Search Results (91)

Tungsten is one of the critical materials with important applications in many areas. Electrolysis of Na₂WO₄-based salt is a short and green process for the production of tungsten metal and alloys. The conventional process for producing Na₂WO₄ is expensive and time-consuming. Scheelite (CaWO₄) is becoming the most important resource for the extraction of tungsten. Based on thermodynamic calculations and phase equilibrium studies, a novel process is proposed to prepare Na₂WO₄-based salt directly from scheelite through a high-temperature process. By reacting with silica and sodium oxide, immiscible layers of liquid salt and slag are formed from scheelite between 1200 and 1300 °C. High-density salt containing Na₂WO₄ is separated from the silicate slag, which is composed of impurities and fluxes. The effects of fluxing agents, smelting temperature, and reaction time on the direct yield of WO₃ and purity of sodium tungsten are investigated in combination with thermodynamic calculations and high-temperature experiments. The salt containing up to 99% Na₂WO₄ is obtained directly in a single process, which can be used for the production of other tungsten chemicals. This study provides a novel research method and detailed information to produce low-cost sodium tungstate directly from scheelite. Full article

This research investigates the micro-mechanisms and process control associated with the recovery of platinum group metals (PGMs) from spent automotive catalysts (SACs) through iron capturing. High-temperature smelting experiments, complemented by SEM-EDS and XRD analyses, demonstrate that PGMs spontaneously migrate from the slag phase to the iron phase, driven by interfacial energy, where they are captured to form alloy droplets with a PGM content exceeding 4 wt.%. The composite flux (CaO/H₃BO₃) markedly diminishes slag viscosity and enhances the density differential between slag and metal. This facilitates the aggregation, sedimentation, and separation of alloy droplets in accordance with Stokes’ law, thereby lowering the effective capture temperature from 1700 °C to 1500 °C and reducing energy consumption. Additionally, the flux inhibits the formation of detrimental Fe-Si alloys. PGMs form substitutional solid solutions that are uniformly dispersed within the iron matrix. This study provides both the theoretical and technical foundations necessary for the development of efficient, low-energy processes aimed at capturing and recovering Fe-PGMs alloys. Full article

Rhenium is one of the rarest and most strategically important metals, indispensable in high-temperature superalloys and platinum–rhenium catalysts used across the aerospace and petrochemical industries. Owing to its limited primary reserves, recovering rhenium from secondary sources, such as spent catalysts, superalloy residues, and metallurgical dusts, has become vital to ensuring supply security. This review examines technological developments between 1998 and 2025, focusing on how operational parameters, including temperature, leaching time, reagent concentration, and solid-to-liquid ratio, govern dissolution kinetics and overall process efficiency. Comparative evaluation of hydrometallurgical, alkaline, and hybrid processes indicates that modern systems can achieve recovery rates exceeding 98% through selective oxidation, alkaline activation, or combined pyro and hydrometallurgical mechanisms. Acid–chlorine leaching facilitates rapid, low-temperature dissolution; alkaline sintering stabilises rhenium as soluble perrhenates; and hybrid smelting routes enable the concurrent separation of rhenium and osmium. Sustainable aqueous systems employing nitric and ammonium media have also demonstrated near-complete recovery at ambient temperature under closed-loop recycling conditions. Collectively, these findings highlight a technological transition from energy-intensive, acid-based pathways towards low-impact, recyclable, and digitally optimised hydrometallurgical processes. The integration of selective oxidants, phase engineering, circular reagent management, and artificial intelligence-assisted modelling is defining the next generation of rhenium recovery, combining high extraction yields with reduced environmental impact and alignment with global sustainability goals. Full article

Cu and Cr are the essential alloying elements for low-Ni stainless steels. An effective and economical method has been developed for the direct production of Cu-Cr-Fe master alloys through the synergistic reduction of chromite and copper smelting slag. The smelting conditions for synergy reduction were systematically investigated by combining thermodynamic calculations and high-temperature experiments. The results indicate that synergistic reduction drives the reactions of Cr₂O₃, FeO, and Cu₂O with carbon in a positive direction, which can increase their recovery and decrease the flux and fuel costs. The optimum slag composition was identified to control the (CaO + MgO)/(SiO₂ + Al₂O₃) ratio between 0.62 and 0.72, where the slag is fully liquid, resulting in an efficient separation of the alloy from the slag. At 1550 °C, with 50 wt% chromite and 50 wt% copper smelting slag as raw materials, a Cu-Cr-Fe alloy containing 5.2 wt% Cu, 28.6 wt% Cr and 57.9 wt% Fe was produced, while the contents of FeO, Cu₂O, and Cr₂O₃ in the final slag were 0.057 wt%, 0.059 wt%, and 0.23 wt%, respectively. Full article

The depletion of the mineral resource base is inevitable. Therefore, it is necessary to adapt and expand the resource base by incorporating non-traditional copper sources in production. Slag samples from the Balkhash Copper Smelting Plant (Kazakhstan) were analyzed for phase composition, microstructure, and metal distribution using X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical and granulometric methods. The slags are characterized by a fayalite structure with a high content of FeO (35–45%) and SiO₂ (25–35%). Sample composition was determined as 0.7–0.8% Cu, 0.39–0.43% Pb, 2.53% Zn, 0.075 g/t Au, and 2.6 g/t Ag. Mineralogical and granulometric analysis revealed a uniform distribution of iron and slag-forming components (SiO₂, Al₂O₃, etc.) across the fractions. In contrast, non-ferrous and precious metals concentrated in the fine classes. Laboratory tests confirmed that the fine dissemination of valuable components led to low efficiency in magnetic and gravity separation, necessitating specific preliminary slag preparation to improve recovery. Flotation tests showed improved recovery, yielding copper concentrates with 4.57% copper content when the material was crushed to 80–90% of the −0.074 mm class. The research creates a basis for the development of environmentally safe and resource-saving technologies and provides initial data for future recovery technologies. Full article

Copper slag, a by-product of copper ore and concentrate smelting, is rich in non-ferrous metals; therefore, it has been considered a valuable raw material in recent years. This study aimed to compare the extraction of zinc, copper, and cobalt from two types of copper slag from a dump located near the village of Eliseyna, Bulgaria, which differ in mineralogical composition and chemical content, using indirect bioleaching with a spent medium of Aspergillus niger and Penicillium ochrochloron. Chemical leaching with sulphuric acid revealed that zinc and cobalt existed mainly as an acidic-soluble phase in both types of copper slag. In contrast, it contained 50–75% of the total copper content. Each fungal species was cultivated for one week, and the biomass and the spent medium were separated a week later. Owing to the production of a higher concentration of citric acid, A. niger facilitated more efficient base metal recovery. However, their effective recovery from the acidic-soluble phase required leaching at a 5% pulp density and supplementing the spent medium with sulphuric acid. The temperature played a secondary role. Conclusions: Non-ferrous metal extraction from copper slag exposed to weathering using a spent medium supplemented with sulphuric acid was achieved under milder leaching conditions and with better selectivity. In contrast, slag unaffected by weathering behaved as a refractory due to the worsened results of base metal extraction under similar experimental conditions. Full article

To address the technical challenges involved in the resource utilization of hot metal containing high levels of vanadium (V: 2–5%) and chromium (Cr: 1–5%), this study proposes a novel method based on pyrometallurgical selective oxidation for simultaneously extracting vanadium and retaining chromium. Through thermodynamic analysis and high-temperature smelting experiments, the competitive oxidation behaviors of carbon, vanadium, and chromium were revealed, and the synergistic control mechanism of temperature and oxygen partial pressure was clarified. The results indicate that within a temperature range of 1693–1753 K, adjusted over 1 h, vanadium preferentially oxidizes over carbon and chromium, while carbon effectively suppresses chromium oxidation. By optimizing ω(FeO) (10.0–15.7%), we achieved a vanadium oxidation efficiency (η_V) of 72.5–82.2% and maintained a chromium retention efficiency (100−η_Cr) exceeding 57.1%. Compared to traditional methods, which rely on high-oxygen blowing (oxygen supply: 43–195 kg/tFe), multi-stage roasting, and hydrometallurgical refining, this approach eliminates roasting and hydrometallurgical steps (such as sodium/calcium roasting and the associated leaching–precipitation units), shortens the process chain, reduces oxygen consumption (>80 kg/tFe), and lowers environmental risks (Cr oxidation reduced > 40%). This study establishes a theoretical framework for achieving sustainable V/Cr separation, enhancing resource efficiency and minimizing pollution (e.g., Cr(VI)-containing wastewater, high-salinity NH₄⁺/Na⁺ wastewater). Full article

Discarded NdFeB permanent magnets will become a significant source of rare earth elements (REEs) in the future. Electric vehicle (EV) motors utilize 2–5 kg of NdFeB magnets, and researchers are prioritizing the development of suitable extraction technologies. The objective of our research is to separate metal materials (Al, Cu, Fe and FEEs) from EV motors, based on their melting temperatures. REE magnets that pose the greatest challenge are melted together with the electrical steel of the motor, and the potential for extracting REEs in a selective manner from the molten steel was examined based on their significant oxidation potential using FeO–SiO₂ compounds, which act as an oxidizing slag-forming agent, to test the extraction method. Fayalite (2FeO·SiO₂) is the most easily created and ideal eutectic compound for carrying oxygen (FeO) and forming slag (${\mathrm{S}\mathrm{i}\mathrm{O}}_4^{4^{-}}$), typically generated during copper smelting. In this experiment, copper slag was used and the results were compared to a smelting test, which had previously used a synthesized fayalite flux as a model. The smelting test, utilizing synthesized fayalite flux, yielded a 91% Nd recovery rate. The Nd recovery rate in the smelting test with copper slag hit a high of 64.81%, influenced by the smelting’s holding time. The steel contained 0.08% Nd. Iron was recovered from the copper slag at a rate of 73%. During the smelting test, it was observed that the reaction between Nd₂O₃ and the Al₂O₃ crucible resulted in the formation of a layer on the surface of the crucible, diffusion into the crucible itself, and a subsequent reduction in the efficiency of Nd recovery. Full article

With the continuous development of easily accessible resources, the exploitation of complex mineral resources, metallurgical waste slag containing high-value metals, and secondary resources is gradually becoming a mainstream trend. Due to the complex distribution characteristics of elements in these resources, efficient recycling is difficult to achieve. A phase reconstruction strategy has been proposed to address the distribution forms of elements. The phase reconstruction strategy employs pyrometallurgical methods to subject complex resources to high-temperature smelting and cooling crystallization. In the cooling crystallization process, the target elements in melt are selectively enriched into engineered artificial minerals (EnAMs). Then, the target elements can be recovered by subsequently separating these EnAMs. However, the concept of and design strategies for EnAMs are still unclear. In this review, the concept of EnAMs is proposed based on previous studies. This review explores how to design EnAMs by phase equilibrium studies and utilizing geochemical behaviors. Additionally, the application cases of EnAMs in treating challenging tantalum–niobium and rare earth element (REE) resources, secondary resource recycling, and metallurgical slag were collected. Furthermore, the challenges and future perspectives of EnAMs for complex resources are discussed. Full article

High-phosphorus oolitic iron ores (HPOIOs) possess abundant reserves but are incompatible with conventional blast furnace ironmaking, as phosphorus migrates into hot metals during carbothermic reduction, preventing the production of low-phosphorus clean steel. To overcome this limitation, an innovative approach integrating alkaline briquette direct reduction and smelting separation was proposed. Briquettes were prepared from oolitic magnetite concentrate (52.01 wt% Fe, 0.29 wt% P, 0.11 wt% S) with a basicity (R) of 2.0 and 5 wt% MgO added as a desulfurizer. After direct reduction and smelting separation, the resulting metallic iron exhibited a content of 98.56 wt% Fe, with 0.036 wt% P and 0.046 wt% S, achieving an Fe recovery of 87.63%. The dephosphorization and desulfurization efficiencies reached 94.67% and 90.56%, respectively, meeting the clean steel requirements. Phosphorus was effectively stabilized within the gehlenite and merwinite phases as a solid solution of Ca₃(PO₄)₂, inhibiting its transfer to iron. Thermodynamic analyses confirmed that high basicity (R ≥ 2.0) significantly suppressed P₂O₅ activity, preventing phosphate reduction. The formation of a Ca₃(PO₄)₂–Ca₂SiO₄ solid solution further obstructed phosphorus migration. This dual mechanism of “chemical fixation and thermodynamic stabilization” enables efficient dephosphorization, offering a sustainable pathway for utilizing HPOIOs. 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

This study explores the application of high-silica flux ore in copper smelting and converting processes at the Zhezkazgan Copper Smelting plant. Pilot-scale experiments and SEM analyses were performed to assess its influence on slag composition, temperature regime, and metal recovery. The results demonstrated that replacing conventional flux with high-silica ore reduced flux consumption by 19%, increased converter slag temperature from 1124 to 1174 °C, and decreased copper content in converter slag from 10% to 4.5%. SEM micro-analysis revealed the formation of lead-containing silicate rims around matte inclusions, which hinder their settling at low temperatures. However, when the slag temperature exceeded 1400 °C, these rims were destroyed, facilitating separation and reducing residual copper. These findings highlight the potential of high-silica fluxes (>90% SiO₂) to improve both energy efficiency and metal recovery in process of copper matte converting, offering practical recommendations for industrial operations. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article

This study investigates the use of the complex reductant FeAlSiCa as an alternative to the conventional FeSiCr in the EAF smelting of FeCr. The smelting process using FeAlSiCa is characterized by a stable furnace operation, active discharge of metal and slag, and effective phase separation. It was found that a 20% excess of FeAlSiCa over the stoichiometric requirement leads to a sharp increase in Si content in the FeCr alloy, with approximately 85% Cr recovery into the metal. A stoichiometric amount of FeAlSiCa results in a metal with 1.5–1.6% Si content and about 80% Cr recovery. A comparable Cr recovery using FeSiCr was achieved only when applying a 20% excess of that reductant. The use of FeAlSiCa also holds promise for technological sustainability due to its low production cost and the utilization of waste materials during its synthesis. The resulting slags are solid and rock-like and show no signs of disintegration after storage for more than 45 days. Full article

This study investigates the behavior of phosphorus during high-temperature smelting of hydrogen-reduced high-phosphorus oolitic iron ore from the Lisakovsk deposit. The preliminary reduction was carried out at temperatures ranging from 600 to 900 °C using hydrogen, aiming to selectively reduce iron to the metallic phase while retaining phosphorus in the oxide form. The resulting reduced products were subjected to wet magnetic separation and liquid-phase separation. It was found that neither method provides effective separation of phosphorus from iron: phosphorus partially enters the magnetic fraction and, during smelting, transfers into the metallic phase. To confirm the mechanism of phosphate reduction by metallic iron, a control experiment was conducted, in which a mixture of reduced iron and raw ore was smelted at 1650 °C. Microstructural and elemental analyses confirmed the redistribution of phosphorus into the metallic phase. These findings indicate that effective separation of iron and phosphorus cannot be achieved by reduction roasting alone and highlight the need for further studies on slag formation conditions and phase separation kinetics. Full article