Reduction Smelting Research Articles

Kinetic Analysis of Molten Oxide Reduction Using Bottom-Blown Hydrogen Injection

Hydrogen-based smelting reduction has received widespread attention as an important technology for realizing low-carbon development in hydrogen metallurgy. In this study, the thermodynamics of smelting reduction was firstly analyzed by using FactSage 8.1 thermodynamic software, on the basis of which smelting reduction experiments of iron oxides by using bottom-blown hydrogen were carried out. The experiments used oxidized pellets as experimental materials, and the effects of the reduction process were analyzed in terms of the reduction temperature, the reduction time, and the hydrogen flow rate. The experimental results show that under the experimental conditions of a temperature of 1550 °C and a hydrogen flow rate of 0.2 Nm3/h, the reduction rate of iron oxides in the process of reducing iron oxides by hydrogen is significantly faster in the first 10 min than after 10 min. The hydrogen utilization rate reached a maximum of 41.87%, then decreased continuously and finally maintained at about 20%. Using the method of model fitting, it was found that the hydrogen-based molten reduction conformed to the phase boundary reaction model (Gα=1−(1−α)1/2), the corresponding mechanism function is fα=2(1−α)1/2, where α stands for the reduction conversion, and the reaction rate constant k(T) is 2.37 × 10−4 s−1 under the experimental conditions.

Vanadium extraction from vanadinite and high carbon v-bearing stone coal by coupling reduction smelting and oxalic acid hydrothermal leaching

Vanadinite and high-carbon vanadium-bearing (V-bearing) stone coals are important vanadium sources widely used in vanadium extraction. The traditional sulfuric acid leaching method for extracting vanadium consumes a large amount of acid, wastes significant amounts of lead and carbon, and causes serious environmental pollution. This study discusses the integration of reduction smelting and oxalic acid hydrothermal leaching for processing vanadinite and high-carbon V-bearing stone coals. Specifically, high-carbon V-bearing stone coal is selectively added to vanadinite to produce coarse lead blocks and V-bearing slag during reduction smelting. Then, the oxalic acid hydrothermal leaching process is employed to extract vanadium from the V-bearing slag. This approach reduces the waste of lead and carbon resources and achieves co-extraction of vanadium from both V-bearing minerals. The results show that when the mass ratio of high-carbon V-bearing stone coal to vanadinite is 25%, and smelting is conducted at 1150°C for 15 min under argon protection, a separation efficiency of 90.67% for metallic lead and V-bearing slag is achieved, the grade of V2O5 in vanadium slag is 12.37%, and the recovery rate is 95.64% by ICP-OES analysis. Furthermore, the leaching rate of vanadium in the V-bearing slag can reach 85.34% via oxalic acid hydrothermal leaching under conditions of a leaching temperature of 100°C, a leaching duration of 30 min, an oxalic acid concentration of 25 wt%, a liquid-to-solid ratio of 10:1 mL/g, and a stirring speed of 500 rpm. The integration of reduction smelting and oxalic acid hydrothermal leaching offers benefits such as improved resource utilization, waste reduction, cost savings, and environmental enhancements. Thus, the findings of this research can serve as references for the vanadium extraction processes of related vanadium-containing minerals.

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.

Interface migration and alloying mechanism of Fe and P for ferrophosphorus alloy production during the carbothermic reduction of phosphorite

Ferrophosphorus (Fe–P alloy), a byproduct in the carbothermal reduction of phosphorite for yellow phosphorus production, has remarkable potential application as foundational precursors to prepare advanced catalysts and energy materials. However, the gas-solid-liquid equilibrium in the reduction smelting of phosphorite and hematite is intricate, and the reduction, volatilization, and alloying mechanisms of Fe and P at higher temperatures should be given close attention to optimize the production of yellow phosphorus vapor and Fe–P alloy. In this study, the reduction smelting behaviors of fluorapatite and hematite in the phosphorite ore were investigated. Carbothermic reduction reactions of Ca5(PO4)3F with and without Fe2O3 are calculated, establishing theoretical fundamentals. The phase and microstructure evolutions of Ca5(PO4)3F and Fe2O3 are researched. This work also emphasizes the interfacial element migration to clarify the reduction, volatilization, and alloying of Fe and P by considering the solid-solid interface of Ca5(PO4)3F–Fe2O3 and the gas-liquid interface of P2 vapor-metallic Fe.

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.

Smelting Reduction of HIsarna Slag with Methane

To study the smelting reduction behavior of methane in the HIsarna process, the isothermal reduction experiments of HIsarna slag with 6 wt% of FeO were conducted at the temperatures of 1450, 1475, and 1550 °C, using 5 vol% CH4‐Ar. The effect of the gas injection flow rate on the overall reduction rate was investigated in the range of 0.5–1.5 L min−1. The results confirm that the decomposed carbon black acts as the dominant reductant in the reduction process compared to hydrogen. Increased gas flow rate increases the reaction rate, while temperature shows no significant effect. The reduction process could be described by the JMAEK model: by fixing the gas flow rate at 1.0 L min−1 with different temperatures, the exponent n value is around 1.5, indicating FeO mass transfer is the limiting step since there are sufficient carbon blacks as nucleation sites. The reduction process follows the first‐order model controlled by the reactant concentration with the gas flow rate being at 0.5 L min−1 and in the second reaction stage of the gas flow rate at 1.5 L min−1. The determined activation energy for the methane reduction is 59.8 kJ mol−1.

Insight into the Extractive Metallurgy of Tin from Cassiterite.

This review details both the conventional and emerging methods of extracting tin from cassiterite. The emerging methods reviewed include sulphuric acid leaching of SnO, cooling crystallization of SnO, sulphide leaching, alkaline leaching, and dry chlorination. From these methods, the conventional approach (direct reduction smelting) stands out as the sole method that is suitable for industrial application, with none of the emerging ones being promising enough to be a contender. The thermodynamics involved in the hydrometallurgical extraction of tin from the mineral are also discussed. ΔGo values calculated at 25 °C for the reduction-dissolution of SnO2 using reducing gases revealed feasibility only when carbon monoxide was used. An indication of the possible species produced during the hydrolysis of the oxide of the metal (SnO2 and SnO) as a function of pH (ranging from -2 to 14 and 0 to 14 for SnO2 and SnO, respectively) was noted and highlighted to link a Pourbaix diagram generated from literature data. This diagram suggests that the solubility of SnO2 in both strongly acidic and alkaline media is possible, but with a small dissolution window in each. The purification and recovery routes of the various processing techniques were then envisaged.

Mineral phase reconstruction of Bayan Obo tailings by smelting reduction and crystallization control of molten slag containing niobium, rare earth and titanium

Niobium (Nb), rare earth elements (REEs), and titanium (Ti) in Bayan Obo tailings are dispersed across various fine mineral phases. To efficiently recover these valuable elements from Bayan Obo tailings, a novel processing method of complex multimetallic-associated ores, utilizing smelting reduction and crystallization control, is proposed and investigated in this study. First, by observing the crystallization behaviors of CaO-SiO2-La2O3-Nb2O5-TiO2 slag, we observed that Nb and La (lanthanum) were easily dissolved in the perovskite phase that was selected as the target phase for mineral phase reconstruction due to its good flotation characteristics. The effects of w(CaO)/w(SiO2) and the temperature control profile on the crystallization behaviors are discussed in detail. Based on the above investigation, a mineral phase reconstruction experiment performed on Bayan Obo tailings using smelting reduction and crystallization control was carried out. The results indicated that after carbothermic smelting reduction at 1,600 °C, the iron oxides in the tailings were selectively reduced to molten iron that could settle separately from the molten slag, while Nb, REEs, and Ti were enriched in the slag. After temperature-controlled crystallization of the molten slag, 94 % of the Nb and 63 % of the REEs precipitated in the perovskite, and this created a good mineral phase for the efficient flotation of Nb, REEs, and Ti. Finally, a novel processing method for Bayan Obo tailings is proposed after a feasibility analysis of reactor selection, product value, energy consumption, and eco-friendliness.

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.

Clean and efficient separation of Pb-Sb alloy by vacuum gasification - Fractional condensation

The Lead (Pb) - Antimony (Sb) alloy derived from Jamesonite (Pb4FeSb6S14) using the "Roasting - Reduction Smelting" method is typically isolated through a separation method known as "High Temperature Ash Blowing - Low Temperature Ash Blowing - Electrolytic Refining". However, the "Low Temperature Ash Blowing" separation method encounters several challenges, including elevated production pressure of refined Pb, significant emissions of smoke and dust, and suboptimal separation efficiency. This study utilizes the "Vacuum Gasification - Fractional Condensation" method as an alternative to the "Low Temperature Ash Blowing" method. The experimental findings demonstrate that by implementing specific optimal experimental conditions, such as a condensation temperature range of 904–1054K, a vacuum degree of 5Pa, a gasification temperature of 1173K, a holding time of 7h, and a height-diameter ratio of 0.27, condensates with Sb content exceeding 99.5 wt% can be procured, resulting in a direct Sb yield of 33 %. The remaining residues, with an Sb content ranging from 14 to 15 wt%, serves as a valuable input for the "Electrolytic Refining" process. This utilization significantly alleviates the burden on refined Pb production during the "Electrolytic Refining" process. The treatment procedure does not require the utilization of chemical reagents, and it generates no wastewater or exhaust gas.

Artificial Slags with Modulated Properties for Controlled Nickel Dissolution in Smelting Process

In pyrometallurgy process involving drying, calcination and reductive smelting steps, Saprolite ore is subjected in an electric arc furnace to produce Fe–Ni alloy and Ni matte. To optimize the nickel smelting step, the slag consisted of MgO–SiO2–FeO and having a lower viscosity and high fluidity is required. In this study, a number of new slag samples with varied degree of compositions are manufactured and used to examine the effect of their viscosity on nickel dissolution. Further correlation between the slag basicity and FeO addition on the smelting was also tested and simulated using Fe–Ni alloy from saprolite ore. As per the observations, the nickel dissolution increases with the increased content of FeO at a certain degree of activity which in turn can cause oxidation of nickel during the process. The slags with the ratio of MgO/SiO2 = 0.4–0.6, 30% fraction of FeO, and a viscosity of 1.8–1.06 poise in the olivine zone are found effective for the lowest dissolution rate of nickel with 0.021, 0.022, and 0.018 wt.%. The lowest dissolution rate is recorded for the slag with MgO/SiO2 ratio about 0.6. These slags with controlled amount of constituents could be used to recover precious metal from nickel smelter at a lower dissolution rate and thereby allowing to reduce the waste of the metal during smelting process.

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting.

Phosphogypsum produced from wet-processed phosphoric acid mainly consists of calcium sulfate dihydrate, which is an important sulfur resource. The traditional sulfuric acid and cement process based on phosphogypsum suffers from unstable cement quality owing to impurities such as phosphorus and fluorine and kiln ringing caused by the low-melting phase. This study investigated sulfur recovery and value-added utilization of liquid slag from high-silica phosphogypsum via carbothermal reduction smelting. A phosphogypsum ingredient (PGI) system was constructed by adding appropriate amounts of silica, alumina, magnesium oxides, and iron oxides to meet the production requirements of slag wool. Carbothermal reduction smelting experiments suggested that the temperature and C/S molar ratio significantly affected the desulfurization rate and phase structure of the slag. More than 97.44 wt % of sulfur could be recovered with a C/S molar ratio of 0.5-0.8 at 1300 °C or above in the molten state, and the molten slag was an amorphous magnesium-calcium-aluminosilicate. The PGI desulfurization mechanism is discussed based on the phase transformation and slag microstructure evolution.

Development and application of matte/speiss/metal thermodynamic database for optimization of processing of drosses, dusts and reverts from lead, zinc and copper production

Detrimental elements such as arsenic and antimony tend to accumulate in dusts and drosses of lead-zinc as well as copper smelters. These by-products are commonly treated in dedicated reductive smelting units producing Cu-rich matte, As-Sb-collecting speiss and Pb-rich metal, as well as liquid slag. Such process would have a complex distribution of elements (Cu, Fe, Pb, Zn, Ni, Sn, Sb, As, Ag, Au, S, etc.) among four liquid phases. Thermodynamic calculations can be used for predictions and optimization of such processes. They must rely on accurate models developed in integration with experimental program. Present study reports results of recent progress in experimental and modelling studies of As, Sb-containing speiss systems and demonstration of calculations relevant for industrial conditions. Experimental methodology consisted of equilibration, quenching and electron probe X-ray microanalysis. Calculations were performed using FactSage software and thermodynamic database developed based on the dedicated recent experiments. The main findings of the paper are: a set of binary and ternary diagrams relevant to matte and speiss formation conditions; distribution of Ag and Au among liquid Pb and speiss in key quaternary systems; and distributions of 10 main elements for industrially relevant matte/speiss/metal multicomponent equilibria.

Effect of high sulfate content on viscosity of recovery boiler molten smelt

A systematic study was conducted to examine the effect of high sulfate content on the freezing temperature of molten smelt and how this may contribute to the formation of viscous jellyroll smelt in recovery boilers. The results show that even for recovery boilers with a smelt reduction as low as 70%, the sulfate content in smelt has no or little effect on smelt freezing temperature, and hence, on molten smelt fluidity. The perceived adverse effect of high sulfate content on smelt fluidity and on jellyroll smelt formation comes from the high sulfate content in deposits that have fallen from the upper furnace. Fallen deposits may or may not form jellyroll smelt, depending on whether or not they can melt and be well-mixed with molten smelt by the time they reach the smelt spouts. It is not the high sulfate content in smelt resulting from the low smelt reduction efficiency that makes molten smelt viscous and forms jellyroll smelt, but rather, it is the incomplete melting of fallen deposits that results in one of the proposed mechanisms for jellyroll smelt formation.

Recovery of Iron and Alumina from Iron-Rich Bauxite, Red Mud, and Fly Ash by Reduction Smelting with Steel Slag

Recovery of Iron and Alumina from Iron-Rich Bauxite, Red Mud, and Fly Ash by Reduction Smelting with Steel Slag

Thermodynamics of Aluminothermic Processes for Ferrotitanium Alloy Production from Bauxite Residue and Ilmenite

Titanium oxide is a major component of bauxite residue (BR) with a high value, but it is often an unwanted element in common BR reuse options such as cement or iron production. Conventional carbothermic reduction smelting of BR produces a slag still containing a large amount of Ti. This study investigates an aluminothermic process for producing an FeTi alloy by combining BR, ilmenite ore, and fluxes. Based on thermodynamic calculations and batch experiments, the amounts of aluminum (reductant) and fluxes were investigated to achieve the optimum alloy production in parallel with a slag that could be further valorized in the cement industry. The mineralogical and chemical analysis of the metallic and slag phase agreed with the thermodynamic calculations. The results obtained by this study can lead to the development of a new process for the complete valorization of BR, paving the way for scaling up aluminothermic processes for producing ferroalloys from all iron-rich residues.

Development of an Integrated Process Flowsheet to Recover Valuable Metals from Waste Cathode Ray Tubes and Printed Circuit Boards

Electrical and electronic waste is considered a valuable stream of secondary metal resources because it contains metals such as copper, silver and gold. However, it is also classified as hazardous waste as it contains toxic heavy metals such as lead and cadmium. If electronic waste is not managed properly, the toxic metals may pose serious risks to the environment and human health, especially complex fractions such as printed circuit boards (PCBs) and cathode ray tubes (CRTs). The current study investigated a new process for the thermal treatment of CRTs and PCBs in an integrated flowsheet for metal recovery. Smelting tests were conducted to demonstrate that oxidative smelting of PCB concentrate and recycled CRT slag can produce a crude copper alloy with a grade of more than 95%. Another set of smelting tests was conducted to demonstrate that reductive smelting of CRT funnel glass and recycled PCB fume can produce a crude lead alloy with a grade of more than 95%. The investigations were undertaken in a pilot-scale top blown rotary converter (TBRC). The PCBs were smelted under mildly oxidising conditions at temperatures up to 1350 °C. The CRTs were smelted under mildly reducing conditions at temperatures up to 1250 °C. The study demonstrated that it is technically feasible to produce crude alloys of copper and lead from electronic waste, using an integrated process flowsheet.Graphical

A metallurgical technology investigation of the Wangxiangping ancient smelting sites at Daye County, Hubei Province

In the spring of 2022, the Beijing University of Science and Technology conducted an archaeometallurgical survey at the Wangxiangping site in Daye County. This exploratory excavation revealed pottery and metal smelting artifacts dating back to the Shang and Zhou dynasties. Charcoal samples from the third stratigraphic layer were carbon-dated to as early as the late Shang Dynasty. The SEM-EDS (Scanning Electron Microscopy-Energy Dispersive Spectroscopy) method was utilized for analyzing metallurgical artifacts across all stratigraphic layers at the site. The findings suggest that both pure copper smelting and tin bronze smelting activities were simultaneously conducted at this location. The analysis indicates that secondary copper oxide ore underwent reduction smelting, leading to the production of pure copper and high-grade matte. Additionally, tin ore was used in bronze production, with tin serving as an alloying element. However, no remnants from casting activities were identified during this survey. The investigation and subsequent analytical processes performed at this site provide substantial evidence supporting further research into copper smelting practices in Daye area during Shang and Zhou dynasties.

Bauxite Residue Valorisation through Reductive Smelting: Production of Inorganic Polymer Fire Resistant Building Materials

Bauxite Residue Valorisation through Reductive Smelting: Production of Inorganic Polymer Fire Resistant Building Materials

Bauxite Residue Valorisation through Reductive Smelting: Coproduction of Pig Iron and Precursor for Inorganic Polymer Fire Resistant Building Materials

Bauxite Residue Valorisation through Reductive Smelting: Coproduction of Pig Iron and Precursor for Inorganic Polymer Fire Resistant Building Materials