Search Results (88)

This study investigates the phase formation and smelting process of a complex Al-Si-Mn alloy based on thermodynamic diagram analysis (TDA). The Fe-Si-Mn-Al system was analyzed considering binary and ternary subsystems, and the standard Gibbs free energy of formation of selected ternary compounds was calculated using the additive method. Based on these results, phase equilibrium diagrams were constructed, and the system was tetrahedralized, leading to the identification of 15 thermodynamically stable tetrahedra. It was established that compositions of industrial interest are predominantly localized within tetrahedra enriched in silicide and aluminosilicide phases, particularly FeSi-Fe₂Al₂Si-Fe₃Al₁₁Si₆-Mn₅Si₃. Experimental verification was carried out in a 250 kVA ore-thermal furnace using manganese ore, high-ash coal, and quartzite. The smelting process was conducted under slag-free conditions with stable electrical operation. The obtained alloy had the following composition (wt.%): Fe ~ 12.1, Si ~ 44.7, Mn ~ 34.5, and Al ~ 5.1, with low impurity levels (C < 0.5%, S < 0.02%, p < 0.09%). Microstructural analysis using SEM-EDS confirmed the formation of silicide (FeSi, Mn₅Si₃) and aluminosilicide phases, which ensure the structural stability of the alloy. It is shown that the localization of alloy compositions within specific tetrahedra of the Fe-Si-Mn-Al system prevents self-disintegration. The results demonstrate that TDA is an effective tool for predicting phase composition and optimizing the production technology of complex ferroalloys. Full article

Steel slags are major by-products of steelmaking, and their variable composition complicates recycling and valorization strategies. This study investigates four representative slag samples obtained from different production pathways at an industrial steel plant in Uzbekistan, using a combined multi-scale characterization approach. Bulk elemental composition was determined using X-ray fluorescence (XRF), while microstructural and phase-level analysis was carried out using scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), including both point analysis and automated phase mapping. The XRF results revealed two distinct compositional groups, with one slag dominated by Mn–Si–O chemistry and three slags characterized by high Ca content. SEM–EDS phase mapping further resolved these differences at the microscale, identifying manganese silicate and oxide phases in the Mn-rich slag, Ca–F–O dominant phases in two slags associated with fluorite flux addition, and a more heterogeneous Ca-based system with localized enrichments of Mn, Zn, and Cu in the fourth sample. The combined results demonstrate that slag composition strongly reflects steel grade and fluxing practice. The integration of XRF and SEM–EDS provides a robust framework for linking bulk chemistry with phase distribution, improving slag classification and supporting informed decisions for reuse and environmental management. Full article

This study investigates the feasibility of producing an Fe-Cr-Mn complex alloy through the recycling of technogenic wastes from metallurgical operations. The feed materials comprised chromium-bearing dust collected from the gas-cleaning system of high-carbon ferrochrome production, iron–manganese ore fines (<10 mm) from the Tur deposit (Kazakhstan), and coal sludge used as a carbonaceous reducing agent. Thermodynamic modeling of the carbothermic reduction of Cr and Mn oxides and the predicted distribution of components among the metal, slag, and gas phases were performed using the HSC Chemistry 10 software package over a high-temperature range. At 1800 °C, the calculated chemical composition of the target alloy was as follows (wt.%): Cr-35.84, Mn-24.47, Si-16.25, Fe-22.63, and C-0.82. To validate the modeling results, experimental smelting trials were carried out in a 100 kVA electric arc furnace, producing both metallic and slag phases. The average composition of the metal phase was (wt.%): Cr-37.17, Mn-14.46, Si-11.48, Fe-33.23, C-3.48, P-0.15, and S-0.021. The experimental results indicate the formation of a Cr-Mn alloy with elevated Cr and Fe contents and a noticeable C level, confirming the carbothermic nature of the reduction reactions. The composition and microstructural features of the smelting products were examined by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS). The findings demonstrate that the combined use of technogenic raw materials and a carbonaceous reductant enables the production of a Cr- and Mn-enriched metallic phase under satisfactory slag-forming conditions. Overall, the results confirm the potential of a resource-saving approach for valorizing fine technogenic wastes in the production of complex ferroalloys and for improving the recovery of target elements through optimization of the charge composition and smelting parameters. Full article

With ongoing development in the process industries, the accumulation of industrial inorganic solid wastes (IISWs) has become increasingly significant. IISWs are characterized by large volume and toxicity and pose challenges in treatment and control. IISWs from chemical processes mainly include red mud (RM), zinc slag, lithium slag (LS), electrolytic manganese residue (EMR), phosphogypsum (PG), water treatment sludge (WTS), sewage sludge, blast furnace slag (BFS), steel slag (SS), coal fly ash (CFA), coal gasification slag (CGS), copper smelting slag (CSS), and lead smelting slag (LSS). Having been chemically processed, they exhibit complex compositions that pose challenges for further utilization. In this paper, we comprehensively review the preparation of adsorbents from IISWs as raw materials, the applications of IISW-derived adsorbents, and their adsorption mechanisms. The obtained adsorbents include modified IISWs, zeolites, porous ceramics, and composite and hybrid adsorbents. The adsorption mechanisms, such as van der Waals forces, electrostatic interactions, and π–π interactions, contribute to the rapid adsorption kinetics and high adsorption capacity observed in these adsorbents. Full article

This study investigates the thermodynamic and technological aspects of smelting medium-carbon ferromanganese from Zhezdinsky manganese ore using ferrosilicomanganese and lime. The equilibrium distribution of components in the oxide-metal system was calculated using HSC Chemistry 10.0 within the temperature range of 573–2073 K. The modeling results revealed the effect of lime and ore consumption on slag phase composition as well as on manganese and silicon contents in the metallic phase. Experimental validation was performed in a laboratory Tamman resistance furnace and in a 100 kVA large-scale laboratory electric arc furnace. The chemical compositions of metal and slag were determined by bulk chemical analysis, while microstructure and local elemental distribution were examined using SEM-EDS. An increase in slag basicity was found to promote the transfer of silicon into the silicate phase while simultaneously reducing manganese losses to the slag. The large-scale laboratory smelting experiments, with a duration of 100–120 min per heat, enabled the establishment of a stable processing regime and the production of a metal with an average composition of 88.1 wt.% Mn, 1.6 wt.% C, and 0.03 wt.% Si. The corresponding slag contained approximately 15 wt.% MnO and 21 wt.% SiO₂. SEM-EDS analysis showed that the alloy possesses a heterogeneous microstructure consisting of an Fe-Mn metallic matrix with finely dispersed silicide microphases. Local silicon concentrations in these phases reach 15–24 wt.%, which explains the discrepancy between local and bulk chemical compositions. The experimental data are in good quantitative agreement with the thermodynamic modeling results, confirming that slag basicity and composition control are key factors for improving manganese recovery and stabilizing metal composition. The identified relationships can be applied in the development of industrially oriented smelting regimes for producing medium-carbon ferromanganese from Kazakhstan manganese raw materials. Full article

This study investigates the reaction thermodynamics of the sodium oxide-fluxed aluminothermic reduction of pyrolusite-based manganese ore under self-propagating high-temperature synthesis (SHS) conditions, using Si, Cr, and Cu as collector metals. The experimental results are compared with thermochemical equilibrium calculations using FactSage 7.3 thermochemistry software. Experimental mixtures were prepared with controlled additions of aluminium, sodium silicate, calcium oxide, and collector metals and heated to the ignition temperature in a muffle furnace preheated to 1350 °C. The resulting alloys and slags were analysed for bulk composition. Collector metals significantly influence alloy carbon saturation and manganese recovery. The individual reaction’s Gibbs free energy values and the gas–slag–metal equilibrium were calculated. Discrepancies between the experimental and equilibrium-predicted results highlight the kinetic factors of SHS processes, particularly with respect to aluminium uptake and manganese volatilisation. The main difference is the alloy’s aluminium uptake. The difference between the calculated and experimental aluminium levels is, in part, due to the higher partial oxygen pressure predicted in the gas–slag–metal equilibrium calculations, compared with that of the likely Al–Al₂O₃ governing reaction equilibrium. Short-circuiting of aluminium to the alloy is also a possible contributing factor. The findings provide insights into optimising feed formulations and process parameters for improved manganese recovery. Full article

This study investigates the thermodynamic and experimental aspects of producing a chromium–manganese ligature under high-temperature smelting conditions using low-grade iron–manganese ore and ferrosilicochrome (FeSiCr) dust as both a reducing agent and a chromium source. Thermodynamic modeling of the multicomponent Fe–Cr–Mn–Si–Al–Ca–Mg–O system was carried out using the HSC Chemistry 10 and FactSage 8.4 software packages to substantiate the temperature regime, reducing agent consumption, and conditions for the formation of a stable metal–slag system. The calculations indicated that efficient reduction of manganese oxides and formation of the metallic phase are achieved at a smelting temperature of 1600 °C with a reducing agent consumption of approximately 50 kg. Experimental smelting trials conducted in a laboratory Tammann furnace under the calculated parameters confirmed the validity of the thermodynamic predictions and demonstrated the feasibility of obtaining a concentrated chromium–manganese ligature. The resulting metallic product exhibited a high total content of alloying elements and had the following chemical composition (wt.%): Fe 35.41, Cr 41.10, Mn 8.15, and Si 4.31. SEM–EDS microstructural analysis revealed a uniform distribution of chromium and manganese within the metallic matrix, indicating stable reduction behavior and favorable melt crystallization conditions. The obtained results demonstrate the effectiveness of an integrated thermodynamic–experimental approach for producing chromium–manganese ligatures from low-grade mineral raw materials and industrial by-products and confirm the potential applicability of the proposed process for complex steel alloying. Full article

Cemented tailings backfill (CTB) is widely used in mining operations due to its operational simplicity, reliable performance, and environmental benefits. However, the poor consolidation of fine tailings with ordinary Portland cement (OPC) remains a critical challenge, leading to excessive backfill costs. This study addresses the utilization of modified manganese slag (MMS) as a supplementary cementitious material (SCM) for fine tailings from an iron mine in Anhui, China. Sodium silicate (Na₂SiO₃) modification coupled with melt-water quenching was implemented to activate the pozzolanic reactivity of manganese slag (MS) through glassy structure alteration. The MMS underwent comprehensive characterization via physicochemical analysis, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) to elucidate its physicochemical attributes, mineralogical composition, and glassy phase architecture. The unconfined compressive strength (UCS) of the CTB samples prepared with MMS, OPC, tailings, and water (T-MMS) was systematically evaluated at curing ages of 7, 28, and 60 days. The results demonstrate that MMS predominantly consists of SiO₂, Al₂O₃, CaO, and MnO, exhibiting a high specific surface area and extensive vitrification. Na₂SiO₃ modification induced depolymerization of the highly polymerized Q⁴ network into less-polymerized Q² chain structures, thereby enhancing the pozzolanic reactivity of MMS. This structural depolymerization facilitated formation of stable gel products with low calcium–silicon ratios, conferring upon the T-MMS10 sample a 60-day strength of 3.85 MPa, representing a 94.4% enhancement over the T-OPC. Scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) analysis revealed that Na₂SiO₃ modification precipitated extensive calcium silicate hydrate (C-S-H) gel formation and pore refinement, forming a dense networked framework that superseded the porous microstructure of the control sample. Additionally, the elevated zeta potential for T-MMS10 engendered electrostatic repulsion, while the aluminosilicate gel provided imparted lubrication, collectively improving the flowability of the composite slurry exhibiting a 26.40 cm slump, which satisfies the requirements for pipeline transportation in backfill operations. Full article

Red mud (RM) and electrolytic manganese residue (EMR) possess inherently complementary acid–base characteristics, and their synergistic utilization offers a promising approach to simultaneously enhance mechanical performance and mitigate environmental risks. However, the environmental behavior of RM-EMR composites, particularly in terms of pH buffering, ammonium nitrogen (NH₄⁺-N) control, and heavy metal mobility, remains inadequately understood. In this study, a composite cementitious paste was developed using RM and EMR, and the effects of the RM-to-EMR ratio (1: 3, 2: 3, 1: 1, and 3: 2), alkali activator dosage (30%, 40%, 50% and 60% by weight), and curing time (3 day, 7 day, 14 day, and 28 day) under standard curing conditions on unconfined compressive strength (UCS) were systematically evaluated. Leaching tests were conducted to assess pH evolution, NH₄⁺-N release, and heavy metal migration. The results showed that the optimal 28-day UCS of 35 MPa was achieved with an RM-to-EMR mass ratio of 2:3 and an activator dosage of 60%. EMR contributed to NH₄⁺-N leaching concentrations as high as 302 mg/L; however, under alkaline conditions (pH > 11), over 50% of the block samples met regulatory limits due to the transformation of NH₄⁺ into gaseous NH₃. Furthermore, Mn and Cd were effectively immobilized. In contrast, Al and Se exhibited elevated leaching, with Al showing particularly high concentrations under water leaching conditions. These results underscore the importance of raw material pretreatment and system optimization. Overall, this study provides new insights into the environmental behavior and safe resource utilization of RM and EMR in cementitious systems. Full article

The article presents the results of a study on the production of a complex chromium–manganese–silicon-containing ferroalloy in a large-scale laboratory ore-thermal furnace using man-made waste—chromium-containing aspiration dust obtained during smelting of high-carbon ferrochrome, fines (−5 mm) of iron–manganese ore currently stored in landfills, and finely dispersed coal sludge formed during enrichment. A single-stage technology for the production of a new complex chromium–manganese–silicon-containing ferroalloy by carbothermal reduction is proposed. A metallurgical assessment of the initial charge materials was carried out by the X-ray diffraction (XRD) phase analysis, and metal samples of the obtained ferroalloy were studied by scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS). The resulting ferroalloy has a complex microstructure with a predominance of carbide and intermetallic phases. A high degree of extraction of chromium (up to 80%), manganese (up to 75%), and silicon (up to 35%) was recorded. The average chemical composition of the obtained ferroalloy, wt.%: Cr—37.41; Mn—17.31; Si—11.84; C—3.81; P—0.14; S—0.02. The slag formed during the smelting of the ferroalloy has satisfactory technological properties: it is characterized by good fluidity, and it actively exits the furnace by gravity. Entanglement of metal kings in the slag is not observed. The results obtained confirm the technological feasibility of the utilization of technogenic raw materials for the production of complex ferroalloys of the FeCrMnSi type. Full article

This paper presents a dual-benefit method for green and sustainable mine construction through developing filling materials using solid waste. In practical engineering applications, there are sulfate ions in mine water, which leads to performance degradation in traditional cement-based filling materials. In this paper, electrolytic manganese slag-based mine filling materials (EBFMs) were developed by utilizing electrolytic manganese residue (EMR), fly ash (FA), phosphorus slag (PS), and quicklime (QL). The effects of EMR content on the basic performance and the sulfate resistance of EBFM in a 5 wt.% Na₂SO₄ solution at different stages of erosion were extensively discussed. The results showed that when the content of EMR was 25 wt.%, EBFM showed the best basic performance and sulfate resistance among all groups. After sulfate erosion, the compressive strength increased and the porosity decreased, and the mass of the samples increased. The EBFM exhibited superior sulfate corrosion resistance at the lowest porosity (4.14%) and the highest mass change rate (5.82%) after 90 days of sulfate erosion. The corrosion resistance coefficient stabilized between 1.23 and 1.24 after 30 days of erosion. In a sulfate environment, sulfate ions contribute to promoting hydration reactions to form more hydration products, which make a denser structure. The Fe-AFt (ferrous ettringite) formed during hydration demonstrates superior stability, representing a key factor for better sulfate resistance. The EBFM transformed the presence of sulfate ions in mine water (a typically adverse condition) into a beneficial factor that enhanced the materials’ performance, thereby exhibiting excellent sulfate resistance. Full article

In response to the pressing environmental challenges posed by electrolytic manganese residue (EMR) and red mud (RM), this study proposes an innovative cementitious material technology for the synergistic co-utilization of these industrial wastes. By employing steel slag (SS) as a calcium-rich skeleton, the system effectively immobilizes sulfates from EMR and alkalinity from RM, converting hazardous wastes into value-added construction materials. Through orthogonal experimentation, an optimal mix proportion was established—30% RM, 20% EMR, and 50% SS at a water-to-binder ratio of 0.28—which achieved a 28-day compressive strength of 20.40 MPa, meeting relevant industry standards for auxiliary cementitious materials. Microstructural analysis unveiled a multi-stage alkali-sulfate synergistic activation mechanism: (1) the high alkalinity derived from RM rapidly activates the dissolution of aluminosilicate phases in both SS and EMR; (2) sulfate ions released from EMR promote extensive formation of ettringite (AFt), enhancing early-age structural integrity; and (3) calcium ions from SS facilitate the development of a dense C-S-H gel matrix, which serves as the primary binding phase. More profoundly, this process exemplifies a self-stabilizing waste-to-resource conversion mechanism, whereby harmful constituents (sulfates and free alkalis) are constructively incorporated into stable hydration products. This work not only elucidates a coherent scientific framework for the safe and efficient reclamation of multi-source solid wastes, but also demonstrates a scalable and ecologically viable pathway for million-ton-scale valorization of EMR and RM. Furthermore, it presents feasibility insights for the application of high-dosage steel slag-based material systems, thereby unifying significant environmental and economic advantages. Full article

Capão da Roça, located in the municipality of Charqueadas, is one of the few areas of coal tailing deposits at the surface within the State of Rio Grande do Sul, Brazil that generates acid mine drainage (AMD). Over the course of 2007, the landfill was characterised in detail, and an active treatment plant involving pH neutralisation and metal precipitation operations was implemented to meet emission standards for mine water. In that year, based on the sulphur mass balance, it was estimated that the process of AMD generation would last for approximately two decades. The objective of this work was to study the temporal evolution of the parameters of the raw AMD. The effluent was analysed for 17 years on a monthly basis in regard to pH, acidity, metals (Fe, Al, and Mn), and sulphates. The results indicated an increase in pH (from 2.1 to 4.7), a decay in the concentration of metals (from 177.8 to 0.1 mg L⁻¹ for iron, 29.0 to 0.1 mg L⁻¹ for aluminium, and 3.1 to 0.6 mg L⁻¹ for manganese), sulphates (from 2023 to 307 mg L⁻¹), and acidity (from 539.5 mg CaCO₃ L⁻¹ to 3.96 mg CaCO₃ L⁻¹), which were adjusted to a first-order kinetic model in agreement with observations at some other mining sites. Over the years, the active lime neutralisation–precipitation treatment system has been efficient in treating the effluent. Today, most water quality parameters already meet emissions standards; however, the AMD treatment plant is still necessary to prevent pH fluctuations and to reduce the concentrations of manganese. For this reason, a transition from an active to a passive treatment system was considered. Pilot scale studies confirmed that channels filled with gravel-size limestone or slag enable the neutralisation/increase in the pH of the effluent and remove residual amounts of some metals, resulting in an effluent with no level of toxicity to the microcrustacean Daphnia magna. Full article

Aluminothermic reduction is gaining renewed interest as an alternative processing route for the circular economy. Aluminium is produced electrochemically in the Hall–Héroult process with minimal CO₂ emissions if electricity is sourced from non-fossil fuel energy sources. The Al₂O₃ product from the aluminothermic reduction process can be recycled via hydrometallurgy, with leaching as the first step. NaAlO₂ is a water-leachable compound that forms a pathway for recycling Al₂O₃ with hydrometallurgy. In this work, a suitable slag formulation is applied in the aluminothermic reduction of manganese ore to form a Na₂O-based slag of high Al₂O₃ solubility to effect good alloy–slag separation. The synergistic effect of added chromium metal as a collector metal is illustrated with an increased alloy yield at 68%, from 43% without added Cr. The addition of small amounts of carbon reductant to MnO₂-containing ore ensures rapid pre-reduction to MnO. This approach negates the need for a pre-roasting step. The alloy and slag chemical analyses are compared to the thermochemistry-predicted phase chemistry. The alloy consists of 57% Mn, 18% Cr, 18% Fe, 3.4% Si, 1.5% Al, and 2.2% C. The formulated slag exhibits high Al₂O₃ solubility, enabling effective alloy–slag separation, even at an Al₂O₃ content of 55%. Full article

Koelreuteria paniculata demonstrates significant potential for remediating manganese (Mn)-contaminated soils, particularly in mining areas. This study investigated its tolerance and enrichment mechanisms through pot experiments under varying Mn stress (0–15 mmol·L⁻¹). The results revealed a typical “low-promotion and high-suppression” response, with optimal growth observed at 5 mmol·L⁻¹ Mn. The species exhibited a strong capacity for Mn accumulation, primarily in the roots (up to 2910.24 mg·kg⁻¹), though the enrichment factor decreased at higher concentrations. Physiological and subcellular distribution analyses indicated that low Mn levels enhanced chlorophyll content and antioxidant enzyme activities, while excessive stress induced membrane lipid peroxidation. Crucially, tolerance was attributed to effective Mn immobilization in root cell walls (46–76%) and vacuolar compartmentalization in leaves (46–52%), which prevented metal translocation to sensitive organelles. These findings clarify the physiological mechanisms behind Mn tolerance in K. paniculata and support its use in practical Mn phytoremediation. Full article