Iron Grains Research Articles

Influence of Na2CO3 and K2CO3 Addition on Iron Grain Growth during Carbothermic Reduction of Red Mud

Red mud is a by-product of alumina production from bauxite ore by the Bayer method, which contains considerable amounts of valuable components such as iron, aluminum, titanium, and scandium. In this study, an approach was applied to extract iron, i.e., carbothermic reduction roasting of red mud with sodium and potassium carbonates followed by magnetic separation. The thermodynamic analysis of iron and iron-free components’ behavior during carbothermic reduction was carried out by HSC Chemistry 9.98 (Outotec, Pori, Finland) and FactSage 7.1 (Thermfact, Montreal, Canada; GTT-Technologies, Herzogenrath, Germany) software. The effects of the alkaline carbonates’ addition, as well as duration and temperature of roasting on the iron metallization degree, iron grains’ size, and magnetic separation process were investigated experimentally. The best conditions for the reduction roasting were found to be as follows: 22.01% of K2CO3 addition, 1250 °C, and 180 min of duration. As a generalization of the obtained data, the mechanism of alkaline carbonates’ influence on iron grain growth was proposed.

Growth behavior of iron grains during deep reduction of copper slag

The change in granularity of iron grains in copper slag during coal-based deep reduction was identified using optical microscopy and the Image J analysis software. The growth behavior of iron grains was investigated based on the Hillert dynamic model. The results indicate that the granularity and sphericity of iron grains are strongly affected by the reduction time and temperature during the deep reduction process. It is found that in isothermal condition, the growth rate of iron granularity increases with time exhibiting an S-shape characteristic. Meanwhile, in non-isothermal condition, the growth rate of iron granularity increases exponentially with temperature. When the reduction temperature is in the range of ~1423–1573 K and the reduction time was in the range of ~30–180 min, the grain growth kinetic parameters are calculated as follows: growth index n = 1.424 ± 0.07855, apparent activation energy Q = 116.17 kJ∙mol−1, and pre-exponential factor as 20,839.38.

Studies on Characterization and Beneficiation of Banded Hematite Jasper of Joda Area, Eastern India

Detailed characterization and beneficiation of the banded hematite jasper (BHJ) from Joda area, eastern India, was studied. The main purpose of this study is to produce a pellet feed from the BHJ ore using a simple flow sheet. The feed sample contained total Fe (35.31%), SiO2 (48.73%), Al2O3 (0.58%) and loss of ignition (1.02%). Characterization studies such as grain size analysis, XRD, liberation study and microscopic study were performed to ascertain different minerals. Size-wise chemical analysis indicated that the finer fraction contained more silica and less iron value. Liberation analysis indicated that maximum iron grains were liberated below 150 micron size. Considering the characterization result, a four-stage processing flow sheet was described for the beneficiation of BHJ ore. The result from beneficiation showed that the iron value could be enhanced to 63.9% with a yield of approximately 29.4% while decreasing the silica value to 8.2%.

A Novel and Green Metallurgical Technique of Highly Efficient Iron Recovery from Refractory Low-Grade Iron Ores

With the shortage of high-grade iron ore resources, there is an increasing demand to utilize low-grade iron ores. However, the utilization of refractory low-grade iron ore resources has always been a challenge for the metallurgical industry. In this paper, a novel and green metallurgical technique of highly efficient iron recovery from refractory low-grade iron ores was proposed. A pilot-scale rotary kiln (φ1.5 m × 15 m) research study proved that products with a metallization ratio of 85.15% can be obtained by this low-temperature but rapid reduction process as ore–coal composite was roasted within temperature zone (1173–1264 K) for 24–32 min. Then, 91.75% of iron can be recycled in the form of iron powder (iron grade reached 93.10%), followed by a grinding–magnetic separation process. Compared to the existing processes, this novel process presents advantages of efficient reduction (only 24–32 min for high temperature reduction) and eco-friendliness (energy consumption: 8.98 GJ/t-DRI; CO2 emission: 800–1100 kg/t-DRI), showing a broad range of application prospects in the resource development and utilization of the same type. To understand this process in depth, in situ dissection research for the pilot-scale rotary kiln reduction process was performed, investigating the temperature field distribution, the iron and silicon minerals transition, and the iron grains formation and growth. A link between materials conversion and external field condition during the rotary kiln reduction course was established, providing technical support for further optimization of this process.

Influence of the multiwall carbon nanotubes on the thermal properties of the Fe–Cu nanocomposites

The relative linear expansion (ΔL/L0), coefficient of linear thermal expansion (CTE), differential scanning calorimetry (DSC), thermal conductivity and thermopower (ETP) of the Fe–Cu-MWCNT nanocomposites (Fe:Cu ratio was 4:1; MWCNT = multi-wall carbon nanotubes of 0, 0.5, 1.0 and 2.0 vol% concentration) were measured and analyzed. It was found that MWCNTs effect on thermal behaviour on these nanocomposites varies in different temperature range and the magnitude of the effect depends on the MWCNTs content. The MWCNTs effect on temperature behaviour is mainly realized via blocking the access of copper atoms to iron grains by the MWCNTs atoms. These processes as well as effect of MWCNTs on the condition of the α-Fe → γ-Fe transformation determine temperature behaviour of the nanocomposites in the range 550–700 °C. Insignificant dependence of the relative expansion and coefficient of linear thermal expansion on temperature for the nanocomposites with 2.0 vol% of the MWCNTs indicates perceptiveness of this composition for application, particularly in motor vehicle industry.

Two‐Step Nitriding Behavior of Pure Iron with a Nanostructured Surface Layer

A two‐step gas nitriding treatment (280 °C for 2 h plus 550 °C for 6 h) is designed for pure iron with a nanostructured surface layer induced by surface mechanical attrition treatment (SMAT). The microstructure and surface properties of the SMAT sample after two‐step nitriding treatment are investigated in comparison with those of the SMAT sample after single‐step nitriding treatment (550 °C for 6 h). Experimental results show that a much thicker compound layer (up to 25 μm in thickness) is generated on the surface of the SMAT sample after two‐step nitriding treatment, in which the mean grain size of the Fe2‐3N phase is below 25 nm. The enhanced nitriding kinetic may be attributed to the formation of a large number of Fe(N) solid solutions and a small amount of dispersed Fe2‐3N particles on the SMAT sample after first low‐temperature nitriding, which enhances the thermal stability of nanostructured iron grains. Due to the enhanced nitriding kinetic and refined nitride structure, the SMAT sample after two‐step nitriding treatment displays higher surface hardness and improved wear resistance relative to its single‐step nitrided counterpart.

Effect of shear-coupled grain boundary motion on coherent precipitation

We examine the interaction between precipitates and grain boundaries, which undergo shear-coupled motion. The elastic problem, emerging from grain boundary perturbations and an elastic mismatch strain induced by the precipitates, is analyzed. The resulting free elastic energy contains interaction terms, which are derived numerically via the integration of the elastic energy density. The interaction of the shear-coupled grain boundary and the coherent precipitates leads to potential elastic energy reductions. Such a decrease of the elastic energy has implications for the grain boundary shape and also for the solubility limit near the grain boundary. By energy minimization we are able to derive the grain boundary shape change analytically. We apply the results to the Fe-C system to predict the solubility limit change of cementite near an $\ensuremath{\alpha}$-iron grain boundary.

Do evolved stars in the LMC show dual dust chemistry?

ABSTRACTWe study a group of evolved M-stars in the Large Magellanic Cloud, characterized by a peculiar spectral energy distribution. While the 9.7 $\mu$m feature arises from silicate particles, the whole infrared data seem to suggest the presence of an additional featureless dust species. We propose that the circumstellar envelopes of these sources are characterized by a dual dust chemistry, with an internal region, harbouring carbonaceous particles, and an external zone, populated by silicate, iron, and alumina dust grains. Based on the comparison with results from stellar modelling that describe the dust formation process, we deduce that these stars descend from low-mass (M < 2 M⊙) objects, formed 1–4 Gyr ago, currently evolving either in the post-AGB phase or through an after-pulse phase, when the shell CNO nuclear activity is temporarily extinguished. Possible observations able to confirm or disregard the present hypothesis are discussed.

Synchrotron X-ray Laue diffraction study of hydrogen-induced blisters on iron grain boundaries

The effects of grain boundaries (GBs) on the initiation of hydrogen-induced blisters in pure iron were investigated using synchrotron polychromatic X-ray Laue nano-diffraction. It was found that the random GBs were more susceptible to blistering than the coincidence site lattice grain boundaries. High strain levels and severe plastic deformation were observed around the random GBs after hydrogen charging, but not on the coincidence site lattice grain boundaries.

Performance of a magnetorheological fluid-based robotic end effector

Robotic end effectors are needed for a variety of terrestrial and space-based tasks. End effectors are commonly inspired by the human hand, with a range of complexity, including varying number of fingers, joints and degrees of freedom. Hand and pincher-type grippers can require complicated actuation and/or a significant sensing and control system to ensure proper orientation of the gripper about the target prior to gripping as well as to avoid crushing the target. Universal grippers, most notably exemplified by the universal Jamming Gripper (Brown et al 2010 Proceedings of the National Academy of Science 107, 18809–18814), provide an alternative design that aims to simplify the actuation, sensing and control of robotic fixturing end-effectors. The universal Jamming Gripper is actuated pneumatically, by applying vacuum to granular media, thereby causing the grains to jam, when confined by an external bladder. We present the design and performance of a universal gripper that is actuated by applying a magnetic field, thereby eliminating the need to supply vacuum (and a reinflation source) to actuate the gripper. The magnetic field actuates a magnetorheological fluid composed of a bi-disperse mixture of carbonyl iron grains suspended in a silicone oil. The performance of this novel gripper design is characterized for a range of target sizes and shapes, and gripper design characteristics.

Finding new grain forms in three dimensions

Topological grain forms in three dimensions are studied experimentally and by large-scale Potts model Monte Carlo simulation. Some new band-faced grain forms are firstly observed among 16,254 pure iron grains, yet none of them is found among 28,049 Monte Carlo simulation grains, which indicate that there is shorter residence times for band-faced grain forms in three dimensions. The combined curvature/topology analysis suggests a possible efficient way of topological transitions of grain forms which is different from the known transition paths.

Iron and zinc grain concentrations diversity and agronomic performance of common bean germplasm collected from East Africa

Iron and zinc are essential micronutrients for normal human growth and development and are commonly deficient in diets of the most vulnerable. Common bean ( Phaseolus vulgaris L.), one of the leading staple foods in East and Central Africa, is a valuable source of quality protein and micronutrients, specifically iron, zinc, and vitamins. Natural variation in micronutrient concentration exists among bean germplasm. Identification of varieties with high iron and zinc seed concentration (FESEED/ZNSEED) for promotion in food systems and utilisation in breeding programs is one strategy of addressing the problem of malnutrition in Africa. Three hundred and four lines sourced from the International Centre for Tropical Agriculture (CIAT) and its partners through the Pan Africa Bean Research Alliance (PABRA), were evaluated for agronomic traits, disease response, yield, FESEED, and ZNSEED. They were organized in four groups; PABRA fast track, Rwanda seeds of hope, HarvestPlus regional nutrition nursery and Uganda collection. Six checks were included; a universal high FESEED climbing bean (MIB465), low FESEED regional climbing bean (Decelaya), universal low FESEED bush bean (DOR500), regional high FESEED bush bean (RWR2154), and two yield checks (CAL96 and Vuninkingi for bush and climbing bean). The FESEED checks were selected based on their relative performance to other genotypes in several experiments by a community of bean breeders through the H+ program. Field trials were established at the National Agricultural Laboratories, Kawanda from 2011 to 2013. Days to maturity and flowering, vigor, yield, and reaction to diseases were evaluated. Micronutrient analysis was conducted using X-ray Fluorescence (XRF) and data confirmed using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Lines were significantly different (P≤0.05) in all the parameters assessed. FESEED and ZNSEED varied highly between seasons and among the entries ranging between 36-90 ppm and 24-47 ppm across the four nurseries. Twenty-six lines were selected as high iron beans (HIBs) based on XRF data; 12 of these were confirmed as HIB based on ICP data that is more accurate. Of these, two bush beans, Jesca (large purple speckled) and RW547 (medium grey) and two climbing beans, CAB2 (medium white seeded) and Ndimirakaguja (small cream) were the most superior in FESEED across seasons. With the exception of CAB2, these lines were relatively high yielding >2000 kgha-1. There was no significant correlation of FESEED or ZNSEED to yield. Nonetheless, FESEED and ZNSEED positively (0.59) correlated indicating that selection for superiority in one variable would result in a high value in the other. Key words : Common bean, Micronutrients, Anemia, Genetic variation, Yield, Diseases

Topology characteristics of three-dimensional grains in polycrystalline materials

The quantitative microstructural analysis in recrystallized pure iron is carried out by serial sectioning experiment coupled with three-dimensional (3-D) grain reconstruction technique. The full 3-D morphology of 16254 pure iron grains, which is the largest experimental 3-D grain dataset to date, is obtained. It is shown that the peak and the mean of the grain face number distribution were 10 and 13.5, respectively. For individual grains, the average trends that the highest and lowest face classes exhibited the highest affinity for mutual contact but the lowest affinity for contact with themselves are experimentally confirmed by 3-D pure iron grains. The pure iron grains are observed to have much more three-edged faces than Monte Carlo grains, resulting in relatively higher average dispersions of the grain edge distribution.

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.

Sulphur and Nitrogen Fertilization as a Potential Means of Agronomic Biofortification to Improve the Content and Uptake of Microelements in Spring Wheat Grain DM

The aim of the field experiment was to analyze the impact of various nitrogen and sulphur doses on the content and uptake of spring grains of iron, manganese, copper, and zinc. The study was conducted in southeastern Poland (2009–2011) on Cambisols (WRB 2007), in conditions of low soil sulphur content. The experiment included 4 doses of N fertilization (0, 40, 80, and 120 kg/ha) and 2 doses of S application (0 and 50 kg/ha). The analysis showed that fertilization with nitrogen and sulphur had a positive effect on the studied features of spring wheat. The combination resulted in beneficial content of Fe, Mn, Zn, and Cu (Fe 45.00, Mn 35.67, Zn 34.63, and Cu 3.65 mg/kg) and beneficial uptake of microelements by grain DM (Fe 216.1, Mn 171.3, Zn 166.4, and Cu 17.52 g/ha). The highest grain yield (5.43 t/ha) was obtained after the application of nitrogen at a dose of 80 kg/ha and sulphur at a dose of 50 kg/ha. In relation to control, this increase of grain yield amounted to 13.3%. Significant correlations were also found between grain yield and the content and uptake of all microelements, as well as between elements. No significant correlation was found only between the content and uptake of Fe and the content of Mn and between the content of Mn and Cu. Sulphur supplementation of NPK fertilization can be a good means of agronomic biofortification for spring wheat in order to increase the content and uptake of micronutrients such as Fe, Mn, Zn, and Cu.

Solid-Phase Reduction and Iron Grain Growth in Red Mud in the Presence of Alkali Metal Salts

The solid-phase carbothermic reduction and the iron grain growth in red mud are studied in the presence of sodium and potassium sulfates and carbonates. The influence of temperature and alkali metal salt additions on the reduction of iron is estimated by Mossbauer spectroscopy during experiments in a laboratory furnace in the temperature range 1000–1200°C. The calculation of the grain size in reduced metallic iron shows that the addition of alkali metal compounds to red mud promotes an increase in the grain size. The experimental data demonstrate that alkali metal sulfates more strongly affect the iron grain growth as compared to alkali metal carbonates. The proposed approach can be used to develop a process of recycling of red mud by solid-phase reduction followed by magnetic separation.

Effects of gangue compositions on reduction process of carbon-bearing iron ore pellets

The influence of gangue compositions (mainly composed of SiO2, CaO, MgO and Al2O3) on the reduction kinetics of carbon-bearing iron ore pellets was estimated at 1373–1473 K in N2 atmosphere. The results showed that gangue content and each component distribution affected the pellets reduction process. The reduction rate was found to follow a linear correlation with quaternary basicity R4 [mass ratio of (CaO + MgO) to (SiO2 + Al2O3)] of the carbon-bearing iron ore pellets; also, the content of SiO2 solid solution in iron oxide had a significant impact on the reduction rate. At the same reduction temperature, a higher R4 resulted in a lower SiO2 free content, weakening its inhibitory effect on the Boudouard reaction. The reduction temperature of Fe2SiO4 could be reduced by increasing the contents of CaO and MgO, improving the iron oxide reduction as well as the precipitation and growth of the iron grains. The gangue content and component distribution showed no effect on the rate-controlling step of the reduction; however, the apparent activation energy of reaction decreased with increasing quaternary basicity. When R4 increased from 0.15 to 0.67, the apparent activation energy decreased from 228.51 to 193.66 kJ/mol.

Carbothermic reduction of ilmenite concentrate in semi-molten state by adding sodium sulfate

The electric arc furnace (EAF) smelting process, which produces titanium slag, is the most popular method for utilizing Panzhihua ilmenite concentrate. However, the EAF process involves high energy consumption, high pollution, and low efficiency due to the high smelting temperature, the large amount of dust produced, and the long smelting period. An economical and clean method for semi-molten reduction followed by magnetic separation to produce titanium slag from Panzhihua ilmenite concentrate was presented. In this paper, the semi-molten reduction process was studied and the effect of reduction temperature, C/O molar ratio, and the addition dosage of Na2SO4 on the metallization ratio, phase transformation, and size of metallic iron grain was discussed. The results showed that Na2SO4 and its subsidiary products can function as fluxing agent for decreasing the melting point of metal and slag, thus promoting the growth of metal particles, and achieving high efficiency and clean reduction of ilmenite concentrate. The action mechanism of Na2SO4 addition is also discussed.

Melting efficiency of troilite-iron assemblages in shock-darkening: Insight from numerical modeling

We studied shock-darkening in ordinary chondrites by observing the propagation of shock waves and melting through mixtures of silicates, metals and iron sulfides. We used the shock physics code iSALE at the mesoscale to simulate shock compression of modeled ordinary chondrites (using olivine, iron and troilite). We introduced FeS-FeNi eutectic properties and partial melting in a series of chosen configurations of iron and troilite grains mixtures in a sample plate. We observed, at a nominal pressure of 45 GPa, partial melting of troilite in all models. Only few of the models showed partial melting of iron (a phase difficult to melt in shock heating) due to the eutectic properties of the mixtures. Iron melting only occurred in models presenting either strong shock wave concentration effects or effects of heating by pore crushing, for which we provided more details. Further effects are discussed such as the frictional heating between iron and troilite and the heat diffusion in scenarios with strongly heated troilite. We also characterized troilite melting in the 32–60 GPa nominal pressure range. We concluded that specific dispositions of iron and troilite grains in mixtures allow for melting of iron and explain why it is possible to find a wide textural variety of melted and unmelted metal and iron sulfide grains in shock-darkened ordinary chondrites. We finally observe shock-melting of albite within a few iron and troilite grain models, and investigate the effects of higher porosity within the olivine matrix in the single iron and troilite grain models.

CHARACTERIZATION OF NATURAL IRON SAND FROM KATA BEACH, WEST SUMATRA WITH HIGH ENERGY MILLING (HEM)

Iron sand is one of the natural resources in West Sumatra that has not been optimally utilized. One of the potential locations to get this iron sand deposits is the coast of Kata. This study aims to analyze the content and size of the iron grains found on the coast of Kata Padang Beach, West Sumatera Province. Coastal sand samples are extracted using permanent magnets to separate magnetic and non-magnetic materials. Characterization of iron sand using Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) and Vibrating Sample Magnetometer (VSM). The result of characterization using SEM-EDX shows that iron sand samples contain Fe and O elements derived from Phase Magnetite (Fe3O4). Keywords: iron sand, magnetic materials, SEM-EDX, VSM