Tons Of Slag Research Articles

Study on the processing technology to clean Lao Cai's yellow phosphorus slag for building materials

AbstractSlag is produced in large quantities during the manufacturing of yellow phosphorus in the Tang Loong Industrial Zone (Lao Cai province, Vietnam). It is required to clean them before using them as building materials. The research findings on cleaning yellow phosphorus slag in water with slaked lime or quicklime as aiding agents are presented in this article. According to experimental findings, the typical water consumption is between 4 and 6 m3 per ton of slag, or 160 g of 20% Ca(OH)2 or 25 g of CaO per 300 L of water. It is simple to reuse the water after rinsing the slag. The processed yellow phosphorus slag's elemental composition data reveal that Ca(SiO2)O, which has a pseudo‐wollastonite structure, is the product's primary constituent. Although P and F are still present, they are mainly in the stable glass phase of Ca(SiO2)O, and there are not many impurities. The treated yellow phosphorus slag can be used in large quantities for building materials due to its safe radioactivity index (I) < 1.

Assessment of Concrete Hollow Blocks Incorporating Polyethylene Terephthalate (PRT) and Copper Slag as a Commercial Concrete Alternative

The increasing demand for durable and sustainable concrete driven by population growth and urbanization, highlights the need for an environmentally friendly alternative to traditional concrete, by innovating and recycling the top waste made by industries, given the country’s vulnerability to natural disasters and the environmental impact of concrete production. Polyethylene Terephthalate (PET) waste accounts for up to 13.9% of all waste plastics, posing a serious hazard to the environment and ecology both on land and in oceans (Ye et al., 2023); similarly, copper slag, a by-product of the smelting and processing of copper ore, is generated at a rate of 2.2 tons per ton of copper produced, leading to an annual figure of 24.6 million tons of slag (Gabasiane et al., 2021). With this, researchers are still finding ways to search for an alternative to lessen the environmental waste whilst contributing to the construction industry. Subsequently, this study aims to test the viability and effectiveness of Polyethylene Terephthalate and Copper Slag-induced concrete hollow blocks as an alternative to traditional commercial concrete hollow blocks. The researchers used a Post-Test Only Controlled Group Design, providing a complete understanding of their effect on concrete performance. By utilizing purposive sampling, the researchers were able to select shredded PET as their chosen samples. The raw data from the test results of varying ratios were treated using ANOVA. In terms of compressive strength and water absorption percentage, the 30-70 ratio emerged as the most durable, while in density, the commercial concrete displayed the highest amount. Upon comparative analysis, the results from the data treatment shows a significant difference in incorporating Polyethylene Terephthalate and Copper slag into concrete, specifically the 30% PET and Copper slag to 70% cement ratio, therefore rejecting the null hypothesis. It is advised to explore more ratios to accommodate different construction demands and have a minimum curing time of 28 days before testing the qualities of the said concrete hollow blocks.

COMPREHENSIVE WASTE-FREE PROCESSING TECHNOLOGY OF COPPER SMELTING SLAGS

More than 140 million tons of slag have been accumulated in the dumps of copper smelting enterprises of the Russian Federation. Maintaining dumps require significant expenses, which makes it necessary to dispose these production wastes as completely as possible. At the same time, these slags contain valuable elements, in particular, iron, copper, zinc, selenium, arsenic and some others; their extraction can make disposal cost-effective. Among these elements iron has the highest cost, which content is at the level of more than 40%; it is almost at the level of some iron ores used in ferrous metallurgy. However, the use of this iron-containing material in conventional ferrous metallurgy processes is complicated by the high (up to 0.6%) copper content. In addition, the extraction of iron by conventional methods does not solve the problems of disposal of newly formed slag. In this work, the technological methods of processing copper-smelting slags by solid-phase reduction of iron in the Tamman reduction furnace, smelting of reduction products in induction furnaces with the production of metallic iron and propants from the slag residue are proposed and worked out in laboratory conditions. The slags and slurries of the Karabash Copper Smelting Plant, where the main component of is iron, were used as the research material. The properties of cast iron grinding media, as well as ceramic proppants for the use in the oil industry, were investigated. As a result, the influence of elements passing into metal (silicon, carbon, copper and sulfur) on the hardness of grinding balls and the influence of the chemical composition of the slag on the strength of the obtained propants was clarified. A technological scheme of complex slag processing has been developed and a set of serially manufactured equipment has been selected. The economic efficiency of the organization of production is estimated.

Mineralogical Properties of the Copper Slags from the SarCheshmeh Smelter Plant, Iran, in View of Value Recovery

Annually, hundreds of thousands of tons of slags are involved in the reverberator and flash smelting as well as converting operations of Cu-Fe sulfide concentrates to produce matte in the Sar Cheshmeh copper smelter plant, Iran, disposed in the landfill and cooled in air. Due to their relatively high average copper content (about 1.5 wt%), a mineral processing plant based on the flotation process has recently been established to produce thousands of tons of Cu-sulfide concentrate after slag crushing and fine grinding operation. In order to make the flotation process more efficient, more knowledge is required on the form and origin of the copper losses in the slag. To achieve this, mineralogical studies of the slags using optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) methods have been carried out. Mineralogical analyses showed the main part of copper losses into the semi- to fully-crystallized magnetite-rich reverberator and flash slags characterized by crystal–glass matrix ratio ≤ 1 is moderate to coarse particles of Cu-Fe sulfides, i.e., chalcopyrite (CuFeS2) and bornite (Cu5FeS4), that are mainly chemically entrapped. In contrast, the mechanically entrapped fine- to coarse-grain (from 20 up to 200 µm) spherical-shaped of high-grade matte particles with chalcocite (Cu2S) composition containing droplets or veinlets of metallic copper (Cu0) are the dominant forms of copper losses into the converter slags characterized by crystal–glass matrix ratio > 1. From the value recovery point of view, our result show that the fully crystallized slags containing moderate- to coarse-grain copper-bearing particles will result in efficient recovery of a significant amount of entrained copper due to better milling response compared to semi-crystallized ones due to locking the fine- to moderate-grain copper particles in the silicate glassy matrix. Laboratory-scale grinding experiments showed that normal (≤74 μm) to fine (≤44 μm) grinding of high- Cu grade slags lead to a significant increase in the liberation degree of copper particles. in contrast, the increase in fine particle fractions (<37 μm) due to re-grinding or ultra-fine grinding of the originally low-Cu grade slags does not lead to the liberation of copper particles, but it will reduce the efficiency of the flotation process. This study suggests that the highest rate of copper recovery of the slag by the flotation process will be obtained at particle size 80% passing 44 µm which has also reached the optimal liberation degree of copper-bearing particles.

Thermodynamic modeling of metal reduction in copper-smelting slags and experimental verification of its results

Over 110 million tons of slag were accumulated in the dumps of the Russian copper-smelting enterprises, and their number is increasing. Environmental taxes and dumps maintenance costs are burdensome, which makes it necessary to make the most complete disposal of these production wastes. At the same time, these slags contain valuable elements, in particular, iron, copper, zinc, selenium, arsenic and some others, the extraction of which can make recycling profitable. The paper presents the results of a thermodynamic calculation of the behavior of copper-smelting slag elements in the mixture with carbon during heating. Modeling was performed using the TERRA software package. The influence of the process temperature in the range of 600 – 1750 °C on reduction of iron, zinc and silicon was analyzed at the amount of carbon in the system corresponding to the stoichiometry of iron reduction reactions and exceeding the stoichiometric one. It was established that when heated above 650 °C, metallic iron appears in the system, and its full reduction is completed at 1250 °C. The appearance of metallic zinc is observed in two temperature ranges: in the first, appearance of zinc is observed with a simultaneous decrease in concentration of zinc oxide; in the second, an increase in concentration of metallic zinc with a simultaneous decrease in concentration of zinc sulfide. At temperatures above 1650 °C, silicon appears in the system. Under laboratory conditions, the processes of solid-phase reduction of iron with the capture of zinc oxide and separation of the reduction products were tested. It was established that as a result of pyrometallurgical separation by melting reduction products, iron-carbon alloys (steel and cast iron) and alloys with high silicon content can be obtained. The results of the work can be used in development of theoretical and technological foundations for the processing of copper smelting slags, which are not processed by existing technologies.

Self Compacting Concrete Using Steel Slag as a Partial Replacement to Fine Aggregates

Concrete is the most widely used material in the building sector. Every year, hundreds of millions of cubic meters of concrete are utilized in India alone. Concrete is composed up of coarse and fine particles that have been cemented together using binding material. The typical concrete process in the construction industry is unsustainable since it consumes large amounts of natural resources such as sand, stone, and millions of tons of cement each year, which is harmful to the environment. Aggregate accounts for 70- 80% of the volume of concrete and has a considerable impact on its various properties. Even industrialized countries have suffered aggregate supply constraints as a result of the significant growth in concrete demand across the world. As a result, research is needed to identify an environmentally benign and readily available alternative to the usage of component elements in concrete. Slag is a by-product of the steel industry, created by impurities in the metals or ores being processed during smelting, welding, and other metallurgical and combustion operations. Slag is generally made up of mixed oxides of elements including silicon, Sulphur, phosphorus, and aluminium ash, as well as byproducts of their interactions with furnace linings and fluxing materials like limestone. According to estimates, around one thousand million tonnes of slag is created as solid waste in India alone, necessitating study into how to use this large byproduct of the steel industry, which is not recyclable, as one of the elements in concrete manufacturing. Steel slag in construction protects natural aggregates while also using slag waste from steel mills, resulting in a higher reduction in environmental pollution. The use of steel slag as a partial substitute for fine aggregate in different concrete mixes where varying percentages of cement have been replaced by fly ash and metakaolin is recommended in this study. The effect of increasing the proportion of steel slag on various parameters was researched and compared, as were tests on compressive strength, tensile strength, and water absorption.

Assessment of operating temperature within the new pavilion for slag management in Terni

The whole metallurgic sector produces up to 200 million tons of slag, which are tapped from the blast furnace (at a temperature of 1,500°C), and then need to be cooled down before disposal. These cooling processes are generally conducted open-air, significantly affecting local environmental quality of the surroundings. The present study aims at investigating the potential of an innovative slag cooling system housed within a pavilion, designed in order to minimize the emission of dust and pollutants out from the metallurgic plant. Such a system consists of a depressurized environment whose top surface is treated with black pigments and cooled down by water streams above it. Air is continuously extracted and then adequately filtered before being released outdoor. A numerical model was elaborated for evaluating the main heat flows developed within and through the pavilion’s envelope for the case study in Terni, central Italy. Once the physical and geometrical properties of the slag and the pavilion were defined, the heat exchanged with the air and water due to convection, as well as the latent heat dissipated through water evaporation was quantified. Results demonstrated the effectiveness of the water-based cooling system in keeping the roof temperature lower than 328 K without compromising the mechanical properties of the material. The evaporated water mass ranged between 4.2 kg h−1 and79.6 kg h−1 and was strongly influenced by seasonal weather conditions.

Characterization of iron oxide waste scales obtained by rolling mill steel industry

Every year, the steelmaking industry produces millions of tons of slags resulting in pollution to the environment. Among the waste, secondary metals and scales rich in iron oxides are also thrown away. There is a need to treat the steel waste in a reasonably way to protect the environment and proposing new cheap technologies for producing advanced materials. In this study we report the morphological and structural characterization of waste scales generated during roll milling steel process at JSC “Arcelor Mittal Temirtau”. The raw slag and annealed at 1000 °C were measured by X-ray diffraction (XRD), scanning electron microscopy adapted with energy dispersive X-ray (SEM- EDX), magnetometry and Mössbauer Spectroscopy (MS). Fe and O were detected by EDX as main chemical elements and Si, S, Ca, Mg, C and Al as minimal elemental composition. XDR for the raw sample revealed α-Fe2O3 (hematite) and Fe3O4 (magnetite) as principal and secondary phase, respectively; whereas monophasic α-Fe2O3 is detected for the scales annealed at 1000 °C. Magnetometry measurements show the Verwey transition for the raw sample and the Morin transition for the annealed at 1000 °C; those are fingerprints for the presence of magnetite and hematite, respectively. MS measurements for the raw sample consist of 6 small peaks of absorption and a broad two-lines absorption peak in the central part. The doublets are associated to the hyperfine parameters belonging to wustite. Magnetite is related to the hyperfine parameters for two sextets in octahedral Fe2.5+ and tetrahedral Fe3+sites and a small sextet that resembles the Mössbauer parameters of α-Fe2O3. Only a well crystallized and weakly ferromagnetic sextet confirm the presence of α-Fe2O3 phase for the sample annealed at 1000 °C due to thermal oxidation.

Re-Use of Silico-Manganese Slag

The world’s rapidly growing demand for raw manganese has made it increasingly important to develop methods for the economic recovery of manganese from secondary sources. The current study aims to present possible ways for the recycling and reuse of silico-manganese slag landfilled in Tulcea, City on the Danube River close to the Danube Delta Biosphere Reserve in order to save the natural resources raw of manganese. In the last three decades, the ferroalloy production plant has over 2.6 million tons of slag. Slag dumping constitutes a significant source of air, water and soil pollution, which adversely affects the environment and human health. Mn present in the slag dump is an environmental pollutant with potentially toxic effects. The results obtained with a leaching method to recover manganese from slag shows two efficient ways to valorize manganese from solid fraction (54%) with size particles between 80 and 315 µm and/or reuse the leaching medium (56% Mn) with a slag size of <80 µm. The motivation of our research is the possibility to recover manganese from slag by saving natural resources of raw of manganese and the remaining fraction can be used as aggregate sources (construction and road rehabilitation by saving extract mineral aggregates and agriculture), in order to decommission the slag dump. The proposed research is in concordance with the sustainable use of natural resources for the achievement of sustainable development of the 2030 Agenda and Waste Management Legislation due of the huge ecological costs regarding non-conforming waste dumping. If we consider the cost-benefit analysis, the environmental future is more important the human health and the benefits on the quality of the population’s health and the environment which are not non-measurable in monetary value.

Prospective Life Cycle Assessment at Early Stage of Product Development: Application to Nickel Slag Valorization Into Cement for the Construction Sector

Pyrometallurgical nickel industry in New Caledonia produces several tons of slag per year, which is stocked on site. There is no valorization today, except for a small transformation into sand. Pyrometallurgy highly consumes fossil-fuel energy and electricity for ore pre-treatment and nickel extraction inside electrical furnaces, which produces significant CO2 emissions. A new valorization approach is suggested to use these two local productions (slag and CO2) to mineralize slag and produce silico-magnesian cement for the construction sector. In order to ensure suitable environmental performances, many questions arise about the target valorized product: where and how to capture CO2 and produce cement, what constraints should be targeted for the mineralization process, can products be exported and where? Moreover, New Caledonia aims to develop renewable energies for electricity grid, which would mitigate local industries impacts in the future. A prospective Life Cycle Assessment (LCA) is used to define constraints on future product development. Two hundred scenarios are defined and compared as well as electricity grid evolution, using Brightway software. Thirteen scenarios can compete with traditional Portland cement for 12 of the 16 impacts of the ILCD midpoint method. The evolution of electricity grid slightly affects the performance of the scenarios by a mean of less than+/−25%, bringing a small difference on the number of acceptable scenarios. The main constraint requires improving the mineralization process by considerably reducing electricity consumption of the attrition-leaching operation. To be in line with scenarios concerning carbon neutrality of the cement industry by 2050, a sensitivity analysis provides the maximum energy consumption target for the mineralization process that is 0.9100 kWh/kg of carbonated slag, representing a 70% reduction of the current energy measured at lab scale. Valorization of nickel slag and CO2 should turn to carbon capture and utilization technology, which allows for the production of supplementary cementitious materials, another product for the construction sector. It will be the topic of a next prospective study.

Partial replacement of a traditional raw material by blast furnace slag in developing a sustainable conventional refractory castable of improved physical-mechanical properties

The exponential growth of industrial waste is a problem that has forced the development of clean technologies for their appropriate management. About 0.25–0.30 tons of slag is generated per ton of crude steel or pig iron in blast furnaces. In this research, blast furnace slag was recycled to progressively replace the fine fraction of flint clay at 0, 5, 10, 15, and 20 wt% in laboratory-scale conventional refractory castable samples fired at 120, 850, 1050, and 1400 °C. The physical properties were measured by linear shrinkage, bulk density, apparent porosity, and water absorption. The mechanical behavior was evaluated by cold crushing strength and cold modulus of rupture. Microstructural and mineralogical characteristics were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The incorporation of 10 wt% of blast furnace slag allowed the development of a slag-containing conventional refractory castable with improved properties compared to those of the reference castable, such as a bulk density of 2.61 g/cm3, percentages of apparent porosity, and water absorption of 10.64% and 4.08%, respectively, and mechanical resistance of 94.5 MPa. A denser microstructure via ceramic body’s porosity reduction is reached by the anorthite crystallization from a silica-rich liquid phase with CaO contents. This densification mechanism improves mechanical resistance by about 74%. The anorthite phase and the physical and mechanical characteristics exhibited by the sustainable refractory castable are attractive and suitable for its possible application in the aluminum industry as smelting furnace lining.

Effect of surface-treated energy optimized furnace steel slag as coarse aggregate in the performance of concrete under corrosive environment

Extraction of a massive volume of stone aggregate from the earth harms the environment through deforestation, air pollution, wasteland development (exhausted quarries), etc. On the other hand, dumping of tons and tons of slag from steel industries occupies more land area and causing pollution. Energy Optimized Furnace (EOF) steel slag (from JSW steels, Macheri, Salem, Tamil Nadu, India) is proposed as a substitute for the natural aggregate utilized in structural concrete. The main objective of the study is to improve the corrosion resistance of steel slag concrete. The porous structure of steel slag affects the durability properties of the concrete made with steel slag. The surface of EOF steel slag was treated with fly ash: cement slurry coating. The effectiveness of the surface treatment on steel slag in concrete was compared with steel slag concrete using corrosion inhibitor. In this present study, concrete specimens were prepared with EOF steel slag, surface-treated steel slag, and steel slag and corrosion inhibitor. The slag concrete was studied for its compressive strength, chloride ion permeability, and risk assessment of steel reinforcement corrosion embedded in concrete. The strength of EOF steel slag concrete is significantly acceptable. The surface modification of steel slag with fly ash: cement proved its significance by reducing the permeability of steel slag concrete. Since, the pores in the steel slag were filled entirely with pozzolanic gel with reduced interconnectivity of the pores. The surface modification of steel slag enhanced the corrosion resistance of steel slag concrete by taking longer times to reach high corrosion potentials.

Hydration Mechanism of Sustainable Clinker-Free Steel Slag Binder and Its Application in Mine Backfill

More than 600 million tons of slag are generated globally every year, leading to multiple environmental issues. Thus, research on applications of slags is crucial. The use of steel slag in cement is limited by its low hydraulic activity and volumetric instability. In the current study, we present a clinker-free steel slag binder (SSB) and discuss the coupled alkali–sulfate activation mechanism. The f-CaO was consumed during hydration, thus minimizing the expansion risk. SSB hydration products demonstrated a higher quantity and quality compared with cement, indicating excellent performance. We tested the SSB in a practical mine backfill application, investigating the effects of binder content, concentration, and aggregate grain size on the mechanical and rheological properties of the backfilling mixtures. The results demonstrate the ability of SSB to completely replace Portland cement with half the binder content dose without affecting the strength or flowability of the backfilling mixtures.

Complex Processing of Copper Smelting Slags with Obtaining of Cast Iron Grinding Media and Proppants


 
 
 The Ural region has a large number of metallurgical companies. The extraction of metals from ore is always accompanied by the accumulation of wastes. Currently, most of the wastes are stored in dumps and storage facilities forming technogenic deposits. One such that occupies huge areas is copper slag from the copper-smelting production. According to current estimations, about 2.2 tons of slag is formed for each ton of copper produced and about 24 million tons are produced annually [1]. In general, a copper slag contains about 35-45% iron and 0.4-0.5 copper, which indicates that this is a valuable secondary resource for recycling and utilization [33]. However, more than 80% of copper slag is not utilized, which makes it possible to consider this waste not only as a valuable material, but also as a potential hazard for the environment; it contaminates the soil and water with heavy elements [8]. Currently, only small amounts of the waste are recycled. In addition, technologies do not allow the complete extraction of valuable elements. This offers potential for the development of new highly efficient technologies for processing copper smelting wastes with extraction of valuable elements such as iron (Fe). Improvement of Fe quality requires a decrease in non-ferrous metal content, especially Cu. In recent years, extensive research was directed at the extraction of valuable materials from copper slags by high-temperature firing of copper conglomerates with subsequent magnetic separation or leaching of non-ferrous metals. However, these studies do not allow the complete processing of copper smelting slags. This work studies the production of iron-containing briquettes from copper-smelting slags, and their subsequent processing to obtain valuable products for metallurgical and oil companies.
 Keywords: briquette, reduction, cast iron, proppants
 
 

Ladle-Furnace-Slag Reprocessing at Evraz Nizhnii Tagil Iron and Steel Works OJSC

Ladle furnaces at Evraz Nizhnii Tagil Iron and Steel Works OJSC produce over 90,000 metric tons of slag per year. As this slag cools, it turns into a fine-grained powder; if the powder cannot be sold, it is temporarily stored until it can be disposed of [1]. We have considered producing easily used flux sinter from the slag generated during ladle processing of steel (hereinafter, ladle-furnace slag or LFS). Since LFS still contains a large number of metallic inclusions, it cannot be included in sinter fed into a hammer mill via the enclosed lime feed trough. LFS was therefore added to the iron flux charge along with the steel smelting fluxes in a duplex and mono process (steel converter slag (SCS) and vanadiumbearing converter slag (VCS)); the fluxes are then crushed in a jaw crusher. A successful test of the use of LFS in sinter was performed, the charge was free of raw limestone, coke consumption was lower, sinter machinery production capacity was higher, and the weight/sample ratio of the sintered product was improved. Since SCS and VCS contain up to 3.0% V2O5, this provided an opportunity to increase vanadium use during the blast-furnace sintering process by more than 100 metric tons of vanadium per month.

Experimental study and industrial demonstration on utilization of Fe, Ti and V from vanadium-bearing titanomagnetite ore sands

In order to achieve highly efficient utilization of three valuable elements Fe, Ti and V simultaneously from vanadium-bearing titanomagnetite ore sands, an improved carbothermic reduction method was proposed and verified in both laboratory scale and industrial test-bed scale. The method combined the process of direct reduction and the process of further reduction and separation. Particularly, pulverized coal injection was introduced. In experimental tests, the effects of parameters such as carbon content in briquette, reduction duration and reduction temperature on the contents of metallic Fe and FeO as well as Fe metallization rate were analyzed. Experimental results indicated that Fe metallization rate in the carbon-containing briquette could reach 75.83%. In the industrial test-bed tests, the effects of carbon content in briquette, reduction duration and reduction temperature were also investigated, respectively. In addition, processes with and without pulverized coal injection were tested. The comparative analysis indicated that the content of TiO2 in titaniferous slag was increased by applying pulverized coal injection, and it can reach 82.5 wt.%. Meanwhile, the energy performance analysis showed that the equivalent electricity consumption of the test-bed dropped significantly to 2071 kWh per ton of slag, about 26.0% less than that of traditional method. Moreover, the investment payback of the test-bed is 3.4 years. Both experiments and industrial test-bed tests demonstrated that the proposed method has the advantages of highly efficient utilization, high energy efficiency as well as good economic performance.

From Waste to Multi-Hybrid Layering of High Carbon Steel to Improve Corrosion Resistance: An In-Depth Analysis Using EPMA and AFM Techniques

Corrosion resistance of steel has attracted substantial interest for manufacturing applications to reduce costs corresponding to part failures, unexpected maintenance, and shortening lifespan. Meanwhile, millions of tonnes of slag, non-recyclable glass, and automotive shredder residue (ASR) are discarded into landfills every year, polluting the environment. Combining these two major issues, we delivered an alternative solution to enhance corrosion resistance of high-C steel. In this research, utilisation of these wastes (which were chemically bonded into steel substrate) as sources for production of multi-hybrid layering—including the multi-phase ceramic layer, the carbide layer, and the selective diffusion layer—was successfully achieved by single step surface modification technology. High-resolution topographical imaging by SEM and chemical composition analysis in micron-volume by electron probe micro analyser (EPMA) were performed. Nano-characterisation by atomic force microscopy (AFM) using the PeakForce quantitative nanomechanical mapping (PF-QNM) method was conducted to define Young’s modulus value of each phase in detail. Results revealed improvement of corrosion resistance by 39% and a significantly increased hardness of 13.58 GPa. This integrated approach is prominent for economic and environmental sustainability, consolidating industry demands for more profits, producing durable, steel components in a cost effective way to reduce dependency on new resources, and minimising negative impacts to the environment from disposal of wastes to the landfills.

A Kinetic Study Investigating the Carbothermic Recovery of Chromium from a Stainless-Steel Slag

In 2018, the stainless-steel industry produced > 10 million tons of slag, which for the most part was landfilled because of chromium oxide contamination. Long-term studies indicate a possible formation of soluble hexavalent chromium, which is classified as carcinogenic. Recent research focuses on the development of a treatment technology to recover chromium from the slag into a ferroalloy, producing an oxidic material that can be utilized in the construction industry. To date, there has been no literature dealing with the kinetics of a carbothermic treatment process to result in a model to predict the necessary treatment time. The present article fills this gap by investigating the reduction kinetics of chromium oxide of a process close to practical applications. Based on experimental measurements, a model has been developed to predict the necessary treatment time to reach a specific final chromium concentration as a function of the starting concentration and required process temperature in the range between 1600 °C and 1700 °C. Finally, presented findings can serve as a guideline to develop kinetic models in similar pyrometallurgical recovery processes.

Use of colemanite in ferronickel smelting

Use of colemanite in metal-slag systems aims primarily to decrease the viscosity of slag and, therefore, achieve better metal-slag separation. Enhanced metal-slag separation is helpful to decrease the number of suspended metal/alloy droplets in slag, i.e. the physical losses. In the literature, successful use of colemanite was reported both in steelmaking and copper matte smelting processes. Ferronickel smelting slags contain nickel in the range of 0.1-0.2% and correspondingly, metal-slag distribution ratio values of nickel are reported even above 200. On the contrary, nickel recoveries are hard to exceed 95%. This can be mostly attributed to the physical losses of nickel due to very high slag volume in ferronickel smelters; for 1 ton of ferronickel, 10-15 tonnes of slag are generated regardless of the type of the laterite, which contains significant quantity of gangue components. The authors thought that use of colemanite could be a solution to decrease physical losses. Therefore, the use of colemanite in ferronickel smelting was investigated in the present work. Laboratory-scale smelting experiments were conducted using calcined and prereduced laterites in a vertical tube furnace under different gas atmospheres. The amount of colemanite added was in the range of 0 - 2.5% of the total charge. The experiments were also performed using ferronickel and slag samples obtained from a ferronickel smelter.

Unit Ladle-Furnace: Slag Forming Conditions And Stabilization

<p>Nowadays almost all smelted steel is processed in "ladle-furnace" (LF), where the steel is processed under refining conditions and brought to the desired temperature and chemical composition. Therefore, large amounts of refining slag are formed. Only in Russia there is about 1.4 million tons of slag exported to dumps annually. This slag cannot be processed by the schemes implemented in the industry, since the slag quickly turns into the tiniest dust during solidification and cooling. Such dust is easily aerated and carried by the wind for long distances; it pollutes soils, dissolves in ground, sedimentary and sewage waters. It also pollutes slag dumps that are suitable for processing for crushed stone.</p>