Smelting Slag Research Articles

Ash melting behavior and mechanism of high-calcium bituminous coal in the process of blast furnace pulverized coal injection

Abstract High-calcium bituminous coal has the advantages on combustibility, but its ash melting point is low, and it is easy to slag in blast furnace injection process. In order to explore the ash melting slag formation mechanism of high-calcium bituminous coal, the mineral evolution of ash in the combustion process of high-calcium bituminous coal and the influence of ash components on the liquid formation in the melting process were studied. The results showed that the melting behavior of ash gradually occurs with the change in the morphology, and the main mineral transformation is carried out around different deposition forms of Ca and Si. The liquid phase formation of ash at high temperature is the essential reason of its melting behavior. The higher the content of CaO, the higher the starting temperature of the liquid phase formation. The higher the content of SiO2, the lower the starting temperature of the liquid phase formation, and the more the liquid phases generated at a given temperature. Increasing the content of Al2O3 can expand the temperature range of reducing the formation of ash liquid phase to 1,473–1,673 K. When the temperature is above 1,573 K, Fe2O3 can promote ash liquid phase formation.

Effect of Fe/SiO2 ratio and cooling regime on As stability in copper smelting slag

The present study investigated the effects of Fe/SiO2 ratio (0.8−1.6) and cooling methods (quenching and cooling with furnace) on the stability of As in typical copper smelting slag (FeO−SiO2−Fe2O3−CaO−MgO−Al2O3). It was determined that iron silicate slag can achieve As vitrification. In addition, the lower Fe/SiO2 contributed to the immobilization and reduced the leaching toxicity of As. FTIR analysis showed that the increase of Fe/SiO2 caused to the depolymerization of the glass structure and promoted the formation of [AlO6]9− octahedra. XPS spectra of O1s and Si2p showed that the amount of non-bridging oxygen (NBO) in the melt increases with increasing Fe/SiO2. In addition, Al2p and As3d spectra indicate that the covalency between the As−O and Al−O bonds decreased with increasing Fe/SiO2 to accommodate glass depolymerization. For the slow-cooled slag, As was mainly enriched in the iron olivine phase, with a small fraction in the silicate matrix. The increase of Fe/SiO2 promoted the precipitation of iron olivine phase and thus the leaching concentration of As increased with the increase of Fe/SiO2.

Mechanism and kinetics for chlorination roasting of copper smelting slag

An efficient process based on chlorination roasting with CaCl2 was proposed to recover zinc from copper smelting slag. The reaction mechanism and the kinetics of the chlorination process were investigated by thermodynamic calculation, thermogravimetry and differential scanning calorimetry (TG−DSC) analysis and X-ray diffraction (XRD) methods. The results demonstrated that the temperatures of oxidative decomposition of CaCl2 and chlorination of all Zn-containing phases were above 774.3 and 825 °C, respectively. The chlorination roasting process was divided into four stages: precipitation of adsorbed water, extraction of crystallized water, oxidation of Fe-containing phases, and chlorination volatilization of zinc. The average apparent activation energies of the iron oxidation and zinc chlorination were 101.70 and 84.4 kJ/mol, respectively. The most probable mechanism function for the iron oxidation process was the Avrami−Erofeev model (n=2). Zinc chlorination followed the shrinking unreacted core model, and the chemical reaction was the rate-controlling step.

Thermodynamic Modeling of the Fuming of Copper Smelting Slag by the Products of Methane Conversion by Oxygen, Water Vapor, and Carbon Dioxide

Thermodynamic Modeling of the Fuming of Copper Smelting Slag by the Products of Methane Conversion by Oxygen, Water Vapor, and Carbon Dioxide

Recovery of Cu-Fe Alloy from Copper Smelting Slag

Copper smelting slag usually contains 1–6 wt% copper, which can be recovered by pyrometallurgical and flotation processes. However, the tailing slags still consist of 0.3–0.7 wt% Cu and 35–45 wt% Fe equivalents to those in the copper and iron ores, respectively. Most of the research was focused on the recovery of iron from the tailing slags. Copper can increase the mechanical strength, corrosion resistance and antibacterial property of some steels. A new process to recover copper and iron directly and fully from hot copper smelting slag is proposed to produce Cu-Fe alloy for steel production. Effects of flux, temperature, reaction time, reductant type and addition on the recovery of copper and iron were investigated by high-temperature experiments and thermodynamic calculations. It was found that, with 5% CaO and 13–16% carbon additions, most of the copper and iron can be recovered from copper smelting slag at 1350–1400 °C. The copper and iron contents of the reduced slag are lower than 0.1% and 0.5%, respectively, at optimum condition. The new process has the advantages of low energy consumption, low flux addition and high recovery of copper and iron.

Influence of MgO on the alkali fusion behavior and mechanism of titanium-containing melting slag

The influence of MgO on the alkali fusion behavior and mechanism of titanium-containing melting slag is unclear. To clarify this, the phase transformation and microstructure of titanium-containing melting slag and alkali fusion slag were compared and analyzed by X-ray diffraction, scanning electron microscopy, and crystal structure analysis. The conversion rate of titanium-containing melting slag with different MgO contents was calculated. The results indicated that titanium-containing phases and other phases transformed into their corresponding sodium salts after the alkali fusion reaction. Upon increasing the MgO content, the phase transformation was complete, and the transformation from Na2TiO3 to NaMO2 (M = Mg, Ti) was more common. MgO greatly influenced the microstructure of slag samples and increased the conversion rate of titanium.

Preparation of phosphogypsum-copper smelting slag-based consolidating body with high compressive strength.

Phosphogypsum (PG) is an industrial waste residue produced during the production of phosphoric acid through the wet process. With strong acidity and a large amount of toxic impurities, PG is difficult to reuse. In this study, the solidified body (PG-S) was made by mechanical compression of the mixture of PG, copper smelting slag (CSS), CaO, NaOH, and water. Results indicate that the composition of the material phases in the PG-S samples changed with hydrated calcium silicate and amorphous silicate derivatives were formed during the reaction; Fe and Ca in the material were transformed; and the prepared geopolymer material had a dense internal structure with the materials being cemented to each other. The highest compressive strength of PG-S cured for 28 days could reach 21.3 MPa with a fixation efficiency of PO43-and F-reaching 99.81 and 94.10%, respectively. The leaching concentration of heavy metals of the PG-S cured for 28 days met the requirements of the Comprehensive Wastewater Discharge Standard (GB 8978-1996). The simulation results of the geochemical model verified the feasibility of the whole immobilization process from the thermodynamic point of view. This work directly uses copper smelting slag and phosphogypsum for coupled immobilization/stabilization treatment not only to achieve the immobilization of pollutants in both solid wastes but also to obtain colloidal masses with certain compressive strength, which also provides a new option for resource utilization of phosphogypsum and copper smelting slag. This work also shows great potential in turning the actual mine backfill into cementitious material.

Effect of CeO2 Content on Melting Performance and Microstructure of CaO-Al2O3-SiO2-MgO Refining Slag

CeO2 can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al2O3 inclusions. The impact through which CeO2 content affects slag’s melting efficiency is still uncertain. The thermal analyzer was used to measure the thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) curves of the slag melting process. According to the study results, with the increase in CeO2 content, the melting temperature of slag decreased first and then increased. The slag’s melting point fell from 1364 °C to 1324 °C and then rose to 1503 °C. XRD and SEM were used to analyze the CaO-Al2O3-SiO2-MgO-CeO2 slag’s microstructure. The mineral-phase structure of CeO2-containing refining slag was primarily composed of Ca2SiO4 and 3CaO·Al2O3, MgO, SiO2, CaO·Al2O3, and Ca8Ce6Al6O26. The proportion of 3CaO·Al2O3, CaO·Al2O3, and Ca2SiO4 decreased as the rare-earth-oxide content increased, while the proportion of Ca8Ce6Al6O26 increased. FactSage was used to estimate the equilibrium-phase compositions of slags with various compositions, and a model for predicting melting points was carried out by a linear regression model. Results were obtained through the analysis of equilibrium-phase composition and crystal structure transformation. The main reasons for the melting point decrease were the change of degree of polymerization and the decrease in contents and complete melting temperature of high-melting-point Ca3Al2O6 and Ca2SiO4 compounds. The latter increase in melting point was due to the number of Ca8Ce6Al6O26 compounds and precipitation temperature increases and the complexity of the structural-network increases.

Control of Copper Content in Flash Smelting Slag and the Recovery of Valuable Metals from Slag—A Thermodynamic Consideration

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to investigate the effects of matte grade, SO2 partial pressure, and the Fe/SiO2 ratio on the liquidus temperature and the copper content of the smelting slag. The possibility to recover valuable metals from the smelting and converting slags through pyrometallurgical reduction by carbon is also discussed. It was found that the flash smelting slag temperature is usually higher than its liquidus temperature and the copper (1.2% Cu) is mainly present in the slag as dissolved copper. In the copper flash smelting process, the copper content in the slag can be decreased by decreasing the Fe/SiO2 ratio and temperature. In pyrometallurgical slag reduction, most Cu, Mo, and Ni can be recovered as an alloy. The conditions of recovery such as the ratio of smelting slag to converting slag, temperature, and reduction extent have been discussed.

Iron production in the ancient Xianyang city of the Qin state: A perspective on iron smelting slags

The ancient Xianyang city was the capital city of the Qin state and Qin empire during the 4th century BCE to the 3rd century BCE. In the past decades, several archaeological excavations and surveys have carried out in the city site and two ironworks have been discovered. The present paper reports the iron production technology applied in one of the ironworks in the ancient Xianyang city site through metallographic and elemental analyses of collected slags. The analytical results provide evidence that both cast iron smelting and fining process were applied in the ancient Xianyang city.

Development of lead smelting slag-based ecological mine backfill material: Performance control and heavy metals solidification

As the heavy metals (Cr, Ni, Cu, Zn, As, and Pb) contained in the hazardous waste lead smelting slag (LSS) can cause irreversible harm to natural ecosystems, the resourceful utilization of LSS is an urgent requirement for promoting ecologically sustainable development. In this study, multi-solid waste-excited LSS was used to prepare eco-mine cemented backfill materials (MCBM). The results show that the optimal ratio of binder composition by mass is 46% for LSS, 20% for lime ash slag (LAS), 13% for slag powder (SP), 17% for cement clinker (CC), and 4% for bischofite (BF), at which time the compressive strengths of specimens at 3, 7, and 28 days are 11.1 MPa, 16.9 MPa, and 24.2 MPa, respectively. Clearly, increasing the ratio of binder-sand will increase the compressive strength of the MCBM. The backfill slurry with a binder-sand ratio of 1:2 and a solid content of 74% has a fluidity of 259 mm and a 28-day compressive strength of 5.48 MPa, which meets the requirements for high-strength grade MCBM for self-weight backfill. The results of XRD, MIP, and SEM indicate that the hydration products are predominantly composed of CSH gels, Friedel’s salts, and other mineral phases that contribute to the strength. As the ratio of binder-sand increases, the relative proportion of harmless pores increases, the mechanical properties of the MCBM improve, the hydration products become denser, and the unclassified tailings sand (UTS) is encapsulated more effectively. According to the results of the TCLP, the solidification ratio of the MCBM for each heavy metal exceeds 70%, and the leaching of heavy metals conforms to the Chinese Class IV groundwater standard. The process is more environmentally friendly, with lower energy consumption and CO2 emissions, in line with the local government’s environmental legislation.

Strong binding of heavy metals in fayalite of copper smelting slags: Lattice site substitution

A deep understanding of the binding relationship between Fe2SiO4 and heavy metals from the perspective of lattice site substitution is essential to improve the theoretical knowledge regarding heavy metals binding in copper smelting slags (CSS). Here, we proposed the lattice site substitution behavior of heavy metals in Fe2SiO4 by preparing M-Fe2SiO4 (M = Cu, Pb, and As). X-ray diffraction refinement, scanning electron microscopy, and Fourier transform-infrared spectroscopy analysis showed that heavy metals were involved in the formation of Fe2SiO4 during the smelting process. Compared with pure Fe2SiO4, the fine structure of M-Fe2SiO4 was significantly changed by the lattice substitution of heavy metals. X-ray photoelectron spectroscopy and Raman and Mossbauer spectra combined with Density Functional Theory calculation confirmed that the divalent metal elements including Cu and Pb were bound to the Fe2SiO4 lattice by replacing M2 site. However, the trivalent As element could substitute both the positions of M2 site and part of the central Si atom through a charge compensation mechanism. Overall, the proposed lattice site substitution behavior of heavy metals in Fe2SiO4 could enrich the theory of the lattice substitution of heavy metals in CSS, also further provide guidance for the comprehensive disposal of CSS.

Determination of occurrence and leaching toxicity of arsenic in copper flash smelting slags

The efficient and safe disposition of arsenic (As)-containing copper slag depends on the accurate understanding of the As species and their corresponding leaching toxicity. The As species in copper smelting slag were investigated by X-ray fluorescence spectrometry, X-ray diffractometry, electron probe microanalyzer, scanning electron microscopy equipped with energy dispersive spectroscopy, and selectively sequential extraction scheme. Based on the accurate fractionation of As species, the potential source of As toxicity of copper slag was investigated. The results show that As can be associated with smelting slag in the forms of water-soluble As, Cu−As intermetallics, Cu−As sulfides, as well as the As incorporated in fayalite and glassy silicates. The removal of readily soluble As and Cu−As intermetallics from smelting slag by flotation can reduce the As leaching toxicity of slag tailings, making them conform to the USEPA and SEPA regulatory thresholds for As.

Аналітичні та експериментальні дослідження властивостей шлаків та шлакоутворюючих сумішей сталеплавильного виробництва

The aim of the study is to analyze and generalize the properties of slags within the CaO-SiO2-Al2O3-MgO-CaF2 system in different ratios of components and their concentrations, which is the basis of refining slags in modern steelmaking. To ensure the technological functions, the slag melt should have a set of optimal values of physical and chemical properties, in particular: viscosity, surface tension, electrical conductivity, melting temperature (beginning and end), enthalpy, density and others, which significantly affect the kinetics of heat and mass transfer processes in the "metal-slag" system. The information resource of researches is provided by own experimental data and data of databases "Slag" and "SFM" containing information about technological properties of melts of slag and oxide systems. The analysis of the data on the dependence of the properties of oxide systems on their chemical composition and temperature was performed. Oxide systems within the chemical composition CaO-SiO2-Al2O3-MgO-CaF2 are considered. The connection of the chemical composition of slag systems with the properties of their melts from the point of view of the concept of directed chemical bonding using integral parameters is established: ρ is the stoichiometry index; ∆e is the average number of electrons localized in the direction of the cation-anion (K-A) bond; d is the average inter-nuclear distance K-A; tgα is the change in the electron density in the direction of the K-A bond; ZA(A-A), ZK(K-A), ZK(K-K) are the weighted average values of cation and anion charges in the A-A, K-A, K-K bonds. Based on the results of experimental and analytical studies, predictive models of the properties of the considered oxide systems were obtained, namely for the calculation of viscosity, electrical conductivity, crystallization temperature and density of slag melts in the range of their temperatures from 1200°C to 1800°C. The presented method of predicting the properties of refining slags can be used to evaluate the use of slags of different composition in the ladle, for example, in ladle-furnace installations.

Методика оцінки фізико-хімічної взаємодії в системі "метал-шлак" як кооперативного іонообмінного процесу під час рафінування сталі

Dephosphorisation and desulphurisation are the most important stages of high-quality steel production, characterized by complex physical and chemical processes of interaction in the metal-slag system. The article is devoted to studying the results and evaluating the efficiency of steel refining processes at different stages of its refinement in modern Ukrainian conditions. The aim of the work is to develop a methodology for assessing the physical and chemical interaction in the metal-slag system during steel refining from the perspective of the concept of a cooperative ion exchange process using the parameters of interatomic interaction in melts. As a result of studying the regularities of sulphur and phosphorus distribution depending on the chemical composition of different steel grades from two plants and their corresponding slags, a methodology has been developed that includes the reasonable use of parameters of interatomic interaction in melts as criteria for assessing the degree of completion of ion exchange processes during steel refining. Along with the use of integral physical and chemical parameters of the chemical and charge state of metal and slag melts (chemical equivalent of metal composition ZY(e) and slag Δe(e), effective charge of element Ze(e)), the paper shows the key role of the influence of the "recharge" parameter of the element ΔZе on the process of interfacial distribution of sulfur and phosphorus. This parameter has also shown its efficiency as a criterion for assessing the deviation of the metal-slag system from equilibrium at different stages of steelmaking and finishing at the ladle furnace unit (LFU). The proposed approach makes it possible to assess the level of completion of steel refining processes in order to develop effective technological solutions. In addition, it lays the foundation for solving specific applied problems at a new level, allowing optimizing existing technologies and developing new methods and reagents for producing steels with reduced sulphur and phosphorus content.

Optimization of physical and mechanical properties of non-autoclaved aerated concrete based on industrial waste

This article presents the results of experimental research on the parameters of aerated concrete porosity strength properties and properties based on industrial waste. The structurally optimal amount of water was determined, reflecting the physical-mechanical, thermal-technical properties of the outer wall structures based on aerated concrete. The test results were carried out in research laboratories using aerated block constructions with high porosity and optimal composition, and improved technological solutions for autoclaved aerated concrete were developed. Study of changes in the properties of aerated concrete with the addition of waste quartz sand and steel smelting slag; optimization of aerated concrete composition by mathematical regression method and determination of physical and mechanical properties; the results of the research on automating the calculation of the proposed composition of aerated concrete and the amount of industrial waste according to its brand are given.

Železářská struska z polykulturní archeologické lokality Boršice v podhůří Chřibů

A piece of iron slag was found on an archaeological site near Boršice on the SE margin of the Chřiby Mts., Czech Republic, which is known by occurrence of artifacts from the Early Neolithic (5700 - 5000 BC), Bronze and Early Medieval Ages. We present results of laboratory investigation of this slag. It is composed mainly of fayalite laths, which belong to two generations, less occur glass phase, wüstite and leucite, exceptionally also metallic iron. The composition of fayalite displays unified chemical trend and ranges in rather narrow span (Fa93.7-96.3 DCS1.1-5.8Fo0.0-5.0Te0.0-0.2). The glass phase contains in addition to common compounds (Si, Fe, Al, alkalis) also elevated contents of P and Ca. The microstructure of the studied slag as well as chemistry of individual phases are very homogeneous across the whole sample. We interpret this slag as an iron smelting slag, originated during production of iron from ores using the direct method. The used ore was in all probability a limonite bog ore, whereas the use of local fresh and/or weathered pelosiderites is not probable on the basis of the recorded phase composition and chemical compositions of individual phases.

Evaluation of the biopositivity of the subgrade

A large amount of industrial waste generates a certain interest in the possibilities of their use in the road industry. The article considers the possibility of using copper smelter slag as a man-made material for the construction of an embankment of roadbeds. The results of the performed elemental composition of the studied slag are presented, as well as micrographs characterizing its structure. As a result of the research, it has been established that copper smelter slags are valuable raw materials with weak binding properties and are potentially applicable for obtaining technogenic soils with high physical, mechanical and operational properties for highways.

The melting performance blast furnace slags with high alumina content

With a view to understanding the performance of the blast furnace slag with high Al2O3 content, the effects of w(MgO)/w(Al2O3), w(CaO)/w(SiO2), and w(Al2O3) on the melting performance (melting characteristic temperature and melting heat) of the blast furnace slag with high Al2O3 content were investigated by the differential scanning calorimeter (DSC) method. Experimental results indicate that melting end temperature (Tend) for almost all the slags has no obvious change with the increase of w(MgO)/w(Al2O3), w(CaO)/w(SiO2) and w(Al2O3) of the slag will raise Tend of the slag. When (w(MgO)/w(Al2O3), R, and w(Al2O3) are high, the melting onset temperature (Tonset) of the slag increases with the increase of any variables. When w(CaO)/w(SiO2) is low, Tonset of the slag decreases with the increase of w(Al2O3). w(MgO)/w(Al2O3), w(CaO)/w(SiO2), and w(Al2O3) within the scope of this study and all these factors lead to the increase of the slag melting heat.

Modeling of thermogasodynamic parameters of neutral gas jets when spreading in converter cavity

The article considers the features and characteristics of spreading of neutral gas jets in the gas-dynamic section before interaction with the slag melt, which is further inflated to apply a refractory skull to the unit lining. The flow of a supersonic jet into the working space of the converter after tapping has the wave structure. The model for calculation of attached mass of the surrounding gas located in the converter working space is considered. The problem statement takes into account the known data on gas dynamics during the formation and flow of the jet, which affect the efficiency of turbulent transfer in the boundary layer. The calculation scheme is based on the hypothesis of existence of an initial boundary through which a chemically active gas from the environment penetrates into the gas jet, and the shape of the limit boundary is assumed to be cylindrical with a radius equal to the maximum radius of the first barrel of the non-calculated jet. Numerical calculations make it possible to determine the average mass velocity and temperature in an arbitrary section of a supersonic non-calculated jet before its introduction into the slag melt. The authors describe the influence of the relative temperature θ, nitrogen temperature in front of the nozzle T0 during spreading of the jet in the converter cavity, and nitrogen flow through the nozzles Vн on value of the attached mass q, the averaged values of velocity and temperature Wx and Tx in an arbitrary cross-section x of a supersonic non-calculated jet in the gas dynamic section. The information obtained can be used in the development of gas-powder purging systems in aggregates and steel ladles, shotcrete systems and the supply of neutral gas jets when replacing oxygen flows during purging and using two-tier tuyeres.