Slag Phase Research Articles

Development of Experimental Techniques for the Phase Equilibrium Study in the Pb-Fe-O-S-Si System Involving Gas, Slag, Matte, Lead Metal and Tridymite Phases

Present society challenges, including metal scarcity, recycling, and environmental restrictions, resulted in the increased complexity and variability of metallurgical feed streams. Metallurgical processes involving complex lead and copper-containing slag and matte phases are now commonly used in response. Optimization of existing and development of new metallurgical processes require fundamental information on slag–matte phase equilibrium. Development of the experimental methodology for the characterization of slag–matte phase equilibrium is presented in the paper. Following a detailed analysis of the potential reaction pathways, experimental techniques have been developed that enable accurate measurement of slag–matte phase equilibrium in the Pb-Fe-O-S-Si system. The application of the techniques has been demonstrated for two important sets of conditions: (i) Condensed phase equilibrium for the slag–matte–metal–tridymite subsystem; and (ii) Gas–slag–matte–tridymite equilibrium at fixed oxygen and sulfur partial pressures. The experimental methodology involves high-temperature equilibration of synthetic samples, fast quenching, and microanalysis of the compositions of phases using electron probe X-ray microanalysis (EPMA). The experimental results are not affected by the changes in the bulk composition of samples during equilibration; this helps to overcome the significant barriers previously encountered in undertaking accurate measurement and characterization of these systems.

Migration of fluorine during the reduction of copper slag from spent cathode carbon produces copper-iron alloys

Spent cathode carbon (SCC) is a hazardous solid waste discharged from the aluminium electrolysis industry that poses a serious environmental pollution risk. In this paper, the migration transformation route and distribution ratio of fluorine during the reduction of copper slag by SCC were investigated. The results show that fluorine accounts for 57.92% of the slag phase, and the main phase is CaF2, which accounts for 41.75% of the gas phase and 0.33% of the alloy phase when reduced at 1460 °C with 10 wt% SCC for 90 min. The recoveries of reduced Cu and Fe reached 94.42% and 40.32%, respectively. After reduction by metallization, the F− leaching toxicity in the leaching slag was 38 mg/L, which is far below the regulatory limit (100 mg/L). In the process of copper slag reduction by SCC metallization, the copper and iron in the slag were effectively recovered, thus realizing the resourceful and harmless utilization of SCC. This achieves the goal of “treating waste with waste” and significantly reduces the treatment cost of SCC.

Tuning of vanadium valence for value-added recycling and utilization of vanadium from spent Selective Catalytic Reduction Catalysts

Spent hazardous selective catalytic reduction (SCR) catalysts are both wastes and secondary resources. The harmless disposal and value-added utilization are necessary. In this paper, we propose a green route to sustainable reutilize vanadium from hazardous wastes as vanadium dioxide (VO2) cathodes for aqueous zinc ion batteries.The valence tuning from V5+, V4+, and V3+ in spent catalysts to V4+ in leaching solution has been realized by reduction acid leaching to ensure the complete recycle. The leaching rate of vanadium is 93.6%, and the vanadium content in the slag phase is less than 0.04%. Most V and few Fe and Al are extracted by P204 in organic phase, then diluted sulfuric acid is used for stepwise stripping from mixed V, Fe, and Al solution. Then high-purity (99.9%) vanadyl sulfate (VOSO4) solution is obtained after extraction and purification, which is used for the preparation of VO2 materials The assembled batteries by prepared VO2 exhibited a discharge capacity of 204.6 mA h g−1 at the first five cycles, and 172.5 mA h g−1 after 100 cycles at 0.1 A g−1. The capacity retention rate is 84.31% after 100 cycles. The mechanism and environmental analysis of greenhouse gas emission of reduction acid leaching are discussed, which reduces carbon emissions by 89.50% compared with routine acid leaching. Moreover, the phase transformation, metal element flow as well as species evolution are described for the deep understanding of valence tuning at molecular level. This paper presents a prospective approach for the short-cut and value-added utilization recovery of vanadium from hazardous wastes.

Mechanism of Selective Chlorination of Fe from Fe2SiO4 and FeV2O4 Based on Density Functional Theory

Vanadium slag is an important resource containing valuable elements such as Fe, V, Ti, and so on. A novel selective chlorination method for extracting these valuable elements from vanadium slag has been proposed recently. The proposed methods could recover valuable elements with a high recovery ratio and less of an environmental burden, while the study on the chlorination mechanism at the atom level was still insufficient. Fe2SiO4 and FeV2O4 are the two main phases of vanadium slag, and the iron element can be selectively extracted via the chlorination of NH4Cl. The NH4Cl decomposes into NH3 gas and HCl gas, which was the true chlorination agent. As a result, the chlorination reactions of Fe2SiO4 and FeV2O4 with HCl were firstly calculated using FactSage 8.0. Then, this paper studied the characteristics of HCl adsorption on the Fe2SiO4(010) surface and the FeV2O4(001) Fe-terminated surface mechanism of the selective chlorination of Fe from Fe2SiO4 and FeV2O4 via DFT calculations. The processes of chlorination of Fe2SiO4 and FeV2O4 involved the processes of removing O atoms from them with HCl gas. The iron in Fe2SiO4 was selectively chlorinated because HCl could adsorb on the iron site but could not adsorb on the silicon site. The iron in FeV2O4 was selectively chlorinated because the electronegativity gap between V and O was more significant than that between the Fe and O elements.

Oxidation behavior of vanadium and phosphorus during simultaneous vanadium extraction and dephosphorization of hot metal

In this paper, the indirect equilibrium method was used to study the equilibrium distribution ratios of vanadium and phosphorus in the metal phase and the slag phase, and simultaneous vanadium extraction and dephosphorization experiments were carried out under different slag basicity (the mass ratio of CaO to SiO2) conditions to explore the oxidation behavior of vanadium and phosphorus during simultaneous vanadium extraction and dephosphorization of hot metal. The results show that with the increase of slag basicity, the equilibrium distribution ratio of V (lgLV) increases slightly and the equilibrium distribution ratio of P (lgLP) increases significantly. With slag basicity increasing from 0.5 to 2.5, lgLV and lgLP increase from 1.7 to 2.0 and 0.1 to 1.9, respectively. Both lgLV and lgLP decrease with the increase of temperature, and increase with the increase of FeO content. High MgO content is not conducive to vanadium extraction. MnO has less effect on lgLV and lgLP. lgLV increases with the increase of V2O3 content, and decreases with the increase of P2O5 content. lgLP decreases with the increase of V2O3 content, and increases with the increase of P2O5 content. Both lgLV and lgLP decrease with the increase of TiO2 content. When the slag basicity is 1.5, the oxidation rate of vanadium reaches 95% after 10 min of reaction. The total mass transfer coefficient of P is in the range of 0.0040–0.0084 cm/s, and increases obviously with the increase of slag basicity. However, the influence of slag basicity on the total mass transfer coefficient of V is not obvious. Both the rate-limiting step of vanadium extraction and dephosphorization are the mixed mass transfer in the metal phase and the slag phase.

Combining experimental analyses and molecular dynamics simulations in impurity removal at the Si/slag interface

Slag refining is a crucial step for Si purification by the metallurgical processes. In this study, the impurity removal at Si/SiO2–CaO–MgO slag interface was investigated experimentally and theoretically. The diffusion couple experiments show that the slag underwent the processes of sintering, solid particle dissolution, and composition homogenization. When the melted slag contacted the Si, the interfacial reaction occurred, and the impurity oxides formed and transferred into the slag phase. The thermodynamic analyses confirmed the existence of the oxidation reaction between impurities and slag. First-principles molecular dynamics simulations of the Si–X–O system (X = Al, B, Ca) clarified the binding behaviors of Al, B, Ca with Si. The calculated binding energy shows that the affinity ability of these impurities with Si are B > Al > Ca at the molecular level, and B impurity is the most difficult one to be removed from Si during the slag refining process.

Biomass and Coal Ash Sintering—Thermodynamic Equilibrium Modeling versus Pressure Drop Test and Mechanical Test

The problem of biomass combustion and co-combustion is a particularly important aspect of many district heating systems, where the use of biomass makes it possible to reduce CO2 emissions. The present article is a continuation of previous studies of the behavior of the mineral matter of selected fuels during the sintering processes. Three biomasses were studied: wheat straw, barley straw and rye straw, as well as two coals from Polish mines: bituminous coal and lignite. The study included ultimate and proximate analyses and oxide analysis. On the basis of the oxide analysis and using FactSage 8.0. software, the sintering process of ash from selected fuels was simulated. In particular, the content of the slag phase as well as the values of the specific heat cp and density were determined without considering the gas phase. The obtained results were compared with the results of measurements of fracture stress (mechanical method) and pressure drop (pressure drop test) determined during the sintering process of the ash samples. The study showed that there is a fairly pronounced correlation between the sintering temperatures determined by the mechanical and pressure drop test and the physical properties of the ashes, such as density and heat capacity, and chemical properties, i.e., the content of the slag phase. The completed research work indicates and confirms that nonstandard methods of studying ash sintering temperatures (mechanical and pressure drop test) are very promising because they directly reflect the behavior of coals and biofuels in combustion systems.

Влияние условий солянокислотного выщелачивания на разложение ниобий-редкоземельного шлака при атмосферном давлении

The article deals with the research on hydrochloric acid leaching of niobium-rare-earth slag obtained during reducing roasting of rare-earth-rare-metal ores of the Chuktukon deposit. The effect of temperature, HCl concentration, and leaching time on degree of decomposition of the slag phases was studied. It was shown that during atmospheric hydrochloric acid leaching, only phases with a britholite structure and a glassy phase can decompose, while the betaphyte and spinel phases remain intact.

Slag refining at various viscosity conditions for SiC inclusion removal during Si scraps recycling

SiC inclusions in cast Si ingots are a key problem for Si quality and in the recycling of top-cut Si scraps. In this paper, SiC separation and Si recovery in the CaO–SiO2–MgO slag refining process were studied by varying temperature, slag/Si–SiC mass ratio, slag composition, and holding time. When the viscosity of the mixed system viscosity was 0.1575 Pa s, it was the best condition for the migration of SiC inclusions from Si to slag, and the removal ratio of SiC is 91.6%. The results indicated that low-viscosity slag and a long holding time are conducive to the migration of SiC. Further Image Pro software analysis showed that increasing the MgO content to 30mol% is beneficial to promote the migration of SiC. It is also found that the system viscosity effected the size of SiC in the slag phase. This work improves the removal of key inclusion SiC, reducing the cost of Si recovery.

Novel fluxing strategy of copper matte smelting and trace metals in E-Waste recycling

The distribution behavior of trace metals between copper matte and spinel-saturated iron silicate slags was investigated at 1250 °C and pSO2 of 0.25 atm at low silica concentrations. The experiments were conducted in magnetite (Fe3O4) spinel crucibles in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature equilibration-quenching technique. The concentrations of trace elements in matte, spinel, and slag were quantified by electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The trace metals (Ag, Ni, Co, and Sn) in all phases and their distribution coefficients were calculated as a function of matte grade. Results show that silver and nickel can be effectively recovered into matte, whereas cobalt and tin are predominantly deported into slag and gas phases, respectively. These results augment the fundamental thermodynamic data of trace metal distributions in copper smelting processes at low-silica fluxing practices.

Formation pathways of endogenous slag in typical charges of cohesive zone

The diffusion behaviour of oxides in FeO·2CaO·SiO2 (FC2S) systems was systematically analysed using slag compositions at different temperatures, and the formation pathway of an endogenous slag in the pellet and sinter of the cohesive zone was determined. The FeO-CaO-Al2O3-SiO2 endogenous slag proved to be the dominant slag phase because of a stronger diffusion capacity of Al3+ than Mg2+ and the less destructive effect of Al3+ diffusion on the original system. The enhanced effect of CaO and FeO on ion diffusion in the systems containing MgO resulted in a more pronounced diffusion of MgO and Al2O3 into the FC2S system at 1200 °C. The formation of the endogenous slag in the pellet and sinter was also established, which confirmed the rationality of the selection of the slag phase formation path. The endogenous slag-phase formation pathway also explained the nature of the cohesive zone.

Optimization of converting process for matte of oxidized nickel ores and sulfide copper ores joint smelting based on thermodynamic simulation

The paper presents the results obtained in the thermodynamic modeling of converting copper-nickel matte (11.3 wt.% Ni + Cu + + Co, 61.5 wt.% Fe, 25.9 wt.% S) produced by joint smelting of oxidized nickel ore and sulfide copper ore. Calculations were made in the approximation of ideal molecular solutions using the HSC Chemistry software package (Outotec Research Oy, Finland). The possibility of low-iron matte, converter slag and gas phase separation was shown. Estimated conditional equilibrium constants of exchange reactions between low-iron matte and slag (KNi/Fe = 0.004÷0.005, KCo/Fe = 0.056÷0.099) are close to ideal values. Statistical data processing was carried out using the mathematical experiment planning method. The converting temperature (t = 1100÷1300 °C) and iron and sulfur oxidation completeness level (q = 0.9÷1.0) determining the air and flux (SiO2) consumption were chosen as the factors to study. Obtained mathematical models of the process were used for its optimization. It was shown that the best converting performance can be achieved at t = 1150 °С and q = 0.950 when the low-iron matte contains 70.7 wt.% Ni + Cu + Co. At a yield of 8.74 % of the charge mass, the nickel, copper and cobalt recovery rates are 67.9, 97.9 and 9.1 %, respectively. The supposed air consumption (145.1 m3 (under normal conditions) per 100 kg of matte) and SiO2 (34.4 kg per 100 kg of matte) as well as slag yield (89.1 % of the charge mass) are close to working regime parameters. The results of the study confirm the possibility of cost-effective processing of poor copper-nickel matte and after experimental verification they can be used to develop automation flowcharts for converter departments at existing and designed production facilities.

Slag Flow in the Packed Bed With Varied Properties and Bed Conditions: Numerical Investigation

Molten slag, which is primarily generated in the blast furnace (BF) cohesive zone, trickles down through the coke packed bed in the form of films, rivulets, or droplets in the lower zone of the BF. During its downward flow, there are significant interactions occurring between slag and other phases such as gas, coke particles, hot metal, and fine powders. In terms of these interactions, slag flow behavior can greatly affect BF productivity and be associated with furnace irregularities such as channeling, hanging, and slipping. Hence, understanding the interactions between phases is useful to maximizing BF efficiency in terms of operating cost, reliability, and production capacity. In the current study, a Volume of Fluid (VOF) modeling technique was applied to track the movement of individual slag droplets in the packed bed at a mesoscopic level, considering various bed permeabilities, more wide-ranging slag properties, and different wettability between slag and packing particles. Results demonstrate the significant role of modeling at a mesoscopic level in understanding macroscopic slag flow behavior. Modeling work helps to visualize the trickling behavior of slag droplets in more realistic and complex conditions representing a BF, and clarify the mechanisms of the different flow patterns generated for variations in operating conditions. Transient flow characteristics such as localized slag accumulation and droplet morphology were identified and analyzed in relation to complex condition changes. The current modeling proved to be a valuable tool to provide a foundation for better understanding the slag flow behavior and its interactions with other phases in the BF lower zone.

DEVELOPMENT OF OPTIMUM TECHNOLOGY REGIMES FOR PROCESSING TITANOMAGNETITE CONCENTRATES IN THE JEP UNIT

For separation of titanium oxides into slag phase the electric arc furnaces are used in the existing technological schemes. A cheaper waste-free technology for processing titanium concentrate based on a continuous metallurgical jet-emulsion process (JEP) and unit was proposed. The following technological features of the new continuous metallurgical process JEP were considered: creation of a large reaction surface with subsequent organization of the forced movement of the formed gas suspension under pressure; implementation of the principle of gas-dynamic locking of the output channel in an oscillator reactor developed on the basis of this idea; creation of a non-equilibrium stationary oscillatory mode at a given pressure level; bottom supply of a two-phase working mixture prepared in an oscillator reactor to a vertical column reactor. The possibility of implementing a waste-free technology for processing titanomagnetite concentrates was substantiated, that simultaneously ensures the production of commercial titanium slag with smelting of the naturally alloyed metal. It was shown that the technology of almost complete separation of the iron-containing and titanium-containing components from titanium-magnetite concentrate is possible to implement in the JEP type unit in order to obtain the titanium slag with Ti2O5 content 46 % or more. The optimal consumption of materials was determined for complete reduction of iron and conversion of the titanium oxides into slag without formation of carbides.

Effect of iron on crystallization and flow properties of coal ash slag: A combined computational-experimental study

The crystallization and viscosity behavior of coal ash slag play a decisive role in the stable slagging of industrial gasifiers. However, the influence of iron on the crystallization and flow properties of slag is still poorly understood for its heterovalent component. Therefore, the influence of iron on the melting and crystallinity of slag was studied by preparing synthetic ashes with different iron contents, in this work. The results demonstrated that the ash fusion temperature (AFTs) could be significantly lowered with the increase of Fe content. This was because of the low-temperature eutectic reaction in slag caused by the increased iron content, which led to the transformation of the sub-liquid phase in slag from high-melting mullite to low-melting anorthite and spinel. At high temperature, iron was mainly presented in slag as Fe2+. At the same time, Fe2+ as an alkaline component could terminate the interconnection between [SiO4]4- and [AlO4]5- tetrahedral by replacing Si4+ and Al3+ in slag. This consequence destroyed the slag network structure and lowered the polymerization degree. Slag with lower polymerization degree exhibited lower viscosity and stronger ionic transport capacity, which was favorable for crystal growth. Meanwhile, thermodynamic and quantum chemical calculations revealed that anorthite was a crystalline mineral during slag cooling.

Mixed burden softening-melting property optimization based on high-silica fluxed pellets

The development of a high proportion of pellets smelting process suitable for China's resource structure can promote low carbon and green development of blast furnace ironmaking. The differences in metallurgical properties, phase evolution, microstructure, and softening-melting characteristics between high-silica acid pellets and high-silica fluxed pellets were compared and analyzed. The high content of low-melting-point liquid phases such as Fe 2 SiO 4 within the high-silica acid pellets, leads to a low initial softening temperature, and a higher amount of quartz in the form of solid phase mass points will reduce the fluidity of the slag and makes the permeability index deteriorate. The high-silica fluxed pellets slag is mostly in the form of Ca 2 SiO 4 , softening-melting behavior, and the permeability of the material layer improving significantly. Using high basicity sinters with a high proportion of fluxed pellets, although not effective in reducing slag amount, was observed to have a synergistic optimizing effect on the softening-melting behavior of the mixed burden. As the proportion of fluxed pellets increases from 35% to 45%, T d decreases from 1455 °C to 1427 °C, and the melting zone narrows from 139 °C to 109 °C, S-value reduced from 1147.98 kPa·°C to 440.36 kPa·°C. With the increase in the proportion of high-silica fluxed pellets, the position of the cohesive zone moves up, the viscosity of the slag decreases, fluidity increases and the permeability of the material layer gradually increases. • Dendritic quartz increases acid pellets' slag phase viscosity and reduces fluidity. • The flux containing calcium optimizes the slag phase composition of the pellets. • The cohesive zone of the high-silica fluxed pellets becomes narrower and the permeability is significantly improved. • As the proportion of high-silica fluxed pellets increases, the permeability of mixed burden gradually improves.

Recovery of Rare Earth Elements from Spent NdFeB-Magnets: Separation of Iron through Reductive Smelting of the Oxidized Material (Second Part)

This paper proposes a pyrometallurgical recycling method for end-of-life NdFeB magnets by oxidizing them in air and subsequently smelting them. The smelting process enabled the recovery of rare earth elements (REEs), producing a new reach concentrate separating the iron as a metallic phase. From the products of smelting, the metallic phase showed a maximum Fe content of 92.3 wt.%, while the slag phase showed a maximum total REE (Nd, Pr, and Dy) content of 47.47 wt.%, both at a smelting temperature of 1500 °C. ICE-OES and XRD analysis were conducted on both phases, and results showed that the metal phase consists mainly of Fe and Fe3C while the slag phase consists of the RE-oxides, leftover Fe2O3, and a mixture of Fe6Nd4. The obtained slag concentrate based on the oxides of rare earth elements is suitable for further pyrometallurgical or hydrometallurgical treatment in order to obtain rare earth elements.

Effect of slag basicity and reduction time on carbothermal reduction behaviour of P-bearing steelmaking slag

ABSTRACT To realize the efficient reduction and recycling of phosphorus resources in P-bearing steelmaking slag, it is necessary to study slag composition and phase changes during carbothermal reduction under different conditions (slag basicity and reduction time). The thermodynamic and kinetic behaviours of carbothermal reduction dephosphorization of P-bearing steelmaking slag are systematically discussed as well. The results show that the reduction rate of FeO and P2O5 show an upward trend with the increase of reduction time at 1823 K. However, the reduction rate of FeO does not change much within 50 minutes. In the range of slag basicity from 0.5 to 2.5, the formation of Ca3(PO4)2 increases with the increase of slag basicity. However, the increase of slag basicity is not good for the occurrence of carbothermic reduction gasification dephosphorization reaction. Taking into account the higher formation of Ca3(PO4)2 and the better dephosphorization effect of carbothermic reduction gasification, the appropriate slag basicity for carbothermic reduction gasification dephosphorization is 1.0–1.5. Carbothermal reduction gasification dephosphorization reaction of P-bearing steelmaking slag is a second-order reaction, and the mass transfer of P2O5 in the slag is the rate-limiting step of the whole process. The kinetic equations that describe the variation of P2O5 content in slag with time are yielded through regression. At 1823 K, by controlling the appropriate slag basicity (1.0–1.5) and reduction time (at least 20 minutes), the gasification dephosphorization rate of the carbothermal reduction can reach more than 80%, which can realize efficient recovery of phosphorus resources in P-bearing steelmaking slag.

Slag heterogeneity of autogenous copper concentrates smelting

ABSTRACT Due to the deterioration of the raw material base of copper production, it becomes necessary to optimise the autogenous smelting of copper sulfide concentrates, intensify the thermal regime and reduce the loss of copper with slags. There were carried out physico-chemical studies of the properties of slag produced during smelting of copper sulfide concentrates from the Balkhash copper smelter (BCS) in Vanyukov furnaces (VF), using X-ray fluorescence, mineralogical, X-ray diffraction, X-ray microanalysis, thermal analysis. Slag samples were taken at various distances from the furnace bottom (800–2400 mm) when the furnace was stopped. An intermediate layer of variable composition and considerable thickness (250–400 mm), was detected especially at lower smelting temperature, it is located at the bottom of the slag melt, directly on the border with the matte in the VF furnace. The novelty in the obtained data consists in finding the dependence of the formation of the intermediate layer between the slag and matte on the temperature and the content of magnetite in the slag. In addition, it was found that the necessary condition for more complete separation of slag and matte and prevention of intermediate layer formation, is the melting of slag phases, regardless of its composition.

Iron Removal from Metallurgical Grade Silicon Melts Using Synthetic Slags and Oxygen Injection.

Novel SiO2-CaO-CaF2-R2O-MgO based synthetic slags (R2O represents alkali metal oxides) with varied binary basicity values were used with oxygen injection to refine silicon melts and remove Fe from metallurgical-grade silicon. Silicon samples and slags at the silicon-slag interfaces were obtained during refinement. The compositions of the silicon samples were analyzed, and the quenched slag samples and mild cooling slags from the final crucible were inspected using scanning electron microscopy and energy dispersive X-ray spectroscopy. After 15 min of refinement, the Fe removal rate ranged from 52.3 to 60.1 wt%. During the refining process, the Fe-concentrated phase formed within the silicon droplets and was then transferred to the silicon-slag interfaces and wetted with slags. The Fe-concentrated phase at the silicon-slag interface can dissolve directly in the slags. It can also be transferred into the slag phase in the form of droplets, which can be affected by the binary basicity of the slags. Ti removal demonstrated a similar mechanism. Fe-bearing crystals were not detected in the quenched slag samples obtained during refinement, while complex Fe-bearing phases were detected in the final slag. This study demonstrates Fe removal from metallurgical-grade Si using slag refining methods and reveals the removal mechanism during the refinement.