1,721,016 research outputs found
Jarosite wastes reduction through blast furnace sludges for cast iron production
No full textJarosite is a dangerous waste derived from the hydrometallurgical route of zinc production, and it cannot be safely disposed of due to its acidic pH and the risk of toxic metal leaching. A new process at laboratory scale for the utilization of jarosite sludges is proposed, with the aim to obtain cast iron and an inert slag, using blast furnace sludges as reducing agent. Jarosite-reducing agent mixes were reduced in a muffle furnace at 1500 °C for 15 min. Two reducing agents were used: pure graphite (as control) and blast furnace sludges. Two CaO concentrations (5, 15%wt. on jarosite mass) and four equivalent C concentrations (7.5, 15, 30, 60%wt. on jarosite mass) were analysed. Cast iron was obtained from all of the mixes, but the highest reduction yield was obtained at 15%wt. equivalent C. The slag obtained from the control batch had a fully crystalline structure, while the one related to the sample with BF sludges showed an incipient vitrified structure, that could prevent the leaching of hazardous elements. The best process parameters to profitably obtain cast iron and a glassy slag are 15% of equivalent C, 5% CaO and blast furnace sludges as reducing agent
Manipulation of the leaching behaviour of high-alloyed steel EAF slags through the particle size modulation
Full text linkThe influence of slag tapping method on the efficiency of stabilization treatment of electric arc furnace carbon steel slag (EAF-C)
Full text linkStudies conducted over the past 10 years have demonstrated the technical suitability of the electric arc furnace slag as an alternative to natural stone in several applications. Steel slag can be profitably used as a road surface layer, for foundations and embankments, or for concrete aggregates. However, a strong limitation to their use is due to the presence of toxic metals (Ba, Cr, V, Mo, etc.) that can be released into the environment in particular conditions, especially for unbound products in which the slag can come into contact with water. Recent studies have investigated the role of chemical composition and microstructure of slag on toxic metal leaching, allowing for the design of suitable stabilization treatments for hindering such leaching. In this work, four batches of electric arc furnace carbon steel slag underwent a stabilization treatment and the obtained results were compared. In two batches, the stabilizer was added directly in the slag pot and the slag was cooled down in the same pot. The other two batches were stabilized during the downfall from slag door to slag pit. Several slag samples were collected before and after the stabilization treatment and were characterized by means of ED-XRF, XRD, and SEM analysis. Leaching tests were carried out in agreement with EN 12457-2 standard on 4 mm granulated slag, and the leachate concentration was compared with the current Italian limits listed in D.M. 3 August 2005 N. 201 and D.M. 5 April 2006 N. 186. The results clearly indicated that the cooling in the slag pot improved the efficiency of the stabilization treatment, leading to a complete transformation of the microstructure by a full development of homogeneous gehlenite matrix and a coarsening of Cr-spinels, assuring better toxic metal retention behavior. On the contrary, stabilization in the slag-pit was rapid and reduced the interaction between slag and stabilizer, leading only to partial transformation of larnite into gehlenite, and also reducing the coarsening of Cr-spinel. In addition, a layering effect was observed, resulting in an inhomogeneous product from top to bottom in terms of chemical composition, microstructure, and leaching behavior
Biochar and other carbonaceous materials used in steelmaking: Possibilities and synergies for power generation by direct carbon fuel cell
Full text linkThe objective of this study is the preliminary investigation of the feasibility of using a low-temperature molten hydroxide direct carbon fuel cell as an additional energy source for steel production by electric arc furnace. For this purpose, four carbonaceous materials related to the steel industry (electrographite, coke, torrefied biochar and hydrochar) were selected and characterized to predict their electrical behavior before their actual introduction as fuels. Special attention was paid to both the morphological effect (bulk/pellet or powder) and the chemical composition of the fuels on the electrical performance of the cell. Electrical measurements showed the positive influence of powder morphology, with coke powder having the highest peak power density value (49.6 mW/cm2). Electrographite was found to be useable only as a powder (18.7 mW/cm2), as the high chemical stability of the bulk morphology, provided by the smooth surface and the pitch used as a binder, acted as inhibitors of the carbon oxidation reaction. Although biochar appeared superior to hydrochar when inserted as powder (23.5 vs. 18.2 mW/cm2), the latter showed promising results also inserted as pellet. the latter also showed promising results when inserted as a pellet. Specifically, once inserted within the molten hydrochar, the binder used to produce the hydrochar is removed changing the morphology from pellet to sandy/powdery, negating the penalizing effect of the lower surface to volume of bulk morphology (15.8 vs. 18.2 mW/cm2) and offering the advantage of avoiding the milling process and related fine particulate production from an industrial point of view
Texture and Anisotropy Study on a Lightweight Steel
No full textHigh Mn and high Al steel alloys are a class a steel on which there is a wide and ongoing research. The main reasons are the lightweight-ness (density 16% lower than a typical stainless austenitic steel like AISI 306L) and the very high mechanical properties (up to 800MPa of Yield Strength and up to 55% of elongation at fracture). As a consequence of their properties, they could be very interesting for the automotive sector, but to be employed in any industrial sectors other properties must be checked and studied e.g., the formability. This class of steels are featured by the precipitation of peculiar type of carbides, called k-carbides, which can have a beneficial effect on the mechanical properties (precipitation strengthening) if they precipitate intra-granularly in the austenite matrix. To exploit such strengthening effect, different thermal treatments have been studied and performed on an austenitic lightweight steel alloy (X100MnAl30-9). The evolution of the anisotropy and the texture in different condition have been studied considering different thermo-mechanical conditions. Texture analysis has revealed different orientations, like Rt-C and α-fiber, depending thermomechanical history of the samples and, due to mechanical testing, good workability and low earing tendency is expected for the alloy in the analyzed conditions
Iron recovery from Bauxite Tailings Red Mud by thermal reduction with blast furnace sludge
Full text linkMore than 100 million tons of red mud were produced annually in the world over the short time range from 2011 to 2018. Red mud represents one of the metallurgical by-products more difficult to dispose of due to the high alkalinity (pH 10-13) and storage techniques issues. Up to now, economically viable commercial processes for the recovery and the reuse of these waste were not available. Due to the high content of iron oxide (30-60% wt.) red mud ranks as a potential raw material for the production of iron through a direct route. In this work, a novel process at the laboratory scale to produce iron sponge (≤ 1300 °C) or cast iron (> 1300 °C) using blast furnace sludge as a reducing agent is presented. Red mud-reducing agent mixes were reduced in a muffle furnace at 1200, 1300, and 1500 °C for 15 min. Pure graphite and blast furnace sludges were used as reducing agents with different equivalent carbon concentrations. The results confirmed the blast furnace sludge as a suitable reducing agent to recover the iron fraction contained in the red mud. For all the conditions tested, the metallization degree was higher than 70%, and the best condition to reduce red mud through blast furnace sludge was identified at 1:1 red mud/blast furnace (B.F.) sludges equal to 0.85 C/Fe2O3
Iron Making in Fornovolasco (Italy) at the End of the Fifteenth Century, the Canecchio Furnace, and an Artifact Characterization
Full text linkThis study investigates the rise of the Este family in Garfagnana (Tuscany, Italy) during the first half of the 15th century. The Este wanted to annex this region to improve their cast-iron production both for military and economic advantages. This article, thanks to a document found in the State Archives of Modena, encompasses an overview of the Fornovolasco settlement, a description of the furnace room, an analysis of the first casting campaign, and an attempt at furnace sizing. In the final section, a brief characterization of a cast-iron artifact found in that region and probably coming from this casting campaign is provided
Chemical Range of Stability for Self-Dusting Ladle Furnace Slags and Destabilizing Effect of Sulfur
Full text linkLadle furnace slags are characterized by volumetric expansions associated with the transition of dicalcium silicate (C2S) from β to γ phase, which generates fine dust during cooling, causing handling and storage issues that further reduce their recycling opportunities. The present work focuses on the effect of slag basicity on dusting and the role of sulfur on slag stability. Seven synthetic ladle slag precursors were made by mixing lime, magnesia, quartz and alumina in different proportions to match effective industrial compositions, increasing the binary basicity and keeping the ternary and quaternary indexes unchanged. Samples were heated to 1500 °C for 15 min and monitored during air cooling (< 5 °C/s) through thermocouples and camera to characterize the behavior, temperature, and time interval of dusting. The cooled samples were characterized chemically, mineralogically and morphologically. Starting from the chemistry of a self-stabilized slag, five additional slag precursors, characterized by increasing amounts of S, were created and analyzed using the same procedures. Experimental evidence showed the presence of three different dusting behaviors (stable, partial and complete) and stabilization of the slag once an optical basicity of 0.748 or higher was reached. In addition, mayenite was identified as the main phase capable of suppressing the β to γ transition by exerting hydrostatic pressure on C2S. Finally, although S can stabilize the β phase when dissolved in it, after saturation it precipitates as CaS, which can react with mayenite, locally decreasing the optical basicity and allowing dusting. Graphical Abstract: [Figure not available: see fulltext.]
Weldability Investigation on Lightweight Steels
No full textA novel class of AHSS (Advanced High Strength Sheet) for the automotive sector is under development. Such steels are featured by high Mn and Al content, low density (16% lower than conventional stainless steel), and high mechanical properties (up to 800MPa of yield strength and up to 55% of elongation at break). Due to the sector of application also other properties must be controlled e.g., weldability. Due to the high content of alloying elements and their nature, it is possible to forecast criticalities in such a process, like abnormal grain growth, and κ-carbides excessive precipitation. Such carbides are exploited for their strengthening effect in the case of coherent carbide intragranular precipitation, but they have a detrimental effect in the case of intergranular precipitation. An austenitic lightweight steel alloy (X100MnAl30-9) has been tested with a standard welding technique and different material starting conditions. The microstructure and mechanical properties of the joints have been investigated. Sturdy joints have been obtained with microstructure and mechanical properties coherent with expected ones and no detrimental effect of the welding has been observed in HAZ
Effect of Particle Size and Starch Gelatinization on the Mechanical and Metallurgical Performance of Jarosite Plus Blast Furnace Sludge Self-Reducing Briquettes
Full text linkJarosite and blast furnace sludge (BFS) are two of the main wastes from hydrometallurgical zinc production and iron production by blast furnace, respectively. Jarosite is a hazardous material that can, however, be reused in the steel industry after the recovering of the iron contained within it through carbothermal reduction in which BFS is exploited as a reducing agent. Yet, both wastes have a powdery nature that makes it necessary to agglomerate them for industrial use. On the other hand, despite the advantages of producing a self-reducing product, the particle size of the starting powders and the level of gelatinization of the binder could play a crucial role on the mechanical and metallurgical performance and, consequently, on the industrial applicability of the briquettes. Accordingly, two powder particle sizes (very fine sand vs. coarse silt) and three degree of corn starch binder retrogradation (10%, 30% and non-gelatinized starch) were used to produce briquettes, and their influence was studied by experimental and statistical investigation. The results showed that gelatinization plays the main role on the mechanical properties of briquettes, while particle size affects both density and reduction behavior; in particular, although all the mixtures were able to recover iron at 950 °C the most optimal mixture were obtained by using a granulometry of 63–125 μm for jarosite and less than 63 μm for BFS, while the local maximum of mechanical performance was obtained for a 30% starch retrogradation level
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