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Traditional ferrites are of poor electromagnetic wave (EMW) absorption while doping rare earth elements (REEs) can greatly enhance their permeability to improve the EMW loss performance. In this study, Co-Zn ferrite nanoparticles doped with various amounts of REEs (Gd3+, Nd3+ and Pr3+) were synthesized by a hydrothermal method, and their particle morphology and an EMW absorption performance were characterized by using transmission electron microscopy (TEM) and a Vector network analyzer (VNA). The results show that the initial spherical Co-Zn ferrite nanoparticles present an irregular quadrilateral structure after Gd3+ doping, and the average particle size of Co0.5Zn0.5−xGdxFe2O4 increases from 26 to 50 nm with x increasing from 0 to 0.35. At x of 0.25, the reflectivity absorbance achieves −27.94 dB at 18 GHz with the effective absorption bandwidth (EAB) of 4.08 GHz at a sample thickness of 2.5 mm. When Nd3+ doping amount reaches x = 0.3, the minimum reflection loss (RL) is −25.63 dB at 18 GHz and EAB is 3.91 GHz. Doping Pr3+ (x = 0.25) in the sample broadens EAB, and the minimum RL is −16.1 dB at 16.81 GHz and EAB is 7.31 GHz. This study shows that the magnetic moment produced by doping REES can form magnetic domains, which affects the incident EMW and improves the magnetic loss. It is expected that REEs-doped Co-Zn ferrite nanoparticles can be used as efficient electromagnetic shielding materials in aerospace.

This study investigates the extraction of vanadium from low-vanadium grade magnetite concentrate pellets using sodium salt. 71.1% of vanadium can be extracted under the following optimal conditions: pelletizing with 5 wt% Na2CO3, preheating at 1050 °C for 10 min, roasting at 1250 °C for 10 min, and water leaching at 120 °C for 120 min with a liquid:solid ratio of 5:1 (mL/g) in the bench-scale experiment. XPS and SEM-EDS results showed that part of trivalent vanadium was not oxidized completely during the sodium salt roasting and still occurred in the iron mineral phase; consequently, this part of vanadium was retained in the leached iron ore. The sodium salt roasting parameters are consistent with those of the iron ore oxidized pellets produced by grate-kiln or straight-grate methods; thus, the production efficiency of sodium salt roasting for vanadium extraction can be improved significantly. Pilot-scale experiment was further performed to verify the feasibility of the recommended method in a traveling grate, a better vanadium extraction ratio of 79.1% was achieved.

In this study, a new approach was proposed to prepare high-quality enstatite-spinel based glass-ceramics from the mixture of ferronickel slag (FNS) and coal fly ash (CFA) by examining the effect of CFA content on the preparation process based on both thermodynamic and experimental analyses. The thermodynamic exploration indicated that choosing enstatite as the main crystal phase in the target glass-ceramics along with spinel was suitable for co-utilization of both wastes. The experimental analysis showed that the crystallization temperature of parent glass, an intermediate product prepared from the mixture, increased from 864 °C to 907 °C as the content of CFA increased from 20 wt % to 35 wt %. Conversely, the depolymerization degree of the glass presented a decreasing trend, implying the denser glass structure which could promote chemical stability of the product. After crystallization of the parent glass, the main phase in the resulting glass-ceramic sample was transformed from enstatite (MgSiO3) to aluminum enstatite (Mg0.96Al0.027SiO3). There were simultaneous microstructural transitions from a spherical structure through a blocky structure to a plate-like prismatic structure, lowering bending strength of the product. By controlling crystallization of the melted mixture of 75 wt % FNS and 25 wt % CFA at 867 °C for 2 h, the resulting enstatite-spinel based glass-ceramic obtained excellent properties, namely density of 3.11 g/cm3, bending strength of 116 MPa, acid resistance of 99.97%, and alkali resistance of 99.70%. With a much higher utilization percentage of FNS, the product had properties comparable to those derived from similar wastes reported in literature. This study provides an efficient method for co-utilization of FNS and CFA.

This study reports treatment of low-zinc EAF dust for obtaining high-grade metallized product with a focus on multiple valuable elements via microwave reduction followed by magnetic separation. In reduction, the conversions of components of iron, zinc, lead, manganese and chromium, mainly in the form of spinel phases, to Fe, Zn, PbCl2, MnO and Cr2O3, respectively, were partially restrained by the formation of complex silicates, e.g., Ca3Al0.84Fe1.16Si3O12. After microwave reduction under the conditions of C/Fe mass ratio of 0.25, temperature of 1323 K, dwell time of 15 min, heating rate of 25 K/min and microwave power of 2200 W, the reduced briquette had the iron metallization degree of 96.20%, with volatilization of 98.38% of Zn and 80.22% of Pb. By magnetic separation, a high-grade metallized product containing 81.77 wt% Fe (79.97 wt% metallic iron) and 0.04 wt% Zn, satisfying the Chinese standard (YB/T 4272–2012) of the first-grade metallized product from dust, was obtained.

Poor permeability and low sintering productivity restrict the development of high-bed sintering. An efficient method of the double-layer sintering process (DLSP) was proposed to achieve high-bed sintering and solve the aforementioned problems. Theoretical calculation and sintering pot experiments were implemented to investigate the double-layer sintering process. Traditional sintering process and DLSP were compared in terms of sintering indices, metallurgical properties and morphology characterization. Under the condition of traditional sintering process, DLSP successfully realized fast velocity and highly productive sintering of 1000-mm high bed. After the sintering bed is charged and ignited twice, the air permeability of the bed has been greatly improved. Sintering time is shortened significantly by simultaneous sintering of the upper and lower feed layers. Under the condition of bed height proportion of 350/650 mm and pre-sintering time of 20 min, the yield, tumbler strength, productivity and solid fuel consumption are 69.96%, 65.87%, 1.71 t (m2 h)−1 and 56.71 kg/t, respectively. Magnetite, hematite, calcium ferrite and complex calcium ferrite are the main phases of DLSP products. The metallurgical properties of DSLP products meet the requirement of ironmaking. It indicates that DLSP is an effective method to solve the disadvantages of bad permeability and low sintering productivity in high-bed sintering.

The chromium-promoted preparation of forsterite refractory materials from ferronickel slag was investigated by microwave sintering of the slag with the additions of sintered magnesia and 0–10 wt% chromium oxide (Cr2O3). The thermodynamic calculations revealed that the addition of Cr2O3 can promote the formations of spinel and liquid phase and maintain high content of forsterite below 1500 °C. The experimental results showed that there existed a stronger promoting effect of Cr2O3 additive on the properties of refractory materials in the microwave field than that in conventional sintering. It was attributed to the preferential formation and growth of spinel with stronger microwave absorption than other phases (e.g., enstatite), the existence of more forsterite, and the enhanced densification in association with the presence of more liquid phase at the same temperature. By microwave sintering of the mixture of ferronickel slag, 25 wt% sintered magnesia, and 4 wt% Cr2O3 at 1350 °C for 20 min, a superior refractory material with refractoriness of 1801 °C, thermal shock resistance of 6 times, bulk density of 2.97 g/cm3, apparent porosity of 1.4%, and compressive strength of 197 MPa was obtained. Compared with that prepared by conventional sintering at 1350 °C for 2 h, the refractoriness and thermal shock resistance were increased by 175 °C and 100%, respectively. The present study provided a novel method for preparing high-quality refractory materials from ferronickel slag and relevant industrial wastes.

To dispose the problem of ferronickel slag for its value-added application, it was used for preparing thermal insulation materials by sintering of the slag in the presence of another waste, fly ash cenosphere (FAC), as pore former. The thermodynamic and experimental analyses revealed that the original phase of the slag, olivine, could be transformed to thermal insulation phases, including enstatite and cordierite, by optimizing sintering temperature in the range 1100–1300 °C. Specifically, after initial decomposition of ferronickel slag, there existed a low-iron olivine phase and cordierite and enstatite became the dominant phases when the sintering temperature increased from 1100 °C to 1300 °C. Except for the phase transformation, the microstructural evolution with proper pore features (porosity and size) contributed to a resulting material with desirable thermal and mechanical properties. It was shown that the ferronickel slag sintered at 1200 °C for 2 h with the addition of 25 wt % FAC exhibited the optimal thermal and mechanical performance. Additionally, it possessed good acid and alkali resistances. The results confirmed the feasibility of co-utilization of ferronickel slag and FAC for producing superior thermal insulation materials at a proper temperature, making efficient utilization of both wastes.

In the sintering of iron ores, the partial substitution of anthracite for coke breeze has been considered to be an effective way of reducing pollutant emissions and production cost. In this study, the basic characteristics of anthracite and coke breeze were compared and the sintering performance at different substitution ratios of anthracite for coke breeze was investigated. The porosity of anthracite is lower than that of coke breeze, but its density and combustion reactivity are higher. The substitution of anthracite for coke breeze has no influence on the granulation effect of the sintering blend. As the anthracite proportion increased, the sintering speed and productivity increased and the sintering yield and tumbler index decreased. As the substitution ratio increased from 0 to 60%, the melting temperature duration and the melt quantity index decreased from 2.59 to 2.03 min and from 3218.28 to 2405.75 °C·min, respectively, leading to insufficient sintering mineralization and bad sintering indexes. For an anthracite substitution ratio of 40%, the sintering speed, sintering productivity, sintering yield and tumbler index were 22.34 mm min−1, 1.49 t·(m2 h)−1, 71.65% and 63.59%, respectively, which entirely satisfies the production requirements. Furthermore, hematite (Fe2O3), calcium ferrite (CaO–Fe2O3), and compound calcium ferrite (CaO–SiO2–Fe2O3) were the major mineral phases, which were embedded with an interwoven structure.

Titanomagnetite concentrate is difficult to agglomerate by the traditional sintering process (TSP). In this study, the agglomeration properties of titanomagnetite concentrate were studied using the composite agglomeration process (CAP). It was shown that, by adding 40 wt.% pelletized feed, an excellent sinter with yield of 74.33%, a tumbler index of 58.93%, and productivity of 1.65 t (m2 h)−1 were achieved, which were increased by 11.72%, 12.03%, and 37.16% compared with TSP, respectively. Meanwhile, for CAP, the solid fuel consumption was only 43.87 kgcoke/tproduct and the reduction disintegration index of RDI+3.15 was 73.53%. They were decreased by 6.34 kgcoke/tproduct and increased by 24.31%, respectively. The better product quality was mainly attributed to a larger proportion of calcium ferrite and silicoferrite of calcium and aluminum group minerals formed in CAP, which restrained the negative effect of perovskite on agglomeration in association with the matrix feed with ultra-high basicity. The results showed that CAP is an efficient method for agglomeration of titanomagnetite concentrate.

Stainless-steel pickling sludge (SSPS) is a hazardous solid waste, which mainly contains CaSO4, CaF2 and a high level of metals such as Fe, Cr and Ni. The high-content of sulfur in the SSPS hinders its adequate treatment and deteriorates the quality of hot ferronickel when the SSPS was used as a feed to the rotary kiln-electrical furnace process (RKEF). Thus, the desulfurization behaviors of the SSPS, including thermodynamics, phase transformation and off-gas emission characteristics during pre-reduction were primarily investigated in this work. Pre-reduction temperature and carbon content were essential for the desulfurization, and the reduction temperature should be higher than 850 °C for sufficient sulfur removal. The presence of laterite ore enhanced the desulfurization of SSPS, and on the other hand, the presence of SSPS facilitated the subsequent reduction smelting. Under optimal conditions, almost all of the sulfur within SSPS could be removed by pre-reduction, and 94.72% Fe, 81.90% Ni and 46.14% Cr were recovered by reduction smelting.

The growing characteristics of metallic iron particles during reductive roasting of boron-bearing magnetite concentrate under different conditions were investigated. The size of the metallic iron particles was quantitatively measured via optical image analysis with consideration of size calibration and weighted ratio of image numbers in the core, middle and periphery zones of cross-section of pellets. In order to guarantee the measurement accuracy 54 images were captured in total for each specimen, with a weighted ratio of 1:7:19 with respect to the core, middle and periphery section of the cross-section of pellets. Increasing reduction temperature and time is favorable to the growth of metallic iron particles. Based on the modification of particle size measurement, in terms of time (t) and temperature (T) a predicting model of metallic iron particle size (D), was established as: D=125-0.112t-0.2352T-5.355×10-4t2+2.032× 10-4tT +1.134×10-4T2.

Effect of distribution of iron concentrates between pelletized and matrix feed on the preparation of blast furnace burdens from two different kinds of fine iron concentrates (magnetite and hematite) by composite agglomeration process (CAP) was explored. It was found that when the mass ratio of iron concentrate A (magnetite) to iron concentrate B (hematite) in the mixed feed was constant, the proportion of iron concentrate A in the pelletized and matrix feed significantly affected the quality of CAP products. Particularly, as the proportion of iron concentrate A in the pelletized feed increased from 0 to 100%, the yield decreased from 82.11% to 79.19% and the tumbler index decreased from 71.33% to 68.27%. The mineralization characterization results indicated that when 100% iron concentrate A was used as the pelletized feed, the crystallization styles of the outer layer and the inner layer of the pellet were different, and a lot of pores exist around hematite and magnetite phases in the pelletized part, with the weak connection of pelletized and matrix part, resulting in poor strength of agglomeration product.

During the soda ash calcining of ludwigite ore, sodium magnesium silicates are generated accompanying the activation of boron. This leads to the excessive consumption of soda ash and in turn enviro...

This study applied microwave energy for rapid self-reduction of electric arc furnace (EAF) dust-biochar composite briquettes to produce powdered direct reduced iron (DRI), based on the good electromagnetic response of EAF dust-biochar composite briquettes. The reduction experimental results showed that the iron-bearing components in the dust were reduced to metallic iron, leading to a high iron metallization degree of the reduced briquettes (94.7%). Meanwhile, the zinc-containing phases of EAF dust in the composite briquettes were converted to metallic zinc which then volatilized together with lead in the form of PbCl2. The volatilization percentages of zinc and lead were 99.6% and 92.9%, respectively, after reduction with the mass ratio of biochar to EAF dust of 0.25 and heating rate of 25 °C/min at 1050 °C for 15 min. By magnetic separation of the reduced briquettes, a magnetic concentrate with iron content of 91.32 wt% and recovery of 87.36% was obtained, meeting the quality requirements of DRI.

The feasibility of recovering magnesium from ferronickel slag by vacuum reduction was evaluated. The thermodynamic calculations indicated that the magnesia in slag can be reduced to gaseous magnesium by Si, FeSi, Al, and C, with the minimum reduction temperatures of 2324, 2530, 1678, and 2580 K at 100 000 Pa, respectively. As the system pressure decreases, the minimum reduction temperatures decline significantly. Si maintains the minimum reduction temperature of 1585–1673 K at the atmospheric pressure of 10–100 Pa, acting as a suitable reducing agent for recovering magnesium. To verify the findings, preliminary vacuum reduction experiments, in which CaO was added to eliminate the adverse impact of SiO2 in slag, were carried out. By reducing slag with additions of 50 wt % Si and 30 wt % CaO at 1573 K for 3 h at 10 Pa, the recovery of magnesium reached 97.74%.

In this study, the composite agglomeration process (CAP) was verified to be an effective route for preparing blast furnace burdens from superfine iron concentrates. It was found that under the cond...

This present study aimed to investigate the reduction behavior of hazardous electric arc furnace (EAF) dust in the presence of biochar (reducing agent) based on self-reduction of their composites u...

The existing methods for MoO3 production from high-grade molybdenite concentrates normally suffer from the inefficiency of oxidation and complexity of the overall process. In this work, a novel method for MoO3 production from alumina-silica-added molybdenite concentrate pellets by simultaneous oxidizing-volatilizing was proposed, validated and compared with other methods. Molybdenite concentrate mixed with additives was fabricated into spherical balls and roasted in air. Molybdenum disulfide was rapidly oxidized, volatilized and thus separated from pellets, wherein additives were sintered to be mullite as porous framework to keep the strength of single pellet, and in turn to support the stacked pellets. With mass ratio of additives to ore 1:2, ratios of S removal and Mo recovery from pellets reached over 99.9% and 97.2% respectively at 1050 °C within 20 min, and the condensed material was identified to be valuable MoO3 with purity over 99.9%. The excellent performance of MoO3 separation was attributed to the construction of firm pellet layers and favorable diffusion conditions inside pellets.

The Co0.33Ni0.33Mn0.33Fe2O4/graphene nanocomposite for electromagnetic wave absorption was successfully synthesized from metal chlorides solutions and graphite powder by a simple and rapid microwave-assisted polyol method via anchoring the Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles on the layered graphene sheets. The Fe3+, Co2+, Ni2+ and Mn2+ ions in the solutions were attracted by graphene oxide obtained from graphite and converted to the precursors Fe(OH)3, Co(OH)2, Ni(OH)2, and Mn(OH)2 under slightly alkaline conditions. After the transformations of the precursors to Co-Ni-Mn ferrites and conversion of graphene oxide to graphene under microwave irradiation at 170 °C in just 25 min, the Co0.33Ni0.33Mn0.33Fe2O4/graphene nanocomposite was prepared. The composition and structure of the nanocomposite were characterized by X-ray diffraction (XRD), inductive coupled plasma emission spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), transmission electron microscopy (TEM), etc. It was found that with the filling ratio of only 20 wt% and the thickness of 2.3 mm, the nanocomposite showed an ultra-wide effective absorption bandwidth (less than −10 dB) of 8.48 GHz (from 9.52 to 18.00 GHz) with the minimum reflection loss of − 24.29 dB. Compared to pure graphene sheets, Co0.33Ni0.33Mn0.33Fe2O4 nanoparticles and the counterparts reported in literature, the nanocomposite exhibited much better electromagnetic wave absorption, mainly attributed to strong wave attenuation, as a result of synergistic effects of dielectric loss, conductive loss and magnetic loss, and to good impedance matching. In view of its thin thickness, light weight and outstanding electromagnetic wave absorption property, the nanocomposite could be used as a very promising electromagnetic wave absorber.

Comparative experiment on MoO3 preparation from a technical-grade Mo calcine by volatilizing in water vapor atmosphere and air atmosphere was investigated. MoO3 deposition in the forms of strip-like α-MoO3 and spherical β-MoO3 were obtained at varying condensing temperatures. By adjusting the carrying gas from air to water vapor, MoO3 separating rate and product purity were remarkably improved, which is attributed to the selectively intensified evaporation of MoO3 from melted calcine. Specifically, MoO3 purity was over 99.99% and its corresponding recovery reached 70.6% when the calcine was evaporated at 1050 °C within 10 min in the water vapor atmosphere. Mechanisms of MoO3 separation from polynary system were furtherly explored and impurities including calcium, iron molybdates and silica were found to exert negative influence on MoO3 separation.

This paper investigated the combustion behavior of coke breeze granulated with other raw materials for iron ore sintering in a broad temperature range up to 1350 °C in air and sintering flue gas atmosphere, based on the exploration of the physiochemical characteristics of the coke breeze granules in industry. It was shown that after granulation the −0.25 mm coke breeze particles adhered to nuclei constituted by other sintering raw materials or served as a component of granules composed of mixed fine particles with homogeneous composition. Conversely, +0.5 mm coke breeze particles acted as nuclei to which fine particles of other materials adhered. The coke breeze particles with size of 0.25–0.5 mm, on the other hand, had dual roles as either adhering fines or nuclei. According to the combustion tests of typical granules consisted of −0.25 or 2–3 mm coke breeze particles, the structure and size of the granules as well as atmosphere strongly affected the combustion behavior of coke breeze. The adhering fines on the surface of coke breeze caused a decrease in its combustion rate in air (e.g., up to 26% at 950 °C and 1050 °C). Compared with the adhering fines, the sintering flue gas atmosphere played a more pronounced role in reducing the combustion rate. In this atmosphere, the combustion rate was in close association with the reaction between coke breeze and iron oxide in adjacent iron ore particles. The granules composed of −0.25 mm mixed particles could exhibit lower reduction reaction temperature (approximately a 100 °C difference) and stronger reduction reaction intensity than those consisted of coarse coke breeze in the size of 2–3 mm, leading to a higher heat loss. Minimizing the addition of −0.25 mm coke breeze, maintaining the highest combustion temperature at around 1300 °C, and keeping relatively high oxygen content in atmosphere are expected to promote combustion efficiency of coke breeze and thus energy utilization in iron ore sintering.

The low-silica and low basicity sintering is an effective measure for improving iron grade of sinter and reducing the slag amount of ironmaking and steelmaking. Sintering of the mixture at basicity (1.9, 1.8, and 1.7) and SiO2 content (5.0, 4.9, 4.8, 4.7, and 4.6) were conducted in a sintering pot, and the microstructures of typical sinters were taken into comparison in this work. Experimental results show that with the basicity decreases from 1.90 to 1.70, there is an obvious change in the tumbler strength index (TI) of sinter; SiO2 content affects mainly on the yield, but to a lesser extent on the TI of sinter. At the basicity of 1.70 and SiO2 content of 4.60%, the TI of sinter is 58.53% which is 5% lower than the sinter at basicity of 1.90 and SiO2 content of 4.98%. At basicity of 1.80 and SiO2 content of 4.60%, the sinter obtains a good performance (yield of 76.07% and TI of 60.09%), which is close to the indexes of sinter at relatively high-silica and high basicity ( basicity of 1.90 and SiO2 content of 4.98%), indicating that low SiO2 content and low basicity sintering can be implemented.

Ferronickel slag, featured by high contents of SiO2 and MgO, is a kind of solid waste produced in the ferronickel alloy process. Proper utilization of ferronickel slag can not only effectively reduce the environmental risk but also realize the high value-added utilization. Based on analysis of the composition and phase characteristics of various kinds of ferronickel slag obtained by different processing methods, the applications of the slag in producing concrete were discussed for providing insight into efficient use of the waste.

In this study, a novel method for producing direct reduced iron (DRI) powders based on microwave-assisted self-reduction of core–shell composite pellets composed of blast furnace (BF) dust and hazardous electric arc furnace (EAF) dust followed by magnetic separation was reported. The proper core–shell structure of the composite pellets was designed according to the rule of impedance matching and properties of BF dust and EAF dust by adjusting the thickness of shell (i.e., thickness of impedance matching layer) via controlling the C/O molar ratio of the raw materials from 0.55 to 0.70. The results showed that the EAF dust with high content of CaO was beneficial to the mechanical strength of green, dried, and metallized pellets (collected after reduction), while the BF dust with high content of carbon enabled sufficient microwave-assisted reduction of the pellets, facilitating subsequent magnetic separation and also the removal of zinc from EAF dust. By reduction of the core–shell BF dust-EAF dust composite pellets with the C/O molar ratio of 0.65 at 1050 °C for 15 min, the resulting metallized pellets showed superior reduction and magnetic separation indexes with higher removal percentages of zinc and lead, in comparison with conventional metallized pellets. The DRI powders obtained after magnetic separation had total iron content of 91.2 wt%, iron metallization degree of 95.8%, yield of 68.1%, and iron recovery of 88.0%. This study provided a good example for efficient and environmentally friendly comprehensive utilization of typical and hazardous wastes in the iron and steel industry.

Existing nano-Mo2C preparation methods suffer from expensive raw materials, subtle operation demands and complex synthesis steps. Herein, both theoretical and experimental studies were performed to develop a more efficient and economical method for nano-Mo2C preparation. Reaction thermodynamics of gas-vapor system of CH4-MoO3-N2 indicates that high-proportion inert gas significantly increases the required carbonization potential (CO/CO2) for Mo2C formation, but surplus carbon produced from methane decomposition can trigger water gas producing reaction and Boudouard reaction to help meet the requirement. Nano-Mo2C was then synthesized by mixing N2-carried MoO3 vapor with CH4 under varying conditions including temperature, gas flowrate and vapor concentration. It is found that MoO3 vapor experienced conversions to monoclinic MoO2 to cubic Mo to hexagonal Mo2C, and all these stages could be finished in as short as about 6 s at 1100 °C with initial molar ratio of CH4 to MoO3 over 3.5. The final products were present as porous plate-like single crystals or chain-like polycrystals, which are determined by initial vapor concentration and gas flowrate. Furtherly, electrocatalytic properties of Mo2C nanocrystals for hydrogen evolution reaction were measured, and the sample with the largest specific surface area and cleaner surface showed competitive performance over reported nano-Mo2C.

A simple method for calculating thermodynamic properties such as enthalpy, entropy, and molar heat capacity of sodium magnesium silicates from their constituent polyhedra is introduced in this work. If it is assumed that the complex silicates are made up of different polyhedron constituents, the thermodynamic properties of complex compounds can be calculated from the linear combination of their polyhedron constituents. Thermodynamic properties of 18 polyhedra were obtained by weighted multiple linear regression analysis based on thermodynamic properties of 48 silicates compounds, which were collected from FactSage database. Standard enthalpy, entropy, Gibbs free energy, and molar hear capacity for the formation of five different sodium magnesium silicates (Na2MgSiO4, Na2Mg2Si2O7, Na4Mg2Si3O10, Na2MgSi4O10, Na2Mg2Si6O15) provide the foundation for evaluating the possibilities and priorities of reactions involving these compounds.

Electric arc furnace (EAF) dust is an important secondary resource from which valuable elements can be recovered. The recovery process can be intensified by the self-reduction of core-shell EAF dust-biochar composite pellets under microwave irradiation. In this study, the effects of various parameters on reduction of the core-shell EAF dust-biochar composite pellets in N2 were explored. It was demonstrated that under the optimal conditions of reduction temperature of 1050 °C, dwell time of 20 min, total C/Fe mass ratio of 0.24, C/Fe mass ratio of pellet core of 0.30, and diameter of pellet core of 6–8 mm, the resulting metallized pellets had total iron content of 70.13 wt %, iron metallization degree of 97.97%, volatilization percentage of zinc of 99.52%, volatilization percentage of lead of 98.49%, manganese content of 2.83 wt % and chromium content of 0.22 wt %. The great reduction performance was attributed to strong gasification of carbon in association with selective distribution of biochar in the composite pellets with good microwave absorption.

Stainless steel pickling sludge is a kind of hazardous solid waste, which mainly contains CaF2, CaSO4, and Fe(OH)3 depending on the pickling and precipitating procedure. In order to depress the decomposition of CaF2 to form toxic fluorine-containing gas at high-temperature metallurgical process, this work was aiming at the utilization of CaF2 from stainless pickling sludge by preparing cuspidine glass-ceramics. Firstly, carbothermic reduction and magnetic separation were conducted to recover iron, in which pickling sludge was reduced at 1000 °C for 1 h by using 5% coke as a reducing agent and separated by magnetic separation with the magnetic intensity of 0.1 T. The main composition of the magnetic concentrate was Fe and Fe3O4 with the corresponding iron recovery more than 80%. Subsequently, the non-magnetic material was mixed with Ca(OH)2 and cullet to prepare cuspidine glass-ceramic. After roasted at 900 °C for 2 h, a cuspidine glass-ceramic with compressive strength of 65 MPa and porosity of 39.74% could be obtained.

Mo-doped titanium dioxide (TiO2)-coated fly ash cenosphere (FAC) was synthesized by the sol-gel method. The novel photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and X-ray photoelectron spectra (XPS). The results showed that the catalyst maintains the structure of anatase (TiO2), and the majority of doped Mo ions existed as Mo6+ substitution in anatase lattice, which caused redshift of TiO2 light absorption wavelength, broadening the light absorption range and making more effective use of solar energy. The photocatalytic activity of Mo-TiO2@FAC sample for the degradation of methylene blue (MB) under visible light irradiation was investigated. The photocatalyst that was calcined at 550 °C with Mo/Ti molar ratio of 0.3% and concentration of 2 g/L exhibited the optimal photodecomposition property.

Ferronickel slag can be used for refractory material production by sintering it with the addition of sintered magnesia in the microwave field. In this study, the influence of microwave sintering temperature and time on the refractoriness and mechanical properties of refractory material was assessed based on determination of the phase transformations and microstructural evolutions of the materials obtained at different sintering temperatures and time. It was shown that a high-quality refractory material with refractoriness of 1730 ℃ was obtained when the sample was sintered at 1350 ℃ for 20 min. The findings can be used for developing an efficient approach for utilization of ferronickel slag and other related industrial wastes.

Blast furnace dust and electric arc furnace dust are two typical solid wastes in iron and steel industry. In order to overcome the shortcomings of traditional processes, such as low metal recovery efficiency and high secondary pollution, microwave energy was applied in this study to intensify the self-reduction of core-shell BF dust-EAF dust composite pellets based on impedance matching for realizing highly efficient migration and separation of iron, zinc, and lead. By reducing the composite pellets in microwave field, it was found that under the optimal conditions of proportion of EAF dust in shell to all EAF dust in the pellet of 20%, reduction temperature of 1000 °C, and dwell time of 15 min, metallized pellets with the total iron content of 68.73 wt %, iron metallization degree of 95.87%, zinc removal percentage of 88.78%, lead removal percentage of 94.38%, and compressive strength of 190.4 N/p were obtained.

Preparation of refractory materials from ferronickel slag by sintering over a broad temperature range (1200°C to 1500°C) with addition of sintered magnesia was explored. The thermodynamic calculations indicated that the amounts of newly generated high-melting-point forsterite and spinel phases increase with increasing temperature. The experimental analysis demonstrated that elevating the sintering temperature promoted conversion and crystallization of forsterite and spinel phases from the original phase of the slag, with simultaneous reduction of low-melting-point enstatite. There was also rapid growth of spinel grains from about 0.5 μm to 5 μm, which should be controlled by selecting an appropriate temperature. The results showed that, by sintering the slag at 1400°C for 3 h with addition of 20 wt.% sintered magnesia, a high-quality refractory material with refractoriness of 1680°C, bulk density of 2.93 g/cm3, apparent porosity of 1.81%, and compressive strength of 166.62 MPa was obtained.

Due to its high carbon and low impurities contents, as well as good reactivity, biochar can partly or totally replace coal or coke as a promising reducing agent in metallurgy. This study offers a new method to produce qualified metallized pellets for steelmaking after microwave-assisted self-reduction of iron ore-biochar composite pellets. The key point was to prepare green composite pellets with good quality indexes which also allowed sufficient self-reduction under microwave irradiation. For this purpose, core-shell iron ore-biochar composite pellets were prepared with inhomogeneous biochar distribution. It was found that high grade iron concentrates A and B could be used together for improving pelletizing. Controlling the distributions and proportions of iron concentrate B (different additions in the core and shell) and biochar (all located in the core of the pellets) would contribute to high-quality iron ore-biochar green composite pellets with the drop number of 3.6 times/0.5 m, compressive strength of 11.1 N/p, and decrepitation temperature of 410 °C under the pelletizing conditions of total proportion of iron concentrate B of 30%, pelletizing time of 16 min, rotation speed of 25 r/min, bentonite dosage of 2.3%, C/Fe mass ratio of 0.225, pellet moisture content of 13.0%, and proportions of iron concentrates A and B in the shell of 10% and 0%, respectively. The subsequent microwave reduction tests showed that the core-shell metallized pellets with the total iron content and metallization degree of 89.15% and 95.52%, respectively, could be obtained after microwave reduction at 1050 °C for 30 min under N2 atmosphere. They had better reduction indexes than those produced from the pellets with homogeneous structure, serving as a good burden for steelmaking directly.

This study reports the role of chromium as a double-edged sword in the preparation of refractory materials from ferronickel slag with the addition of sintered magnesia based on the thermodynamic analysis and experimental exploration of the phase transformation of ferronickel slag during the sintering process. The results of thermodynamic calculation, X-ray diffraction, and electron probe microanalysis revealed that in the presence of sintered magnesia (20 wt %) and Cr2O3 (0–6 wt %), forsterite, donathite (instead of magnesium chromate spinel generated without addition of Cr2O3), magnesium aluminate spinel, and enstatite were formed. The forsterite and spinel phases contributed to high refractoriness of the prepared material by sintering. However, with excessive addition of Cr2O3 (>6 wt %), the quantity of enstatite increased obviously, which would lower the refractoriness of refractory material. For this reason, the addition of chromium or its content in the slag should be carefully controlled to fully ex...

The feasibility of a facile technological route to preparation of refractory materials from a ferronickel slag with the addition of sintered magnesia was verified in this study based on the thermodynamics analysis and the experimental exploration of the effect of the sintered magnesia addition on the phase transformation of ferronickel slag during the sintering process. For the first time, the results of thermodynamics calculation, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses revealed that the original phase of the slag can be transformed to high melting point phases by addition of MgO during the sintering process at high temperatures (e.g., 1350 °C). Specifically, the olivine in ferronickel slag decomposed initially, generating a low-iron olivine phase and an enstatite phase. With increasing addition of sintered magnesia, the enstatite phase changed to forsterite, and the iron, aluminum, and chromium components in the ferronickel slag c...

The potassium niobate (KNbO3) sample was hydrothermally synthesized using Nb2O5 and KOH solution as precursors. X-ray diffraction (XRD) results show that the synthesized KNbO3 is a single-phase material with an orthorhombic crystal structure and the unit cell parameters are: a = 3.9743 (2) A; b = 5.6954 (2) A; c = 5.7229 (2) A; α = β = γ = 90°, V = 129.54 (1) A3. The temperature-dependent phase transitions and enthalpy changes of KNbO3 were investigated by Differential Scanning Calorimetry (DSC) method. The heat capacity was measured experimentally by relaxation time method via physical property measurement system (PPMS, 2–300 K) and DSC sapphire method (280–820 K), respectively. The heat capacity of KNbO3 (2–300 K) was piecewise fitted into polynomials as: Cp = 3.242 × 10−1 T + 1.540 × 10−3 T3 + 1.056 × 10−4 T5-1.098 × 10−6 T7 + 2.946 × 10−9 T9 (2–10 K), Cp = 3.275 + 0.005 T + 0.044 T2-6.816 × 10−4 T3 + 4.628 × 10−5 T4-1.343 × 10−6 T5 + 1.090 × 10−8 T6 (10–50 K), Cp = 88.211 + 69.280 × 10−3 T-0.580 × 105 T−2-8.685 × 105 T2 (50–300 K). Consequently, the changes of enthalpy, entropy, Gibbs free energy and equilibrium constant were calculated based the dependence of heat capacity and temperature (280–820 K).

The CaO–MgO–Al2O3–SiO2 (CMAS) glass-ceramics are a new type of building decoration materials. They can be prepared using silicate-bearing metallurgical slags as raw materials for both economic and environmental benefits. This study offered a systematic review of preparation of CMAS glass-ceramics from various metallurgical slags based on analyses of characteristics, preparation methods of slag-based glass-ceramics, and the influence of heat treatment, chemical components and nucleating agents on the phase composition, microstructure and properties of glass-ceramics. It was found that a large number of metallurgical slags, including blast furnace slag (BFS), steel slag (SS), stainless-steel slag (SSS), electric furnace ferronickel slag (EFFS), copper slag (CS), ferromanganese slag (FS) and lead fuming slag (LFS), have the potential to serve as the main raw materials for producing CMAS glass-ceramics because of their chemical composition similarities to the products. However, the minor or residual elements, such as chromium, in the slags may directly affect the properties of the glass-ceramics mainly because of their impacts on the nucleation and crystallization in parent glasses which are in need of control. Special attention of this review was devoted to the challenges from the aspects of cost, safety and diversification in preparing the glass-ceramics from metallurgical slags and to corresponding solutions for maximizing utilization of the wastes with desirable product quality.

The rotary kiln-electric furnace (RKEF) process has undergone a rapid development during the past decade, producing a significant quantity of ferronickel slag. At present, the ferronickel slag has become the fourth largest industrial solid waste in China with a utilization ratio of less than 10 wt%. It is urgent to seek an efficient method for utilization of ferronickel slag. In this study, the thermodynamic characteristics of ferronickel slag sintered in the presence of magnesia (additive) for preparing refractory materials were assessed by calculating relevant thermodynamic functions and phase diagrams. The thermodynamic results showed that by sintering ferronickel slag with the addition of magnesia at appropriate temperatures, it is possible to promote the formation of forsterite and spinel phases, which would contribute to high refractoriness of the refractory materials derived from the slag.

Oxidative roasting-ammonia leaching is the most popular method to extract Mo from molybdenite concentrates. However, the pyrometallurgical process has long suffered from the exhaust gas treatment for acid-making using low-concentration SO2. Technically, gas circulation can work as an effective means to enrich SO2 in exhaust gas and meantime to reduce overall emissions. However, with SO2-enriched atmosphere, roasting behaviours of the components in concentrates would be changed, thereby influencing the recovery of Mo. In this study, both thermodynamic and experimental studies were carried out to explore the thermal transformations of main components in molybdenite concentrates under SO2-containing atmosphere. Thermal behaviours including oxidation of sulphides and formation of molybdates and sulphates were discussed. It was found that SO2 has a minor effect on sulphides oxidation, and raising the temperature and proportion of SO2 and O2 are effective means to extract the associated Mo from molybdates, which demonstrate the potential of applying exhaust gas circulation (EGC) technology in oxidative roasting of molybdenite concentrates.

Electric arc furnace (EAF) dust is a kind of secondary resource which contains multiple metallic elements, including Fe, Mn and Cr. Pyrometallurgical processes for recovering metal elements from EAF dust have been investigated for many years although they are suffered from high energy consumption due to the spinel-structured components of EAF dust. In this study, the thermodynamic analysis of carbothermic reduction of EAF dust was performed. The main components of EAF dust were magnetite (Fe3O4), hausmannite (Mn3O4) and chromate spinel (FeCr2O4). The gangue minerals were mainly composed of magnesium silicates. The thermodynamic analysis indicated that magnetite and hausmannite can be reduced to metallic iron and MnO, respectively. Meanwhile, the chromate spinel will be reduced to chromium oxide and then to form CaCr2O4. The results also demonstrated that the gangue components can promote the separation of Fe and Cr, agreeing well with the experimental results.

The reduction of ferromanganese spinel (MnFe2O4) in microwave field using biochar as reducing agent was investigated in this study. It was found that the MnFe2O4-biochar composite briquette possessed good microwave absorption capability with microwave penetration depth less than 20 mm at 2.45 GHz, enabling its efficient self-reduction under microwave irradiation. The MnFe2O4 was initially reduced to monoxide and then transformed to metallic iron and MnO. The iron metallization degree of reduced briquette reached 90.19% under the conditions of the C/MnFe2O4 molar ratio (n(C)/n(MnFe2O4)) of 3, reduction temperature of 1050 °C, and dwell time of 15 min. The selective heating effect of microwave induced the transformation of MnFe2O4 and promoted the breaking of chemical bond between Mn and Fe based on the density functional theory analysis. The microwave heating mechanism was associated with the phase transformation in the reduction process. At low temperatures, the dielectric loss due to interfacial polarization and dipolar polarization and the magnetic loss originated primarily from natural resonance controlled the heating process. As the temperature exceeded 572.9 °C, the composite briquette had a sharp decrease of magnetic response. The formation of (FeO)x(MnO)1-x led to slight fluctuations of permittivity with increasing temperature. When the temperature was higher than 903.5 °C, the conductive loss increased dramatically because of the formation of metallic iron, which could speed up the reduction process due to the “lens effect” of microwave. Based on the combined use of microwave energy and sustainable reducing agent with a focus on the correlation between phase transformation and microwave heating mechanism, this study has validated the feasibility of the route for comprehensive utilization of spinel-structured metallurgical solid wastes, showing the bright prospect of its industrial applications.

Two-thirds of the global nickel output can be attributed to the rotary kiln-electric furnace process. Due to the high contents of MgO and SiO2 in laterite, a high temperature (∼1600 °C) and corresponding energy (approximately 14 GJ/t-ferronickel) are required during the electric furnace smelting. This work verifies the feasibility of decreasing the smelting temperature by controlling the slag formation for an energy-saving production. The slag regulation method was upgraded through the coordination of the quaternary basicity [ = R4 = m(CaO + MgO)/m(SiO2+Al2O3)] and FeO content. The melting temperature was decreased, and the melting rate of the feed was increased after slag control, owing to the generation of diopside and olivine eutectics instead of olivine and pyroxene. The viscosity of the slag was decreased, thus lowering the required smelting temperature. After regulating the quaternary basicity from 0.58 to 0.61 and the FeO content from 5.0 to 12.5 wt% in the final slag, the smelting temperature decreased by 86 °C. The energy consumption decreased from 13.75 to a minimum of 11.16 GJ/t-ferronickel. Furthermore, a long-term industrial practice (annual output: 0.24 million tons of ferronickel) demonstrated that the total energy consumption could be decreased by 0.16 million GJ a year, which is equivalent to reducing carbon dioxide emissions by 45 kilotons a year.

Existing methods for processing molybdenite (MoS2) concentrates into pure materials suffer from waste pollution and complex procedures. In this work, a new flowsheet for pure MoO3 production from MoS2 concentrates has been established based on the combination of calcified roasting, sublimation, and flue gas recirculation (FGR). Fundamentals of MoO3 separation from CaCO3-added MoS2 concentrate pellet with the atmosphere containing O2 and high-proportion SO2 are investigated. The reaction feasibilities and rates of MoS2 oxidation, CaMoO4 transformation and MoO3 sublimation are fully discussed, along with the influence mechanism of CaCO3. The results indicate that SO3 formation plays an important role in CaMoO4 transformation, and the addition of CaCO3 can result in faster MoO3 separation due to the increase of melting point of oxidized pellet and the formation of highly porous structure. With the guidance of fundamentals, detailed experiments are performed to obtain suitable conditions for improving the recovery efficiency of Mo. As a result, over 94% of Mo is separated as pure MoO3 when MoS2 concentrate pellets are added with 60% CaCO3 and roasted at 775 °C for 2 h in the atmosphere containing 25% SO2. Finally, an overall flowsheet for pure MoO3 production from MoS2 concentrate is presented and evaluated. Compared with existing processes, the new flowsheet can achieve higher production efficiency and less pollution.

A hetero-structured few-layer MoS2-coated MoO2 (MoS2@MoO2) has been fabricated and applied as an anode material for LIBs. The MoS2@MoO2 was synthesized via two-step fire process: reducing MoO3 vapor with H2 for producing Mo powder, and oxidizing-sulfurizing Mo powder with SO2. With the aid of thermodynamic computations, it is found that Mo oxidation under SO2 atmosphere produces limited amounts of S2 vapor, which will locally sulfurize the particles nearby, resulting in finite and even sulfurization. The as-prepared MoS2@MoO2 includes few-layer MoS2 (about 3 nm thick) covering the surface, which serves a well-spreading and active material that synergizes with inner MoO2 to boost the performance for LIBs. Thus, the MoS2@MoO2 could deliver a high reversible specific capacity of 1263 mA h g−1 after 40 cycles at 0.1 A g−1, and maintain a specific capacity of 1052 mA h g−1 after 150 cycles at 0.2 A g−1. Even at 0.5 A g−1, the specific capacity could still keep above 650 mA h g−1 for over 500 cycles. The new method for MoS2@MoO2 synthesis is facile and effective, and may be extended to produce hybrids composed of other transition metal oxides and sulfides.

A large amount of coal gangue from coal mining and processing is regarded as waste and usually stockpiled directly. In order to recycle the valuable elements from the coal gangue, an integrated process is proposed. The process consists of three steps: 1) concentrating alumina from the coal gangue via activation roasting followed by alkali leaching of SiO2 which produces alumina concentrate for alumina extraction by the Bayer process; 2) synthesizing tobermorite whiskers from the filtrated alkali liquor containing silicate via a hydrothermal method and reusing excess caustic liquor; and 3) enriching titanium component from the Bayer process residue by sulfuric acid leaching. Alumina concentrate with 69.5% Al2O3 and mass ratio of alumina to silica (A/S) of 5.9, pure 1.1 nm tobermorite whisker and TiO2-rich material containing 33% TiO2 are produced, respectively, with the optimal parameters. Besides, the actual alumina digestion ratio of alumina concentrate reaches 80.4% at 270 oC for 40 min in the Bayer process.

The hydrothermal synthesis of tobermorite fibers was explored using mixture of coal fly ash (CFA) and slaked lime. Only tiny tobermorite fibers with 2–3 μm in length and 0.01–0.5 μm in diameter could be obtained at 220 °C for 3–7 h. In the presence of 20 g/L NaOH, the dissolution of silicon- and aluminum-bearing constituents in CFA was accelerated, and well-crystalline tobermorite fibers with 5–10 μm in length and 0.01–0.5 μm in diameter were synthesized at 220 °C for 1 h. Tobermorite fibers were aggregated into porous spherical constructions, making the synthetics potential for production of energy-saving building materials.

Utilization of bauxite residue is an urgent issue confronting the worldwide alumina industry. A CaTiO3-rich material has been successfully collected from bauxite residues based on our previous work, and the possibility of applying this obtained CaTiO3 as photocatalyst for degradation of rhodamine B was evaluated in this study. X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, UV–vis spectroscopy, photoluminescence microscopy, and Brauner-Emmet-Teller surface area analyzer were employed to characterize the CaTiO3 samples. Interactive effects of dominant factors on degradation of rhodamine B were examined through surface response methodology and optimal conditions were obtained. H3PO4 acidification was effective to enhance the photocatalytic activity of CaTiO3. More than 10 h was required for RhB degradation in presence of CaTiO3 while only 3 h was needed to achieve 85% removal of RhB using the acidified CaTiO3. CaTiO3 has larger band gap and lower separation efficiency of photoelectrons-hole pairs than TiO2, but H3PO4 acidification significantly reduced the recombination of photoelectrons-hole pairs and thus made more photoelectrons/holes participate in reactions. This study has validated a promising routine towards fully comprehensive utilization of bauxite residues, and simultaneously addressed a novel idea for using solid-waste to treat wastewater, thereof was very favorable to the sustainable development of environment.

The composite agglomeration process (CAP) aims at sintering a pelletized feed and a matrix feed together to produce a high-quality burden for a blast furnace. The pelletized feed is balled from fine iron concentrate or refractory iron-bearing resources, while the matrix feed is granulated from iron ore fines, fuels, fluxes and so on. Through mathematical calculation, heat accumulation regularity and heat-homogenizing of the sinter bed are acquired in CAP when pelletized feed is uniformly distributed. Then they are studied in the composite agglomeration process with optimized pelletized feed distribution, which is a novel and perfect sinter bed structure. Results show that large heat input gaps exist in the sinter bed under condition of even sinter mixture distribution, and it is very difficult to realize bed heat-homogenization by directly varying the solid fuel dosage among each layer. An optimized pelletized feed distribution realizes more heat in the upper layer together with heat-homogenization of the middle-lower layer when the proportions of pellets increase first in the middle-upper layer and then decrease in the middle-lower layer of the sinter bed. Under these circumstances, the sinter bed has much better available accumulation ratios with a maximum value of 78.29%, and possesses a greater total heat input of 6754.27 MJ when the coke breeze remains at the original dosage. To make full use of the available heat accumulation and adjust the pellet distribution, a good energy saving effect is obtained because the coke breeze mass declines by 13.91 kg/t-sinter. The current gross heat inputs of each unit are reduced remarkably, leading to a total heat input decrease of 25.95%. In pot tests of CAP, the differences of thermal parameters in whole bed are obviously reduced with the optimized pelletized feed distribution, which contributes to sinter homogeneity and energy savings.