Smelting Reduction Process Research Articles

Investigation of converter copper slag reduction using spent cathode carbon as a reductant

ABSTRACT Aiming to address the difficulty of harmless treatment of fluorine in spent cathode carbon (SCC) and high metal content in copper slag, a new method of sustainable production of Fe-Cu alloys by reducing converter copper slag with SCC is proposed. Thermodynamic studies show that Fe-Cu alloys can be obtained at temperatures higher than 1250 °C and fluorine can be effectively fixated. Feasibility experiments were carried out in conjunction with theoretical analyses to clarify the feasibility of the method. At 1500 °C, the recovery of copper and iron reached 93.37% and 78.51%, respectively. During the smelting process, the iron-bearing phases in the slag forms Fe-Cu alloys with copper under high temperatures reducing conditions, and the fluorine is fixated in the slag through conversion to CaF2. This method achieves the effective utilisation of SCC during the reduction smelting process. The phase transformation and thermodynamics of the reduction process were investigated, and reaction mechanism was revealed. The process provides new ideas and perspectives for the environmentally sound treatment of SCC through a pyrometallurgical processes.

Effect of CaO/MgO on rheological properties and structure of CaO–MgO–SiO2–Al2O3-50 % TiO2 slag with SiO2/Al2O3=1.0

The rheological properties, including viscosity, melting temperature, surface tension, density, and viscous activation energy (Eη) were systematically investigated in the CaO–MgO–SiO2–Al2O3-50 % TiO2 slag system with SiO2/Al2O3 = 1.0. The effect of CaO/MgO on the structure and phase composition of the slag was studied using Raman spectroscopy and X-ray diffraction (XRD). The results of viscosity properties indicate that as the CaO/MgO ratio in the slag increase, viscosity and the viscous activation tend to decrease. Melting temperature and surface tension decreases with increasing CaO/MgO, while density increases. As the CaO/MgO ratio in the slag increases, polymerization decreases, leading to the dissociated basic oxides into metal cations and oxygen anions. This addition of basic oxides provides more O2−, increasing the O/Si ratio, disintegrating complex silica-oxygen composite ions into simple silica-oxygen composite anion, and reducing viscosity. Anosovite (MgTi2O5), CaAl2Si2O8, Mg (Al, Ti)2O4, spinel (MgAl2O4), augite (Ca (Mg, Fe, Al) (Al, Si)2O6) and Ca12Al14O33 were identified as the primary phases in slag. The appropriate CaO/MgO should not exceed 0.76. These findings will serve as a valuable technical foundation to support the development of the direct reduction smelting process for the comprehensive utilization of vanadium titanomagnetite.

Enabling CO2 neutral metallurgy for ferrochromium production using bio-based reducing agents

The metallurgical industry is a major source of anthropogenic greenhouse gas emissions. This study explores the replacement of fossil-reducing agents with potentially CO2-neutral bio-based reducing agents. Since reducing agents remove oxygen bonded with metal oxides present in the ore, they are a necessity for the production of metallic elements. The investigated metal is chromium, a major part of stainless steel, and therefore a highly relevant element for the transition from a fossil-based energy system to a renewable one. The state-of-the-art smelting reduction and pre-reduction process followed by subsequent smelting using various reducing agents are investigated in this article. The obtained products, metallurgical efficiencies, energy consumption and off-gas generation were compared. While the products produced with bio-based reducing agents are comparable with the reference trials using metallurgical coke regarding the major components in the metal, the concentration of detrimental phosphorus is significantly higher using bio-based reducing agents. The metallurgical efficiency of the process is comparable to the usage of bio-based reducing agents and coke. However, the energy consumption and the generation of off-gas is higher, when coke is replaced by bio-based reducing agents.

Critical Review of the Metallurgical Operation of the Greek Nickel Industry and Perspectives, based on the recent Industrial Experience on Smelting Reduction Process

The mining and industrial production of Greek ferronickel industry LARCO have ceased since 30.07.2022. The last LME nickel price crisis, exclusion from bank loaning, extremely high cost of electrical energy, management issues, resulted inter alia, in a prohibitive operational cost. Nevertheless, LARCO faces the challenge of restructuring and reoperation in the future, given that privatization is in progress, including the acquisition of the company’s assets to a joint venture enterprise.
 Within this framework, the current paper aims to contribute to the discussion for developing a new management strategy for the optimization of pyrometallurgical process, focusing on the critical step of smelting reduction. Based on industrial experience concerning open bath submerged arc electric furnaces, factors which critically affect the safety and cost-effectiveness of smelting reduction are detected and presented by means of case studies, being mainly classified as following: i) Optimal raw materials’ feed management, including laterite ores (domestic or not), solid fuels and electrode paste. Moreover, taking for granted the need for Ni-rich ‘foreign’ ores to increase the recovery and reduce the cost of the process, the extent of dependence on Fe-rich domestic ores is investigated, in order a safe and stable operation to be ensured. ii) Focus on preventive maintenance management. Substantial increase of the facilities’ operational index and cost saving is obtained, as proved by operational case studies. iii) Modern human resources management strategy. Their economical footprint is further discussed.

Enrichment and reconfiguration of titanium-bearing phase in vortex smelting reduction process of vanadium–titanium magnetite

Enrichment and reconfiguration of titanium-bearing phase in vortex smelting reduction process of vanadium–titanium magnetite

Iron ore wires as consumable electrodes for the hydrogen plasma smelting reduction in future green steel production

In this work we investigate the feasibility and optimisation pathways for using oxide-filled consumable electrodes as both ore feeding system and reducing/melting arc carrier in the hydrogen plasma smelting reduction process. Similar in nature to Söderberg-type electrodes, but free of C-containing substances, this approach has the potential advantage of eliminating the carbon emissions stemming from conventional electric arc furnace electrodes while drastically simplifying the ore feeding into the process. Using a commercial welding setup with a 1.2 mm thick oxide-cored steel wire, area investigations indicate that approximately 50% of the introduced iron ore could be reduced to metallic iron at 100 A arc current under an Ar-10% H2 atmosphere independent from deposition time. The reduction efficiency was negatively affected by increasing arc current and it was increased by using the wire as the anode. Based on the performed variation of deposition parameters, microstructural characterisation results, high speed footage and first upscaling trials, the key scientific questions and engineering pathways for technological optmisiation towards future green steel production technology are outlined and discussed.

Green and efficient recovery of valuable metals from waste copper slag via co-modification with CaO and Na2O

In this work, a novel carbon-free smelting reduction process is proposed to recover valuable metals from molten copper slag, in which secondary aluminum dross is used as the reductant via co-modification with CaO and Na2O additions. The influence of Na2O addition on the metal recovery and slag properties under different CaO/SiO2 ratios was investigated at 1550 °C. The results show that the modifier Na2O not only reduces the melting temperature of the slag, but also inhibits the precipitation of spinel and prevents the polymerization of aluminosilicate units to a certain extent by providing more O2-, which results in a relatively lower slag viscosity. These effects are more significant at the CaO/SiO2 of 0.9. The multiple strengthening mechanisms improve the kinetic conditions for smelting reduction, resulting in optimal results when the Na2O addition reaches 4 wt% at the CaO/SiO2 of 0.9, at which 99.1% of iron and 98.5% of copper in the slag can be recovered as the high-purity alloy. The leaching toxicity of the tailings is 2–3 orders of magnitude lower than the original slag, suggesting that they are clean sources for ceramic production. Furthermore, the assessment of the proposed process indicates that it is technically feasible even without an external energy supply, which indicates that the process is green, efficient, and cost-effective.

From waste to wealth: Valuable metals recovered from waste tungsten leaching residue by a smelting reduction process using CaO-Fe capture agent

Tungsten leaching residue (W-residue), a hazardous waste generated from the industrial recovery of the spent tungsten carbides, poses a threat to the environment. The W-residue contains high grades of SiO2 and TiO2 oxides, and low grades of high-value metal oxides such as WO3, CoO, Ta2O5, and Nb2O5. Herein, a smelting reduction process was proposed to effectively recover the high-value metals from the W-residue and obtained a medium-entropy carbide (MEC) composite. During the smelting process, the valuable metals were recovered as alloy consisting of (Fe, Co)-rich silicide, (Fe, Cr, W)-rich silicide, and (W, Ta, Nb, Ti)C, respectively. The addition of flux CaO lowered the liquidus temperature of the molten slag, and effective alloy-slag phase separation was achieved by adding Fe as a metal collector to capture the alloy droplets entrapped in the slag. Under the optimal conditions, the total recovery rate reached 86.8%. Moreover, the obtained (W, Ta, Nb, Ti)C as MEC exhibited a Vickers hardness of over 19 GPa and can be used as a wear-resistant alloy. This study proposed a strategy for extracting high-value metals from hazardous tungsten residue, which could complement existing recycling processes towards a closed-loop process in the tungsten industry.

Mechanism of arsenic distribution and migration during iron extraction by copper slag-steel slag combined reforming: A potential solution to refractory wastes

In this study, a combined reforming and reduction smelting of copper slag-steel slag was proposed to recover iron (Fe) from solid waste while lowering the environmental risks associated with the management of such waste. In this process, copper slag was mixed with steel tailing to sinter, and made into pellets after magnetic separation. These two products were extracted by a smelting reduction process to obtain Fe, with a recovery rate of 98.63% and a grade of 92.91%. The migration and enrichment behaviors of arsenic (As) in the process were studied, and its mechanism was analyzed by X-ray diffraction, electron probe micro-analyzer, and X-ray photoelectron spectroscopy. The sequential extraction procedure was adopted to analyze the occurrence form of the hazardous As in the copper slag, while leaching tests allowed evaluating the environmental risk of the slag upon reduction smelting. The results proved that such reduction slag represent a stable and low-risk material. However, As was dispersed and released in each procedure of the process, potentially propagating its hazards into subsequent processes and life cycles. This study highlights the potential of an alternative route for the treatment of waste copper slag while recovering Fe from it. The reformed copper slag has strong adaptability, and the smelting reduction method exhibits a high recovery rate of Fe and low-risk reduction slag that can be widely used. It provides a valid reference for the safe management of heavy metal emissions and environmental risk awareness and helps to achieve large-scale consumption of copper slag and steel slag.

Applicability of the reduction smelting recycling process to different types of spent lithium-ion batteries cathode materials

The high-temperature smelting process based on pyrometallurgy is influential in the field of recycling spent lithium-ion batteries (LIBs) on an industrial scale. However, there are a variety of cathode materials for spent LIBs. The applicability of the high-temperature smelting process to different kinds of cathode materials has not been reported. In this work, the applicability of the reduction smelting process to four different cathode materials is studied. The phase transition, distribution and existence of target elements and the characteristics of the smelting products when different cathode materials are used as raw materials are systematically discussed. The results show that the reduction smelting process can recover the four different cathode materials (LiCoO2, LiFePO4, LiMn2O4, LiNi0.8Co0.1Mn0.1O2) of spent LIBs. The reduction smelting process is also suitable for complex feedstocks containing the four cathode materials. The target elements Co, Cu, Ni, Fe and P are transferred to the alloy. The target elements Li and Mn volatilize into the gas phase. In addition, the future application of the reduction smelting process on an industrial scale is discussed and proposed. This study reveals the excellent applicability of the reduction smelting process to different LIB cathode materials and provides support for the development of a high-temperature smelting process based on pyrometallurgy.

Efficient Utilization of Limonite Nickel Laterite to Prepare Ferronickel by the Selective Reduction Smelting Process

Ferronickel products obtained from the traditional process used to treat limonite nickel laterite usually assay very low-grade Ni, only 3–5% Ni due to the high Fe/Ni ratio of limonite nickel laterite. This paper describes an investigation conducted to upgrade limonite nickel laterites for the preparation of ferronickel by using selective reduction smelting technology. By means of thermodynamic calculations and smelting experiments, the smelting separation mechanism and the behavior of P and S removal in the smelting process, as well as the influence of smelting factors, have been systematically identified. The best production index of ferronickel is obtained under optimized conditions as follows: smelting the pre-reduced lumps at 1525 °C for 45 min with a basicity of 0.60, MgO/SiO2 ratio of 0.30, and nickel and iron metallization rate of 94.30% and 10.93%, respectively. The resulting ferronickel features a nickel and iron grade of 12.55% and 84.61% and a nickel and iron recovery of 85.65% and 10.87%, respectively. In addition, the content of S and P contained in ferronickel is only 0.11% and 0.0035%, respectively. The ferronickel obtained from the selective reduction smelting process is a fine material for the subsequent stainless steel smelting due to its high Ni grade and low content of impurities.

Study on the Bath Smelting Reduction Reaction and Mechanism of Iron Ore: A Review

Against the background of low global carbonization, blast furnace ironmaking technology with coking puts huge amounts of pressure on the global steel industry to save energy and reduce emissions due to its high pollution levels and high energy consumption. Bath smelting reduction technology is globally favored and studied by metallurgists as a non-blast furnace ironmaking technology that directly reduces iron ore into liquid metal without using coke as the raw material. The smelting reduction reaction of iron ore, which is the core reaction of the process, is greatly significant to its productivity and energy saving. Therefore, this paper focuses on the behavior and mechanism of iron ore’s smelting reduction. This work focuses on three key aspects of smelting reduction, namely, the thermal decomposition characteristics of iron ore during the smelting reduction, the smelting reduction mechanism of iron-ore particles, and the smelting reduction mechanism of FeO-bearing slag. The experimental study methods, reaction mechanisms, influencing factors, and kinetic behavior of the three are highlighted. In this work, the reaction mechanism of thermal iron-ore decomposition, iron-ore particle smelting reduction, and FeO-bearing slag smelting reduction on the three reactions were observed, providing a theoretical basis for how to select and optimize raw materials for the bath smelting reduction process. Moreover, the kinetic study clarifies the limiting steps of the reactions and provides guidance for an improvement in the reaction rate. However, certain blank points in previous studies need to be further explored, such as the differences in the research results of same factor, the large variation in reaction activation energy, and the coupling mechanism and inter-relatedness of the three key aspects’ reactions with each other.

Cracking and Microstructure Transition of Iron Ore Containing Goethite in Fe-C Melt Based on the HIsmelt Process

The phenomenon of cracking and deterioration of iron ore particles is a widespread scientific problem in the field of mineral processing and metallurgy. In this paper, the thermal decomposition properties of iron ore were investigated by a non-isothermal method using thermogravimetric equipment, and the crack evolution behavior of iron ore within Fe-C melt was investigated experimentally, by scanning electron microscopy and Micro-CT. The results show that the start decomposition temperature of #2 iron ore is 292.7 °C, which is 37.3 °C higher compared to that of #1 iron ore, because of its smaller pores and the difficulty of water vapor diffusion. The initial decomposition of iron ore is the decomposition goethite to form water vapor, and as heat transfer continues, hematite particles break into smaller particles and decompose to form Fe3O4. During the smelting reduction process, the Crack index (CI) of #1 iron ore was 5.50% at 4 s, and the CI index increased to 23.54% when time was extended to 16 s, and the internal evolved from locally interconnected holes to cracked structure. The iron ore maintains a relatively intact form during reduction within the Fe-C melt, and interfacial reduction reaction is dominant in the later stage.

Impact of Iron Ore Pre-Reduction Degree on the Hydrogen Plasma Smelting Reduction Process

To counteract the rising greenhouse gas emissions, mainly CO2, the European steel industry needs to restructure the current process route for steel production. Globally, the blast furnace and the subsequent basic oxygen furnace are used in 73% of crude steel production, with a CO2 footprint of roughly 1.8 t CO2 per ton of produced steel. Hydrogen Plasma Smelting Reduction (HPSR) utilizes excited hydrogen states with the highest reduction potentials to combine the simultaneous reduction and smelting of iron ore fines. Due to the wide range of iron ore grades available worldwide, a series of hydrogen plasma experiments were conducted to determine how pre-reduced iron ore and iron-containing residues affect reduction behavior, hydrogen consumption, overall process time, and metal phase microstructure. It was discovered that, during the pre-melting phase under pure argon, wet ore increased electrode consumption and hematite achieved higher reduction levels, due to thermal decomposition. The reduction of magnetite ore yielded the highest reduction rate and subsequent hydrogen conversion rates. Both hematite and magnetite exhibited high utilization rates at first, but hematite underwent a kinetic change at a reduction degree of 80–85%, causing the reduction rate to decrease. In comparison to fluidized bed technology, it is possible to use magnetite directly, and the final phase of the reduction can move along more quickly due to higher temperatures, which reduces the overall process time and raises the average hydrogen utilization. A combination of both technologies can be considered advantageous for exhaust gas recycling.

Simulation and experimental investigation on one-step process for recovery of valuable metals and preparation of clean mineral wool from red mud

Red mud (RM) is a hazardous alumina industrial solid waste and its utilization faces three major challenges, namely, efficient recovery of valuable metals, favorable control of hazardous substances, and complete utilization of residues. We simultaneously achieved the three goals in a short one-step process, which was inspired by green chemistry principles and focused on multi-objective coupled control. Iron-based metal elements were recovered in reduction smelting process to produce pig iron. Molten slags after smelting were rapidly cooled and fiberized to produce mineral wool and hazardous alkaline substances were immobilized in vitreous fibers. The smelting-reduction process, fibration capacity of RM-based molten slags, and performance and environmental impact of prepared mineral wool were investigated using thermodynamic, molecular dynamics simulations, and experimental methods. The results indicated the recovery rate of Fe could reach above 87%. The obtained mineral wool showed satisfactory properties with the fibrosis rate of around 73%–92%, the mean fiber diameter of 1.57–5.62 μm, and the mean fiber tensile strength of 1520–6700 MPa. The highest Na+ leaching concentration was under 1.42 mg/L and the solidification rate of Na+ in different samples was above 99.8%. This paper provided a fresh approach to achieve clean and high value-added utilization of RM.

Hydrogen plasma smelting reduction process monitoring with optical emission spectroscopy – Establishing the basis for the method

In the world of ever-increasing demand for carbon-free steel, hydrogen and recycling have an undeniable role in achieving net-zero carbon dioxide emissions for the steel industry. However, even though steel is one of the most recycled materials globally, the quantity of steel that can be made from recycled steel will probably not match the demand in the future. This in turn means that steel must be also produced from the conventional resource, the iron ore. Hydrogen has been proposed as an environmentally friendly alternative to carbon as a reducing agent. To tackle the problems related to the usage of hydrogen for this purpose, hydrogen plasma smelting reduction has been studied extensively in the last few years. This article aims to provide means for process control of the hydrogen plasma, which may show erratic and chaotic behavior during the smelting process. The method used is optical emission spectroscopy, with which the plasma can be characterized, its composition can be evaluated, and its temporal evolution can be assessed. This study sheds light on how the plasma behaves with different electrode gaps and flow gas compositions together with how the position of the arc with respect to the center of the crucible can be assessed. In Ar/H2 plasma, the plasma temperatures derived with OES varied between 4000 and 10000 K, and up to a 26% decrease in electron density was observed when increasing the electrode gap in 1 cm increments.

A New Methodological Approach to the Characterization of Optimal Charging Rates at the Hydrogen Plasma Smelting Reduction Process Part 1: Method.

The development of a carbon lean steel production process following the concept of direct carbon avoidance is one of the most challenging tasks the iron and steel industry must tackle in just a few decades. The necessary drastic reduction of 80% of the process’s inherent emissions by 2050 is only possible if a new process concept that uses hydrogen as the primary reductant is developed. The Hydrogen Plasma Smelting Reduction (HPSR) of ultra-fine iron ores is one of those promising concepts. The principle was already proven at a lab scale. The erection of a bench-scale facility followed this, and further scaled-ups are already planned for the upcoming years. For this scale-up, a better understanding of the fundamentals of the process is needed. In particular, knowledge of the kinetics of the process is essential for future economically feasible operations. This investigation shows the principles for evaluating and comparing the process kinetics under varying test setups by defining a representative kinetic parameter. Aside from the fundamentals for this definition, the conducted trials for the first evaluation are shown and explained. Several differences in the reduction behavior of the material at varying parameters of the process have already be shown. However, this investigation focuses on the description and definition of the method. An overall series of trials for detailed investigations will be conducted as a follow-up.

Efficient separation and recovery of lithium through volatilization in the recycling process of spent lithium-ion batteries

Spent lithium-ion batteries (LIBs) comprise different kinds of valuable metals with recovery and reuse value. Aiming to address the difficulty of recycling lithium from spent LIBs through conventional pyrometallurgy, a new method of high-efficiency separation and recovery of lithium through volatilization is proposed. In this new method, spent LIBs as the raw material, copper slag as the only flux and CaCl2 as an additive are utilized to recover lithium from spent LIBs. Under the optimal conditions, the volatilization rate of Li was 96.87%. During the smelting process, lithium is volatilized into the gas phase in the form of LiCl, where lithium can be recycled from the dust. In light of the experimental results, the addition of CaCl2 contributes to the formation of LiCl. The kinetics study showed that the volatilization of LiCl was controlled by an interfacial chemical reaction, and the apparent activation energy was 42.57 kJ/mol. In addition, Li2CO3 could be obtained from lithium-containing dust using a precipitation process. This method achieves efficient separation of lithium during the reduction smelting process. The phase transformation and kinetics of the separation process were investigated, and reaction mechanism was revealed. Importantly, the novel process provides new ideas and perspectives for the separation of lithium from spent LIBs through a pyrometallurgical process.

A New Methodological Approach on the Characterization of Optimal Charging Rates at the Hydrogen Plasma Smelting Reduction Process Part 2: Results.

To meet the target for anthropogenic greenhouse gas (GHG) reduction, the European steel industry is obliged to reduce its emissions. A possible pathway to reach this requirement is through developments of new technologies for a GHG-free steel production. One of these processes is the hydrogen plasma smelting reduction (HPSR) developed since 1992 at the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben in Austria. Based on the already available publication of the methodology in this work, potential process parameters were investigated that influence the reduction kinetics during continuous charging to improve the process further. Preliminary tests with different charging rates and plasma gas compositions were carried out to investigate the impacts on the individual steps of the reduction process. In the main experiments, the obtained parameters were used to determine the effect of the pre-reduction degree on the kinetics and the hydrogen conversion. Finally, the preliminary and main trials were statistically evaluated using the program MODDE® 13 Pro to identify the significant influences on reduction time, oxygen removal rate, and hydrogen conversion. High hydrogen utilization degrees could be achieved with high iron ore feeding rates and low hydrogen concentrations in the plasma gas composition. The subsequent low reduction degree and thus a high proportion of oxide melt leads to a high oxygen removal rate in the post-reduction phase and, consequently, short process times. Calculations of the reduction constant showed an average value of 1.13 × 10−5 kg oxygen/m2 s Pa, which is seven times higher than the value given in literature.

Effect of Sulfur Content on Copper Recovery in the Reduction Smelting Process

This work discussed the advantages of reducing copper in molten copper slag with low S content. FactSage calculated the distribution of copper at equilibrium under different sulfur contents. The effect of sulfur content on copper recovery under different oxygen partial pressures in 1400 °C was pointed out. The effect of sulfur content on copper recovery in the actual reduction process was explored through experimental research. Under the condition of low sulfur, the recovery ratio of copper and the stability of the experiment have an ideal result in fixed C/O in the experiment.