Slag Samples Research Articles

Deep insight into the ash fusibility and viscosity fluctuation behavior during co-gasification of coal and indirect coal liquefaction residue

Co-gasification of coal and indirect coal liquefaction residue (ICLR) is an effective approach to large-scale utilization of ICLR. In this work, the effect of ICLR addition on ash fusion characteristics and viscosity-temperature characteristics of YCW coal were studied by means of ash fusion temperature analyzer (AFTA), XRD, high-temperature-rotary-viscometer, high-temperature heating stage coupled with optical microscope (HTSOM) and FactSage thermodynamics software. The results showed that with the increase of ICLR mass fraction, the low-temperature eutectic anorthite melted into a liquid phase, resulting in a linear decrease of AFTs. Moreover, the causes of viscosity fluctuation were revealed according to the in-situ crystallization morphology variation and viscosity-temperature characteristic curves. It was found that the formation of a large number of “barbed-shape” needle-like crystals during the cooling process was the main reason for the significant viscosity fluctuation. With the addition of ICLR, the length-diameter ratio and volume fraction of the “barbed-shape” needle-like crystals decreased significantly, resulting in the decrease of viscosity fluctuation. When the addition amount of ICLR was 3%, the “barbed-shape” needle-like crystals were not precipitated during the entire crystallization process, and the viscosity no longer fluctuated. As the mass fraction of ICLR increased to 5%, no crystals precipitation was observed in the cooling process. At this time, the slag sample showed the glass slag characteristics. Therefore, for entrained-flow gasification, the addition of ICLR could improve the gasification efficiency by reducing the gasifier operating temperature, and avoid slag-tapping problems by alleviating the viscosity fluctuation. More importantly, it could realize the resource treatment of hazardous waste and transform hazardous waste into solid waste.

Study on Solidification Treatment of Electrolytic Manganese Slag and Numerical Simulation of Slope Stability

Manganese slag contains a large number of easily migrated heavy metals and ammonia nitrogen and other pollutants, which have a negative impact on the ecological environment. To verify the feasibility of manganese slag as highway subgrade material, manganese slag samples were solidified by mixing fly ash, cement and quicklime, and the solidification effect was compared. The permeability coefficient, cohesion and internal friction angle of manganese slag were measured by permeability test and triaxial test. On this basis, optimization of manganese slag road sections under different slope heights and different slope ratios in a total of 50 schemes was carried out. GeoStudio software is used to perform finite element simulation on the slope stability of manganese slag slopes under dead weight and rainfall. This study provides a reference for highway construction projects using manganese slag.

The use of blast furnace slag as a supplementary cementitious material

Waste material recycling in mortar production not only provides a promising resource for producing high-quality mortar, but it also aids in properly addressing the waste disposal issue. This study investigates the potential of utilizing blast furnace slag wastes as a supplementary cementitious material in blended cement-based mortars.The experimental program includes investigation of compressive strength of cement-based mortar composites contained different types and percentages of slag wastes. The mortar specimens were prepared and cured following related international standards. After curing, the compressive strengths of the tested specimens were assessed and compared with control specimens. The influence of the chemical composition of the investigated slag types on the resulted strength of the blended cement mortar was also discussed. Results of this study revealed that the chemical compositions of the raw slag wastes have significant effects on the pozzolanic activity of the produced slag. Slag samples contained higher percentages of calcium oxides present the most promising results regarding the production of supplementary cementitious material.

Experimental Determination of the MnO Activity Coefficient in High-Manganese Slags Using the Chemical Equilibrium Method

The thermodynamics of manganese oxide in high-MnO-containing slags was investigated using the chemical equilibrium method in the temperature range of 1623 to 1723 K. MnO-SiO2-Al2O3 slags were brought into equilibrium with molten silver (Ag) under controlled CO/CO2 gas atmosphere. The equilibrium Mn concentration in the silver was measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy) analysis after the experiment. Slag samples were analyzed by EPMA (electron probe microanalyzer) analysis. The obtained activity aMnO and activity coefficient γMnO were derived as a function of the slag composition and temperature. The activity coefficient of MnO within the investigated slag system increased with an increasing MnO/SiO2 ratio. The derived temperature dependence of the activity coefficient and partition ratio of Mn between the metal and the slag was strongly influenced by the slag composition. The thermodynamic assessment of the activity and activity coefficient of MnO was carried out by applying the regular solution model (RSM) on the basis of interaction energies of the cations and with FactSageTM 7.3. The theoretical calculations were compared with the experimentally derived values.

Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al<sub>2</sub>O<sub>3</sub>-Based Inclusions from Liquid Steel

Dissolution of Al2O3-based inclusions are paramount during production of special steel and slag engineering is key to enhance this phenomenon. This work evaluates the influence of thermodynamic driving force (ΔC) and effective viscosity (ηe) on steel cleanliness of three distinct steel grades and slag composition (Steel/Slag A, Steel/Slag B and Steel/Slag C). Initial and final steel and slag samples were withdrawal on an electric steelmaking facility. The first samples after addition of aluminum as deoxidizer and the second after vacuum degassing stage. X-ray fluorescence and optical spectrometry obtained initial and final samples chemical composition. An ASPEX Explorer acquired inclusions data and FactSage v.7.2 performed thermodynamic calculations. Analysis of steel Al and O content highlighted an inefficient dissolution of Al2O3-based inclusions for Steel/Slag A, deteriorating steel cleanliness. Furthermore, this phenomenon is supported by average inclusions composition on initial and final samples plotted in pseudo-ternary diagram. Steel/Slag B and C provided improved results regarding the dissolution of Al2O3-based inclusions with a final inclusion density below 0.50 mm-2. These two slags composition achieved values of ΔC above 25 and ηe close to 0.10 Pa·s. In addition, their combined effect (ΔC/ηe) presented values above 250 and had the highest linear fit among these analyses. These properties are influenced by slags chemical composition and can be improved controlling parameters as binary basicity and CaO/Al2O3 ratio. Slags B and C were selected to define an optimal range for these parameters, with binary basicity between 3.00–3.50 and CaO/Al2O3 ratio in a range from 2.50–3.50.

Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Influence of Process Parameters on Copper Content in Reduced Iron Silicate Slag in a Settling Furnace

During the pyrometallurgical extraction of copper, a significant fraction of this metal is lost with discard slag, which decreases profits and overall copper recovery. These copper losses can be reduced by using a settling furnace, in which suspended droplets containing copper separate from slag under the influence of gravity. An industrial trial was conducted in a settling furnace to increase the knowledge of the effect of temperature and settling time on the copper content of slag, and thus enhance the settling process to increase copper recovery. Slag samples were collected from four sample points: the ingoing and outgoing slag stream, within the furnace during settling, and the granulated slag. The chemical composition of the slag samples was analyzed and compared between batches with different temperatures and settling times. The appearance of copper and its associated phases were analyzed using a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector (SEM-EDS). The results indicated that the outgoing slag copper content increased with an increase in temperature, and it was also concluded to be influenced by the attachment of copper to spinels and gas bubbles. The results indicate that regulating the settling furnace temperature to a lower interval could increase copper recovery.

Recovery of rare earths, lithium and fluorine from rare earth molten salt electrolytic slag via fluoride sulfate conversion and mineral phase reconstruction

To solve the problem of rare earths (RE) lithium (Li) and fluorine (F) recovery in rare earth molten salt electrolysis slag, a recovery method was developed based on magnetic separation, sulfuric acid leaching, HF recycling, water leaching, fluorination precipitation. First, RE, Li and iron-containing phases in a slag sample were separated using a magnetic separation method. Second, sulfuric acid-leaching was used to reconstruct the phases of RE and Li in the non-magnetic fraction, which were transformed into a rare earth sulfate easily dissolved in water. At the same time, the HF generated in the sulfuric acid leaching process is recovered by multistage adsorption. Finally, qualified fluoride rare earth products were obtained by HF cycle precipitation. The results show that the recovery of iron is 85.30% under the condition that the magnetic separation intensity of 0.668 T, particle size of 58–75 μm, and the main phase in the non-magnetic fraction is the rare earth phase, and the iron content is only 2.90%. Under the conditions of a concentrated acid concentration of 98.00%, a temperature of 633 K, a liquid–solid ratio of 2:1, a particle size of 58–75 μm, a constant stirring speed of 300 r·min−1, and reaction time of 3 h, the removal rate of F is 95.30%, and the transformation rates of Nd, Pr, Dy, and Li reached more than 95.00%. Through water immersion and fluorination precipitation, rare earth fluoride products can be obtained. The purity, particle size, and water content of the products met the standards required for industrial rare earth molten salt electrolysis.

Distribution and modes of occurrence of heavy metals in opposed multi-burner coal-water-slurry gasification plants

To understand the migration and modes of occurrence of heavy metals in the opposed multi-burner (OMB) coal-water-slurry (CWS) gasification process, samples of coal, coarse and fine slags were obtained from two plants with different capacities. Concentrations of nine hazardous heavy metals (HMs) in these samples, i.e., Ba, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn, were determined to show their migration and enrichment behaviours. A four-step sequential extraction method was implemented to reveal the modes of occurrence of these HMs. Results demonstrated that fine slags were mainly fragmentized spheres and were covered by fine floccules, whilst coarse slags were vitreous, angular and less porous than fine slags. Majority of the heavy metals were more concentrated in fine slags. Chromium was enriched in coarse slags, while Pb and Zn were accumulated in fine slags as indicated by the relative enrichment index. The sequential extraction demonstrated that for the coals, Cr, Cu, Ni, V and Zn were primarily associated with residual fractions (48.8–82.6 wt%), while Co, Mn and Pb were dominant in oxidizable (78.1 wt%), acid soluble (60.0 wt%) and reducible fractions (99.2 wt%), respectively. In fine slags, except for Zn, the other HMs were mainly distributed in residual fraction with 42.3 to 94.8 wt% in fine and coarse slags, respectively. Mobile fraction of HMs was the highest in coals (19.4–93.6 wt%), followed by fine slags (11.6–73.1 wt%) and coarse slags (5.1–41.0 wt%). Based on the leaching ability, except Cu, the HMs content in all slags were above the standard for direct landfill disposal.

Materiales metalúrgicos hallados en la ciudad de Ibiza (Islas Baleares)

The analyzes of six samples of slag found during urban development works in the city of Ibiza (Balearic Islands) are presented. These samples, which are one of the first samples of slag analyzed from the old town of Ibiza town, correspond to products from a metallurgical workshop dedicated to the bronze industry. The first three samples to be discussed are remains of ternary bronze metallic elements (copper, tin and lead) in the production phase. These metals would be mixed in ceramic vessels (crucibles), to which the last three samples correspond, which in some cases retain traces of these three elements (copper, tin and lead). These fragments of crucibles are made of clays rich in iron and lime, the addition of which is possibly intentional judging by historical parallels.

The Modeling and Optimization of Titanium Dioxide Extraction, Case study: The Slag Sample of Blast Furnace

In this research work, the application of the Response Surface Methodology (RSM) and the Central Composite Design (CCD) techniques for modeling and optimization of some of the operating variables on the titanium dioxide extraction were studied. This study was performed, using sodium hydroxide roasting and sulfuric acid leaching. Four main parameters, i.e., leaching temperature, time, liquid to solid ratio, and the concentration of acid, were changed during the experiments. The two parameters of the stirring rate (250 rpm), and the feed size (d80= 106 micrometers) were considered to be constant. Based on the findings, several empirical equations were modeled for the titanium dioxide extraction with the above mentioned parameters. The empirical equations were then individually optimized by employing the quadratic programming to maximize the extraction within the experimental range. In conclusion, the optimum conditions were accordingly obtained at 85°C, 235 minutes, liquid to solid ratio of 15, and the acid concentration of 2.4 M, in which the maximum TiO2 extraction of 81.32% was achieved.

Simultaneous Removal of Cu2+, Zn2+ and Cd2+ from Aqueous Solutions by Alkali Activated Slag

Electric Arc Furnace (EAF) slag containing larnite, gehlenite, wuestite, montcellite and calcite as the main crystal phases was alkali activated using the alkali activator prepared by the mixing of two solutions, sodium silicate and NaOH. Alkali Activated (AA) slag based on EAF slag is used as an adsorbent for Cu2+,Cd2+ and Zn2+ from aquatic solutions performing the batch adsorption test at the range temperature between 20 and 45 °C. AA slag sample is characterized by XRPD, FTIR and SEM/EDS analysis and the results indicate crystalline-amorphous structure of AA slag that contains Calcium Aluminate Silicate Hydrate (C-A-S-H) phase. Concentration of Cu2+, Cd2+ and Zn2+ in aqueous solution was determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results obtained indicate that, in a multicomponent system of three dissolved ions, AA slag shows highest affinity towards the Cu2+. The order of the metal ion adsorption onto AA slag was: Cu2+, Cd2+ and Zn2+. The highest adsorption of Cu2+ is attributed to the highest electronegativity and lowest hydrated ionic radii of cation in comparison to Cd2+ and Zn2+. Pseudo-first-order and pseudo-second-order kinetics models, Langmuir and Freundlich isotherm models were applied in order to investigate the adsorption process. The results have shown that data better fitted the pseudo-second kinetic and Langmuir isotherm models The investigation of mechanism of adsorption indicate that both film diffusion and intra-particle diffusion have occurred during the adsorption process. The thermodynamics parameters of adsorption process indicate the spontaneous and endothermic character of heavy metals adsorption on the AA slag.

Influence of seawater on alkali-activated slag concrete

This study examines the use of natural seawater as mixing water for alkali-activated slag concrete and reports the characteristics of alkali-activated slag concrete with exposure to seawater. Preliminary experiments were conducted on pastes in order to measure pH and select optimum activator content under the experimental conditions. Wet-sieved pastes from fresh concrete were used to evaluate the mineralogical and microstructural characteristics of reaction products. Compressive strengths and chloride contents were measured with the hardened concrete samples. The activators used in alkali-activated slag concrete were sodium hydroxide (5% weight of slag) and liquid sodium silicate (5% weight of slag). The alkali-activated slag samples showed the carbonation of calcium silicate hydrate (C–S–H), which resulted in the reduction in strength with time. The seawater-mixed alkali-activated slag samples produced additional reaction products, C4AH13, and chloride-bearing hydrocalumite, and they improved the strength. The seawater-mixed alkali-activated slag samples exposed in seawater exhibited improved mechanical performance compared to other samples. C–S–H carbonation did not occur, refinement of the pore structure was confirmed, and the compressive strength increased after exposure to seawater. The release of partial chloride ions, which were bound in solid phases, occurred; however, such slight leaching did not affect the strength of the samples. The investigation within the experimental conditions of this study showed a positive result regarding the use of seawater as mixing water in alkali-activated slag concrete.

Study on the Pneumatic Lime Injection in the Electric Arc Furnace Process: An Evaluation on the Performance Benefits

The pneumatic lime injection during the electric arc furnace (EAF) process by insufflation lances mounted on the furnace walls has gained much interest in the latest years. The main advantages, in comparison to the traditional procedure of lime lumps addition within the scrap bucket, can be summarized in raw materials consumption reduction, foaming benefits, operational cost benefits, and improvement in environmental aspects. In the proposed work, the advantages of a new lime injection system developed by Unicalce S.p.A. and installed on a 90 t EAF of Acciaierie di Calvisano are analyzed. Data from more than 1200 heats are acquired and compared with the traditional practice from an energetically and emissions point of view. To evaluate the benefits on the slag foamability, several slag samples, taken at the beginning and at the end of refining stage, are analyzed through isothermal solubility diagrams (ISDs). The ISD analysis results are then compared and validated with the total harmonic distortion (THD) of the arc in the corresponding heat. The upgrade to lime injection drives to considerable savings in electrical consumptions, oxygen, methane, and lime, with an overall save of more than 4,000 t year−1 of equivalent CO2.

Study on carbonation reactivity of silicates in steel slag accelerated by Bacillus mucilaginosus

Using steel slag to fix CO2 to prepare building materials is beneficial to reducing carbon emissions and recycling industrial waste. A novel approach for accelerating CO2 fixation and improving the mechanical properties of steel slag-based materials was proposed based on using microorganisms. Silicates are the main mineral phases of steel slag. This paper focused on the effects of microorganisms on carbonated conversion rate, compressive strength, and products of β-C2S and C3S. The results showed that microorganisms could accelerate carbonation and improve the conversion of β-C2S and C3S. The conversion level of β-C2S and C3S were increased by 16% and 12%, respectively, the compressive strength increased by 48.13% and 32.13%. The mineralization and carbonation products of β-C2S and C3S were characterized by XRD, FTIR, TG-DTC, and MIP methods. The main products of mineralized β-C2S and C3S were CaCO3, and the main crystal types were calcite and vaterite. The amorphous phases were silica and C-S-H gel. Compared with carbonation products, mineralization products had higher calcium carbonate content, a larger proportion of calcite, higher decomposition temperature, smaller crystal grain size, and lower porosity of paste samples. Besides, the compressive strength of mineralized steel slag samples was significantly higher than that of carbonated samples, showing a good strength improvement effect.

Characterization of steel slag by SEM-EDS, XRD, and INAA

Steel slag is considered a by-product of the steel industry and its reuse is a strategy for environmental protection, since it consists of potential polluting materials. Its main applications involve the use of large quantities of the raw material, but the extraction of ores in smaller proportions can be attractive. For example, magnetite (Fe3O4) may be of great interest for its magnetic properties in the production of composites with different applications. On the other hand, rare earth elements (REE) production is vital for new technologies and since traces of the different REE are found in most iron ores, their extraction can be conducted together. However, previous characterization of the slag is necessary; since they vary in mineralogical composition conform to steelmaking operations. Classical characterization techniques of ores such as X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) may be limited to characterize small fractions of materials. Therefore, in this study, neutron activation analysis was used as the characterization technique to confirm the presence of iron and REE in the slag. The steel slag composite sample of the Linz-Donawitz (LD) process was collected in a steelwork localized in the Iron Quadrangle, Minas Gerais, Brazil. The steel slag sample was characterized by instrumental neutron activation analysis (INAA), using the nuclear research reactor TRIGA MARK I IPR-R1. The results are compared with the characterizations made with XRD and SEM-EDS. Although XRD and EDS results indicated the presence of magnetite in a small proportion, INAA was decisive confirming the presence of REE in the mineralogical composition of the composite sample collected.

Chemical and physical effects of high-volume limestone powder on sodium silicate-activated slag cement (AASC)

This study aims at discussing physical and chemical influence of limestone powder (LS) on the AAS system. General properties, including fluidity, setting time, drying shrinkage, and mechanical strength of AAS pastes/mortars, were examined. Pore structure change and phase assemblages of LS-AAS composites were studied. The results showed that the addition of 50 wt% LS increased the fluidity and setting time of AAS pastes, but reduced the total drying shrinkage of AAS mortars. Meanwhile, around 30% reduction in mechanical properties were found at the same replacement ratio. The pore structure was refined in the pastes with LS replacement<25 wt%, but was coarsened in the sample with 40 wt% LS. Limited new phase was formed in the sodium silicate activated slag samples, which was believed to depend on the modulus of the activator. Around 30% hydration degree of LS was achieved in 40 wt% LS-replaced AAS pastes hydrated for 7 ~ 28 d as determined by TG-DSC analysis. The main drawbacks of AAS, fluidity, setting time, and drying shrinkage, are improved by using high-volume LS, so use of high-volume LS in AAS system can be an option for the purpose of environmental protection.

Comparison of trace element mobility from MSWI ash before and after plasma vitrification.

A common perception of plasma arc treatment systems for municipal solid waste incineration ash is that the resulting vitrified slag is inert from an environmental perspective. Research was conducted to examine this hypothesis and to assess whether reduced pollutant release results from pollutant depletion during the process of the ash with plasma, or encapsulation in the glassy vitrified matrix. The concentrations of four discrete municipal solid waste incineration ash samples before and after plasma arc vitrification in a bench-scale unit were compared. Slag and untreated ash samples were leached using several standardized approaches and mobility among the four metals of interest (e.g. As, Cd, Pb and Sb) varied across samples, but was generally high (as high as 100% for Cd). Comparison across methods did not indicate substantial encapsulation in the vitrified slag, which suggests that reduced pollutant release from plasma arc vitrified slag is due to pollutant depletion by volatilization, not encapsulation. This has significant implications for the management of air pollution control residues from waste-to-energy facilities using plasma arc vitrification.

АНАЛИЗ И ПЕРСПЕКТИВЫ УТИЛИЗАЦИИ ТЕХНОГЕННЫХ ШЛАКОВЫХ ОТХОДОВ СВИНЦОВОГО ПРОИЗВОДСТВА

The article presents the analysis and results of the study of technogenic slag waste of lead-zinc production. Slags of lead-zinc production contain a large number of toxic compounds: lead, zinc, osmium, cadmium, which are dangerous sources of environmental pollution. Due to the open storage of slags, it was found that the maximum permissible concentrations of lead were exceeded. Utilization of man-made slag waste is of great importance for reducing the negative impact on the safety of life and improving the environmental situation in the region. At the same time, slags are valuable raw materials containing compounds of non-ferrous and rare-earth metals. The article shows the results of laboratory studies of slags to determine the qualitative and quantitative composition of valuable components in the waste of lead production and the possibility of their further processing and disposal. Studies of the material of the heavy slag fraction were carried out on an electron probe microanalyzer of the JEOL IXA-8230 Electron Probe microanalyzer brand. X-ray diffractometric analysis of the average slag sample was performed on a DRON-4 diffractometer with Cu radiation, graphite monochromator. Samples were selected heavy fraction and manufactured artificial polished sections (briquettes). The sections were studied under the microscope of the brand LEICA DM 2500P and immersion in liquids. According to the results of research, it was found that lead slags contain a sufficiently high amount of non-ferrous metal compounds: lead oxide up to 0.7 % and zinc oxide up to 8.5 % of the weight amount of slag, which makes the process of recycling toxic waste from lead production technically and economically feasible.

Thermochemical and analytical approach to describe secondary slag phase formation and local process conditions in a full-scale BGL gasifier

This study aims to directly analyze untreated process samples from a full-scale BGL gasifier. It assesses as well as categorizes the findings to identify the most important effects governing the behavior of slags under gasifier conditions. A process slag sample from the Schwarze Pumpe BGL-type waste gasifier is thoroughly analyzed via X-ray diffraction (XRD), X-ray fluorescence (XRF), and using a scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX). The results are interpreted with the aid of thermodynamic equilibrium calculations using the FactSage™ software package to yield the main influence factors on slag viscosity and -structure. Since these are derived from full scale process samples, the severity of the impact to these processes can be assessed. Especially the effect of secondary phases apart from the main slag phase is evaluated. The differences between laboratory measurements and full-scale processes are identified. The composition of the gas atmosphere above the slag bath cannot easily be determined. This study uses a method to determine and include this gas atmosphere into the process slag analysis through thermodynamic equilibrium calculations. The temperature of the slag bath and the gas atmosphere around the slag is backtracked via analytically validated thermodynamic equilibrium calculations.