Search Results (24)

The pollution of soil by potentially toxic elements in industrial–agricultural transition zones threatens global food security and public health owing to their persistence and bioaccumulation. This study focused on Miyi County, Sichuan (China), a typical region with intensive vanadium–titanium magnetite mining and modern agriculture, and systematically analyzed eight heavy metals and metalloids (Cd, Hg, As, Pb, Cr, Cu, Zn, and Ni) across the categories of atmospheric deposition, irrigation water, agricultural inputs, and soil–crop systems. A rigorous four-stage full-chain diagnosis (concentration–load–ecology–health) was executed to evaluate pollution levels and pathways. The single-factor pollution index identified cadmium (Cd) as the primary pollutant, exhibiting a maximum index of 32.63. The Håkanson potential ecological risk index (RI) demonstrated that Cd was the absolute dominant contributor, reaching a catastrophic single-element risk factor (Ei) of 2191.8 and contributing over 70% to the comprehensive ecological risk. Spatially, soils displayed a distinct point-source cluster diffusion pattern: the northern metallurgical zone was dominated by a Cr-Zn-Cu-Ni industrial assemblage, while the southern zone was enriched in Cd, Pb, As, and Hg. Positive matrix factorization (PMF) source apportionment quantitatively demonstrated that industrial emissions via atmospheric deposition were the primary driver, contributing 55–75% of the total soil exogenous inputs, while agricultural sources (livestock manure and legacy arsenic pesticides) exacerbated localized accumulation. While overlying irrigation water remained safe, channel sediments acted as historical pollution sinks. The human health risk model revealed that children in industrial core areas faced unacceptable carcinogenic hazards, with a lifetime carcinogenic risk (LCR) reaching 5.6 × 10⁻⁴. These highly specific multi-media findings support a macro spatial risk zoning and source interception strategy to decouple economic growth from regional food safety degradation in global transition economies. Full article

Vanadium–titanium magnetite is a polymetallic resource in which the low reactivity and complex phase constitution of Ti-bearing smelting slag restrict the coordinated recovery of Fe, V, and Ti. In this study, a coupled route involving laboratory-scale induction-furnace smelting separation, magnetic separation, NaOH activation roasting, and staged leaching was investigated for upgrading ground vanadium–titanium magnetite metallized pellets. At 1690 °C for 20 min with 2.5 wt% coke under natural slag basicity, a vanadium-bearing metallic product containing 92.07 wt% Fe and 1.27 wt% V was obtained, while Ti was concentrated in a slag containing 47.83 wt% TiO₂. Increasing slag basicity improved vanadium partitioning into the metallic phase but decreased the TiO₂ content and subsequent upgrading performance of the slag. Following magnetic separation and NaOH-activated roasting at 900 °C for 90 min with 40 wt% NaOH, staged leaching yielded a rutile-rich product containing 90.70 wt% TiO₂, with a Ti recovery of 88.75%. These results demonstrate that controlling the phase constitution of smelting-derived Ti-bearing slag is important for its subsequent alkali-activation upgrading and Ti enrichment. Full article

Vanadium–titanium-bearing direct reduced iron (V-Ti DRI) is a promising feedstock for the full-value utilization of V-Ti magnetite. Selective partition of V and Cr into the metal phase, with Ti retained in the slag, requires quantitative thermodynamic guidance. We investigate this slag–metal distribution using the ion and molecule coexistence theory (IMCT). An eight-component slag model with 33 complex-molecule equilibria is coupled to reduction thermodynamics through an iterative mass-balance procedure; the metal-phaseWagner activity is temperature-scaled by Chipman’s rule, and the dissolved oxygen concentration is closed through the C-CO-O equilibrium. The equilibrium V and Cr recovery ceilings (metal side) rise from 89%/96% at 1400 °C to approximately 99.4% at 1500 °C and exceed 99.8% at 1550 °C. Ti-in-slag retention (slag side) drops steadily from 99.998% at 1400 °C to 99.4% at 1700 °C, giving a V/Ti separation factor above 104. Fe recovery to the metal phase exceeds 97% at 1600 °C and above, driven by the strong reduction of FeO, which constitutes approximately 32 wt.% of the initial slag. Carbon activity exerts a cubic power-law effect: at 1450 °C, the V recovery ceiling collapses from 97.4% at a_C = 1 to 6.5% at a_C = 0.05, identifying imperfect carbon saturation as a primary thermodynamic mechanism behind the ceiling-to-pilot gap. Once temperature and oxygen closure are enforced, the ceilings are only weakly sensitive to metallization, basicity, coke ratio, and TiO₂ content. Comparison with pilot data shows the ceilings exceed reported yields by 16–29 percentage points (pp), quantifying the kinetic/mass-transfer deficit and providing a benchmark for scale-up. Full article

Magnetite-rich iron ores present analytical challenges due to mineralogical complexity, including titanium–vanadium (Ti-V) substitution within magnetite and variable silicate gangue contributions. Reliable iron (Fe) quantification in such systems is essential for accurate resource evaluation and beneficiation planning, particularly in layered intrusion-hosted deposits. This study compares fusion-based inductively coupled plasma optical emission spectroscopy (ICP-OES) and fused-bead X-ray fluorescence (XRF) methods for the determination of Fe and associated major elements in magnetite-bearing Fe ores from the Bushveld Igneous Complex, South Africa. Four representative ore samples and certified reference materials were analysed using both techniques. Comparative statistical parameters like the t-test and F-test exhibit no significant differences in either precision and mean concentration between fused-based ICP-OES and fused-based XRF methods for the determination of Fe and other elements. The results indicate that, despite the existence of titanomagnetite and lithologies that are rich in silicates, both fusion-based methods provide consistent and reliable bulk chemical analysis datasets. While both approaches show suitability for routine chemical analysis, fusion-based ICP-OES offers a practical advantage in terms of throughput and operational efficiency. This work emphasises the importance of matching analytical methods with mineral ore characterisation in order to ensure reliable Fe grade determination in complicated oxide deposits. Full article

Vanadium–titanium magnetite is a strategically important resource for iron, vanadium, and titanium production, yet its utilization in conventional blast furnace–basic oxygen furnace routes is limited by the dilution of titanium into low-value slag. This study investigates an integrated process route combining pellet preparation, hydrogen-based shaft furnace reduction conducted in the temperature range of 800–1000 °C, and subsequent electric furnace smelting for efficient recovery of Fe, V, and Ti. Pellets prepared from 100 wt.% vanadium–titanium magnetite exhibited sufficient mechanical strength but showed poor reducibility and severe low-temperature reduction disintegration, rendering them unsuitable for hydrogen-based shaft furnace operation. To overcome these limitations, systematic ore blending was applied. An optimized pellet composition comprising 40 wt.% vanadium–titanium magnetite, 50 wt.% high-grade iron ore, and 10 wt.% titanium concentrate achieved reduction degrees above 90%, acceptable swelling and bonding behavior, and low reduction disintegration indices meeting industrial HYL requirements. Industrial trials in a hydrogen-based shaft furnace demonstrated stable operation and consistent product quality, producing direct reduced iron with controlled metallization and enrichment of titanium and vanadium. Subsequent electric furnace smelting achieved clear slag–metal separation, yielding hot metal with high iron and vanadium recovery and a TiO₂-rich slag containing approximately 45 wt.% TiO₂. Recovery rates of Fe, V, and Ti exceeded 90%, confirming the technical feasibility of the proposed process route. Full article

Ti-bearing blast furnace slag (TBS), a byproduct of vanadium–titanium magnetite smelting, serves as an important secondary resource for titanium recovery. However, the complex mineralogical composition and finely dispersed nature of titanium in TBS present significant challenges for efficient extraction. This review systematically examines four major titanium extraction routes: hydrometallurgical leaching, pyrometallurgical smelting, molten salt electrolysis, and selective precipitation, focusing on their limitations and recent improvements. For instance, conventional acid leaching suffers from acid mist release, a colloidal formation that hinders titanium recovery, and waste acid pollution. The adoption of concentrated sulfuric acid roasting activation effectively suppresses acid mist emission and prevents colloidal generation. Pyrometallurgical approaches are hampered by high energy consumption and substantial carbon emissions, which can be alleviated through the use of gaseous reductants to enhance reaction efficiency and reduce environmental impact. Molten electrolysis faces issues such as polarization and undesirable dendritic deposition; these are mitigated by employing liquid metal cathodes integrated with vacuum distillation to achieve high-purity titanium products. Selective precipitation struggles with strict crystallization conditions and low separation efficiency, though advanced techniques like supergravity separation show improved extraction performance. We propose an integrated technical strategy termed “Online conditioning driven by waste heat-mineral phase reconstruction-directional crystallization-optimized liberation.” This approach utilizes the inherent waste heat of slag combined with electromagnetic stirring to enhance homogeneity and promote efficient titanium recovery, offering a sustainable and scalable solution for industrial TBS treatment. Full article

Titanium (Ti) and vanadium (V) are metals critical for the sustainable development of our society. Their growing demand and the depletion of ores rich in these metals along with technological development lead to a reconsideration of sources that were previously considered unpromising. The present work is devoted to the study of an iron (Fe) ore from southeastern Bulgaria, containing Ti and V in low but potentially recoverable concentrations. The aim was to check whether it is possible to obtain an iron concentrate containing Ti and V in concentrations comparable to those in similar market products. The material was examined by optical microscopy, XRD, SEM-EDS, and ICP MS. Magnetic separation was applied with and without predating gravity separation. By applying wet gravity beneficiation followed by a low-intensity magnetic field, an iron concentrate (40%–65% Fe) bearing 3%–5% Ti and 0.4%–0.59% V was obtained. Using only a low-intensity magnetic field, without gravity separation, an iron concentrate (59.4% Fe) containing 3.5% Ti and 0.44% V was obtained. Vanadium was extracted in the highly magnetic material, while a significant amount of Ti was left in the weak magnetic fraction. An additional 1.5% may be recovered by applying a high-intensity magnetic field. The main processing challenge appears to be the recovery, without flotation beneficiation, of magnetite that is oxidized to non-magnetic hematite and maghemite. Using magnetic separation (with or without preliminary wet gravity beneficiation) avoids pollution of the processing waste with reagents. Thus, the waste from the beneficiation of the studied type of ore can be used as a soil improver. As a result, the extraction of critical metals using a practically waste-free technology may be achieved. Full article

This study proposed a selective leaching method to address the challenge of excessive iron (Fe) leaching during a sulfuric acid treatment of magnetite pellets, which complicates the subsequent extraction and precipitation of vanadium (V). The approach involved constant-pH sulfuric acid leaching of calcined and roasted vanadium–titanium (V–Ti) magnetite pellets to enhance V recovery while minimizing Fe dissolution. A comparison between constant-pH leaching and conventional heap leaching was conducted. The results showed that, under optimal leaching conditions, the V leaching rate remained largely unchanged, while the Fe leaching rate was significantly reduced compared with conventional heap leaching. Specifically, under optimal conditions—acid concentration of 2 mol/L, liquid–solid ratio of 1:3, temperature of 90 °C, and leaching time of 360 h—the V leaching rate reached 72.21%, while the Fe leaching rate remained as low as 0.91%. Additionally, the valence states of V and Fe in the pellets before and after leaching, as well as the main phase compositions during the leaching process, were analyzed. The results indicated that the primary phases in the calcined and roasted pellets remain unchanged before and after leaching, and most of the V and nearly all divalent Fe were effectively leached. Full article

The iron and steel industry, as a major energy consumer, was critically required to enhance operational efficiency and reduce CO₂ emissions. Conventional blast furnace processing of vanadium–titanium magnetite (VTM) in China had been associated with persistent challenges, including suboptimal TiO₂ recovery rates (<50%) and elevated carbon intensity (the optimal temperature range for TiO₂ recovery lies within 1400–1500 °C). Shaft furnace technology has emerged as a low-carbon alternative, offering accelerated reduction kinetics, operational flexibility, and reduced environmental impact. This study evaluated the low-carbon PLCsmelt process for VTM smelting through energy–mass balance modeling, comparing two gas-recycling configurations. The process integrates a pre-reduction shaft furnace and a melting furnace, where oxidized pellets are initially reduced to direct reduced iron (DRI) before being smelted into hot metal. In Route 1, CO₂ emissions of 472.59 Nm³/tHM were generated by pre-reduction gas (1600 Nm³/tHM, 64.73% CO, and 27.17% CO₂) and melting furnace top gas (93.98% CO). Route 2 incorporated hydrogen-rich gas through the blending of coke oven gas with recycled streams, achieving a 56.8% reduction in CO₂ emissions (204.20 Nm³/tHM) and altering the pre-reduction top gas composition to 24.88% CO and 40.30% H₂. Elevating the pre-reduction gas flow in Route 2 resulted in increased CO concentrations in the reducing gas (34.56% to 37.47%) and top gas (21.89% to 26.49%), while gas distribution rebalancing reduced melting furnace top gas flow from 261.03 to 221.93 Nm³/tHM. The results demonstrated that the PLCsmelt process significantly lowered carbon emissions without compromising metallurgical efficiency (CO₂ decreased about 74.48% compared with traditional blast furnace which was 800 Nm³/tHM), offering a viable pathway for sustainable VTM utilization. Full article

This study investigates the mineral chemistry and iron isotope composition of the Pertek Fe-skarn deposit in the Eastern Taurides, Turkey, to elucidate skarn formation and ore genesis through chemical and isotopic parameters. The deposit consists of substantial and dispersed magnetite ores formed by the intrusion of a dioritic suite into marbles. Mineral assemblages, including hematite, goethite, andradite garnet, hedenbergite pyroxene, calcite, and quartz, exhibit compositional variations at different depths within the ore body. Magnetite is commonly associated with hematite, goethite, garnet, pyroxene, calcite, and quartz. Extensive LA–ICP–MS analysis of magnetite chemistry reveals elevated trace element concentrations of titanium (Ti), aluminum (Al), vanadium (V), and magnesium (Mg), distinguishing Pertek magnetite from low-temperature hydrothermal deposits. The enrichment of Ti (>300 ppm) and V (>200 ppm), along with the presence of Al and Mg, suggests formation from high-temperature hydrothermal fluids exceeding 300 °C. Discriminant diagrams, such as Al+Mn versus Ti+V, classify Pertek magnetite within the skarn deposit domain, affirming its medium- to high-temperature hydrothermal origin (200–500 °C), characteristic of skarn-type deposits. Magnetite thermometry calculations yield an average formation temperature of 414.53 °C. Geochemical classification diagrams, including Ni/(Cr+Mn) versus Ti+V and TiO₂-Al₂O₃-MgO+MnO, further support the skarn-type genesis of the deposit, distinguishing Pertek magnetite from other iron oxide deposits. The Fe-skarn ore samples display low total REE concentrations, variable Eu anomalies, enrichment in LREEs, and depletion in HREEs, consistent with fluid–rock interactions in a magmatic–hydrothermal system. The δ⁵⁶Fe values of magnetite range from 0.272‰ to 0.361‰, while the calculated δ⁵⁶Fe_aq values (0.479‰ to 0.568‰) suggest a magmatic–hydrothermal origin. The δ⁵⁷Fe values (0.419‰ to 0.530‰) and the calculated 10³lnβ value of 0.006397 indicate re-equilibration of the magmatic–hydrothermal fluid during ore formation. Full article

Persulfate-based advanced oxidation processes have emerged as a promising approach for the degradation of organic pollutants in aqueous environments due to their ability to generate sulfate radicals (SO₄^−·) within catalytic systems. In this study, peroxydisulfate (PDS) and peroxymonosulfate (PMS) were investigated with the natural vanadium–titanium magnetite (VTM) as the activator for the degradation of acid orange II. The degradation efficiency increased with higher dosages of VTM or persulfate (both PDS and PMS) at lower concentrations (below 10 mM). However, excessive PMS (higher than 10 mM) in the PMS/VTM system led to the self-consumption of free radicals, significantly inhibiting the degradation of acid orange II. The VTM-activated PDS or PMS maintained an effective degradation of acid orange II in a wide pH range (3~11), suggesting remarkable pH stability. The SO₄^−· was the main active species in the PDS/VTM system, while hydroxyl radical (·OH) also contributed significantly to the PMS/VTM system. In addition, PMS exhibited better thermal stability during VTM activation. Coexisting ions in an aqueous environment such as bicarbonate (HCO₃^–), carbonate (CO₃^2–), and hydrogen phosphate (HPO₄^2–) had obvious effects on persulfate activation. Our study systematically investigated the different activation processes and influencing factors associated with PDS and PMS when the natural VTM was used as a catalyst, thereby providing new insights into the persulfate-mediated degradation of organic pollutants in aqueous environments. Full article

This paper investigated a pellet ore production process in which vanadium was extracted from vanadium and titanium magnetite concentrates using sulfuric acid leaching. Calcium and magnesium were added to the iron ore concentrate during pellet production to produce calcium vanadate and magnesium vanadate after roasting. The pellets were leached with sulfuric acid solution to extract V⁵⁺. The resulting pellets had a compressive strength of 3375 N after primary roasting, a good pellet morphology after acid leaching, and simple liquid–solid separation. Under the optimal experimental conditions, the vanadium leaching rate in the pellets reached 77.86%, while the iron leaching rate was only 1.17%. The pellets did not fragment, which was an improvement upon existing vanadium extraction methods. The strength of the pellets after vanadium extraction decreased to 563 N, but after secondary roasting, the compressive strength of the pellets reached 2578 N, which was suitable for blast furnace ironmaking. The roasting and acid leaching experiments showed that the vanadium extraction process resulted in suitable pellet properties. The use of low compound additives can effectively improve the leaching effect, while avoiding the previous problems of too many additives, pellet iron grade reduction, or the pursuit of high vanadium extraction rate pellet breakage and serious high secondary use process costs. Full article

As the byproduct in the smelting process of vanadium titano-magnetite, titanium-bearing blast furnace slag (TBFS) can be converted to a titanyl sulfate (TiOSO₄) solution containing MgSO₄ and Al₂(SO₄)₃ impurities via dissociation by concentrated H₂SO₄ (80–95%) at 80–200 °C, followed by leaching with H₂O at 60–85 °C. In this study, hydrated TiO₂ was prepared by hydrothermal hydrolysis of a Mg/Al-bearing TiOSO₄ solution at 120 °C and the hydrolysis law was investigated. The experimental results indicate that MgSO₄ and Al₂(SO₄)₃ accelerated the hydrolysis and significantly affected the particle size (increasing the primary agglomerate size from 40 to 140 nm) and dispersion (reducing the aggregate size from 12.4 to 1.5 μm) of hydrated TiO₂. A thermodynamic equilibrium calculation showed TiOSO₄ existed as TiO²⁺ and SO₄²⁻ in the solution, and MgSO₄ and Al₂(SO₄)₃ led to little change of [TiO²⁺], but an obvious decrease of [H⁺], which favored the hydrolysis process. At the same time, the coordination–dissociation mechanism of SO₄²⁻ and Al(SO₄)₂⁻ facilitated the lap bonding of Ti-O-Ti, promoting the growth of hydrated TiO₂ synergistically. Full article

In this study, a clean pellet production method of calcium roasting and sulfuric acid leaching of vanadium from vanadium and titanium magnetite concentrates is proposed, which can effectively separate vanadium and iron, and the pellets after acid leaching and vanadium extraction can be used as raw material for iron making after secondary roasting. During the experiment, only 2% Ca(OH)₂ was added as the calcifier to make pellets, and vanadium was extracted by acid leaching after calcination. Under the optimum conditions, the vanadium leaching rate was 74.51%, and the iron leaching rate was only 1.05%. After secondary roasting, the compressive strength of the pellets was 2358 N, and the qualification rate was 97%. Additionally, after acid leaching and vanadium extraction, the impurities in the pellet were partially removed, and the iron content of the pellet increased by 6.6%, which is more conducive to subsequent ironmaking. The roasting and acid leaching experiments show that based on the production of iron smelting pellets, the use of pellets can better extract vanadium from the titanium magnetite concentrate, while avoiding the problems of excessive additives to reduce the iron grade of pellets. Or the pursuit of high vanadium extraction rate pellets, which can be seriously damaged and difficult to use later. This process can perform a comprehensive utilization of vanadium titanium magnetite, and has certain guiding significance for industrial production. Full article

Massif-type mafic intrusions (gabbro and anorthosite) are known for their considerable resources of vanadium-bearing iron–titanium oxide ores. Massive-type gabbroic and anorthosite rocks are frequently associated with magmatic rocks that have significant quantities of iron, titanium, and vanadium. The most promising intrusions that host Fe-Ti oxide ores are the gabbroic rocks in the south-eastern desert. The ilmenite ore deposits are hosted in arc gabbroic and anorthosite rocks. They are classified into three types, namely black ore, red ore, and disseminated ore. The black ilmenite ore is located at the deeper level, while the oxidized red ore is mainly located at or near the surface. Petrographically, the gabbro and ilmenite ores indicate a crystallization sequence of plagioclase, titaniferous pyroxene, and ilmenite. This reveals that the ilmenite is a magmatic deposit formed by the liquid gravity concentration of ilmenite following the crystallization of feldspar and pyroxene. Meanwhile, quartz, tremolite, zoisite, and opaque minerals are accessory minerals. The Fe-Ti ores are composed of ilmenite hosting exsolved hematite lamellae of variable sizes and shapes, gangue silicate minerals, and some sulfides. The X-ray diffraction (XRD) data reveal the presence of two mineral phases: ilmenite and hematite formed by the unmixing of the ferroilmenite homogeneous phase upon cooling. As a result, the ore is mostly made up of hemo-ilmenite. Using an electron microscope (SEM), as well as by observing the textures seen by the ore microscope, ilmenite is the dominant Fe-Ti oxide and contains voluminous hematite exsolved crystals. Under the scanning electron microscope, ilmenite contained intergrowths of hematite as a thin sandwich and lens shape. The formation of hematite lamellae indicates an oxidation process. Mineral chemistry-based investigations reveal late/post-magmatic activity at high temperatures. The examined ilmenite plots on the ferro-ilmenite line were created by continuous solid solution over 800 °C, whereas the analyzed magnetite and Ti-magnetite plot near the magnetite line and were formed by continuous solid solution exceeding 600 °C. Full article