pig iron from copper smelting slag increases with increasing smelting temperature and duration. The recovery rate of pig iron varied greatly depending on the reaction temperature.

The oxidation behavior of fayalite (Fe2SiO4) in water vapor at 1000°C was investigated. The phase constitution and microstructure of the solid products were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The gas product was continuously measured online by a gas analyzer. The results showed that fayalite was completely decomposed into magnetite (58.8 wt%), hematite (21.6 wt%) and silica (19.6 wt%) at 1000 °C for 40 min under water vapor condition. Compared with the result obtained in dry air, water vapor could promote fayalite to transform into magnetite by decreasing oxygen fugacity. In addition, the iron oxide product was further enriched via alkaline cleaning in 1 mol/L NaOH. As for the gas product, the hydrogen production capacity reached 24.41 mL/g when exposed to 50 vol% water-50 vol% Ar at 1000°C for 40 min.

The present work discusses the morphology and pickling behavior of tertiary oxide scale formed on 4 types of hot-rolled steels (0.008 Si-0.019 Cr, 0.43 Si-0.017 Cr, 0.35 Si-0.525 Cr and 0.034 Si-0.72 Cr (wt.% basis)) in four successive tanks of acid containing 4, 6, 8 and 12% HCl solution, respectively, with the addition of strong oxidizer like FeCl3 and HNO3 along with inhibitor. The presence of fayalite (Fe2SiO4) in oxide scale of 0.43 Si-0.017 Cr and 0.35 Si-0.525 Cr steels was confirmed. This fayalite layer is difficult to be removed by pickling. Therefore, pickling was done at room temperature and at 80 ± 3 °C with different strong oxidants, such as FeCl3 and HNO3 added to the pickling liquor and it was found that even at room temperature, the addition of 0.1N FeCl3 and 0.1N HNO3 could remove the oxide scale completely for the high Si-containing steel too. However, only the addition of 0.1N FeCl3 was sufficient to remove the fayalite layer when pickled at 80 ± 3 °C. Additionally, an inhibitor helped to restrict the over-pickling. [ABSTRACT FROM AUTHOR]

In this study, carbothermal reduction of low grade banded hematite jasper iron ore (Fe~38%) is systematically investigated. The thermodynamic calculations revealed that single phase iron oxide can be reduced to Fe at 700 °C. The thermal pretreatment at 600 °C induced significant random cracks in the underlying matrix. The carbothermal reduction was evaluated using Box Behnken statistical design and was found effective for iron enrichment. Temperature was found as significant factor for optimization of both iron grade and recovery. At a higher temperature, the formation of fayalite and wustite deteriorates the iron grade-recovery. Under optimal conditions (700 °C, 30 min, 9% charcoal, minus 75 μm) a concentrate (FeG–61.2% and FeR–82%) was obtained and can be used for blast furnace feedstock and alternative sponge iron making. Coarser particle size and alternative reductants do not have a significant effect, however, the fused fraction comprising 85%Fe with retained austenite and martensitic iron was obtained. Unlabelled Image • Processing of low grade banded iron ore (Fe~38%) is investigated. • Carbothermal reduction was found successful for iron enrichment. • Optimal concentrate (Fe G –61.2% and Fe R –82%) with hematite and magnetite phases. • Fused mass ̴ 85% Fe with retained austenite-martensitic iron phase was obtained. • Concentrate obtained suitable for sponge iron making and blast furnace feedstock. [ABSTRACT FROM AUTHOR]

This paper investigated the oxidation of fayalite (Fe2SiO4) in iron-rich nickel slag (INS) for iron recycling via an oxidation-magnetic separation method. A phase stability diagram of the FeO–SiO2–MgO–CaO–O2 system drawn by FactSage 7.1 illustrates that magnetite (Fe3O4) can be crystallized from liquid slag in an air atmosphere, but the further oxidation to Fe2O3 in molten slag was extremely hard. The mass content of divalent iron (w(Fe2+)) decreased and the ratio of trivalent iron to divalent iron (w(Fe3+)/w(Fe2+)) increased gradually with increasing oxidation time. The results show that an air flow rate of 300–500 mL/min, a basicity of 0.90–1.10, and a temperature of 1658–1728 K are conducive to the oxidation of Fe2SiO4 in INS. Fe3O4 is the main iron-bearing phase, and Fe2O3 is not observed in the X-ray diffraction (XRD) patterns. Silicates in the oxidized nickel slag (ONS) are mainly augite (Ca(Mg,Fe)Si2O6), forsterite ((Mg,Fe)2SiO4), and monticellite (CaMgSiO4), while akermanite (Ca2MgSi2O7) is observed only for a basicity up to 1.10. The oxidation kinetics of Fe2SiO4 in INS are first order with an apparent activation energy (Ea) of 315.16 kJ/mol. [ABSTRACT FROM AUTHOR]

The present work explores the preparation of fayalite α‐Fe2SiO4, the iron‐rich end‐member of the olivine solid‐solution series, as a tar removal catalyst for biomass gasification. The synthetic procedure was developed starting from the stoichiometric mixture of hematite and micrometer size silicon carbide and employing thermal treatments in controlled atmospheres at 1000‐1100°C supported by thermodynamic modeling to assess the required redox conditions. The treatments in dry and humidified inert gas yielded phase mixtures containing metallic Fe as one of the main phases, thus emphasizing a shortage of oxygen supply. XRD and TGA studies of precursor mixtures on heating in dry CO2 demonstrated a multistep mechanism of the overall reaction including (a) fast reactivity between silicon carbide and hematite at ~920°C with formation of metallic Fe and amorphous silica followed by (b) formation of fayalite involving oxygen supplied in the form of CO2 and competing with (c) over‐oxidation to thermodynamically favorable Fe3O4+SiO2 mixture. Comparative studies of reactivity in powdered and pelletized samples emphasized the importance of the kinetic factor in the formation of Fe2SiO4 while preventing further oxidation. The preferential formation of fayalite in the CO2 atmosphere is shown to be favored by shorter treatments of compacted samples at higher temperatures. The procedure was designed (2‐step heating to 1100°C in CO2 followed by fast cooling) for the preparation of pelletized fayalite α‐Fe2SiO4 catalyst with only minor traces of surface over‐oxidation which can be suppressed by adding 10 vol.% of forming gas to CO2 flow. [ABSTRACT FROM AUTHOR]

Thermal stability of fayalite (Fe2SiO4) is studied at hydrogen pressures up to 7.5 GPa and temperatures up to 400 °C. Powder samples of Fe2SiO4 were exposed to a hydrogen or deuterium atmosphere for 24 h in the Toroid-type apparatus at pre-selected pressures and temperatures followed by quenching to the temperature of liquid nitrogen. The phase and chemical compositions of the quenched samples were examined by energy-dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy at ambient pressure. The chemical composition of volatile products was studied by quadrupole mass spectroscopy in the course of heating from − 196 to 20 °C in a pre-evacuated quartz tube. In these experiments, deuterated samples were used to be sure that the detected compounds could only be formed in the reaction of fayalite with the high-pressure D2 gas. The obtained data allowed us to construct the line of thermal stability of fayalite at hydrogen pressures up to 7.5 GPa. The decomposition temperature of fayalite was proved to nonlinearly decrease from ~ 375 °C at the pressures PH2 = 1.4–2.8 GPa to ~ 175 °C at PH2 = 7.5 GPa. At higher temperatures, fayalite fully decomposed to a mixture of silica, water and metallic Fe or FeH depending on the pressure and temperatures of the hydrogenation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The occurrence state of zinc in the copper slag is obtained theoretically. • Zn(II) substitutes for the iron sites in the internal Si O Fe(II) (M2) bond to form Fe 2-x Zn x SiO 4. • Formation mechanism is actually an ion exchange process between Zn(II) and Fe(II). • The priority of the substituting for the iron site in the fayalite structure is proved by MS software calculation. Abstract The interactions between Fe 2 SiO 4 and ZnO play an essential role in the recovery of zinc from copper slag. The dissolution and substitution mechanism of ZnO in fayalite were investigated by using TG-DSC, XRD, PPMS DynaCool, XPS, Mossbauer and SEM-EDS analyses and compared with MS calculation results. The results indicate that the dissolution and substitution are actually processes of the penetrating dissolution of Zn(II) ions that can be divided into three steps: 1) ZnO dissociates into Zn 1-y O and Zn(II) ions; 2) Zn(II) penetrates the gap of the octahedron outer layer to substitute Fe(II) sites in the internal structure of Si O Fe(II) (M2) to form (Fe 2-x , Zn x)SiO 4 ; 3) Fe(II) is forced to migrate to the surface of (Fe 2-x , Zn x)SiO 4 to form (Zn 1-y , Fe(II) y)O. These findings can be derived the occurrence state and distribution of zinc in copper slag theoretically. [ABSTRACT FROM AUTHOR]

A sample of slag from the Flotation Bor, RTB Bor, was mineralogical tested after granulation in the laboratory conditions. Minerals contained in the sample of granulated slag are: fayalite and ferrite that form the basis with rarely sprayed fine particles of magnetite, pyrite, chalcopyrite, bornite, copper matte and elemental - native copper [6, 7]. Granulation of slag was conducted in the laboratory conditions on the device specially designed for this purpose.

Olivine group minerals are ubiquitous in extrusive igneous rocks and play an important role in constraining equilibria for samples in the upper mantle and above. All Raman spectra of the olivine group minerals in the solid solution between forsterite (Fo, Mg2SiO4) and fayalite (Fa, Fe2SiO4) have a high-intensity doublet between 800 and 880 cm–1. Previous studies used small sample suites with limited compositional ranges and varying spectrometers to relate energy shifts of these two bands to Mg/Fe contents. In this work, Raman spectra of 93 olivine samples were acquired on either Bruker's 532 nm (laser wavelength) Senterra or BRAVO (785/852.3 nm) spectrometer. This paper compares the two-peak band shift univariate method with two multivariate methods: partial least squares (PLS) and the least absolute shrinkage operator (Lasso). Data sets from several instruments are also examined to assess the most accurate method for predicting olivine composition from a Raman spectrum. Our 181-spectra PLS model is recommended for use when determining olivine composition from a Raman spectrum. For Raman spectra of mixed phases where only the olivine doublet can be identified, composition can best be determined using the position of the peak ca. 838–857 cm–1 through use of the regression equation %Fo = –0.179625x2 + 310.077x –133 717 (where x = DB2 centroid in units of cm–1). In situ methods for predicting mineral composition on planetary surfaces are critically important to extraterrestrial exploration going forward; of these, Raman spectroscopy is likely the best, as shown by the impending deployment of several Raman instruments to Mars (ExoMars and Mars 2020). More broadly, application of machine learning methods to spectral data processing have implications to multiple fields that use spectroscopic data. [ABSTRACT FROM AUTHOR]

Copper slag is a by-product obtained during smelting and refining of copper. Copper smelting slag typically contains about 1 wt.% copper and 40 wt.% iron depending upon the initial ore quality and the furnace type. Main components of copper slag are iron oxide and silica. These exist in copper slag mainly in the form of fayalite (2FeO ·SiO2). This study was intended to recover pig iron from the copper smelting slag by reduction smelting method. At the reaction temperature of below 1400°c the whole copper smelting slag was not smelted, and some agglomerated, showing a mass in a sponge form. The recovery behavior of pig iron from copper smelting slag increases with increasing smelting temperature and duration. The recovery rate of pig iron varied greatly depending on the reaction temperature. [ABSTRACT FROM AUTHOR]

This study was undertaken to simulate experimentally the weathering of slags disposed nearby soil rhizosphere. The aim of the research was to differentiate the effect of pH and organics on slags dissolution as well as to indicate weathering sequence of phase components. The studied slags are mainly composed of Fe (34.5 wt%) and Si (17.9 wt%) and contain up to 3761 mg kg −1 of Cu and 3628 mg kg −1 of Zn. The main identified phases are fayalite and glass, whereas sulfides and metallic Cu are volumetrically minor. A 30 days long slag weathering experiment was carried out with artificial root exudates (43.7 mM) and demineralized water at initial pH = 3.5 and pH = 6.7. The highest metal release (up to 10.9% of Zn and 4.6% of Cu) was observed in ARE solution at initial pH 3.5. Dissolution of sulfides and fayalite was mainly driven by pH. Artificial root exudates enhance glass dissolution as compared to demineralized water regardless of initially fixed pH. Based on this study following weathering sequences are delineated: i) under ARE 3.5 conditions: silicates > glass > sulfides, ii) under DW 3.5 conditions: sulfides > silicates > glass, iii) under near-neutral conditions: sulfides > glass > silicates. [ABSTRACT FROM AUTHOR]