A Comparative Study of Ultra-Fine Iron Ore Tailings from Brazil

This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is expected to provide a basis for the development and choice of mineral-processing techniques suitable for the tailings characteristics of each mine. Particle size separation was done by wet sieving and in a cyclosizer, whereas particle size distribution was determined by laser diffraction (Cilas). The powders were further characterized by chemical analysis, X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. The tailings had a significant content of iron (from 44% to 64%), mainly in the form of hematite (α-Fe₂O₃) and goethite (α-FeOOH). Mössbauer results showed that the amount of goethite increased as the particle size decreased. Furthermore, the hematite content was always greater in the coarser fractions (>10 μm). The phosphorus contents were high and associated with the presence of goethite in most samples. Scanning electron microscopy showed that the vast majority of the particles were not spherical and that the cyclosizer does not separate the material in the intended fractions efficiently. The particles obtained by wet sieving had much more uniform shape and size.     

Microstructural Aspects of Second Phases in As-cast and Homogenized 7055 Aluminum Alloy with Different Impurity Contents

The microstructural factors such as type, area fraction, morphology, distribution, and size of second phases in as-cast and homogenized 7055 aluminum alloy and the influence of impurity content variations have been investigated by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). In as-cast microstructures, the dominant second phases of η [Mg(Al, Cu, Zn)₂] with extended solubility of Cu and Al, a small amount of impurity phases of Al₇Cu₂Fe and Al₃Fe with a little solubility of Cu and Si, and trace Mg₂Si are identified. The variations of Fe and Si contents have no significant influence on the area fraction of η phases, but the area fraction of Fe-rich phase decreases from 0.231 to 0.102 pct with Fe content decreasing from 0.080 to 0.038 wt pct. Decreasing Fe contents reduces the size parameters of Fe-rich phases and refines their morphology correspondingly. After being homogenized at 753 K (480 °C) for 24 hours, η phases are largely dissolved, but the coarse impurity phases are insoluble. Compared with as-cast microstructures, the area fraction and composition of Fe-rich phases change a little but their morphologies are slightly coarsened.     

Characterization and Reduction Roasting Studies of an Iron Rich Manganese Ore

The article presents the reduction roasting followed by low intensity magnetic separation studies of a low grade Mn ore assaying 27.7% Mn and 26.1% Fe in order to obtain a Mn rich non-magnetic concentrate. The reflected light microscopic studies followed by the liberation studies of the as-received sample using quantitative mineralogical evaluation by scanning electron microscope suggested a poor liberation pattern of the constituent Mn and Fe minerals owing to a complex association of the different phases present. The reduction roasting studies carried out while varying different process parameters such as ore particle size, temperature, reductant content and residence time ended up with products containing 45–48% Mn with a Mn/Fe ratio of 5–6 at a yield of ~ 60% with the optimum level of conditions such as temperature: 800–850 °C, time: 90–120 min and charcoal: 10–12%. The scanning electron microscopy–energy dispersive X-ray spectroscopy studies of the roasted product reported manganite as the major Mn bearing phase while magnetite was found to be the major iron bearing phase.     

Microbial Beneficiation of Salem Iron Ore Using Penicillium purpurogenum

High alumina and silica content in the iron ore affects coke rate, reducibility, and productivity in a blast furnace. Iron ore is being beneficiated all around the world to meet the quality requirement of iron and steel industries. Choosing a beneficiation treatment depends on the nature of the gangue present and its association with the ore structure. The advanced physicochemical methods used for the beneficiation of iron ore are generally unfriendly to the environment. Biobeneficiation is considered to be ecofriendly, promising, and revolutionary solutions to these problems. A characterization study of Salem iron ore indicates that the major iron-bearing minerals are hematite, magnetite, and goethite. Samples on average contains (pct) Fe₂O₃-84.40, Fe (total)-59.02, Al₂O₃-7.18, and SiO₂-7.53. Penicillium purpurogenum (MTCC 7356) was used for the experiment. It removed 35.22 pct alumina and 39.41 pct silica in 30 days in a shake flask at 10 pct pulp density, 308 K (35 °C), and 150 rpm. In a bioreactor experiment at 2 kg scale using the same organism, it removed 23.33 pct alumina and 30.54 pct silica in 30 days at 300 rpm agitation and 2 to 3 l/min aeration. Alumina and silica dissolution follow the shrinking core model for both shake flask and bioreactor experiments.     

Study on Phosphorus Removal of High-Phosphorus Oolitic Hematite by Coal-Based Direct Reduction and Magnetic Separation

In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe₂O₃ → Fe₃O₄ → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe₂SiO₄ → Fe or FeO → FeAl₂O₄ → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.     

Titanium Carbide Reinforcement in Iron Matrix Through Carbothermal Reduction of Mechanically Milled Hematite and Anatase

This study investigated the influence of the duration of milling on the formation of TiC-reinforced iron composite through carbothermal reduction of a hematite and anatase mixture. Mixtures of hematite, anatase, and graphite powders were mechanically activated in a planetary ball mill in an argon atmosphere with different milling times (0 to 60 hours). X-ray diffraction showed that with increasing milling time, the crystallite size of the hematite decreased to nanometer range, accompanied by an increment in internal strain. Prolonging the milling process increased dislocation density of the as-milled powder. The as-milled powder was consolidated by cold pressing under 100 MPa and sintered in vacuum at 1373 K (1100 °C). High temperature during sintering resulted in the formation of iron and titanium carbide phases as confirmed by X-ray diffraction, scanning electron microscope, and energy dispersive X-ray analysis. Without mechanically activated milling, the reaction forming TiC did not occur during sintering at 1373 K (1100 °C), indicating a reduction in reaction temperature promoted by mechanical milling. An increase in milling time resulted in an increase in sintered density and hardness due to the fineness of the composite powder, together with complete TiC and iron phase formation.     

Mass Loss and Direct Reduction Characteristics of Iron Ore-coal Composite Pellets

Mass loss and direct reduction characteristics of iron ore-coal composite pellets under different technological parameters were investigated. Meanwhile, changes of iron phase at different temperatures were analyzed by using X-ray diffraction （XRD）, and characteristics of crushed products were studied by using a scanning electron microscope （SEM）. The results showed that heating rate had little influence on the reduction, but the temperature played an important role in the reduction process. The mass loss rate increased rapidly from 800 to 1 100 ℃. The reduction process can be divided into three steps which correspond to different temperature ranges. Fe2 03 began to transform into Fe304 below 500 ℃, and FeO was reduced into Fe from 900 ℃. At 900 ℃, the reduction product showed a clear porous structure, which promoted the reduction progress. At 1000 ℃, the metallic Fe dominated the sample, and the reduction reached a very high degree.     

The Effect of Iron Content on the Iron-Containing Intermetallic Phases in a Cast 6060 Aluminum Alloy

The effect of iron content, ranging from 0.1 to 0.5 wt pct, on the formation of Fe-containing intermetallic phases in a cast 6060 aluminum alloy was investigated. Various characterization techniques, including optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to examine the identity, morphology, and prevalence of the Fe-Al and Fe-Al-Si intermetallic phases. The predominant phase is found to be β-Al₅FeSi at lower Fe levels, but this is replaced by α-AlFeSi (bcc structure) with increasing Fe content. The Fe containing intermetallic phases observed are compared to those predicted using the Scheil module of THERMO-CALC software, and the similarities and discrepancies are discussed.     

Iron intermetallic phases in the Al corner of the Al-Si-Fe system

The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied using thermal analysis, optical microscopy, and image, scanning electron microscopy/energy dispersive X-ray, and electron probe microanalysis/wavelength dispersive spectroscopy (EPMA/WDS) analyses. The alloys were solidified in two different molds, a preheated graphite mold (600°C) and a cylindrical metallic mold (at room temperature), to obtain slow (}0.2 °C/s) and rapid (}15 °C/s) cooling rates. The results show that the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well as with the decrease in cooling rate. The low cooling rate produces larger-sized intermetallics, whereas the high cooling rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions in producing intermetallics. The alloy composition and cooling rate control the stability of the intermetallic phases: binary Al-Fe phases predominate at low cooling rates and a high Fe:Si ratio; the β-Al₅FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-Al₈Fe₂Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al₄FeSi₂ intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt pct and higher. Calculations of the solidification paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification paths, due to the fact that solid diffusion is not taken into account in the equation. The theoretical models of Brody and Flemings^[44] and Clyne and Kurz^[45] also fail to explain the observed departure from the Scheil behavior, because these models give less weight to the effect of solid back-diffusion. An adjusted 500°C metastable isothermal section of the Al-Si-Fe phase diagram has been proposed (in place of the equilibrium one), which correctly predicts the intermetallic phases that occur in this part of the system at low cooling rates (}0.2 °C/s).     

CHARACTERIZATION AND PROCESSING OF LOW-GRADE IRON ORE SLIME FROM THE JILLING AREA OF INDIA

Detailed characterization followed by beneficiation of low-grade iron ore slime from Jilling Langalota deposit, India, was studied. The work involved separating the gangue minerals viz. quartz and kaolinite to form iron-bearing minerals, mostly hematite and goethite, as identified using XRD analysis to produce a suitable concentrate for downstream processing. The feed slime sample assayed 37.86% total Fe, 19.08% silica, and 14.4% alumina. Detailed characterization data indicated that a substantial amount of the sample was below 20 µm in size. The finer fraction contained larger amount of gangue while the coarser fraction was richer in iron. Considering the characterization data, two flowsheets were conceptualized for the beneficiation of the slime sample with two- and four-stage processing, respectively. In the two-stage operation, the grade of the slime could be improved to 60.26% Fe, 4.45% silica, and 3.98% alumina with an overall yield of about 20%. The results from the four-stage operation showed that it is possible to upgrade the iron value to 66.97% with a yield of 14.4% while reducing the silica and alumina content down to 1.7% and 1.52%, respectively. A simple flowsheet has been suggested to improve the yield substantially for the production of sinter/pellet grade concentrate from this slime.     

Iron intermetallic phases in the Al corner of the Al-Si-Fe system

The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied using thermal analysis, optical microscopy, and image, scanning electron microscopy/energy dispersive X-ray, and electron probe microanalysis/wavelength dispersive spectroscopy (EPMA/WDS) analyses. The alloys were solidified in two different molds, a preheated graphite mold (600 °C) and a cylindrical metallic mold (at room temperature), to obtain slow (∼0.2 °C/s) and rapid (∼15 °C/s) cooling rates. The results show that the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well as with the decrease in cooling rate. The low cooling rate produces larger-sized intermetallics, whereas the high cooling rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions in producing intermetallics. The alloy composition and cooling rate control the stability of the intermetallic phases: binary Al-Fe phases predominate at low cooling rates and a high Fe:Si ratio; the β-Al₅FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-Al₈Fe₂Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al₄FeSi₂ intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt pct and higher. Calculations of the solidification paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification paths, due to the fact that solid diffusion is not taken into account in the equation. The theoretical models of Brody and Flemings^[44] and Clyne and Kurz^[45] also fail to explain the observed departure from the Scheil behavior, because these models give less weight to the effect of solid back-diffusion. An adjusted 500 °C metastable isothermal section of the Al-Si-Fe phase diagram has been proposed (in place of the equilibrium one), which correctly predicts the intermetallic phases that occur in this part of the system at low cooling rates (∼0.2 °C/s).     

Innovative Method for Separating Phosphorus and Iron from High-Phosphorus Oolitic Hematite by Iron Nugget Process

This study puts forward a new method to separate phosphorus and iron from high-phosphorus oolitic hematite through iron nuggets process. Firstly, the physical, chemical, and microscopic characteristics of high-phosphorus oolitic hematite are investigated. Then, the reaction mechanisms of high-phosphorus hematite together with feasibility to separating phosphorus and iron by iron nugget process are discussed. Meanwhile, the experiments of high-phosphorus hematite used in rotary hearth furnace iron nugget processes are studied as well. The results indicate that the iron nugget process is a feasible and efficient method for iron and phosphorus separation of high-phosphorus oolitic hematite. The phosphorus content in iron nuggets is relatively low. Through the optimization of process parameters, the lowest of phosphorus in iron nuggets is 0.22  pct, the dephosphorization rate is above 86  pct, and the recovery of Fe is above 85  pct by the iron nugget process. This study aims to provide a theoretical and technical basis for economical and rational use of high-phosphorus oolitic hematite.     

Behaviour and characterization of hematite process for iron removal in hydrometallurgical production

The separation of zinc and iron is essential in hydrometallurgical processes, especially for treating high-iron sphalerite. The hematite precipitation process for removing iron is an effective way to achieve the high-efficiency separation of zinc and iron. The authors studied the effect of temperature and time on the precipitation behaviour and characterised the precipitation products through X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and chemical analysis. The hematite precipitate contained more than 50% iron, less than 0.5% zinc, 0.1% arsenic and 5% sulfur; more than 95% K, 50% Na and 50%–60% F were co-precipitated, and less than 1% Zn, Mg, Mn and Cl remained in the residue. Because of the uncontrolled supersaturation conditions, jarosite and goethite were generated. Extension of the reaction time and increasing the reaction temperature enabled conversion of most of the goethite and sodium jarosite to hematite during the hematite precipitation process.     

Recovery of Iron from Pyrite Cinder Containing Non-ferrous Metals Using High-Temperature Chloridizing-Reduction-Magnetic Separation

This study presents a new technique that uses high-temperature chloridizing -reduction-magnetic separation to recover iron from pyrite cinder containing non-ferrous metals. The effects of the reduction temperature, reduction time, and chlorinating agent dosage were investigated. The optimized process parameters were proposed as the following: CaCl₂ dosage of 2 pct, chloridizing at 1398 K (1125 °C) for 10 minutes, reducing at 1323 K (1050 °C) for 80 minutes, grinding to a particle size of 78.8 pct less than 45 μm, and magnetic field intensity of 73 mT. Under the optimized conditions, the Cu, Pb, and Zn removal rates were 45.2, 99.2, and 89.1 pct, respectively. The iron content of the magnetic concentrate was 90.6 pct, and the iron recovery rate was 94.8 pct. Furthermore, the reduction behavior and separation mechanism were determined based on microstructure and phase change analyses using X-ray powder diffraction, scanning electron microscope, and optical microscopy.     

印尼某褐铁矿型红土镍矿原矿微观结构的探讨

研究对象印尼某红土镍矿为褐铁矿型红土镍矿,具有品位低、成分复杂等特点。为了查明印尼某红土镍矿的微观结构特征从而达到合理且最大程度地回收矿物中Ni、Fe组分,实验利用偏光显微镜、扫描电镜(SEM)、X射线衍射(XRD)和矿物自动解理系统(MLA)等多种测试分析手段对原矿的物相组成、主要矿物的嵌布特征等展开研究。结果表明:100~900℃的温度梯度范围内,该褐铁矿型红土镍矿先后经历了针铁矿脱羟基转变成赤铁矿和铁橄榄石相的形成过程。该印尼红土镍矿中金属矿物主要由针铁矿、铬铁矿、赤铁矿等氧化物组成,脉石矿物主要由石英、铁橄榄石和绿泥石等硅酸盐组成。针铁矿是Ni、Cr、Co、Al的主要赋存矿物,且都是以类质同象的形式代替Fe元素形成的固溶体矿物,该矿物也是后期Ni、Fe分离的目的矿物。     

Column Bioleaching of a Low-Grade Silicate Ore of Uranium

The bioleaching of a low-grade Indian uraninite ore (triuranium octoxide, U₃O₈: 0.024%), containing ferro-silicate and magnetite as the major phases, and hematite and pyrite in minor amounts, has been reported. Experiments were carried out in laboratory scale column reactors inoculated with enriched culture of Acidithiobacillus ferrooxidans isolated from the source mine water. The pH effect on uranium recovery was examined with the same amounts of ores in different columns. With the presence of 10.64% Fe in the ore as ferro-silicate, the higher uranium biorecovery of 58.9% was observed with increase in cell count from 6.4 × 10⁷ to 9.7 × 10⁸ cells/mL at pH 1.7 in 40 days as compared to the uranium recovery of 56.8% at pH 1.9 with a corresponding value of 9.4 × 10⁸ cells/mL for 2.5-kg ore in the column. The dissolution of uranium under chemical leaching conditions, however, recorded a lower value of 47.9% in 40 days at room temperature. Recoveries were similar with 6-kg ore when column leaching was carried out at pH 1.7. The bioleaching of uranium from the low-grade ore of Turamdih may be correlated with the iron(II) and iron(III) concentrations, and redox potential values.     

Experimental Investigation and Thermodynamic Calculations of the Bi-Ge-Sb Phase Diagram

A phase diagram of the Bi-Ge-Sb ternary system was investigated experimentally by differential thermal analysis (DTA), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray powder diffraction (XRD) methods and theoretically by the CALPHAD method. The liquidus projection; invariant equilibria; and three vertical sections, Sb-Bi_0.5Ge_0.5, Ge-Bi_0.5Sb_0.5, and Bi-Ge_0.5Sb_0.5, as well as isothermal sections at 773 K and 373 K (500 °C and 100 °C), were predicted using optimized thermodynamic parameters for constitutive binary systems from the literature. In addition, phase transition temperatures of the selected samples with compositions along calculated isopleths were experimentally determined using DTA. Predicted isothermal sections at 773 K and 373 K (500 °C and 100 °C) were compared with the results of the SEM-EDS and XRD analysis from this work. In both cases, good agreement between the extrapolated phase diagram and experimental results was obtained. Alloys from the three studied vertical sections were additionally analyzed using the Brinell hardness test.     

Corrosion and Passive Film Formation Studies on Modified 9Cr–1Mo Steel in Different Sodium Hydroxide Concentrations at Room Temperature and in Boiling Condition

Studies were carried out on modified 9Cr–1Mo steel to understand its corrosion as well as passive film characteristics in caustic environment. Potentiodynamic anodic polarization studies were carried out in 1–8 M sodium hydroxide solutions at room temperature (RT) and in boiling conditions. The specimens were passivated at 0.0 V(SCE) for 1 h in 3 and 8 M sodium hydroxide solutions at RT as well as in boiling condition. Laser Raman spectroscopic (LRS) analysis was carried out to examine the nature of oxides/hydroxides formed on the surface of the specimens. Corrosion rates increased by one order of magnitude whereas passive current density increased by almost two orders of magnitude in boiling solution compared to the RT values. Appearance of only maghemite (γ-Fe₂O₃) peaks in passivated steel in 3 M sodium hydroxide solution at RT compared to that in the 8 M sodium hydroxide solution, which showed Fe(OH)₂, maghemite, magnetite, goethite (α-FeOOH) and CrO(OH), Cr₂O₃ peaks, indicated corrosion attack on the outer layer of the passive film. The passivated steel specimens in 3 and 8 M boiling solutions showed maghemite, magnetite, goethite, hematite (α-Fe₂O₃) (only in 8 M) and extremely weak peaks of Cr(OH)₃ and Cr₂O₅. These observations indicated dissolution of the outermost part of the passive film with superficial attack on the inner part of the passive film exposing Cr oxide/hydroxides in boiling 3 M solution. However, passivated steel in 8 M solution showed molybdenum oxides, apart from the other iron and chromium oxides/oxyhydroxides. The scanning electron microscopic (SEM) studies on the morphology of the corrosion products along with LRS analysis/characterization confirmed these observations. These results showed increased corrosion attack during passivation with increase in concentration of alkali and temperature.     

Recovery Improvement of Fine Magnetic Particles by Floc Magnetic Separation

The performance of floc magnetic separation (FMS) has been compared with wet high-intensity magnetic separator (WHIMS). This study was performed on low-grade iron ore slime contained 59.58% Fe with 4.57% silica and 3.78% alumina. Detailed characterization data indicated that a substantial amount of the slime was below 20 µm in size. Beneficiation studies indicated that the FMS process is effective to recover fine hematite and goethite particles, compared with the conventional magnetic separation. In conventional magnetic separation, the extent of the fluid drag force exceeds the magnetic force exerted on ultrafine particles. Thus, ultrafine magnetic particles were usually not recovered effectively by magnetic separators, resulting in the loss of valuable ultrafine slime particles. The FMS process significantly increases the magnetic force on the ultrafine iron ore in the form of hydrophobic flocs in a magnetic field, thus the ultrafine particles can be picked up effectively as magnetic concentrates. The FMS process improved the Fe recovery from 37.35% to 79.60%.     

Effect of Manganese on the Formation of Fe-rich Phases in Electromagnetic Stirred Hypereutectic Al-22Si Alloy with 2 % Fe

The effect of Mn on the microstructure of electromagnetic stirred hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results show that the alloy with a Mn/Fe ratio zero, contained plentiful α-Al₄FeSi₂ phases existing as mainly intermetallic compounds in the solidified microstructures by electromagnetic stirring (EMS) process. With EMS process, the alloy with 0.61 % Mn contained acicular β-Al₅(Fe, Mn)Si, δ-Al₄(Fe, Mn)Si₂ and blocky α-Al₁₅(Fe, Mn)₃Si₂ phases in the solidification microstructure of the stirred A1 alloy. As the Mn/Fe ratio increased to 1, intermetallic compounds were mainly in the form of blocky and fine α-Al₁₅(Fe, Mn)₃Si₂ phases in the microstructure. The intermetallic compounds were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. The acicular δ-Al₄(Fe, Mn)Si₂ and blocky α-Al₁₅(Fe, Mn)₃Si₂ phases were also analyzed by transmission electron microscopy.