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In the electro-deoxidation process, carbon parasitic reaction (CO32– + 4e– = C + 3O2–) usually occurs when using carbon materials as the anode, which leads to increase of the carbon content in the final metal and decrease of the current efficiency of the process. The aim of this work is to reduce the negative effect of carbon parasitic reaction on the electrolysis process by adjusting anode current density. The results indicate that lower graphite anode area can achieve higher current density, which is helpful to increase the nucleation site of CO2 bubbles. Most of CO2 would be released from the anode instead of dissolution in the molten CaCl2 and reacting with O2– to form CO32–, thus decreasing the carbon parasitic reaction of the process. Furthermore, the results of the compared experiments show that when the anode area decreases from 172.78 to 4.99 cm2, CO2 concentration in the released gases increases significantly, the carbon mass content in the final metal product decreased from 1.09% to 0.13%, and the current efficiency increased from 6.65% to 36.50%. This study determined a suitable anode current density range for reducing carbon parasitic reaction and provides a valuable reference for the selection of the anode in the electrolysis process.

The increasing use of high-sulfur coal contradicts with the stringent environmental pressure in metallurgical industry. Microwave has been confirmed to have efficient effect for coal desulfurization. However, the removal behavior of thiophenic sulfur, as the most difficult sulfur to remove from coal, is still unclear in microwave field. In this work, the feasibility of removing thiophenic sulfur from coal by microwave was evaluated by dielectric properties test, the chemical thermodynamics and kinetics of thiophenic sulfur migration with microwave irradiation were further analyzed by density functional theory (DFT) calculation. Dielectric properties test indicates that thiophenic sulfur is strong for converting electric field energy to heat energy than coal, which means the thiophenic sulfur will be selectively heated in the process of coal desulfurization by microwave. The magnetic loss powers of coal and thiophenic sulfur are very small and can be ignored. DFT calculation shows that under microwave irradiation, the energy barrier and activation energy of rate-limiting step for thiophenic sulfur removal decrease by 7.6 kJ/mol and 2.24 kcal/mol, and the logarithm of rate constant increases by 11.2 s−1. It suggests that the thiophenic sulfur removal is promoted by catalyzing the breaking of C–H and C–C bonds. In addition, the optimal removal path of thiophenic sulfur is also changed, accompanying the variation of sulfur-containing products from carbon monosulfide (CS) to thioketene (C2H2S). These findings reveal the catalytic mechanism of microwave on the thiophenic sulfur removal from coal, which are conducive to the sustainable utilization of high-sulfur coal in metallurgy process.

A large amount of dust is formed as one of the primary by-products during the blast furnace ironmaking process. Besides iron and carbon, it contains a variety of valuable metals such as zinc, lead, and indium widely applied in many industry fields. However, it is difficult to recycle and reutilize blast furnace dust (BFD) due to complex composition, fine particle size, and strong hydrophobic property. The extensive utilization of BFD wastes precious metal resources and decreases the additional value of recovery. Environment-oriented technologies have raised great attention in the recycling of precious metals. This article presents an overview of various technologies and the prospect of utilization on the recovery of BFD. The source, composition, and characteristics of BFD, as well as the recycling technologies within the blast furnace system are analyzed. Fundamental studies regarding pyrometallurgy and hydrometallurgy for recycling valuable metals from BFD such as direct reduction, leaching, and extraction, as well as its advantages and challenges, are also discussed. There is also great potential for BFD in other fields, including flocculants, cement raw materials, and adsorbents. The diverse chemical properties of BFD make it a contender for selective separation and adsorption in water pollution treatment. The development of pyrometallurgy technologies is mainly to realize its green and clean production. The innovative technologies in hydrometallurgy mainly aim to improve the leaching and extraction efficiency of high-valued metals. The combination of pyrometallurgy and hydrometallurgy technologies achieves the environment-friendly and sustainable recycling for precious metals with a higher recovery rate.

Nanostructured metal carbides have numerous applications in catalysis and energy storage. However, directional construction remains a significant challenge. In this work, a novel strategy for the direct synthesis of nanostructured metal carbides using nanostructured metal oxides as the precursor is developed. TiO2 nanotube arrays (TiO2 NTAs) can be successfully transformed into TiC nanotube arrays (TiC NTAs) through electro-deoxidation and carbonization reactions in a low-temperature molten salt. TiC NTAs have a highly oriented and ordered array structure, which shows the advantages of large specific surface area, direct electron transport, and good chemical stability. Here, TiC NTA electrodes and PVA-H3PO4 electrolyte gel were assembled into a flexible quasi-solid-state supercapacitor to characterize their energy storage performance. The results show that the TiC NTA electrodes exhibit a high areal capacitance of 53.3 mF cm−2, excellent cycling stability, and mechanical flexibility. Moreover, the energy densities can reach 4.6 μW h cm−2 at a power density of 78.9 μW cm−2. This work provides a new strategy for the directed synthesis of nanostructured metal carbides and demonstrates the energy storage application potential of TiC NTAs. It is expected that this work will contribute to the development of the synthesis and application of nanostructured metal carbides.

Molten salt electrolysis is a clean and low-cost Ti production technology that allows the direct conversion of metal oxides into metals or alloys via electrochemical reduction. However, carbon contamination can always be found due to the formation of CO32− and erosion of the graphite anode during electrolysis. Herein, we explore the reduction of carbon contamination by controlling CO32− formation. By adjusting the electrolyte composition, it is possible to improve the wettability between the molten salt and the anode and reduce the O2− solubility in molten salt to reduce CO32− formation. This approach reduces carbon contamination, and the current efficiency is also increased by adding 30 wt pct KCl to pure molten CaCl2. The carbon content in the cathode product decreased by 94 pct and the current efficiency was increased by 51 pct, compared with electrolysis in pure CaCl2 molten salt. In addition, the anode corrosion decreased, and the weight loss of the graphite anode decreased by approximately 65 pct after 18 hours of electrolysis.

Based on the first-principles calculations of density functional theory, co-adsorption models of C or CO with Cl2 on rutile TiO2 (100) surface were established. The adsorption structures and electronic properties during chlorination process were predicted. Then, the adsorption energy, charge density, electron density difference and density of state of the adsorption structures were calculated and analyzed. The stabilities of the adsorption structures and the charge distributions between atoms were studied. It was found that both C and CO could promote the adsorption reactions of Cl2 on TiO2 (100) surface, and C was more favorable to the adsorption process. The results show that the adsorption process of Cl2 on TiO2(100) surface was physisorption, and the co-adsorption processes of C or CO with Cl2 on TiO2(100) surface were chemisorptions.

The thermal behavior of poplar-fat coal (biomass-coal) blends and organic functional structure of formed coal-char in the co-pyrolysis temperature were investigated using Thermogravimetric analyzer, Differential scanning calorimetry, Mass spectrometry and Attenuated total reflection Fourier transform infrared spectroscopy analysis. Furthermore, the interactions between poplar and coal during co-pyrolysis were deduced. The results indicate that poplar decomposed prior to the decomposition of fat coal is not surprising, but results also indicate that the presence of poplar enhanced the thermal decomposition of fat coal at low temperature. The occurring interactions showed positive and negative effects with increasing temperature, which could be explained by chemical reaction and physical interaction, respectively. In the blends, these interactions lowered the apparent activation energy and frequency factor. The added poplar had a positive effect on decomposition of the organic functional groups. Interactions would indirectly cause higher hydrocarbon-generating potential and thermal maturity, and reduced aliphatic chains length and aromaticity. The synergistic effects between fat coal and poplar during co-pyrolysis occurred mainly at lower temperature. For the better application of poplar-fat coal blends, the suitable blending ratio of poplar to coal is below 16%. In addition, the pyrolysis temperature should be kept in 345–390 °C to obtain biomass-coal tar.

The electrochemical synthesis of sulfur-doped nanostructured graphite including graphene and carbon nano-tube via direct electrochemical conversion of CO2 in CaCl2 NaCl CaO Li2SO4 has been realized at a relative low temperature (675 °C). The results indicate that sulfur can successfully incorporate into carbon matrix and the graphitization degree can also be enhanced by introducing sulfur. In addition to SO42−, Li+ will also have positive effect on improving the graphitization of carbon deposition. Aggregated carbon particles are included in all samples while ultrathin graphite sheet, wire-like carbon, carbon nano-tube and interwoven carbon chains can be obtained in some cases at different electrolytic conditions. This work opens up a novel way to fabricate heteroatom-doped nanostructured carbons from carbon dioxide.

The use of iron ores bearing titanium as a raw material is an effective measure to prevent hearth erosion and prolong the life of a blast furnace. In this research, the effect of titanium content on the precipitation behaviors of high-melting phases of carbon-saturated molten pig iron were studied by confocal scanning laser microscopy. The results showed that, when the titanium content was less than 0.25wt%, Fe3C was precipitated as a single phase from the molten carbon-saturated iron. The growth rate of the precipitated Fe3C crystals was very high, reaching 7387 μm2/s. When the titanium content in the molten pig iron was greater than 0.47wt%, TiC crystals precipitated first. The shape and size of the precipitated TiC crystals did not obviously change. After TiC was precipitated, the fluidity of the molten pig iron worsened. With a decrease in temperature, Fe3C was also precipitated but the growth rate of Fe3C was limited by the presence of the first precipitated TiC phase. The crystal size of the precipitated Fe3C was much smaller than that of pure Fe3C.

The wettability between different molten salts and a graphite anode was studied using the sessile drop method, and the effect of the wettability of the anode on the reduction of titanium dioxide was also investigated. The results indicate that KCl exhibits superior wetting of the graphite anode, and that the addition of KCl improves the wettability of graphite by CaCl2-based mixed molten salts. The amount of KCl added should be controlled due to its poor oxygen solubility. The results of the electro-reduction of TiO2 in different molten salts demonstrates that the wettability of the anode by the molten salts greatly affects the deoxidation efficiency. Better wettability of the graphite anode by molten salt could accelerate the deoxidation rate of TiO2.

High-entropy alloys (HEAs) have attracted extensive attention due to their excellent properties for various applications. In this work, single-phase equiatomic CoCrFeNi high-entropy alloy (HEA) was prepared by one-step electrolysis of solid oxides in molten CaCl2 at 900 °C and the cathodic reduction mechanism is discussed. The effect of solid oxides porosity on the current efficiency was investigated using X-ray diffractograms and oxygen/nitrogen/hydrogen analyzer. Varying the porosity of solid oxides, the CoCrFeNi HEAs ranging from powders to solid block could be prepared which provides a possibility for additive manufacturing. The aim of the current study is to highlight the versatility of a simple electrochemical method for HEAs preparation in a straightforward, low-energy, and cost-affordable process.

The CaTiO3 phase is the intermediate phase at the cathode in the preparation of titanium metal through the direct electrochemical deoxidization of titania in molten CaCl2. The formation mechanism of CaTiO3 in the cathode and the releasing of Cl2 from the anode were studied during deoxidation of TiO2 by FFC Cambridge process. Experiments were conducted, where a preformed TiO2 cylindrical pellet was dipped into molten CaCl2 at 900 °C under high-purity Ar to evaluate the formation of CaTiO3 from the hydrolysis of molten CaCl2. Partial electrolysis experiments were also used to confirm the formation of CaTiO3 in molten CaCl2, particularly short-time electrolysis (1, 5, 10, 20, and 30 minutes). In addition, Cl− was observed to discharge at the anode. The results show that the behaviors of both electrodes are closely related to current–time curve. After the turning point on the current–time curve, Cl2 will no longer be released, maybe no CaTiO3 will be formed.

Cokes were produced in an electrical furnace from a coal blend containing varying levels of added TiO2. The effects of TiO2 levels on coke structure and properties were then considered. Mercury int...

The kinetics of carbothermal reduction of titanium-bearing blast furnace (BF) slag has been studied by thermogravimetric analysis and quadrupole mass spectrometry. The kinetic parameters (activation energy, preexponential factor, and reaction model function) were determined using the Flynn–Wall–Ozawa and Satava–Sestak methods. The results indicated that reduction of titanium-bearing BF slag can be divided into two stages, namely reduction of phases containing iron and gasification of carbon ( 1095°C). CO2 was the main off-gas in the temperature range of 530–700°C, whereas CO became the main off-gas when the temperature was greater than 900°C. The activation energy calculated using the Flynn–Wall–Ozawa method was 221.2 kJ/mol. D4 is the mechanism function for carbothermal reduction of titanium-bearing BF slag. Meanwhile, a nonisothermal reduction model is proposed based on the obtained kinetic parameters.

Titanium-bearing blast furnace slag contains a considerable amount of unused titanium and thus causes both resource waste and environmental pollution. The enrichment and extraction of titanium from titanium-bearing blast furnace slag is an urgent problem to be solved. In the present work, the crystallization behavior of TiO2–CaO–SiO2 ternary system slag was investigated both theoretically and experimentally in the binary basicity (CaO/SiO2 mass ratio) range from 1.0 to 1.4. Thermodynamic calculation indicated that perovskite (CaTiO3) and sphene (CaTiSiO5) were the two main titanium-containing phases and perovskite was the first precipitated phase during the cooling process. With the increase of basicity, the mass percentage of both perovskite and wollastonite (CaSiO3) increased while that of sphene decreased. The experimental results showed good agreement with the thermodynamic calculation. Also, it was found that the crystals appeared to have hexagonal, leaf vein and dendritic shapes macroscopically, and their size reached the centimeter level. Observation of the three-dimensional topography suggested that the perovskite phase existed as dendrite with the orthorhombic crystal, and the sphene grew by taking the perovskite crystal as its nucleus and then wrapping the perovskite crystals.

AlxCoCrFeNi high-entropy alloys with different Al contents (x in molar ratio, x = 0 – 2.0) were prepared by electrochemical process using the mixed metal oxides as the precursor. The effects of Al addition on the crystal structure, microstructure, mechanical property and corrosion behavior were investigated by XRD, XPS, SEM, FE-EPMA, universal tensile testing machine, Vickers hardness tester and electrochemical workstation. With the increase of Al contents, the crystal structure of AlxCoCrFeNi HEAs transformed from FCC to the mixed crystal structures of FCC and BCC, finally, to BCC + B2. The σ-phase was formed in AlxCoCrFeNi (x = 0.8 – 1.5) HEAs during the electrolysis deoxidization. The bulk HEAs could be prepared successfully via vacuum hot pressing sintering process. The bulk HEAs exhibit excellent ultimate tensile strength (UTS) and hardness. The hardness of the Al0 (245.2 HV) HEA and Al0.3 (261.2 HV) HEA was twice high of the sample prepared by arc-melting method. Compared with 304 stainless steel (304SS) and AlxCoCrFeNi HEAs prepared by other method, AlxCoCrFeNi HEAs prepared by the united process shows a comparable corrosion resistance in acid, alkali and salt aqueous solutions.

In this study, microwave heating was used to dry nickel laterite, which contains significant quantities of free water, crystal water, and hydroxy water. The results show that the main phase of crys...

Density functional theory (DFT) calculations have been employed to investigate the adsorption behaviors of CO and H2 on various FeO surfaces in order to explore the mechanism process in the conversion of FeO to Fe and predict the main growth orientation of metallic iron precipitated on FeO surfaces. For adsorption of CO onto the FeO(100) and FeO(110) surfaces, the CO tends to adsorb to the Fe sites through the C-Fe bonds formed on both surfaces. For adsorption of CO onto the FeO(111) surface, both Fe and O sites are active enough for the chemisorptions of CO. Moreover, the CO2 species is generated on the surface when CO adsorbs to the O top site. For adsorption of H2 onto three FeO surfaces, the least and most stable configurations are the adsorptions of H2 onto the FeO(100) and FeO(111) surfaces, respectively. Especially, the H2 molecule dissociates heterolytically and forms one O-H bond and one Fe-H bond when H2 adsorbs to the FeO(110) surface. In addition, the H2O species is generated on the surface when H2 adsorbs to the O top site on FeO(111) surface.

The microwave irradiation experiment of Nantong coal (NTC) and Laigang coal (LGC) has been carried out in a microwave oven and the transformation of organic sulfur and its functional groups was investigated via compact sulfur tester and Fourier transform infrared spectra. The dielectric properties of coal sample are also measured by an Agilent N5244A network analyzer. The result shows that a certain amount of organic sulfur in both NTC and LGC is transformed into iron sulfide, sulfate, and sulfur-containing gas after irradiation of microwave. The retention proportion of the three typical sulfur-containing functional groups in coal is ranking as: disulfide bond (S-S) > sulfinyl (SO) > sulfydryl (-SH), and such phenomenon has been explained by the first principle calculation based on the density functional theory. The calculation results of Fukui indices, electrostatic potential, and frontier orbital analysis indicate the reactivity of the SO and SS is lower than that of the -SH. The calculated bond dissociation enthalpies and bond dissociation times indicate the chemical bonds of -SH and S-S need more time to rupture than SO when microwave power is 1000 W. © 2019 Wiley Periodicals, Inc.

Adding titanium ore in the blast furnace is an efficient method to prolong its hearth life. The content of titanium is important for prolonging blast furnace life. In this study, the dissolution kinetics of titanium in carbon-saturated iron was studied. The carbon-saturated pig iron was heated to 1200, 1250 and 1300 °C, respectively, and then an appropriate amount of titanium-iron alloy powder was added. After a certain period of time, a quartz tube was used to take out the samples from the molten iron and the solubility of titanium was measured by an inductive coupled plasma emission spectrometer (ICP). By fitting the experimental results with different solid–liquid reaction kinetics models, the limiting step of the whole process was determined. The results show that in the process of dissolution the mass diffusion is the limiting step. According to the Arrhenius empirical equation, the activation energy of the dissolution is about 450.96 kJ/mol.

The content of TiO2 has an important influence on both the basic structure and the crystallization behavior of titanium-bearing blast furnace (BF) slag. The results of thermodynamic calculations show that, when the mass content of TiO2 is smaller than 25%, CaTiO3 increases as the content of TiO2 increases. However, when the TiO2 content is more than 25%, the CaTiO3 content decreases and TiO2 gradually increases. The results of a confocal laser scanning microscopy (CLSM) experiment show that, when the TiO2 mass content is 10%, Ca2MgSi2O7 and Ca2Al2SiO7 are the main crystallized phases resulting from the molten slag. Furthermore, when the TiO2 mass content is 20%, CaMgSi2O6, Ca(Ti,Mg,Al)(Si,Al)2O7 and dendrite CaTiO3 are the crystallized phases, while when the TiO2 mass content increases to 30%, CaTiO3 is the sole phase. The discrepancy between the CLSM results and the thermodynamic calculations occurs mainly due to the high melting point of the titanium-bearing BF slag. During the cooling process for the molten slag, CaTiO3 is crystallized first, due to its high crystallization temperature. Furthermore, the molten slag is solidified in its entirety before the other phases crystallize.

With the improvement of CO2 emission requirements of steel enterprises, it is significant to explore new technologies to reduce CO2 emission. In this work, the closed recycle method of vent gas from the reduction processes was proposed to research on the utilization of CO2 in vent gas and the reduction of the iron ore with different particle size was investigated in detail in this process. The results suggest that CO2 could be converted into CO completely in the closed recycle system and the reduction degree of the iron ore can reach up to 90%. Considering in average reaction rate and grinding cost, iron ore in diameter of 4–10 mm was the optimal size. This study may provide important perspectives for the application of the closed recycle of vent gas and the reduction of industrial CO2 emission.

The Cr2AlC is a typical ternary intermetallic who possesses unique properties such as good high temperature oxygen resistance, excellent mechanical strength, and so on, making it a potential ceramic candidate to be utilized under a relatively strict circumstance. In this paper, a straightforward and cheaper process was proposed to synthesize high quality and uniform micron-size Cr2AlC, via electrochemical reduction of Cr2O3/Al2O3/C mixed powder at only 850 °C. It is demonstrated that Cr2AlC was formed by the following three steps. Firstly, Cr2O3 was reduced to metallic Cr and react with carbon to form CrnCm. Then formed CrnCm will react with reduced alumina to form Cr2AlC. The SEM-EDS images confirmed the homogeneous distribution of Cr, Al and C in micron-size Cr2AlC powder. And the TEM and TG results further demonstrate the excellent layered structure and good oxidation resistance of Cr2AlC powder. This work realizes and provides a low-cost and scalable low temperature technique to prepare homogeneous MAX phase powders for commercial applications.