Reduction Of Slag Research Articles

Study of Li2O reduction in mould slag for continuous casting of low-carbon steel slab

The addition of Li2O increases production costs for continuous casting, despite its enhancement of the melting and flow properties of mould slag. Initially, laboratory research focused on assessing the individual impacts of Li2O, F, Na2O and Al2O3 on the viscosity and melting temperature of the slag, using a basicity of 0.95. Subsequently, four stages of industrial testing were conducted to optimise the slag, evaluating parameters such as temperature and friction force curves of the mould copper plate thermocouple, steel slag consumption per ton and strand surface quality. The optimised slag achieved a basicity of 0.98, a viscosity of 0.29 Pa·s and a melting temperature of 1115 °C, meeting all performance requirements for low-carbon steel mould slag. Compared to the original flux, the mass percentage of Li2O decreased significantly from 1.54 to 0 wt-%, while Na2O increased from 2.36 to 7.35 wt-%, and Al2O3 decreased from 7.28 to 3.49 wt-%. The operation of the optimised flux remained stable, with smooth fluctuations observed in the mould copper plate thermocouple temperature and friction force curves. These research findings hold significant reference and practical value for further development and application.

Physicochemical properties of CO2-cured belite-rich cement with electric arc furnace reduction slag as a partial replacement

This study investigates the physicochemical properties of CO2-cured belite-rich cement with electric arc furnace (EAF) reduction slag as a partial replacement at varying weight percentages (0 to 20%). The results revealed that water-cured specimens (WRS) showed significant increases in the numbers of gel and medium capillary pores, while carbonation-cured specimens (CRS) demonstrated increases in the numbers of large capillary and macro pores. Moreover, up to 10% replacement of the slag led to a decrease in the compressive strength, accompanied by increased CO2 absorption and reduced alkalinity. When the EAF reduction slag content increased from 15% to 20%, CRS exhibited a trend reversal in the compressive strength, marked by an increase in the pH, approaching compressive strength comparable to those of WRS. This signified that higher percentages of EAF reduction slag are advantageous for enhancing CO2 sequestration due to the potential reactivity of magnesium oxide in EAF reduction slag with CO2.

Extraction of Rare Earth and CaF2 from Rare Earth Calcium Thermal Reduction Slag by Using CaO Roasting–Acid Leaching Method

The rare earth calcium thermal reduction slag (RCS) generated during the production of heavy rare earth metal contains large amounts of rare earth and fluoride compounds. In this study, rare earth elements (REEs) and fluorine in the RCS were recovered by the CaO roasting–hydrochloric acid leaching method. Firstly, the thermodynamic feasibility of converting rare earth fluoride to rare earth oxides through CaO roasting was demonstrated. The influence of roasting conditions and leaching conditions on the leaching rate of the REEs was investigated. Optimal results, a 95.48% leaching rate of the REEs, were obtained under the following conditions: a CaO dosage of 15%, a roasting temperature of 1000 °C, and a roasting duration of 90 min. XRD, SEM, and EDS results revealed that during the calcination process, the REEs present in fluorite (CaF2) in isomorphic form were transformed into acid-soluble rare earth oxides; furthermore, the rare earth metallic in the RCS remained unchanged even after roasting. In the leaching process, rare earth metals and rare earth oxides are efficiently extracted, while CaF2 rarely dissolves. The leaching slag contained 97.31% CaF2 with a F recovery of 96.92%. The kinetics of the rare earth leaching process was analyzed, and the results show that the three-dimensional diffusion control at the phase interface of the kinetic model best fits the process. The calculated apparent activation energy for the leaching rate of REEs is 20.869 kJ/mol. Therefore, efficient comprehensive recovery of rare earth and fluorite from RCS can be achieved by using the CaO roasting–hydrochloric acid leaching method.

High-value terminal treatment: Utilizing copper slag heat in the manufacture of copper-containing weathering steel

Copper slag, a bulk non-ferrous solid waste, is critical in establishing a closed-loop cycle in the copper metallurgy industry. Currently, the processing techniques for copper slag are characterized by prolonged procedures, secondary waste discharge, limited value utilization, and high energy consumption. A novel approach was proposed to harness the thermal energy inherent in molten copper slag for producing copper-bearing weathering steel and cement while simultaneously synergistically recovering lead and zinc. The results indicate that under the conditions of smelting temperature of 1500 °C, alkalinity of 1.06, smelting time of 60 min, and mechanical stirring, the recovery rates of copper, iron, lead, and zinc in copper slag reached 98.83%, 99.59%, 97.45%, and 98.51%, respectively. Furthermore, the feasibility of this approach was validated by laboratory-scale preparation of Q355GNH-grade copper-bearing weathering steel and S95-grade cement clinker. Computational analysis for the direct carbothermal reduction of molten copper slag in its thermal state reveals that, compared to the traditional flotation process, this approach saved 1177 MJ of thermal energy per metric ton of copper slag, equivalent to a reduction of 147 kg of carbon dioxide emissions. This study facilitates the zero-waste, high-value, and sustainable development of the copper smelting industry.

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.

Pyrometallurgical Reduction of Copper Slag with Biochar for Metal Recovery

Large amounts of slag are generated during pyrometallurgical processing in copper production. Due to the presence of valuable elements, the improper disposal of huge quantities of copper slag produced, results in significant loss of resources as well as environmental issues. Analyses of the copper slag show that it contains valuable metals, particularly copper and nickel. In this work, four biochars were employed as fossil-free reducing agents to recover valuable metals from the slag. Reduction experiments were performed in a vertical furnace at temperatures 1250, 1300 and 1350 °C for 60 min in order to investigate the effect of temperature. Moreover, the effect of time on reduction progress was studied at 1250 °C and the concentrations of CO and CO2 in the off-gas were measured with a gas analyzer. Copper slag was reacted with metallurgical coke for comparison and the products were analyzed with EPMA and LA-ICPMS. The results revealed that reduction rapidly progresses to the formation of metal alloy within 10 min. Valuable metals like copper, nickel and arsenic were the first to be reduced to the metal phase. As reduction time increased, iron was also reduced and combined with the metal droplet. The use of biochar as reductant was shown to be more effective than coke especially at lower temperatures. In addition, thermodynamic modelling was performed with FactSage and HSC and compared with the experimental results. The simulations with HSC showed the sequence of reactions taking place and the calculations by FactSage were in agreement with the experiments.Graphical

Reduction of Copper Smelting Slag by Carbon for Smelting Cu-Fe Alloy

Reduction of Copper Smelting Slag by Carbon for Smelting Cu-Fe Alloy

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.

High Temperature Corrosion Resistant and Anti-slagging Coatings for Boilers: A Review

AbstractHigh temperature corrosion and slag deposition significantly reduce the thermal efficiency and lifespan of biomass-fired boilers. Surface modification with protective coatings can enhance boiler performance and prevent commercial losses due to maintenance and damage. This review focuses on the development of corrosion-resistant coatings (CRCs) and anti-slagging coatings (ASCs) over the past decade. CRCs are explored through thermal spray processes that include arc spray, atmospheric plasma spray (APS), high-velocity oxygen fuel (HVOF), detonation gun (D-gun™), and cold spray. Studies on alloys, ceramics, and ceramic–metal composites are summarised, highlighting the high temperature corrosion prevention mechanisms and discussing new coating materials. ASCs are reviewed in the context of advancements via thermal spray and slurry spray methods. The mechanisms for slag reduction, testing methods to evaluate ASC effectiveness, and the necessary architecture for preventing slag deposition are examined. A lab-based rig simulating fly ash deposition onto water-cooled coating coupons for anti-slagging investigations is also presented. Further research is needed to develop and evaluate materials for ASCs effectively. Graphical Abstract

Engineering properties as a supplement cementitious material of ground copper reduction slag extracted valuable metal from Cu slag

We have examined whether the copper reduction slag (CRS) generated after recovering valuable metals from copper slag (CS) by reduction process can be used as supplementary cementitious materials (SCMs). According to the test results, the Cu secondary slag with low Fe, Cu, and heavy metal contents had a suitable oxide composition for using as a SCM. CRS showed better grinding efficiency than that of ground blast furnace slag (GGBS). Ground CRS contributed to the formation of tobermorite under autoclaved curing conditions. The compressive strength of CRS mortar replacing 50 % of OPC generated 93 % of that of the OPC mortar. Based on the results of this study, we found that the CRS has highly appropriate engineering characteristics for using as SCMs for concrete. In addition, it is judged that the method of using secondary slag as a material for precast concrete produced under hydrothermal conditions can greatly contribute to the construction process of buildings by securing mechanical performance.

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.

Investigation of Direct Reduction of Copper Slag Using Castor Oil as a Green Reductant: Metal Recovery, Reduction Characterization and Kinetic Analysis

Investigation of Direct Reduction of Copper Slag Using Castor Oil as a Green Reductant: Metal Recovery, Reduction Characterization and Kinetic Analysis

Microstructure evolution, mechanical characteristics and erosion behavior of Cr2O3–Al2O3–MgO–ZrO2 refractories in molten reduction slag

In order to overcome the serious corrosion problem of furnace hearth refractory materials for smelting reduction ironmaking, the Cr2O3–Al2O3–MgO–ZrO2 refractories were synthesized, and the phase component, microstructure, mechanical characteristics, and slag erosion behavior of composite refractories were investigated and evaluated. The results indicate that the composite refractories mainly consist of Mg(Al, Cr)2O4 spinel phase, (Al, Cr)2O3 solid solution and ZrO2. The content of Mg (Al, Cr)2O4 spinel significantly increases with the increasing MgO content, while the content of (Al, Cr)2O3 obviously decreases. Furthermore, the comprehensive mechanical properties of the MgO modified composite refractories can be obviously enhanced by increasing the MgO content, and sample S4 presents the best mechanical characteristics when the MgO addition is 10 wt%. The corresponding hardness, compressive strength and bending strength are 14.22 GPa, 267.14 MPa and 80.0 MPa, respectively. This is mainly because the formation of Mg(Al, Cr)2O4 significantly improves the densification of composite refractories, and a large number of high-strength Mg (Al, Cr)2O4 spinel “bridge” formed between the large-sized (Al, Cr)2O3 grains. The erosion test results indicate that increasing the MgO content can significantly improve the slag infiltration resistance of composite refractories, because the formation of Mg (Al, Cr)2O4 spinel layer significantly improves the densification of MgO reinforced composite refractories. Although the slag corrosion resistance of Mg(Al, Cr)2O4 is lower than that of (Al, Cr)2O3, the Cr2O3–Al2O3–MgO–ZrO2 refractories still presents good erosion resistance, permeability resistance, and excellent mechanical characteristics.

Computational Fluid Dynamics Numerical Simulation on Flow Behavior of Molten Slag–Metal Mixture over a Spinning Cup

Centrifugal granulation technology using a spinning cup opens a potential way to recycle steel slag that is currently difficult to reuse. The objective of this research was to study the flow characteristics of a molten slag–metal mixture that was produced during smelting reduction in molten steel slag, passing over a spinning cup, so as to explore the feasibility of using centrifugal granulation technology to treat the steel slag. This was achieved by developing and implementing a computational fluid dynamics (CFD) model that incorporated free-surface multiphase flow to predict the thickness of the liquid slag film at the edge of the spinning cup (slag film thickness for short), which was an important parameter for estimating the size of the slag particles resulting from centrifugal granulation of the molten slag–metal mixture. The influences of various relevant parameters, including spinning cup diameter, slag feeding rate, cup spinning speed, etc., on the slag film thickness were analyzed. Additionally, hot experiments on centrifugal granulation of a molten slag–metal mixture were conducted to verify the results of the numerical simulations. The experimental results indicated a progressive reduction in the Sauter mean diameter of the slag particles as the metallic iron content in the slag increased. Specifically, when the iron content rose from 5% to 15% at a cup spinning speed of 2500 RPM, the Sauter mean diameter decreased by 13.77%. The numerical simulation results showed that the slag film thickness had a positive relationship to the slag feeding rate but a negative relationship to the spinning cup diameter and the cup spinning speed. Furthermore, the ratio between the mean slag particle diameter and the slag film thickness decreased nearly linearly with the increase in the metallic iron content in slag, with the average ratio being approximately 4.25, and this relationship was useful for estimating the slag particle size from the slag film thickness. Therefore, the present research results can provide theoretical guidance for the industrial application of spinning cup centrifugal granulation technology to effectively treat and recycle steel slags.

Depletion of converter slags to waste in the Vanyukov furnace during pyrometallurgical copper production at JSC Almalyk MMC

The article shows the possibility of involving man-made formations in the pyrometallurgical production of copper in the form of slag and clinker-zinc production for the purpose of comprehensive extraction of non-ferrous and precious metals from them at Almalyk MMC JSC. Clinker, a technogenic waste from zinc production, contains a significant amount of reducing elements in the form of metallic iron and carbon, as well as gold in the amount of 2.3 g/t and silver 250 g/t. In research, clinker works as a reducer of magnetite contained in the converter slag during its depletion and in the process of depletion (reduction) of the converter slag, noble metals are extracted into matte, and then into blister copper up to 95-98%. Converter slags from copper production of Almalyk MMC JSC contain 2.0-3.5% copper, and they, as a circulating product, are depleted in a reverberatory furnace with copper extraction of 75%. To increase the yield of copper from converter slag in Vanyukov furnaces, it is necessary to first deplete the converter slag in reduction processes and then transfer it for processing. It was found that using clinker, a technogenic waste from zinc production with a particle size of +5 - -10 mm, the recovery of converter slag in a converter from magnetite to wustite using the developed technology in 10-15 minutes exceeded more than 50.0% (the amount of magnetite decreased from 21.9 % to 9.8%). As a result of processing recovered converter slags in the Vanyukov furnace, it was possible to reduce the copper content in converter slags of copper production from 2.2-3.5% to 0.58-0.72% in waste slag. To increase the yield of copper from converter slag in the reverberatory and Vanyukov furnaces, it is necessary to first deplete the converter slag in reduction processes and then transfer it for processing.

Carbothermic Reduction of Copper Slag in the Presence of Borax

ABSTRACT The low temperature carbothermic reduction of copper slag with charcoal in the presence of borax followed by leaching with H2SO4 was investigated in this study. The copper slag sample was characterized using the XRD. Thermogravimetry was used to study the thermal degradation processes of copper slag. The standard Gibbs free energy at each reaction temperature was calculated using the HSC Chemistry® software. In the reduction experiments, the effects of charcoal and borax, as well as the reduction temperature and time, were investigated in order to identify the mechanism of enhanced reduction. The degree of metal dissolution was investigated in the leaching experiments in relation to leaching time and acid concentration. According to the results of the mineralogical analysis, the primary phases in the copper slag were fayalite, and magnetite. The HSC Chemistry results on equilibrium phase composition show that the carbothermic reduction of magnetite at various temperatures proceeded stepwise as Fe3O4 → FeO → Fe. Meanwhile, fayalite was first catalyzed at low temperature of 300°C before being reduced to metallic phase at 545oC. Thermochemical calculations, phase characterization and experimental results demonstrate that using borax in carbothermic reduction can accelerate phase transformation, lower the temperature of fayalite reduction, and improve the extraction of Co, Cu, and Fe at 850°C.

Study on Resourceful Treatment and Carbon Reduction Intensity of Metro Shield Slag: An Example of a Tunnel Interval of Shenzhen Line 13

At present, the scale of subway construction in Chinese cities has reached a new height, and the shield slag produced by it has also surged year by year. Untreated subway shield slag not only occupies the space resources of the country, but also carries CO2, which causes negative impacts on the environment and which, as a result, is not conducive to the realization of the goal of the national “double-carbon” strategy. Therefore, how to effectively manage the shield slag produced by subway construction has become a scientific problem that needs to be solved urgently. In order to scientifically dispose of metro shield slag and quantify the carbon reduction intensity of its disposal, based on the new shield slag integrated recycling technology, and taking a tunnel interval of Shenzhen Line 13 as an example, this study systematically sorted out the shield slag disposal process, clarified the management path of the on-site resource utilization of slag, and quantitatively compared the carbon emissions before and after the treatment as well as carbon reduction intensity. The results show that the on-site disposal process is basically feasible, and that, it is possible to achieve a shield structure slag reduction of resource products and mud cake water content of less than 40% of the target, in the case of 160,000 m3 of shield structure slag resource utilization after a total carbon reduction of about 4240.13 t CO2, of which each preparation of 1 m3 of recycled bricks can bring about a benefit of carbon reduction of 240.09 kg CO2. Compared with the conventional mud head truck slag disposal, shield structure slag resource utilization can save a utilization cost of about 10.4 million yuan, meaning that, in terms of economic and social levels, this method can achieve good benefits. This case verifies the feasibility of the new technology, and the results of the study can provide experience for other metro projects’ shield slag resource utilization, and provide stakeholders with a shield slag recycling management strategy for government departments to scientifically formulate metro shield slag management policy to provide data support.

A Crucial Step Toward Carbon Neutrality in Pyrometallurgical Reduction of Nickel Slag

This study aims at recovering valuable metals from nickel slag by employing pyrometallurgical techniques. A large amount of slag is generated during the nickel matte smelting. Nickel slag contains valuable elements such as copper, nickel, and cobalt, which can be recovered. Disposal of this slag results in loss of resources and may cause pollution of the environment. It is important to retrieve these metals for environmental and economic reasons. In this study, the slag was reacted with non-fossil reducing agents (biochar) which were produced from hydrolysis lignin and black pellet biomass by pyrolysis at 600 and 1200 °C, and with metallurgical coke for comparison. The reduction experiments were done at 1400 °C for 15, 30, and 60 min under inert gas atmosphere. The samples were quickly quenched and analyzed with Electron Probe X-ray Microanalysis. The results showed that the use of biochar resulted in faster reaction kinetics in the reduction process compared to coke. Moreover, thermodynamic modeling was also performed using Factsage to simulate equilibria with different amounts of biochar. The metal-to-slag distribution coefficient calculated from the results of thermodynamic modeling was consistent with experimental results.Graphical

Reduction and reconstruction of vanadium-containing steel slag at high temperature

The effective recovery of metallic iron and vanadium from steel slag and ensuring the gelling properties of the residual slag after metal separation are crucial for their high-value-added utilisation. In this study, we established suitable process conditions for high-temperature reduction and reconstruction using the Si/Al ratio as an adjustment parameter and employing rice husk ash, SiO2, and Al2O3 as the adjustment materials. The influence of the reconstructed steel slag composition and structure on the iron reduction rate and vanadium migration was investigated. Additionally, we tested the compressive strength of the cement slurry at different times to compare the gelling performance of the tailings after iron reduction from the Vanadium-containing steel slag.The results showed that the high-temperature reduction method effectively reduced metallic iron and vanadium in the steel slag. The iron reduction rate reached as high as 98.53%, and inert components such as the CaO-FeO-MgO-MnO solid solution (RO) phase, C2F, and Fe3O4 in the original steel slag could be effectively reconstructed to form a glass-phase structure with certain gelling properties. Moreover, the content of the glass phase remained stable above 90%. For the same temperature, the liquid viscosity of the reconstructed steel slag increased, and after cooling, the glass-phase content decreased with decreasing Si/Al ratio. This resulted in an increase in the amount of crystalline-phase minerals such as Ca3Mg(SiO4)2, Ca2Al2SiO7, and C2S. The iron reduction rate generally exhibited a downward trend, and the change in the vanadium content was consistent with the iron reduction rate. Following the reduction and reconstruction of iron separation, the gelling properties of the vanadium-containing steel slag improved, with a 28-day strength that was 64.26% higher than that of the original steel slag.

Application of Sunflower Husk Pellet as a Reducer in Metallurgical Processes.

In relation to the climate policy being introduced, the search for a replacement for solid fossil fuels with renewable raw materials is ongoing. In this study, a potential biomass (sunflower husk pellet) application in the process of copper slag reduction was assessed. For the purpose of raw material characterisation, thermogravimetric tests were carried out and characteristic temperature points were determined with the use of a high-temperature microscope. The slag reduction tests led to the recovery of 97% of copper and a decrease in this metal content in the slag to less than 0.5% Cu, which enables safe storage or use in other industrial branches.