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In this study, AMCs have been prepared by incorporating natural mineral ilmenite (FeTiO3) into base alloy Al–Si17Cu4Mg through stir casting process. Three different size ranges of ilmenite viz. 75–106, 50–75, and 32–50 µm were used to fabricate the composites. The micro-hardness test on different phases has shown good interfacial bonding between the ilmenite particles and the Al–Si17Cu4Mg aluminum matrix. Wear test was carried out at different applied loads ranging from 1 to 7 kg and at sliding velocity of 1.6 m/s to study the influence of particle size range. At an applied load of 1–7 kg, the wear rate was improved by nearly 38% in the run-in wear region and nearly 28% in the steady-state region when compared with base alloy. Moreover, composite containing 15 wt% ilmenite (32–50 µm) has shown maximum improvement in wear resistance more than 50% at all applied loads as compared to Al–Si17Cu4Mg alloy. The wear rate of cast iron used for different automobile applications was also measured and compared with 15 wt% (32–50 µm size) ilmenite-reinforced composite. It was nearly 8% and 5% lower at 1 and 7 kg applied load, respectively. The coefficient of friction of 15 wt% composites reinforced with the ilmenite particles (32–50 µm) was 48 % and 29 % less than Al–Si17Cu4Mg alloy at 1 and 7 kg applied load, respectively. The microstructural analysis of worn surfaces revealed the abrasive and adhesive wear mechanism as the predominant factor of material losses.

We propose a hydrogen-based preliminary reduction process for primary ilmenite before the smelting process in titanium dioxide pigment production, because of its advantages of low energy consumption and carbon dioxide mitigation. The hydrogen-based gaseous reduction of primary ilmenite concentrate was investigated at temperatures between 1273 K and 1473 K (1000 °C and 1200 °C) in an H2–CO atmosphere and compared it with the carbothermic reduction of secondary ilmenite. Between 1273 K and 1373 K, hydrogen reduction was faster than carbothermic reduction for the entire time of the reaction. However, at 1473 K, CO evolution by the Boudouard reaction caused the carbothermic reduction to be faster initially; however, hydrogen reduction was faster after 70 minutes. The phases of the final product by the gaseous reduction were metallic iron, TiO2, and a pseudobrookite solid solution. Numerous cracks and pores were generated, and agglomerated iron was observed throughout the particles. The gaseous reduction reaction was controlled by a chemical reaction with an activation energy of 42 kJ/mol. For the subsequent smelting process, the use of ilmenite concentrate feeds reduced by hydrogen during the preliminary reduction process decreased the energy consumption and CO2 emissions.

The kinetics and mechanisms of carbothermic reduction of a complex Kalimantan weathered ilmenite (FeTiO3) using palm kernel biomass were investigated in the temperature range 1273–1473 K. The study included a combined thermodynamic assessment together with reduction experiments. Results were contrasted with data from similar experiments conducted using graphite as the reductant. Thermodynamic simulations showed that the major phases formed during reduction were pseudobrookite and metallic iron with reduction using biomass predicted to produce more metallic iron compared to the use of graphite in the same temperature range. Incomplete dissociation of ilmenite by biomass was noted at 1473 K and 30 min reaction time however increasing the reaction time to 180 min resulted in near complete ilmenite dissociation. The kinetic analysis indicated that the reduction process followed a diffusion-controlled mechanism. This was confirmed by a microstructural analysis that showed the reduced ilmenite grains had a three-layer structure. The microstructural analysis also revealed that pores and cracks present in the initial weathered ilmenite promoted metallic iron formation. The apparent activation energy for ilmenite reduction using biomass and graphite was determined to be 217.00 ± 0.06 kJ mol−1 and 239.44 ± 0.06 kJ mol−1, respectively. Based on the findings, a general micro-mechanism for the carbothermic reduction of weathered ilmenite was developed.

The intertidal zone as well as sand dunes of Gopalpur coast, Odisha contains heavy minerals of varying proportions ranging from 6.51 to 8.45 wt% out of > 63 µm fractions. The heavy mineral assemblages are ilmenite, magnetite, garnet, sillimanite, zircon, rutile and hornblende of which ilmenite is dominant. Electron probe micro analysis of ilmenite grain indicates that it contains TiO2 in the range of 50.72% to 58.96% and FeO 37.4% to 57.15% in addition to Cr2O3 (0 to 0.12%), NiO (0 to 0.27%), MnO (0.06% to 2.04%) and MgO (0.17% to 2.16%). Mn/Mg ratios show lower values (0.13 to 2.76) for most of the samples, indicating basic rock source such as pyroxene granulites. Few ilmenite grains are having higher Mn/Mg values varying between 4.55 and 6.58, might have been derived from charnockite and khondalites in the hinterland. Scanning electron microscope photographs of ilmenites show sub-rounded to rounded grains with few grains having angular to sub-angular feature. Their micro morphological features indicate effect of mechanical and chemical weathering. Flattened striated surface with grooves feature may be due to mechanical weathering. Etch marks and pits may be due to differential chemical action in low energy sub-aqueous environment of deposition.

Electro-deoxidation of ilmenite (FeTiO3) is an economical production method of FeTi, particularly, if the end use is hydrogen storage. In this study, we show that electro-deoxidation of impure FeTiO3 with Ti content lower than Fe, as in the case of low-grade FeTiO3 ore, results in the formation of a two-phase material consisting of FeTi and Fe2Ti. The presence of Fe2Ti is detrimental to the hydrogen storage efficacy. We show for the first time that it is possible to avoid the formation of Fe2Ti or β-Ti as a second phase under similar operating conditions only by tailoring the composition of the cathode precursor, i.e., the addition of TiO2 to low-grade FeTiO3 so that the atomic ratio of Fe:Ti in the precursor is ~ 1:1. Low-grade FeTiO3 with 10 wt% TiO2 resulted in single-phase FeTi with the atomic ratio of Fe:Ti ~ 1:1 in the precursor and in the final reduced alloy. The hydrogen storage capacity of the single-phase FeTi is nearly 36% higher as compared to the two-phase alloy consisting of FeTi–Fe2Ti.

The present communication describes an investigation on the preparation of metallized composite pellets from ilmenite concentrate. It was observed that the pellet size in the range of 8–12 mm, a binder dosage of 4 wt%, and internal carbon of 5 wt% are the optimum levels that help the pellets attain the desired drop number (~ 10) and dry strength (~ 30 kg/pellet). When subjected to reduction tests at a temperature of 1200 °C for 6 h, the composite pellets show better metallization (~ 80%) than the raw ilmenite pellets with an equal amount of reductant. The reduced ilmenite composite pellets also display a reasonable decrepitation value of 4.9%, thereby making them suitable to be used directly in arc furnaces for titania slag production. A comparative characterization study by SEM–EDS indicated that larger amounts of metallic grains are uniformly distributed throughout the matrix in the composite pellets.

Peridotites in ophiolites exposed along Himalayan suture zone open window to study deep Earth processes. We report c.2 km thick well exposed mantle section of Shergol ophiolite in the Indus Suture Zone (ISZ). The mantle section comprises lherzolite, serpentinised peridotite with cumulate chromitites. The in situ evidences from micron-sized mineral exsolutions are studied using optical microscopy, scanning electron microscopy and micro-Raman spectroscopy. From the ISZ lherzolite, ilmenite mineral exsolution is noted in the olivine grain. The exsolved ilmenites are oriented topotactically following former {111} planes of magnetite, providing evidence of spinel precursor. In another observation, the disoriented 1–3 µm wide and 10–80 µm long ilmenite needles are hosted in the olivine, is characterised by Raman peaks at 685, 370 cm−1 with low peaks at 308 cm−1,523 cm−1, 683 cm−1, 693 cm−1 and 731 cm−1 point to mixed mineral phases of magnetite with Cr–Fe–Al. Based on morphologies, crystal-chemical structure and modal calculation of exsolutions, we infer, exsolved Fe–Ti phases in Shergol peridotite is sourced from deeper part of the upper mantle. With the Fe–Ti phases, tiny silicate inclusions in chrome spinel and accompanying opaque base metal sulphides are also observed in the same peridotite, attributes successive stages of partial melting and subsequent cooling of metal enriched mantle. These observations, challenge shallow intra-oceanic arc setting for Shergol ophiolite and proposes, part of exsolved mineral phases in ophiolite has deep Earth origin. These mineral phases would ascent at the shallow mantle level beneath Neotethyan spreading ridge aided by dunite channel.

The effect of pre-oxidation degree of Panzhihua ilmenite concentrate on the gaseous reduction by carbon monoxide was investigated. The raw ilmenite concentrates were pre-oxidized at 600, 700, 800, 900, and 1000 °C for 2 h, respectively. The phase change, FeO content, and morphology after the oxidation at various temperatures were characterized. The oxidation degree was calculated according to the change of FeO content. Thermogravimetry was performed on the oxidized ilmenite concentrate samples (oxidized at 600, 800, and 1000 °C) at 850, 900, and 950 °C, respectively. The results show that the pre-oxidation of ilmenite concentrate can accelerate the reduction process: the higher pre-oxidation degree, the faster reduction rate. The high pre-oxidation degree of ilmenite concentrate is beneficial to accelerate the subsequent reduction process in two ways. Three stages of the reduction process were divided via the first derivatives of reduction degree, and the reduction mechanism and apparent activation energy were discussed subsequently.

Petrography and rock magnetic properties of the Dalma volcanics (DV) and associated meta-sediments of Singhbhum mobile belt (SMB) are presented to describe magnetic grain size and Fe-Ti oxide mineralogy of the volcano-sedimentary sequence. Petrography revealed the presence of Ti-magnetite, hematite, ilmenite and pyrite in quartz-biotite-sericite-muscovite schists, quartzites, and volcanic rocks. The average value of magnetic susceptibility (χ) is 5.6 × 10−7 m3/kg, anhysteretic remanent magnetization (ARM) is 2.25 × 10−5 Am2/kg, saturating isothermal remanent magnetization (SIRM) is 403.33 × 10−5 Am2/kg, soft IRM is 240.2 × 10−5 Am2/kg, hard IRM is 77.56 × 10−5 Am2/kg, and natural remanent magnetization (NRM) is 54.1 mA/m. The central tendency of the inter-parametric ratio ARM/χ is 0.06 kAm−1, SIRM/χ is 111.04 kAm−1 and S-ratio is 0.8. Based on results, magnetic mineralogy indicated that the bulk magnetic carrier is stable single domain (SSD) or pseudo single domain (PSD) grains of Fe-Ti oxides with minor iron sulphides such as pyrite, greigite and pyrrhotite. Petrography and rock magnetic studies suggest that the magnetic carriers are chiefly secondary in origin and the NRM is modified over time.

We present a model for the lattice vibrational density of states of MgTiO3 (geikielite) and FeTiO3 (ilmenite) that predicts thermodynamic properties, in agreement with observational data. The model is based on Kieffer’s method combined with spectroscopic data. For both substances experimental data sets are influenced by non-stoichiometry. For geikielite that affects the volume, whereas for ilmenite volume and bulk modulus are affected. We show that Kieffer’s method enables predicting bulk moduli in pressure–temperature space. We demonstrate that intrinsic anharmonicity or electronic effects significantly affect the heat capacity of ilmenite, whereas that is not the case for geikielite. We use Kieffer’s method to derive multiple-Einstein models, from which we demonstrate that thermodynamic properties are insignificantly influenced by dispersion in Grüneisen, mode-q and anharmonicity parameters for both substances. We show that our results enable predicting thermodynamic properties and shear modulus of the solid solution formed from geikielite and ilmenite. Geikielite and ilmenite are added to our thermodynamic database for the system MgO–SiO2–FeO, to enable modeling phase stability and physical properties of titanium-rich reservoirs in the Earth’s Moon.

Natural iron minerals and zero-valent metals have been widely tested as catalysts for the Fenton-like process, but the systematical comparison study about their catalytic performance was rarely conducted, and the risk of the secondary pollution of toxic heavy metals was still not uncertain. In this paper, a comparison study of applying pyrite, ilmenite, vanadium titano-magnetite (VTM), zero-valent iron (ZVI), and zero-valent copper (ZVC) as Fenton-like catalysts for the removal of imidacloprid was performed. The results showed that ZVI exhibited the highest activity among the recyclable solid catalysts with a removal rate of 96.8% at initial pH 3 using 10.78 mmol/L H2O2, due to iron corrosive dissolution. Vanadium titano-magnetite (VTM) exhibited the best activity at first use among tested minerals but with low reusability. Pyrite with stable morphology showed a medium but sustainable ability to degrade imidacloprid, achieving a removal rate of 10.5% in the fifth use. The reaction much favored the acidic condition of initial pH around 2 or 3. Meanwhile, there was a significant positive correlation between removal efficiency and dissolved Fe or Cu concentration. Pyrite was considered to be a promising catalyst in Fenton-like reaction. It was suggested that the system proceeded predominantly through a homogeneous route via dissolved Fe or Cu ions. Except ZVC and VTM, other tested catalysts showed the low possibility of causing secondary pollution of toxic metals in the application of Fenton-like process.

The value addition potential of ilmenite was examined using several characterization techniques. Raw ilmenite is composed of 93.65 wt.% of FeOTiO2, 3.55 wt.% of SiO2, 1.22 wt.% of Al2O3, and the remainder being other minor oxides. Ilmenite and powdered carbonized coconut shells were mixed in the weight ratio of 4:1. A separate fraction of the same mixture was added with powdered seashells in the weight ratio of 4:1:0.5. Six fractions of each mixture were distinctly milled from 1 to 6 h in a planetary ball mill. XRD spectra (broadened and diminished reflections of ilmenite) and FTIR observations (Ti―O―C bonding) of milled samples indicate the possible incorporation of carbon into the ilmenite structure. Any clues of an occurrence of new rutile peaks were not observed in XRD spectra of milled samples. Consequently, the carbothermic reduction has not been initiated during mechanical activation. In this case, samples powdered for 6 h in a mill were isothermally annealed for 2 h under normal airflow at temperatures of 800 °C, 1000 °C, and 1200 °C, respectively. According to the X-ray diffractograms, the annealing temperatures of 1000 °C and 1200 °C exhibited almost similar trends with rutile (R), pseudobrookite (PB) and elemental iron (F), and a very few ilmenite (I) peaks. Consequently, 6 h of milling and 1000 °C annealing were concluded as the optimum conditions for the carbothermic reduction. Moreover, this study indicated seashells as a potential rate raiser for the carbothermic reduction of ilmenite at 800 °C. Therefore, this process is applicable to upgrade ilmenite into a mixture of synthetic rutile and elemental iron.

The cost of Ti production can be reduced by replacing rutile ore with abundant and cheap ilmenite ore (FeTiO3). However, the conventional processes for Ti production, including the Kroll process, require significant energy and yield a large amount of byproducts. To overcome these environmental challenges, we investigated the effects of the reaction temperature and time on the sulfurization of FeTiO3 by Na2SO4 below 1673 K. Fe-S-C metal and Ti-rich oxysulfide phases were generated, and the metallic phase could be removed from the oxysulfide phase via magnetic separation. With an increase in temperature, the Fe content in the oxysulfide phase decreased, while the Ti content increased. After the sulfurization of FeTiO3 for 1 h at 1673 K, the Fe content in the oxysulfide phase decreased by approximately 4 wt.%. The Ti content in the obtained oxide was determined through a simple cleaning treatment using dilute hydrochloric acid.

To reduce the consumption of aluminum in the traditional production process of ferrotitanium, the use of economic electrical energy is considered to replace the chemical energy provided by the reaction of aluminum and heating agent. Analysis of slag by x-ray diffraction (XRD) and FactSage 7.2 revealed that heating-assisted aluminothermic reduction of ilmenite was a thermal explosion process. Increasing the Al ratio could promote the reduction of ilmenite and increase the recovery rate of Ti according to inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis and calculation. The optimal molar ratio of CaO to Al2O3 was 1:4 for the preparation of FeTi50, achieving good separation of alloy and slag and better Fe and Ti recovery rates than without CaO addition.

As the titanium industry rapidly develops, low-grade ilmenite resources are drawing global attention. The direct use of low-grade ilmenite can result in low production efficiency and heavy pollution. In addition, the production of high-titanium slag via electric furnace melting consumes significant energy and possesses low production efficiency. Therefore, a novel process with low energy consumption is necessary for producing ultra-grade slag (UGS) for chlorination. For low-grade ilmenite, semi-molten reduction and magnetic separation were suggested in this study. The effects of carbon content, reduction time, and Na2CO3 addition on the reduction and separation behavior were studied. The results showed that the addition of Na2CO3 favored the formation of a semi-molten state, which was more conducive for the diffusion, aggregation, and growth of the metal phase. In this regard, excess carbon was not helpful, and it weakened the growth of the metal phase. Wet grinding and magnetic separation were used for beneficiation of the reduced sample for efficiently separating the slag iron and preventing the formation of agglomerates between slag and metal. For the sample with a carbon dosage of 13 pct, Na2CO3 dosage of 8 pct, reduction temperature of 1673 K (1400 °C), and 90 minutes holding time, high-titanium slag with a TiO2 grade of 81.63 pct and iron content of 4.53 pct was produced, with the TiO2 recovery rate of 93.43 pct and the yields of 55.37 pct. High-titanium slag can be used as a high-quality raw material to produce UGS for chlorination by leaching.

Sediment samples obtained from pits in the Mbiame floodplain gemstone prospect in the northwestern part of Cameroon were studied for their bulk geochemical properties together with the mineral composition of the gemstones found therein to decipher their provenance. Five main layers were isolated in each pit comprising an organic rich humus layer, muddy layer, unconsolidated and poorly sorted sandy layer, clay layer and gravel layer. The gravel layer is the most high-yielding in terms of gemstones content. The sediments have high rare earth element (REE) concentrations varying between 135 and 456 ppm with variable light/heavy rare earth element (LREE/HREE) ratio values (5.8–21.5). REE chondrite normalized patterns show similar high LREE enrichment and no Eu anomalies (Eu/Eu* = 0.9 − ~ 1) for all samples. The gemstones selected from the various horizons range in color from light gray, light blue/green, dark blue, pale brown and red. Some of the grains have zircon and ilmenite mineral inclusions while some of the zoned grains show simple core—rim zonation as well as oscillatory and sectorial zoning patterns. Bulk sediment geochemistry of sediments from the Mbiame gem prospect suggests an igneous provenance generally of felsic intermediate source input. The alluvial gemstones from the Mbiame gem prospect are the sapphire variety of corundum and the grains combined with zircon and ilmenite inclusions and megacrysts suggest a derivation from felsic to intermediate igneous rocks.

The use of the magnetic fraction (MF) of a low-grade titanium ore (TO) and two oxidants (H2O2 and NaClO), testing each one separately, were compared in photo-Fenton like systems to degrade thiabendazole (TBZ) as a model micropollutant. As far as the author’s knowledge goes, this work presents for the first time the assessment of NaClO as an alternative to H2O2 in heterogeneous systems, where the Fenton-type photocatalyst is a natural mineral; TO has a Mexican origin and its magnetic fraction is mainly composed of Ilmenite (47.8% w/w FeTiO3). The experiments were carried out at bench scale in a solar simulator, using a batch raceway pond reactor. Oxidant and MF concentrations were optimized by a composite experimental design, which allowed to achieve 97% TBZ degradation at 15 and 30 min for NaClO and H2O2 systems, respectively, when the initial concentration of TBZ was 37 µM. Pointing out that both pseudo-first order rate constants ( $$k^{\prime}$$ ), $$k_{NaClO}^{^{\prime}}$$ = 0.226 min−1 and $$k_{{H_{2} O_{2} }}^{^{\prime}}$$ = 0.065 min−1, are in the order of homogeneous photo-Fenton applied to degrade TBZ; however, the time to achieve the same level of TBZ degradation is halved when NaClO is used instead of H2O2, thus the capacity of treatment plants can be increased. Furthermore, better results of mineralization (54%), DQO (76%), DBO5 (44%) and acute toxicity (74%) removal were observed when NaClO was used as an oxidant compared to H2O2, whose values were 42, 67, 38 and 58% for the parameters aforementioned. These positive results demonstrate the feasibility of the use of NaClO as an alternative oxidant to H2O2 in the heterogeneous photo Fenton like process.

The effect of the content of an SiO2 additive on the electrochemical reduction of ilmenite concentrate to prepare ferrotitanium is investigated in CaCl2 molten salt. A thermodynamic analysis of the Ti-Fe system and possible reactions has been carried out, and it demonstrated that SiO2 and FeTiO3 can be readily reduced to Si and intermediates (Fe and CaTiO3), respectively. The experimental results demonstrated that the optimal molar ratio of Ti:Fe:Si in the cathode mixtures is 1.2:1:0.2. The porous ferrotitanium with uniform particle sizes were successfully obtained by electrolysis at 1173 K with a cell voltage of 3.2 V for 2 h. The SiO2 additive plays an important role during the formation process of ferrotitanium, which is first reduced to Si and then serves as a reductant to catalyze CaTiO3 and Fe to form FeTi alloys.

The ilmenite-chloride process has used for the production of TiCl4 from the ilmenite (FeTiO3) ore, which produces cyclone dust containing mostly iron chloride and includes a range of metal chlorides. The utilization of iron values present in waste chlorides of cyclone dust is becoming a crucial issue to make this process competitive. The current work demonstrates a beneficial process that can selectively separate iron values from the chloride residue. Using CaCO3 as a precipitating agent, the iron component was selectively isolated from the aqueous solution of the chloride residues. The selective extraction of iron was carried out at a wide range of concentrations, and the yield of iron species was over 95%. The precipitate is in the form of Fe(OH)3, which converts to Fe2O3 when annealed in air. In the next step, the remaining metal impurities were removed as solid precipitates through the pH tuning with CaO. Finally, CaCl2 and CaCO3 were obtained by adding CO2 to the residual solution. This study provides a method of treating cyclone residues to recover CaCl2 as well as Fe(OH)3, which represents significant progress towards the utilization of iron-rich wastes.

Ilmenite is the prime mineral used for the production of titania-rich slag and ferrotitanium alloy throughout the globe. In the current research, a 30 kW DC extended arc plasma reactor is employed for the aluminothermic reduction of ilmenite into ferrotitanium. For low-temperature operation, flux is added targeting low melting slag where CaO/Al2O3 ratio is varied from 0.8 to 1.6. Further, to lower down the Al consumption, carboaluminothermic reduction tests are carried out in stages without interruption. The effect of stage-wise reductant addition and CaO/Al2O3 ratio on ferrotitanium yield and titanium recovery is studied, corroborated to the slag chemistry. FeTi26 alloy is obtained through the carboaluminothermic smelting route with 25% excess stoichiometric Al in charge composition. The formation of calcium titanate and calcium aluminates governs slag chemistry and reduction kinetics.

The effects of corrosion temperature, oxygen flow rate and corrosion time on the transformation of metallic iron were systematically studied, and the effects of mineral phases of Fe-bearing products on Ti–Fe separation were investigated. The reaction mechanism of metallic iron in corrosion process was proposed. The results showed that corrosion temperature played a key role in determining the transformation of metallic iron in reduced ilmenite during corrosion process. Under suitable corrosion conditions, Fe-bearing mineral in reduced ilmenite could be converted to amorphous ferric hydroxide, lepidocrocite, hematite and magnetite, respectively, and lepidocrocite was the most easily separated Fe-bearing mineral from corrosion products owing to the significant density difference between lepidocrocite and Ti-rich materials. The Ti-rich material with 77.81 wt.% TiO2 and Fe-bearing product with 52.69 wt.% total Fe were obtained by gravity separation. The Ti recovery ratio and Fe recovery ratio were 91.16% and 86.27%, respectively.

A carbothermic reduction of complex Kalimantan ilmenite (FeTiO3) with palm kernel shell biomass as a reducing agent using regular electric and simulated solar heating has been investigated. The results demonstrate that palm kernel shell biomass can be used as an alternative reductant for the carbothermic reduction. Incomplete ilmenite dissociation was observed at 1000°C and 1100°C for 60 min reaction time using an electric furnace. Complete ilmenite dissociation was attained at 1200°C using both electric and solar furnaces. The major phases formed upon reduction at 1000°C were TiO2 (rutile) and Fe(m). Pseudobrookite (Fe, Mg, Mn)(Ti2O5) was formed at 1100°C, and higher concentrations were observed at 1200°C for 60 min reaction time. Reduction at 1200°C using a solar furnace promoted pseudobrookite formation, and a unique streak morphology of Fe(m) was observed as opposed to a globular structure found in samples heated in an electric furnace. It is suggested that this may be due to localized overheating by solar radiation that promoted rapid local reduction.

Titanium-bearing magnetite ore is generically defined as magnetite with > 1% titanium dioxide (TiO2) and is usually vanadium-bearing. The iron and titanium occur as a mixture of magnetite (Fe3O4) and ilmenite (FeTiO3) with vanadium oxide usually occurring within the solid solution of the titanium-bearing magnetite phase. These ores are currently widely processed in blast furnaces via modified ironmaking processes. Typically, vanadium is recovered as a by-product from the ironmaking process, while the diluted titania slag is stockpiled. Fluxless smelting in a direct-current open-arc furnace is proposed as an opportunity to improve iron and vanadium recovery and potentially unlock the titanium as a slag product. Slags produced from a pilot study are compared to industrial slags produced from ilmenite. The findings from the pilot test show that slag produced under fluxless smelting conditions in an open-arc electric furnace is remarkably similar to industrial ilmenite slags. The test conditions were varied to evaluate the slag and metal composition, and furnace operation, under increasing reducing conditions. The study showed that the slag and metal product was remarkably similar to industrial slag produced from ilmenite.

To elucidate the effects of FeS on the carbothermic reduction of ilmenite, a series of tests were conducted using non-isothermal thermogravimetric analysis at heating rates of 10°C/min, 15°C/min, 20°C/min, and 25°C/min. The Malek method was used to analyze the reduction mechanism and obtain a kinetic model, and the Starink method was used to calculate the apparent activation energy. The morphology of the reduction products was examined by scanning electron microscopy. A complementary series of isothermal carbothermic reductions tests was also performed in a vertical tube furnace to study the effect of FeS on the metallization of Fe and TiO2 grade in the slag phases. The results show that the carbothermic reduction of the ilmenite concentrate in the presence of FeS proceeds in four stages. FeS showed a negative effect to the carbothermic reduction of ilmenite as its addition of 2.5 wt.% increased the apparent activation energy from 486 kJ mol−1 to 565 kJ mol−1 and decreased metallization by 11.1% and TiO2 grade in the slag phases by 7.2%.

Carbonization of TiO2, which is a process typically used to synthesize TiC, consumes a huge amount of energy. Low-temperature synthesis of TiC from carbon-infiltrated TiO2 has been investigated in this study to develop an energy-saving process. Porous TiO2 was first obtained by hydrochloric acid leaching of ilmenite (FeTiO3) ore. Then, carbon-infiltrated TiO2 was prepared from the porous TiO2 using a tar impregnation method, and its reaction behavior was observed. The carbon-infiltrated TiO2 was completely converted into TiC which contained 3.0 mol pct oxygen at 1300 °C for 2 hours. In contrast, a mixture of reagents TiO2 and carbon did not react when it was subjected to the same treatment. This major difference is due to the effect of close contact between TiO2 and carbon through the nanopores generated in TiO2 obtained by acid leaching of ilmenite ore. It was concluded that this method has significantly lower temperature and much shorter reaction time than those of conventional methods.

The effects of adding 5 to 25 wt pct of ilmenite ore to hematite ore sinter were investigated employing a horizontal tube furnace to clarify the phase development. The temperature was raised nonisothermally at 10 °C/min to 1150 °C in an Ar atmosphere. When the target temperature was reached, 1 L/min of air was injected to allow combustion of the carbon in the pellets. The development of the phases in the sinters was studied using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA). The tumbler index (TI) decreased with the increase in ilmenite addition up to 20 wt pct, which increases TiO2 (s) and Fe3O4 (s) content in the sinter blends. Addition of more than 2 wt pct TiO2 (s) to the sinter blends resulted in the formation of perovskite (CaO·TiO2), which affected the development of bonding phases. These changes deteriorated the reduction degradation index (RDI). The estimated melt formation temperature of the sinter blends increased with ilmenite addition up to 15 wt pct and decreased thereafter. An attempt was made to predict the development of phases in the ternary phase diagram of CaO-Fe2O3-TiO2. The reduction behavior of the sinter blends was affected by the type of the bonding phase.

Presently, ilmenite concentrates from Odisha Sands Complex at Chhatrapur, India are utilized to produce TiO2 slag by direct smelting in an electric arc furnace. However, the process involves the consumption of excess electrical energy and difficulty in handling the arc furnace due to frothing effects. A more efficient process of pre-reducing the ilmenite before smelting has been proposed in the present communication. In particular, studies have been undertaken on the reduction process of ilmenite-coke composite pellets. The difference in the reduction behaviour of raw ilmenite and ilmenite-coke composite pellets has been established and compared with that of the pre-oxidized raw pellets. The effects of various processing parameters like temperature, residence time, and reductant percentage on the metallization of composite pellets in a static bed have been investigated. Metallization of about 90% has been achieved at 1250 °C for a reduction period of 360 min with a 4°% coke composition. Furthermore, the reduced pellets have been characterized through chemical analysis, optical microscopy, field emission scanning electron microscopy and X-ray diffraction analysis. The reduction behaviour of composite pellets has also been found better than that of pre-oxidized pellets indicating the former to be more efficient.

A simple and novel technique for the preparation of anatase TiO2 nanopowders using natural ilmenite (FeTiO3) as the starting material is reported. Digesting ilmenite with concentrated H3PO4 under refluxing conditions yields a white α-titanium bismonohydrogen orthophosphate monohydrate (TOP), Ti(HPO4)2·H2O, which can be easily isolated via gravity separation from unreacted ilmenite. The addition of ammonia to the separated TOP followed by calcination at 500°C completes the preparation of anatase TiO2. Calcination at temperatures above 800°C converts the anatase form of TiO2 to the stable rutile phase. The removal of iron from ilmenite during the commercial production of synthetic TiO2 is problematic and environmentally unfriendly. In the present study, the removal of iron was found to be markedly simple due to the high solubility of iron phosphate species in concentrated H3PO4 with the precipitation of TOP. The titanium content of the prepared samples on metal basis with silica and phosphorous as major impurities was over 90%. Prepared TiO2 samples were characterized using X-ray fluorescence, Fourier-transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction analyses. The photocatalytic potentials of the commercial and as-prepared TiO2 samples were assessed by the photodegradation of rhodamine B dye.

The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate (VTC) by adding CaCO3 was investigated. Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and CaCO3 in a reductive atmosphere, where ilmenite is more easily reduced by CO or carbon in the presence of CaCO3. The effects of CaCO3 dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test. Appropriate increase of CaCO3 dosages and reduction temperatures were found to be conducive to the formation of calcium titanate, and the optimum conditions were a CaCO3 dosage of 18wt% and a reduction temperature of 1400°C. Additionally, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO3 addition was of higher purity with particle size approximately 50 µm. Hence, the separation of calcium titanate and metallic iron will be the focus in the future study.

The recycling of household aluminium waste metals will be very effective and efficient only when a proper process of recycling is chosen. This paper is an attempt to provide a non-traditional method of utilising the exothermic heat of different Al sources (from automobiles, appliances, windows and doors and other products) for recycling and producing ferrotitanium alloy. Titania slag (75% TiO2) produced from carbothermic reduction of low-grade ilmenite (50% TiO2) and its produced fine dust from top dome are taken as a feed material. Aluminothermic processing of fine dust gives a possibility in the direction of ferrotitanium, followed by the successful execution with titania slag, which include smelting of titania slag with household Al scrap chips and lime in a thermal plasma reactor. The alloy formation is supported with characteristic properties of XRD and FESEM.

Pollution prevention and treatment of reservoir silt constitute important environmental protection challenges. Scandium, a key metal, is found in Chinese reservoir silt. However, due to the low scandium content and complex composition of the silt, it is not feasible to directly extract this valuable constituent. With the aid of scanning electron microscopy and polarizing optical microscopy analyses, samples of silt were examined and the different types of minerals containing scandium identified together with their disseminated features. The results reveal that the silt is a high silicon, calcium, magnesium, aluminum vein ore, containing a small amount of iron and titanium complex mineral groups, among which ilmenite and titanaugite are the main minerals containing scandium. The raw silt contains about 6.6 g/t scandium. Based on the silt composition, particle size distribution, and occurrence state of scandium, studies were conducted on preconcentration of scandium oxide from reservoir silt. Based on the results of these experiments, a beneficiation process was developed and validated on pilot scale based on the use of electrical separation for scandium enrichment. A scandium concentrate was obtained with scandium content of 96.23 g/t and recovery of 62.11 wt.%.

Congruently grown LiNbO3 (LiTaO3) is known to be highly defective due to its significant Li2O deficiency. We present in this work a comparative study between normal LiNbO3 (LiTaO3) and ilmenite structural LiNbO3 (LiTaO3). Namely, the normal cation stacking sequence is replaced by ilmenite ordering ‘…Nb (Ta) Li vacancy Li Nb (Ta) vacancy Nb (Ta) Li vacancy Li Nb (Ta) vacancy…’. From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models, we calculated the Curie temperature in ilmenite LiNbO3 (LiTaO3). We have shown that ilmenite structural LiNbO3 (LiTaO3) is in excellent agreement with the result of the experiment compared to normal LiNbO3 (LiTaO3).

Steel weld metals containing Ti were prepared with Mn contents of 0.35%–2.98%. The inclusion characteristics in the weld metals were investigated by means of thermodynamic calculations coupled with electron probe microanalyses and transmission electron microscopy. The results show that with an increase in Mn content, the primary constituent phases of the inclusions are changed from pseudobrookite to a combination of pseudobrookite and spinel and eventually to a mixture of (Mn–Si–Al)-oxide, spinel and ilmenite. Ti3O5, MnTi2O4 and MnTiO3 are the primary constituents of the pseudobrookite, spinel and ilmenite solid solutions, respectively. Spinel and ilmenite have higher amounts of Mn but lower amounts of Ti compared with that of pseudobrookite. The formation of large amounts of ilmenite and spinel leads to the development of a Mn-depleted zone (MDZ) in the vicinity of the matrix/inclusion interface. Acicular ferrite has a Baker–Nutting orientation relationship with MnTi2O4.

Effects of calcium compounds on the carbothermic reduction of vanadium titanomagnetite concentrate (VTC) were investigated. It was found that calcium compounds had great effects on the metallization rate of the reduction product, the order of the metallization rate of reduction product being CaCO3 > no additive > CaSO4 > CaCl2, which indicated that the addition of CaCO3 was more conducive to promoting the reduction of iron than other calcium compounds. Gas analysis showed that there were mainly two processes in the carbothermic reduction of VTC, a solid-solid and a solid-gas reaction. The concentrations of CO and CO2 were highest when CaCO3 was added, while that in a roasting system decreased the most when CaCl2 was added. X-ray diffraction (XRD) analysis showed that calcium compounds could change the reduction process of ilmenite in VTC. The phase compositions of the reduction products were changed from metallic iron (Fe) and anosovite (FeTi2O5) to metallic iron (Fe) and perovekite (CaTiO3) when calcium compounds were added. Additionally, CaSO4 and CaCl2 could significantly promote the growth of metallic iron particles, though the existence of Fe-bearing Mg2TiO4 in reduction products was not conducive to the reduction of iron. The formation of FeS would further hinder the reduction of iron after adding CaSO4.

To provide new insights into the interaction of ultramafic alkaline melts with the subcontinental lithospheric mantle, we present results of a petrographical-mineralogical study of ilmenite-bearing mantle xenoliths from the Grib kimberlite, Archangelsk, Russia along with results from reaction experiments between harzburgite and Fe–Ti bearing carbonate–silicate melts similar to aillikite. The compositions of orthopyroxene, ilmenite and garnet from our mantle xenoliths are similar to compositions of minerals of the low-Cr megacryst suite from different kimberlite occurrences worldwide including the Grib kimberlite as well as minerals from sheared lherzolite xenoliths captured by the Grib kimberlite. This suggests that ilmenite-bearing xenoliths, megacrysts, and sheared lherzolite xenoliths could have a common origin and/or formed under similar conditions. The reaction experiments were performed at 4 GPa and 1200 °C with varying proportions of aillikite (0, 10, and 50 wt%) that reacted with harzburgite. The experimental runs with 10% and 50% aillikite resulted in two layers within the capsule, with an ilmenite-bearing reaction zone at the contact between aillikite and harzburgite, and an ilmenite-free zone characterized by higher garnet and clinopyroxene abundances. An increase of aillikite melt is directly correlated with increasing TiO2 and decreasing Cr2O3 contents and Mg# values in the mineral phases, most significantly for pyroxenes. Overall, the experiments produce a chemical gradation of minerals from Cr-rich (Fe–Ti-poor) to Cr-poor (Fe–Ti-rich) which is strikingly similar to the chemical gradation observed in minerals from natural mantle-derived xenoliths from kimberlites. In summary, comparison of our experimental data with natural samples indicates possible links between the generation of megacrysts and Ti-rich metasomatism of the lithospheric mantle by ultramafic alkaline (aillikite-related) melts and their possible evolution towards kimberlites. Our results illustrate the importance of melt-rock ratios in generating the mineralogical and chemical diversity in mantle xenolith suites.

Monazite and magnetite are sensitive indicators of local fluid chemistry, pressure, and temperature during metasomatism. In this study, the role of fluids, during the metamorphism of a granite to metagranite, (Jiao-Liao-Ji orogenic belt, North China Craton), is explored via monazite, magnetite, and pyrite microtextures and mineral chemistry coupled with zircon and monazite Th–U–Pb dating. CL bright zircon cores (2163 ± 17 Ma) record the crystallization age of the granite. BSE dark monazite cores (1876 ± 36 Ma) are characterized by high U and Ca and low Nd contents. The surrounding BSE bright mantle (1836 ± 14 Ma) is characterized by abundant fine-grained huttonite inclusions, a high porosity, a high Th and Si content, and a low P, La, Ce, and Y content. The monazites are surrounded by a three-layered concentric corona consisting of first fluorapatite, followed by allanite, and then epidote. TiO2 in the primary magmatic magnetite (Mag1–1) has been mobilized to form a series of compositionally and texturally distinct magnetites (Mag1–2, Mag2, Mag3, Mag4, and Mag5) associated with ilmenite, rutile, and titanite reaction textures. Combined, these results suggest that external NaCl and sulphate-bearing fluids derived from a local sulphate-bearing evaporate infiltrated the granite and induced the formation of pyrite and enriched the pre-existing monazite in S at around 1904 Ma. In situ δ34S values for pyrite range from 13.03 ‰ to 13.41 ‰, which is typical of metamorphic pyrite. Sporadic synchysite-(Y) inclusions in the pyrite indicate a local CO2-rich component in the fluid. The BSE bright mantle around monazite formed from later fluids from the same local evaporite deposit during the decompression stage of the Jiao-Liao-Ji orogenic belt at around ~ 1840 Ma, which overlaps with zircon dark rims at 1849 ± 12 Ma. This same Na-bearing fluid induced the albitization of the feldspars, formation of apatite–allanite–epidote coronas around monazite, and formation of rutile–titanite–epidote alteration textures associated with magnetite and ilmenite exsolved from the magnetite. During subsequent much later greenschist facies metamorphism, muscovite, chlorite, and Mag5 were precipitated along mineral grain boundaries, mineral cleavage, micropores, and fractures and pyrite experienced partial alteration to goethite.

We investigated the 300 K high-pressure behavior of ilmenite using Raman spectroscopy to 54 GPa. Upon compression, we observe a Fermi resonance between the lowest frequency Ag symmetry peaks (ν4 and ν5) between ~ 10 and ~ 30 GPa: bands that involve major components of Ti–O and Fe–O-related displacements, respectively. The peaks’ relative intensities switch at ~ 18 GPa and they also reach their minimum separation at ~ 20 GPa, indicating that their maximum resonance occurs between 18 and 20 GPa. The negative shift of the Ti–O-associated ν4 vibration under compression is fully consistent with a shift in valence of Ti from 4 + to 3 + under compression. Anomalously small mode shifts of other, more localized vibrations are also consistent with a charge transfer from Fe to Ti under compression. At higher pressures, we have not found definitive evidence for a transition to the perovskite-structure at 300 K, which has been well characterized at high pressures and temperatures. At 40 GPa, we observe an apparent reversible disordering that persists up to our highest pressure. The 300 K mode shifts of the Raman active modes in FeTiO3 under pressure are notably different from those of other ABO3 compounds (where A = Mg, Mn and B = Ti, Si); in other ilmenite-structured compounds, the peaks shift at a faster rate and there has not been any observation of Fermi resonance. Thus, iron’s complex electronic structure, and its charge transfer with titanium, appears to play a primary role in the behavior of phonons in FeTiO3 ilmenite.

Fe3+ and XFe3+, defined as Fe3+/(Fe2+ + Fe3+) on a molar basis, are now recognised as key parameters in phase equilibrium modelling. A hindrance is that it is only possible to routinely measure total Fe, and not Fe3+ and Fe2+, in minerals using the electron microprobe. Charge balance techniques can be used to estimate Fe3+ and Fe2+ for some minerals, but not for those that contain vacancies. Whilst other analytical techniques can determine XFe3+ in minerals, these are not commonly applied by metamorphic petrologists. Therefore, researchers must rely on estimates. This study collates wet chemical, Mossbauer spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy analyses of XFe3+ in metapelitic minerals and rocks from the literature. The resulting database of 77 studies contains 591 samples, of which 261 have XFe3+ determined for the whole rock. There are XFe3+ measurements for 483 biotites, 192 white micas, 78 chlorites, and 32 staurolites. Average (± 1σ) XFe3+ values in whole rock, biotite, white mica, chlorite, and staurolite are 0.23 ± 0.16, 0.11 ± 0.08, 0.55 ± 0.18, 0.08 ± 0.07, and 0.07 ± 0.06, respectively. The average (± 1σ) number of Fe3+ cations in biotite, white mica, chlorite, and staurolite is 0.28 ± 0.19 (22 O + Ti cations per formula unit, pfu), 0.17 ± 0.13 (22 O pfu), 0.31 ± 0.27 (28 O pfu), and 0.20 ± 0.17 (46 O pfu), respectively. The mean whole rock XFe3+ is similar for metapelites containing ilmenite and magnetite, as well as those that report no Fe-oxide, but is considerably higher for hematite-bearing rocks. Whilst there is little variation with pressure and temperature, there is an increase in the number of Fe3+ cations and XFe3+ of both white mica and biotite with the type of Fe-oxide present. Our observations are compared with the predictions of phase equilibrium modelling using thermodynamic dataset 6.2 (Holland and Powell, J Metamorph Geol 29:333–383, 2011) and the solution models of White et al. (J Metamorph Geol 32:261–286, 2014a) for Fe3+ and XFe3+ in these minerals. The predicted XFe3+ and number of Fe3+ cations in biotite, chlorite, and staurolite broadly match natural observations, but for white mica the predicted mean XFe3+ is underestimated by 0.2–0.4 and the number of Fe3+ cations by 0.05–0.2. Whilst modelling correctly predicted increases in the XFe3+ of white mica and biotite with whole rock XFe3+, it also predicted variations in mineral XFe3+ as a function of pressure and temperature which are not observed in the natural samples.

Selective HCl dissolution of ilmenite components for obtaining Ti or titanium dioxide (TiO2) has been highly recognized due to its advantages, greater environmental friendliness, and simplicity, compared to H2SO4 and Cl2 methods. The effect of numerous parameters has been studied with the one-factor-at-a-time method. The present study aimed to evaluate the effect of key operation parameters, such as acid-to-solid ratio (A/S: 5 to 20 mL/g), reaction temperature (T: 70 °C to 100 °C), and acid concentration (A pct: 15 to 30 wt pct), on the dissolution of Fe in HCl solution with the minimum Ti losses to the leachate from its abundant, domestic, and low-cost mineral source (Kahnooj ilmenite concentrate) using central composite design–response surface methodology. After 90 minutes of leaching, the Ti/Fe (pct) in terms of dissolved amounts was selected as the process assessment response function. Based on the conducted experimental and statistical analysis, increasing the levels of parameters in the studied domain leads to an increase in Ti/Fe (pct), in the order of A pct > T > A/S. Two statistically significant mutual interactions between A/S-T and T-A pct, with 95 pct confidence level, were revealed for the first time in this study. The optimization strategy was set to the minimization of Ti/Fe (pct) by considering the objective of study and the selected response function. The A/S, T, and A pct were determined to be 5 mL/g, 70 °C, and 15 pct, respectively, for maximum impurity dissolution and minimum Ti loss to the leachate.

The possibilities of obtaining porous permeable cermet SHS-materials with catalytic properties are studied. The charge composition consists of powders of alloy steel scale, ilmenite concentrate, aluminum or chromium oxides, the basis of material forming the backbone of cermet (Al2O3) and reduced iron, and also added metaloxides. The material obtained is intended for the catalytic purification of diesel engine exhaust gases, particularly from nitrous oxide, carbon monoxide and soot.

This study presents mineralogical characterization of opaque assemblages from I- and S-type granites from the Aracuai orogen, southeastern Brazil that belong respectively, to the pre- and syn-collisional stages of the orogeny. Although these granites are geochemically well-characterized, with a robust geochemical, isotopic and geochronological database, their opaque minerals have not yet been investigated, and they provide important information about the oxygen fugacity and temperature conditions of their magmas. I-type granites (G1 Supersuite) consist of biotite hornblende granites and their opaque assemblage is ilmenite + pyrite + pyrrhotite ± magnetite ± Fe-Ti oxides ± chalcopyrite. S-type rocks (G2 Supersuite) are biotite muscovite sillimanite granites with ilmenite + graphite + pyrrhotite + pyrite as opaques. Our results combined with literature data show that ranges for oxygen fugacity (fO2) are: I-type granitoids containing magnetite and free of pyrite and phyrrhotite likely crystallized under fO2 between 10−15 bars and 10–8.5 bars, whereas magnetite free rocks containing pyrite and pyrrhotite should have crystallized with fO2 higher than 10−18 bars and lower than 10−15 bars. Regarding S-type granites, they must have crystallized under fO2 lower than 10−18 bars.

The optical absorption spectrum of natural ilmenite was measured on a narrow translucent rim zone of a thin polished slide of thickness ca. 0.004 mm, mounted with epoxy resin upon a supporting glass plate. The color of the material in the zone is dark red. At conoscopic observation between crossed Nicols, it displays a very dark, vague, off-centered conoscopic figure. Unpolarized optical absorption spectrum of ilmenite, measured in the transparent zone, consists of a very intense high-energy absorption edge which covers a major part of the visible range and causes the dark-red color of ilmenite. On the edge tail, which extends far to the NIR range, there is an intense, broad, asymmetric, vaguely structured absorption band with maximum at around 7000 cm−1. On the account of high iron and titanium contents (0.82 and 0.86 apfu, respectively), it may confidently be attributed to Fe2+/Ti4+ IVCT transition, though its energy is unusually low compared to other Fe2+, Ti4+-bearing minerals studied so far. This most probably proved that the effect of lowering of energy of IVCT bands with increasing number of ion pairs, established by Amthauer and Rossman (Phys Chem Miner 11:37–51 1984), on Fe2+/Fe3+ IVCT bands also takes place in case of electronic Fe2+/Ti4+ IVCT transition in ilmenite.

The IOCG deposit at Olympic Dam (South Australia) is hosted within the Roxby Downs Granite, which displays a weakly mineralised contact to the orebody (hereafter ‘outer shell’). In a mineralogical-geochemical characterisation of Fe-oxides from the outer shell, we show silician magnetite (Si-magnetite) and HFSE-bearing hematite define the early stages of alkali-calcic alteration. This association forms in the presence of hydrothermal K-feldspar and calc-silicates via overprinting of magmatic magnetite and ilmenite breakdown. Geochemical modelling, at ≥ 400 °C, shows such reactions occur at pH-fO2 conditions coinciding with shifts from K-feldspar to sericite, and ilmenite to rutile stability. The subsequent Si-magnetite+siderite association forms down-T in the absence of K-feldspar. Transition from granular to bladed morphologies in Si-magnetite is part of a series of Fe-oxide interconversions, followed by formation of zoned, U-W-Sn-Mo-bearing hematite. Enrichment in REE, Y and U in Si-magnetite and the prevalence of U-W-Sn-Mo-bearing hematite support a granite-derived fluid. Combined, petrographic and geochemical evidence show a transition among Fe-oxides from the outer shell to the orebody attributable to the evolution of the same fluid. Unusual massive magnetite intervals and Fe-oxide nodules in granite are considered due to either the presence of inherited lithologies, metasomatic products, or the result of magnetite-rich, crystal mush forming in the melt. We propose a model, corroborated by recently published data including high-precision U-Pb dating of magmatic zircon and hydrothermal hematite, in which an ‘outer shell’ is initiated at the 6–8 km depth of granite emplacement during volatile release from fluids ponding at intrusion margins. Granite cupola collapse at shallower levels (2–3 km?) follows via uplift along faults, facilitating intense brecciation and ore formation.

Fluidized bed reduction of iron ore fines is typically inhibited by the onset of “sticking” at temperatures above 973 K, which leads to particle agglomeration and defluidization of the bed. Here, we report the sticking-free fluidized bed reduction of titanomagnetite (TTM) ironsand at 1223 K in Ar-H2 gas mixtures. We show that sticking is prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. This protective shell prevents iron-iron contact between particles throughout the reduction process, enabling metallization degrees of 93 pct to be attained without sticking occurring. Phase evolution during the reaction has also been analyzed using q-X-ray diffraction and scanning electron microscope/energy dispersed spectroscopy. We find that the reduction proceeds through four separate stages. During the initial stage, approximately half of the initial TTM phase is converted to wustite, forming a network of sub-micron wustite channels which interlace the TTM matrix. During this stage, Ti and Al are enriched within the TTM matrix, due to the low solubility of both species in wustite. This enrichment stabilizes the remaining TTM, meaning that wustite is then preferentially reduced to metallic iron in stage 2 of the reduction. In stage 3, the remaining Ti-enriched TTM is reduced directly to metallic iron and ilmenite. The final stage of reduction involves the conversion of ilmenite into rutile and pseudobrookite. Our findings clarify the important role played by titanium species during the reduction of TTM and suggest that New Zealand ironsand can offer significant advantages over conventional hematite ores when used as a feedstock for fluidized bed direct-reduced iron processes.

Zones of massive to semi-massive Fe-Ti oxide mineralization are present in the Northwest River Anorthosite, a ca. 1625-Ma Paleoproterozoic massif-type anorthosite located in the Grenville Province of south-central Labrador. The oxide mineralization is predominantly composed of coarse to very-coarse grained V-rich magnetite with less abundant coarse granular ilmenite and pleonaste that formed by exsolution from the primary, chemically impure magnetite; all observed oxide minerals have complex and abundant subsolidus reequilibration and exsolution textures. Using petrography, oxide mineral chemistry, whole-rock geochemistry, and oxide-anorthosite field relationships, a three-process model is proposed for the formation of the oxide mineralization: (1) late-stage magmatic crystallization of impure magnetite; (2) concentration of Fe-Ti oxides via solid-state remobilization; and (3) reequilibration during subsequent post-emplacement cooling and Grenvillian metamorphism. These subsolidus processes significantly modified the primary magmatic composition of the magnetite through exsolution and reequilibration. Results from in-situ magnetite EPMA and LA-ICPMS analyses were plotted on magnetite mineral chemical discrimination diagrams. The data display a wide spread and typically do not plot exclusively in the expected anorthosite-hosted Fe-Ti-V magnetite fields. This is most likely due to modification of magnetite chemistry during subsolidus cooling and reequilibration. As such, care must be taken when using magnetite discrimination diagrams for Fe-Ti-V deposits given the complex petrogenetic histories that magnetite within these types of deposits experience.

Oxygen potential of TiO2-FeO-Ti2O3 ternary slags was determined by the electromotive force (EMF) method based on the solid electrolyte oxygen sensor at 2003 K (1730 °C). The effect of FeO content and Ti3+/Ti4+ mass ratio on the oxygen potential of the high-titania slag was also studied. At a fixed Ti3+/Ti4+ mass ratio of 3.11, the oxygen potential increased with increasing FeO content. Increase of Ti3+/Ti4+ mass ratio from 2.29 to 3.60 caused a significant decrease in the oxygen potential of the slag. Comparing measured oxygen potential with the calculated values indicated that the oxygen potential of the slag might be determined by FeO/Fe equilibrium reaction rather than TiO2/Ti2O3 reaction. In addition, the experimentally measured oxygen potential values were modeled by multiple linear regression analysis, and a semi-empirical mathematical correlation was established between the oxygen potential and slag compositions. The iso-oxygen potential distribution diagram based on the mathematical model was obtained for the high-titania slag.

The carbothermic smelting reduction process of ilmenite ore at high temperature was investigated by thermodynamic calculations in conjunction with smelting experiments. Based on thermodynamic calculations, conducting the smelting process at a higher temperature was recommended to achieve a larger amount of FeO reduction, i.e., higher Ti-enrichment, as less precipitate and thus large amounts of a liquid slag were predicted. However, even though the reduction of FeO in ilmenite ore at the initial stage seemed to be faster as the temperature increased, no significant difference in the TiO2 or FeO concentration was observed after the reaction was complete, regardless of the temperature. This was caused by the precipitation of pseudobrookite due to the local depletion of FeO during reaction at higher temperatures, by which further reduction reaction was prohibited. The apparent rate constant increased with increasing temperature and the activation energy of the reduction process was estimated to be 144 kJ/mol, from which it was concluded that the reduction reaction of FeO in ilmenite slag by carbonaceous reductant was generally controlled through the mass transfer in the slag phase. Additionally, the formation of TiC also occurred in the iron bath. At 1923 K (1650 °C), approx. 20 pct more TiC was generated as compared to TiC formation at 1823 K (1550 °C), which also prevented further reduction of Fe at higher temperatures.

The reduction process of pre-oxidized ilmenite concentrate powder in 30%CO–70%N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis system at the temperature from 1073 to1223 K. The isothermal reduction results show that the reduction process is divided into three stages and the corresponding apparent activation energies are obtained by iso-conversional method and model-fitting method, respectively. For the first stage, the conversion degree increases sharply with increasing time, and the reduction process is controlled by the random nucleation and subsequent growth model (A2 model). For the second stage, the conversion degree increases slowly with increasing time, and the reduction process is controlled by the diffusion of carbon monoxide in the reduced layer (D1 model). For the third stage, the reduction processes at different temperatures are controlled by the diffusion of carbon monoxide in the reduced layer (1073 K and D1 model), phase boundary chemical reaction (1123 K and R2 model), random nucleation and subsequent growth (1173 to 1223 K, A2, and A3 models), respectively. For the whole reduction process, the apparent activation energies obtained by iso-conversional method and model-fitting method are 71.72 and 31.92 kJ mol−1, respectively.