Metallic Iron Grains Research Articles

Spatially resolving the AGB star V3 in the metal-poor globular cluster 47 Tuc with VLTI/GRAVITY

Context. Mass loss at the asymptotic giant branch (AGB) plays an important role not only in the final fates of stars, but also in the chemical evolution of galaxies. Nevertheless, the metallicity effects on AGB mass loss are not yet fully understood. Aims. We present spatially resolved observations of an AGB star, V3, in the metal-poor globular cluster 47 Tuc (NGC 104). Methods. The AGB star 47 Tuc V3 was observed using the GRAVITY instrument at ESO’s Very Large Telescope Interferometer (VLTI) at 2–2.45 μm, with a projected baseline length of up to 96 m. Results. The object 47 Tuc V3 has been spatially resolved and stands as the first to attempt to spatially resolve an individual star in a globular cluster. The uniform-disk fit to the observed data results in an angular diameter of ∼0.7 mas. Our modeling of the spectral energy distribution and near-infrared interferometric GRAVITY data suggests that the observed data can be explained by an optically thin dust shell with a 0.55 μm optical depth of 0.05–0.25, consisting of metallic iron grains, likely together with effects of the extended atmosphere of the central star. The dust temperature at the inner shell boundary is 500–800 K (corresponding to 23–90 stellar radii), significantly lower than observed in nearby oxygen-rich AGB stars. Radiation pressure on small (< 0.05 μm) iron grains is not sufficient to drive stellar winds. Therefore, iron grains may grow to larger sizes, even in the metal-poor environment. Alternatively, it is possible that the observed iron grain formation is a result of the mass outflow initiated by some other mechanism(s). Conclusions. The sensitivity and angular resolution of VLTI provides a new window onto spatially resolving individual stars in metal-poor globular clusters. This allows us to improve subsequent studies of the metallicity dependence of dust formation and mass loss.

Synergistic conversion of iron ore sintering dust and waste biochar to produce direct reduction iron and syngas: Gasification, reduction behavior and thermodynamic analysis

Waste biochar from biomass power generation and sintering dust from ferrous metallurgy were skillfully used to produce direct reduced iron (DRI) and syngas via a synergetic conversion in this study. The thermodynamic analysis of their related reactions, biochar conversion and reduction behavior of sintering dust were investigated. The biochar gasification and reduction of sintering dust were coupled and promoted by each other at 1000 °C for 60 min with 1.2 mol (C/Fe). For biochar conversion, adding sintering dust deepened the pyrolysis of the volatiles in the waste biochar to generate more CH4, and it provided more oxygen atoms, gasifying carbon atoms in the fixed carbon to generate more CO. The CO and CH4 yield from biochar conversion with iron oxides of sintering dust increased by 633.8% and 41.5% to its pyrolysis alone. For the reduction of sintering dust, the whole conversion process of sintering dust was the generation, aggregation and growth of the iron grains, including the generation of metallic iron grains, forming curved bars and composite flocculent metallic iron, and its larger lumps particles finally. A DRI with a 92.4% metallization ratio, meeting the requirements of the subsequent electric arc furnaces, was obtained at 1000 °C for 60 min with 1.2 mol (C/Fe). This study achieves an efficient and reciprocal conversion of these two solid waste resources. It offers an essential research reference for fuel gasification and DRI processes.

Beneficiation of Nb and Ti carbides from pyrochlore ore via carbothermic reduction followed by magnetic separation

Beneficiation of niobium and titanium carbides from pyrochlore ore via carbothermic reduction followed by magnetic separation was investigated in this work. During carbothermic reduction, Nb, Ti and Fe oxides within the pyrochlore ore could be reduced into NbC, TiC and metallic iron, respectively. The carbides gather around and dissolve into the metallic iron grains, enabling the enrichment of niobium and titanium carbides by magnetic separation with the carrier of metallic iron. Under the optimal conditions: coke dosage of 6%, reducing temperature of 1400 °C and time of 120 min, a magnetic concentrate with 4.18% Nb, 4.60% Ti and 70.57% Fe can be obtained followed by wet magnetic separation. The corresponding recoveries of Nb, Ti and Fe were 70.5%, 59.8% and 92.6%, respectively.

Hydrogen reduction behaviors and mechanisms of vanadium titanomagnetite ore under fluidized bed conditions

Vanadium titanomagnetite ore has prominent latent applications in the recovery of iron, vanadium and titanium. In this study, the reduction effect and product characteristics of vanadium titanomagnetite ore using hydrogen as reductant under fluidized bed conditions were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer. Under the optimal condition of gas flow rate of 1000 mL·min−1, reduction temperature of 850 °C, reduction time of 30 min and H2 concentration of 80%, the reduced product with a metallization degree of 90.22% was obtained. The titanium-bearing maghemite in raw ore was reduced to titanomagnetite, the massive generated rutile and minor hardly reducible Fe3-xMxO4(M = Mg/Al/Si/) hindered the further aggregation of metallic iron grains, and there was no FeO detected during the whole reduction process. Thus,the phase transformation process of vanadium titanomagnetite is suggested as follows: γ-(Fe,Ti)2O3 → Fe3-xTixO4 → FeTi5O8 → Fe2TiO5 → Fe2TiO4 → Fe + FeTiO3 → Fe + TiO2.

The Growth Characteristics and Kinetics of Metallic Iron in Coal-Based Reduction of Jinchuan Ferronickel Slag

As the fourth-largest industry waste residue, after iron slag, steel slag, and red mud, in China, the comprehensive utilization of nickel slag is imminent. Coal-based reduction combined with magnetic separation was considered an efficient method to extract iron from nickel slag. During the coal-based reduction of Jinchuan ferronickel slag, the growth characteristics and kinetics of metallic iron were investigated in this paper. The metallisation rate and metal iron grain size gradually increased with the reduction temperature or the reaction time, and the coal-based reduction process was divided into the rapid formation period and the aggregation growth period of the metallic phase. The granularity distribution of metallic iron obeyed the Doseresp sigmoidal function, and the activation energy of grain growth at different stages were 52.482 ± 4.448 kJ·mol−1 and 26.426 ± 3.295 kJ·mol−1, respectively. Meanwhile, a mathematical growth model of the metallic iron grains was also established.

Influence of SiO2 on the gas-based direct reduction behavior of Hongge vanadium titanomagnetite pellet by hydrogen-rich gases

In this study, the influence and mechanism of SiO2 on the gas-based direct reduction behavior of Hongge vanadium titanomagnetite pellet (HVTMP) by hydrogen-rich gases was investigated. Increasing SiO2 during the initial stage caused the reduction degree of HVTMP to initially increase and then decrease. At the later stage, SiO2 retarded the reduction, and this effect increased upon increasing the SiO2 addition. SiO2 caused the decrease of the metallization degree by forming hardly reducible Fe2SiO4 and hindering the further reduction of Fe2TiO4 to Fe. The size of metallic iron grains diminished gradually, and the boundary between the metallic iron phase and the slag phase became less obvious with the increase of SiO2 addition. Additionally, the number of metallic iron whiskers decreased, and the growth of metallic iron whiskers transformed from dispersed to close clusters, which decreased the reduction swelling. This study provides a theoretical and technical basis for the smelting of Hongge vanadium titanomagnetite in shaft furnaces by hydrogen-rich gases.

Reduction behaviors of vanadium‑titanium magnetite with H2 via a fluidized bed

Vanadium‑titanium magnetite, a kind of composite ore with iron, vanadium and titanium, has not been utilized on large scale by steel plants. An efficient and clean utilization technique for vanadium‑titanium magnetite based on fluidized bed hydrogen reduction was developed in present study. The effect of reduction temperature, H2 concentration, reduction time and gas flow rate on the metallization degree of the reduced product were studied. The phase compositions and microstructures of sample were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Experimental results indicated that a metallization degree of 91.30% was obtained under the optimal conditions of reduction temperature of 850 °C, H2 concentration of 80%, reduction time of 30 min and gas flow rate of 900 mL·min−1. As the number of metallic iron grains increased, adjacent metallic iron grains gradually aggregated and formed flakes. While, the metallic iron grains precipitated by reduction of raw ilmenite gathered into strips. It is noteworthy that no intermediate phase wustite is detected in all reduced samples, which may be due to the wustite is immediately reduced or decomposed after being formed. Therefore, the possible reduction paths of titanomagnetite are suggested as follows: (1) Fe3-xTixO4 → Fe + FeTiO3 → Fe + TiO2, (2) Fe3-xTixO4 → FeO + FeTiO3 → Fe + TiO2, 0.5 < x < 1.

Impact shock origin of diamonds in ureilite meteorites

The origin of diamonds in ureilite meteorites is a timely topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within Earth's mantle. We investigated fragments of three diamond-bearing ureilites (two from the Almahata Sitta polymict ureilite and one from the NWA 7983 main group ureilite). In NWA 7983 we found an intimate association of large monocrystalline diamonds (up to at least 100 µm), nanodiamonds, nanographite, and nanometric grains of metallic iron, cohenite, troilite, and likely schreibersite. The diamonds show a striking texture pseudomorphing inferred original graphite laths. The silicates in NWA 7983 record a high degree of shock metamorphism. The coexistence of large monocrystalline diamonds and nanodiamonds in a highly shocked ureilite can be explained by catalyzed transformation from graphite during an impact shock event characterized by peak pressures possibly as low as 15 GPa for relatively long duration (on the order of 4 to 5 s). The formation of "large" (as opposed to nano) diamond crystals could have been enhanced by the catalytic effect of metallic Fe-Ni-C liquid coexisting with graphite during this shock event. We found no evidence that formation of micrometer(s)-sized diamonds or associated Fe-S-P phases in ureilites require high static pressures and long growth times, which makes it unlikely that any of the diamonds in ureilites formed in bodies as large as Mars or Mercury.

Efficient and green treatment of ultrapure magnetite to prepare powder metallurgy iron powders

In this paper, coal-based rotary kiln direct reduction‑hydrogen reduction process was demonstrated to an efficient way to prepare the PMIP. Under the optimum conditions, a superior PMIP with 98.5% iron grade and only 0.31% H2-loss can be achieved. Meanwhile, PMIP have the perfect physical properties of 2.45 g/cm3 bulk density, 38 s·50 g−1 flow rate and 6.40 g/cm3 compressibility, which all meet the standard of MHF80·235 (first class goods). Moreover, the enhancing mechanism of PMIP properties was investigated as well, and the results show that the growth of metallic iron grains can obviously reduce the porosity and promote the densification of PMIP structure, which is beneficial for the bulk density and flow rate. This finding can point a new direction to improve the performances, including bulk density and by appropriately extending carbon reduction duration to promote the grain growth and improve the densification of PMIP structure.

Measurement and Characterisation of Metallic Iron Particles on Coal-Based Reduction and Magnetic Separation of Refractory Titanomagnetite

Coal-based reduction followed by magnetic separation is a promising technology for processing refractory iron ores. Analysis of the size distribution of metallic iron particles is an effective approach for exploring the mechanisms of coal-based reduction. As metallic iron particles exhibit very complex shapes compared with nature ores, approaches for measuring and characterising metallic iron particles still remain unclear. In this study, the size of metallic iron particles was measured and characterised using manual point-counting by optical microscopy technics and image analysis. The effects of CaF2 as an additive on behaviour of the particle size distribution (i.e. mean size and cumulative frequency distribution) were also determined. Results indicate that CaF2 had a significant effect on the growth of metallic iron particles. When the CaF2 dosage increased from 0 to 8%, the mean size according to the area method increased from 9.03 to 16.28 μm, while the promotion effect gradually weakened and generated many fine metallic iron particles when the CaF2 dosage exceeded 8%. An increase in CaF2 dosage also led to cumulative distribution curves gradually shifting to the right mainly because F− can break the crystal structure of each phase during the carbothermic reduction of titanomagnetite and reduce the stability of the lattice structure, thus reducing the melting point and accelerating the growth of metallic iron grains. Compared to different measuring methods, the area method is a more suitable approach for measuring and characterising the size of metallic iron particles.

Effect of Al2O3 on the gas-based direct reduction behavior of Hongge vanadium titanomagnetite pellet under simulated shaft furnace atmosphere

As a successive work to develop a novel and clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite (HVTM), the effect of Al2O3 on the gas-based direct reduction behavior of HVTM pellet (HVTMP) under simulated shaft furnace atmosphere was systemically investigated in this study. It was found that the reduction rate was accelerated by Al2O3 at the initial stage due to the increase of original porosity of HVTMP; however, as the reduction proceeded, the reduction degree significantly decreased with the increase of Al2O3 due to the formation of FeAl2O4, which was difficult to reduce. With the increase of Al2O3, the amount and size of metallic iron grains decreased, and the grains visibly separated from each other. In addition, FeAl2O4 was entrapped with metallic iron grains and remained in the Ti-rich phase, which retarded further reduction. The increased Al2O3 changed the distribution of metallic iron whiskers from close to dispersed clusters and decreased their hardness, leading to the increase of reduction swelling. The findings of this study not only establish a relationship between Al2O3 and its reduction behavior, but also greatly contribute to the effective utilization of HVTM either in blast furnace or shaft furnace.

Recovery of Iron from Pyrite Cinder with Reduction–Magnetic Separation Process in Presence of Sodium Salt

This paper investigated the iron recovery form pyrite cinder with the coal-based reduction–magnetic separation process in the presence of sodium sulfate additive. The functional mechanism of sodium sulfate, reduction behavior of pyrite cinder, and separation mechanism of iron mineral and gangue were investigated through discussing the influences of sodium sulfate dosage, reduction temperature, reduction time, and grinding fineness and analyzing the reduced briquette and magnetic concentrate by using X-ray diffraction, optical microscope and scanning electron microscope and energy-dispersive spectrometer (SEM–EDS). The results show that sodium sulfate can improve the occurrence state and embedded relationship of gangue. Furthermore, the sodium sulfate can promote the interconnection of metallic iron grains, which intensifies the separation of iron mineral and gangue. Under the conditions of pyrite cinder briquette containing 3% Na2SO4, reducing at 1050 °C for 80 min, the grinding fineness of 76.8% less than 45 μm, and magnetic field intensity of 73 mT, the iron grade of magnetic concentrate and iron recovery rate were 92.02% and 98.63%, respectively.

The selenium isotopic variations in chondrites are mass-dependent; Implications for sulfide formation in the early solar system

Element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter. The precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains. The transfer of selenium to solids likely occurred through a similar pathway, allowing the formation of iron selenides concomitantly with sulfides. The formation rate of sulfide however remains difficult to assess. Here we investigate whether the Se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system. We present high precision Se concentration and δ82/78Se data for 23 chondrites as well as the first δ74/78Se, δ76/78Se and δ77/78Se data for a sub-set of seven chondrites. We combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites.Our Se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites. Our overall average δ82/78Se value for chondrites is −0.21±0.43‰ (n=23, 2 s.d.), or −0.14±0.21‰ after exclusion of three weathered chondrites (n=20, 2 s.d.). These average values are within uncertainty indistinguishable from a previously published estimate. For the first time however, we resolve distinct δ82/78Se between ordinary (−0.14±0.07‰, n=9, 2 s.d.), enstatite (−0.27±0.05‰, n=3, 2 s.d.) and CI carbonaceous chondrites (−0.01±0.06‰, n=2, 2 s.d.). We also resolve a Se isotopic variability among CM carbonaceous chondrites. In addition, we report on δ74/78Se, δ76/78Se and δ77/78Se values determined for 7 chondrites. Our data allow evaluating the mass dependency of the δ82/78Se variations. Mass-independent deficits ro excesses of 74Se, 76Se and 77Se are calculated relative to the observed 82Se/78Se ratios, and were observed negligible. This rules out poor mixing of nucleosynthetic components to account for the δ82/78Se variability and implies that the mass dependent Se isotopic variations were produced in a once-homogeneous disk.The mass-dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high H2S–H2Se contents in the region of enstatite chondrite formation. Experimental studies showed that high H2S contents favor the formation of compact sulfide layers around metallic grains. This decreases the reactive surface, which tends to inhibit the continuation of the sulfidation reaction. Under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light S and Se isotopes in solids; This hypothesis provides an explanation for our Se isotope as well as for previously published S isotope data. On the other hand, high δ82/78Se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration, or could reflect the contribution of ices carrying photo-processed Se from the outer solar system.

Formation and characterization of metallic iron grains in coal-based reduction of oolitic iron ore

To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally reduced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the reduced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumulative frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol−1, and 922.05, respectively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.

Synchronous Upgrading Iron and Phosphorus Removal from High Phosphorus Oolitic Hematite Ore by High Temperature Flash Reduction

In this paper, an effective method was developed to remove phosphorus and upgrade iron from high phosphorus oolitic hematite ore by high temperature flash reduction—a wet magnetic separation process. A thermodynamic analysis of iron and phosphorus mineral reactions and experiments with Fe-P separation process were performed, and the mechanism of phosphorus removal and beneficiation of iron is discussed as well. The results show that under the proper conditions, a final metallic iron powder assaying over 91% Fe and 0.25% P was obtained with iron recovery of 90% and phosphorus removal rate of 91.79% using the new process, indicating that the high temperature flash reduction process is a feasible and efficient way to process this kind of complex and refractory iron ore. Moreover, sodium sulfate is found to be capable of improving the removal of phosphorus and the upgrading of iron, as well as enhancing the growth of metallic iron grains significantly for higher recovery of iron.

Separation of aluminium and preparation of powdered DRI from lateritic iron ore based on direct reduction process

Lateritic iron ore has not been used effectively due to excess content of multiple metals. In this work, separation of aluminium from a high-aluminium lateritic iron ore was achieved by the process of ‘direct reduction with sodium sulfate-magnetic separation’, with a powdered direct reduced iron (DRI) produced. It is found that the presence of 12% sodium sulphate during reductive roasting significantly improves separation of iron and aluminium in magnetic separation: the total iron grade (TFe) of powdered DRI increases from 80.6 to 92.0% and the Al2O3 content decreases from 9.8 to 1.3% correspondingly. The presence of sodium sulphate results in formation of sodium aluminosilicates instead of FeAlO2. Moreover, sodium sulphate significantly promotes growth of metallic iron grains which is beneficial to sufficient liberation and separation of metallic iron grains from gangue minerals in grinding and magnetic separation.

Effect of Sodium Sulfate on Direct Reduction of Beach Titanomagnetite for Separation of Iron and Titanium

The effect of sodium sulfate on direct reduction of beach titanomagnetite, followed by magnetic separation, to separate iron and titanium was investigated. Direct reduced iron (DRI) with a high Fe content, low TiO2 content and low iron recovery was obtained after adding sodium sulfate. When the sodium sulfate dosage was increased from 0 to 10 mass %, the Fe content of the DRI increased from 90. 00 mass% to 93. 55 mass% and the TiO2 content decreased from 1. 27 mass% to 0. 70 mass%. The reduction mechanism of sodium sulfate was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). Results revealed that the metallic iron grains in the reduced ore with sodium sulfate were larger than those in the ore without sodium sulfate. Sodium sulfate promoted the migration of iron as well as the accumulation and growth of metallic iron grains by low-melting-point carnegieite and troilite formed in the redox system. Low-melting-point carnegieite decreased the melting point of the system and then promoted liquefaction. Troilite could decrease the surface tension and melting point of metallic iron grains.

Enrichment of Rare Earth and Niobium from a REE-Nb-Fe Associated Ore via Reductive Roasting Followed by Magnetic Separation

REE-Nb-Fe ore is a typical refractory resource rich in valuable elements. In this article, coal-based reductive roasting followed by magnetic separation is proposed to recover rare earth element (REE), niobium (Nb), and powdered metallic iron (Fe) concentrate from a REE-Nb-Fe raw concentrate containing 31.9% total iron grade (TFe), 3.2% rare earth oxides (REO), and 2.9% Nb2O5. Sodium sulfate is employed to enhance the reduction of iron oxide and to facilitate the growth of metallic iron grains. A magnetic fraction with TFe of 89.3%, iron metallization of 95.8% and iron recovery of 91.5% is obtained by magnetic separation after the raw concentrate is reduced to 1100°C for 120 min in the presence of 15 wt.% sodium sulfate. The contents of rare earth and niobium in the nonmagnetic fraction are enriched to 5.4% (REO) and 4.6% (Nb2O5) with recoveries of 96.1% and 95.8%, respectively. The TFe in the nonmagnetic fraction obtained after the separation is decreased to 4.8% accordingly. The reactions between sodium sulfate and SiO2/Al2O3 enhance the reduction by destroying the mineral structure. The separation of iron from rare earth and niobium is highly improved as metallic iron grains grow markedly when roasted in the presence of sodium sulfate.

Behavior of phosphorus during the carbothermic reduction of phosphorus-rich oolitic hematite ore in the presence of Na2SO4

Recently, additives such as Na2SO4 and Na2CO3 have been proven to be capable of enhancing the reduction of phosphorus-rich oolitic hematite ore and the recovery of dephosphorized iron by magnetic separation. In this study, the behavior of phosphorus during the carbothermic reduction of a phosphorus-rich oolitic hematite ore in the absence or presence of Na2SO4 was characterized. Thermodynamic calculations of the reactions of fluorapatite with SiO2, Al2O3, or Na2SO4, phase transformations during reduction and the distributing characteristics of phosphorus in the metallic iron and non-metallic phases of the reduced pellets were investigated. Thermodynamic analysis demonstrates that SiO2, Al2O3, and Na2SO4 influence the reduction of fluorapatite significantly. XRD and SEM-EDS results confirm that when the oolitic hematite ore was reduced in the presence of Na2SO4, reactions between Na2SO4, SiO2, and Al2O3 are prior to the reduction of fluorapatite. Therefore, the phosphorus content of the metallic iron phase in the pellet decreased markedly. With the sodium sulfate dosage varying from 0% to 20%, the mean phosphorus mass content in metallic iron grains decreased from 0.877% to 0.02%. The dephosphorized iron is then recovered by magnetic separation subsequently.

Effect of Coal Type on the Reduction and Magnetic Separation of a High-phosphorus Oolitic Hematite Ore

Coal-based direct reduction followed by magnetic separation technique was employed to produce direct reduction iron powder (DRI powder) from a high-phosphorus oolitic hematite ore, and the effects of type and particle size of coal and C/O (Fixed carbon/Oxygen) mole ratio on this process were investigated. The results showed that when using coarse-sized and medium-sized coals, bitumite and lignite presented better iron recovery as compared with anthracite, while this advantage disappeared as the particle size of coals decreased. In addition, the iron content of the DRI powder increased with improving of the coal rank depended on fixed carbon contents, while decreased with the decrease of particle size of coals. Increasing the C/O ratio resulted in a sharp rise of P content of the DRI powder. X-Ray Diffraction (XRD) analysis revealed that more liquid phase was formed in the briquettes during reduction with anthracite as reductant. SEM (scanning electron microscope) observation confirmed that the size of the metallic iron grains formed in reduced briquettes decreased with decreasing of the rank of the coal and the particle size of coal.