Reduction Smelting Research Articles

Optimization of HIsmelt reactor parameters for efficient combustion and heat transfer by numerical simulation

HIsmelt, as one of the non-blast furnace ironmaking processes, is rapidly becoming a focus of attention in the steel industry due to its outstanding advantages in terms of low requirements for raw materials and short and environmentally friendly process. In HIsmelt, a reasonable inner shape of a smelting reduction vessel has an important influence on combustion and heat transfer through changing flow field. Therefore, in this study, the effects of HIsmelt reactor parameters including oxygen-lance insert depth, and smelting reduction vessel body height and throat angle on combustion and heat transfer are investigated through the numerical simulation of the flow field, temperature field, and CO2 concentration field inside smelting reduction vessel. The results show that the heat transfer effect is further improved when increasing the oxygen-lance insert depth because the U-shaped vortex affects a wider area. In addition, as the smelting reduction vessel body height increases and the throat angle decreases, the U-shaped vortex gradually moves away from the melt pool and increases the scouring of the sidewalls. The increased temperature difference and low CO2 concentration indicate that this change reduces the combustion and heat transfer efficiency.

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.

Reduction-Sulfurization Smelting Process of Waste Hydrogenation Catalysts, Automotive Exhaust Purifier Waste Catalysts, and Laterite Nickel Ore.

Reduction-sulfurization smelting is an effective method for treating solid hazardous waste and recovering valuable components from them. In this work, a waste hydrogenation catalyst (WHC), an automotive exhaust purifier waste catalyst (AEPWC), a vulcanizer, and laterite nickel ore were mixed, and the reduction smelting behavior of this solid waste was investigated. XRD (X-ray diffractometry), TG-DSC (thermogravimetric/differential scanning calorimetry), SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy), OM (optical microscopy), and ICP-OES (inductively coupled plasma-optical emission spectrometry) methods were used to examine the chemical composition, thermal stability, structure, and morphology, as well as the metal content of the samples. Under the Al2O3-FeO-SiO2 ternary slag system, at a smelting temperature of 1450 °C, smelting time of 2 h, mass ratio of coke, pyrite, and CaO to waste catalysts of 16, 25, and 0%, respectively, nickel (Ni) and molybdenum (Mo) recovery reached 91.1 and 92.9%, respectively, where average PGMs (platinum group metals, platinum (Pt), palladium (Pd), rhodium (Rh)) recovery reached 96%, although vanadium (V) recovery was only 25.1%. The characterization of the slag shows that Al, Si, and Fe are mainly bound in the form of chemical compounds, while V is intercalated with ferro- or aluminosilicate, which hinders the reduction and sulfurization of V. A series of tests using reduction smelting without sulfurization were also conducted, after which the Ni, Mo, and V recovery reached 96.8, 96.6, and 89.7%, respectively, while PGMs (Pt, Pd, Rh) recovery ranges from 90.2 to 98.0%. The collaborative disposal of primary ore and multisource solid waste has been achieved through two process paths: reducing smelting and reducing sulfurization smelting, which provide reference for the collaborative smelting of multisource secondary resources.

An Analysis of Long-Process Ironmaking in a Reduction Smelting Furnace with Hydrogen-Enriched Conditions

The blast furnace and basic oxygen furnace (BF-BOF) is still the main process used for the production of iron and steel in China. With the approach of the “dual carbon” target, the iron and steel industry needs to transform and upgrade to “green” and “low-carbon” practices. At present, the low-carbon hydrogen metallurgy technology route based on hydrogen instead of carbon is mainly adopted at home and abroad, and the domestic route is mainly based on oxygen-rich BFs and hydrogen-based shaft furnaces (SFs). It promotes the transformation of the traditional BF to hydrogen-rich, oxygen-rich, and carbon-recycled (Hy-O-CR) technology. A new ironmaking system and method for a reduction smelting furnace (RSF) with Hy-O-CR is presented in this paper. The ironmaking system includes nine sets of equipment, such as an RSF, gas dust collector, dryer, CO2 separator, electrolytic water device, blower, heat exchanger, storage tank of reduction gas, and chimney. From top to bottom, the RSF includes an indirect reduction zone, a soft melting dripping zone, and a coke combustion zone. The ironmaking methods include coke and ore mixed charging, injection of the mixed reduction gas composed of electrolytic green hydrogen and circulating gas from the furnace gas into the indirect reduction zone, injection of oxygen into the coke combustion zone, CO2 recovery of the furnace top gas, and slag and iron treatment. By redesigning the size of the furnace type and optimizing the parameters, the metallization rate of the indirect reduction zone can be as high as 85–95%, and the carbon consumption per ton of hot metal can be greatly reduced. By using oxygen to recycle the reduction gas produced by its reactor, the process achieves the goal of reducing CO2 emissions by more than 50%, thus realizing green and low-carbon metallurgy.

Thermodynamic assessment of tin-smelting from cassiterite concentrates

ABSTRACT Tin is a critical and rare metal produced via carbothermic reduction smelting of upgraded concentrates in two steps, primary and secondary reduction. There is limited literature available on cassiterite smelting and the thermodynamic behaviour of Sn during primary and secondary reduction processes. The present work performs a systematic assessment/optimisation of smelting parameters of a simplified cassiterite concentrate for the first time. This assessment was carried out with the aid of thermochemical analysis. The effect of process variables including reduction extent, temperature, and flux addition on the outputs of the primary and secondary reduction steps was studied. The effects of temperature and slag composition on slag liquidus temperature and viscosity were determined. The effect of recycling the process byproduct, the hard head (HH), on operational parameters and outcomes, especially Sn recovery, was also investigated, and a series of optimum process conditions was proposed.

How much hydrogen is in green steel?

Hydrogen-based reduction of iron ores is the key technology for future sustainable ironmaking, to mitigate the CO2 burden from the steel industry, accounting for ~7–8% of all global emissions. However, using hydrogen as a reductant prompts concerns about hydrogen embrittlement in steel products. This raises the question of how much hydrogen remains from green ironmaking in the metal produced. We answer this question here by quantifying the amount of hydrogen in iron produced via two hydrogen-based ironmaking processes, namely, direct reduction and plasma smelting reduction. Results suggest no threat of hydrogen embrittlement resulting from using hydrogen in green steel production.

Development of the Recycling of Alloyed Metallurgical Waste: Features of Phase and Structural Transformations

The features of structural and phase transformations during the processing of alloyed metallurgical wastes using reduction smelting are determined herein. This is necessary in order to determine the technological parameters of the melting process that ensure the reduction in the losses of alloying components. The use of X-ray phase analysis in combination with the methods of raster electron microscopy and X-ray microanalysis ensured the identification of the microstructure features and the chemical composition of individual phases and inclusions in the metal. Our study identified new technological aspects of high-alloyed technogenic waste processing using reduction smelting. The obtained parameters of the resource-saving alloying compound provide the possibility to replace parts of the standard ferroalloys in steelmaking processes.

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.

Antimony and arsenic substance flow analysis in antimony pyrometallurgical process

Substance flow analysis was applied to an antimony pyrometallurgical system. By taking antimony and arsenic as the objective elements, the mass balance and substance flow charts based on the production system were established, and evaluating indicators such as the direct recovery rate, waste recovery rate, and resource efficiency were set up. The results show that the resource efficiency of antimony is 89.21%, and the recovery rates of antimony in volatilization smelting, reduction smelting, and refining are 78.79%, 91.00%, 96.06%, respectively. At the same time, for 1 t of antimony produced, 11.94 kg of arsenic is carried into the smelting system. Arsenic is a major impurity element in the smelting process. The distribution behavior of arsenic in the main process was analyzed. Based on the substance flow analysis, some recommendations for improving the resource efficiency of antimony and cleaner production were proposed.

Analysing the HIsmelt process for smelting vanadium–titanium magnetite

ABSTRACT In response to the problem of rich vanadium–titanium magnetite (VTM) resources in China contrasting with low blast furnace utilization, a HIsmelt process for smelting VTM is proposed. The influence of the process parameters on smelting reduction is analysed under laboratory conditions by simulating smelting reduction. The results show that extending the reaction time reduces the FeO content in the slag by 15.34 wt-%, increasing the reaction temperature reduces the FeO content in the slag by 26.38 wt-%, and increasing the basicity reduces the FeO content in the slag by 11.26 wt-%. The control temperature for smelting VTM using the HIsmelt process is 1425°C, with a reduction time of 20–30 min, which is conducive to the transfer of vanadium to the molten iron and the enrichment of titanium in the slag. To ensure vanadium and titanium are efficiently utilized, a basicity control of 0.8 is appropriate.

Ferrum extraction in cast iron via reduction smelting of red mud

Ferrum extraction in cast iron via reduction smelting of red mud

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.

Studies of the thermal stability of briquettes based on microsilica

The object of study in this work is microsilica. Microsilica is a pulverized technogenic waste generated during the smelting of technical silicon in industries. The intended use of this material is to obtain the highest quality grades of technical silicon in the end result without the use of expensive quartz. Microsilica is a finely dispersed powder, the direct processing (without preliminary preparation) of which into technical silicon is impossible in ore-thermal furnaces. That requires the manufacture of high-strength briquettes based on it, meeting all the requirements for raw materials for ore-thermal furnaces. In this paper, the authors present the results of a study of the thermal stability of microsilica-based briquettes in order to optimize the physicochemical properties of the resulting briquettes. The tested microsilica briquettes with various carbonaceous reducing agents (screenings of coke of thermo-oxidative coking, screenings of charcoal, etc.) were obtained on a large-scale laboratory roller briquetting press ZZXM-4. The evaluation of the thermal stability of the briquettes was carried out according to the method in which the resulting briquettes are subjected to thermal shock followed by abrasion on a special drum. The thermal resistance of a briquette is defined as the ratio of the weight of the main body of the briquette after the abrasion test to the sum of the weight of the main body and the crumbled material. The dependence of thermal stability on the granulometric composition of briquettes was also determined. The optimal granulometric composition was determined, with which the briquettes have satisfactory thermal stability. Thus, the most technologically advanced granulometric composition of the briquetting charge for reduction smelting in an ore-thermal furnace was established. It is best to use briquettes with granulometric compositions of the appropriate ratio of fractions 0-1; 1-3; 3-5 mm with the following proportions 35/35/30 and 60/20/15, as well as briquettes with particle size distribution within these ranges of variation.

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.

An approach of cobalt recovery from waste copper converter slags using pig iron as capturing agent and simultaneous recovery of copper and tin

Massive amounts of waste copper converter slags have been produced from pyrometallurgical extraction of copper from copper concentrates, and the disposal of them in landfills creates serious environmental problems. However, this converter slag contains numerous valuable heavy metals, including copper, cobalt and tin etc. In this research, due to similar properties of iron and cobalt, pig iron with a low melting point was creatively used as capturing agent for cobalt recycling in a smelting reduction. The recovery of copper and tin was also studied. The phase transformation during reduction process was clarified by X-ray diffraction and Scanning electron microscope-energy dispersive spectrometer analyses. After the reduction performed at 1250 °C, the copper, cobalt and tin were recovered in a copper-cobalt-tin-iron alloy. The addition of pig iron improved cobalt yield, which was ascribed to the enrichment of cobalt in an iron–cobalt alloy phase. This decreased activity of the reduced cobalt and promoted reduction of cobalt oxide. As a result, the cobalt yield had a significant increase from 66.2% to 90.1% by adding 2% pig iron. Similarly, the copper also accelerated tin recovery through the formation of a copper–tin alloy. The copper and tin yields reached 94.4% and 95.0%, respectively. This work provided a high efficiency method to recover copper, cobalt and tin from waste copper converter slags.

Relation between Viscosity and Conductivity of CaO-MgO-FeO-Al2O3-SiO2 System for Copper Smelting Slags

The viscosity and conductivity of the smelting slag of copper oxide concentrate are important for reducing the operating temperature. In this study, seven slag samples were prepared by the reductive smelting of copper oxide concentrate with different ferrous oxide contents. The viscosity and conductivity data of these CaO-MgO-FeO-Al2O3-SiO2 samples were measured in the temperature range of 1290~1410 °C. Based on the structural features of aluminosilicate melts, the change and dependency relationships of their viscosity and conductivity were analyzed. The results show that there is a strong tendency to form orthosilicate even when the slag composition is acidic. The formation of fayalite would allow more Al3+ to form pyroxene with the six-coordinated structure. As a result, the polymerization degree and viscosity of the melt will be reduced. The [AlO]45− as a network former will reduce the bonding strength of the structural units, thus reducing the slag viscosity at high temperature. In the experimental range, the logarithm of viscosity of each slag sample has a good linear relationship with its logarithm of conductivity. However, there is no uniform linear equation for these complex slags with wide composition variations. These results have potential guiding significance for the copper smelting process.

Investigating the leaching performance of ferric chloride solution for metallic alloys resulting from reduction smelting of spent lithium-ion batteries

Smelting reduction of spent lithium-ion batteries (LIBs) produces metallic alloys containing Co, Ni, Cu, Mn, and Fe. Finding suitable reagents in terms of efficiency, economics, and friendly environment for the dissolution of these metals from the alloys is very important for the recovery process of the metals. In this work, the employment of ferric chloride solution for the dissolution of the metals from the alloys was studied. The effect of parameters like FeCl3 concentration, temperature, time, and pulp density on the leaching efficiency of metals was investigated. Our results indicate that ferric ions in the leaching solutions act as oxidizing agents for the dissolution of the metals, while chloride anions as ligands for the formation of the complexes of the dissolved metal ions. The best conditions for the dissolution of full metals were 0.7 mol/L FeCl3, 12.5 g/L pulp density, 22oC, and 30 min. In comparison with HCl or H2SO4 leaching agents, ferric chloride shows some advantages like a decrease in the dosage of acids and oxidizing agents, fast reaction kinetics, and low energy consumption. With its advantages, ferric chloride solution is considered a potential leaching agent in the recovery process of valuable metals from spent LIBs.

Extraction and Recovery of Critical Metals from Electronic Waste Using ISASMELT™ Technology

Electronic goods are a major consumer of many critical metals, including copper, nickel, tin, zinc, lead, and precious metals. The processing of end-of-life electronic equipment (E-Scrap) is becoming increasingly important to maintain the supply of the critical metals required globally, and to reduce environmental pollution. Currently, the dominant route for E-Scrap processing is pyrometallurgical processing, with the first stage of processing being reductive smelting to produce a black copper and a ‘clean’ discard slag. The management of the slag in this first step is central to the success of the E-Scrap recycling process. The E-Scrap ISASMELT™ furnace has a highly turbulent bath, providing conditions that generate high rates of zinc fuming and allow a wide range of operable slag conditions. This enables efficient E-Scrap smelting to occur, whilst overcoming the challenges associated with alternative technologies. Operable slag compositions and high zinc fuming are heavily influenced by kinetic processes, with piloting critical to understanding the performance of this process. ISASMELT™ pilot tests were performed, with a wide range of fluxing targets tested to confirm these benefits. The testing demonstrated that high levels of zinc fuming (>80%) are obtained in the E-Scrap ISASMELT™ furnace, decreasing the iron and silica flux additions required to manage the detrimental viscosity effects of zinc in the slag. In addition, it was demonstrated that slags containing high concentrations of alumina (>10 wt%) are operable in an ISASMELT™ furnace. The ISASMELT™ technology was demonstrated to be the only E-Scrap furnace technology able to produce a ‘clean’ discard slag with low concentrations of zinc and minimal fluxing requirements.

Study on Mechanism of Titanium Slag Smelting in DC electric Arc Furnace

Based on the production practice of a 30MWA large DC electric furnace in Yunnan, this paper discusses the basic reactions in smelting titanium slag, and discusses the thermodynamic and kinetic behaviors of the main elements and impurities. The results show that the reduction reaction in the smelting process is carried out simultaneously in the multi-component system of Al2O3-CaO-MgO-SiO2-TiO2. The titanium slag containing more than 80% TiO2 can be obtained by enrichment smelting of ilmenite in a large high-power enclosed direct current electric arc furnace, and the output includes by-product pig iron. Impurities MgO, CaO and Al2O3 in titanium concentrate will not be reduced during reduction smelting; SiO2, MnO and V2O5 will be reduced in varying degrees, and the reduced products Si, Mn and V will dissolve in the metal Fe phase or be enriched in titanium slag.