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3 pages, 158 KiB

Open AccessEditorial

Editorial for Special Issue “Metallurgical Slags”

by Jakub Kierczak and Vojtĕch Ettler

Minerals 2021, 11(1), 24; https://doi.org/10.3390/min11010024 - 28 Dec 2020

Cited by 3 | Viewed by 1609

Abstract

Exploitation and further processing of mineral resources are of great importance for modern society [...] Full article

(This article belongs to the Special Issue Metallurgical Slags)

Research

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16 pages, 6025 KiB

Open AccessArticle

Reduction and Dissolution Behaviour of Manganese Slag in the Ferromanganese Process

by Xiang Li, Kai Tang and Merete Tangstad

Minerals 2020, 10(2), 97; https://doi.org/10.3390/min10020097 - 22 Jan 2020

Cited by 8 | Viewed by 3880

Abstract

The reduction and liquidus behaviour of manganese slag with different basicities were studied in non-isothermal experiments in the temperature range of 1400–1500 °C. Certain amounts of quartz were added to Assmang ore (South Africa), and lime was added to Comilog ore (Gabon), to [...] Read more.

The reduction and liquidus behaviour of manganese slag with different basicities were studied in non-isothermal experiments in the temperature range of 1400–1500 °C. Certain amounts of quartz were added to Assmang ore (South Africa), and lime was added to Comilog ore (Gabon), to adjust the charge basicity to 0.5, 0.8 and 1.2. The extent of manganese ore reduction as a function temperature were determined by thermo-gravimetric (TG) balance. Morphology of ores and its change in the course of reduction was examined by scanning electron microscopy (SEM). The results show that the reduction rate of Assmang slag decreases with decreasing basicity, as the liquidus temperature of slag decreases. When spherical MnO phase is present, the activity of MnO is high, and the reduction rate is rapid. Comilog slags show a much higher reduction rate than Assmang slags. The activation energies of MnO reduction between 1400 to 1500 °C are estimated in this study and found to be 230 kJ/mol for Assmang charges and 470 kJ/mol for Comilog charges. The dissolution behaviours of Assmang and Comilog slags were also studied by FactSage simulation and verified by experiments. Full article

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23 pages, 2803 KiB

Open AccessArticle

Trace Elements of Cu-(Fe)-Sulfide Inclusions in Bronze Age Copper Slags from South Urals and Kazakhstan: Ore Sources and Alloying Additions

by Dmitry A. Artemyev and Maksim N. Ankushev

Minerals 2019, 9(12), 746; https://doi.org/10.3390/min9120746 - 30 Nov 2019

Cited by 29 | Viewed by 5235

Abstract

In the paper, the results of an investigation into trace elements found in slag sulfides from 14 archaeological Bronze Age settlements of the Cis-Urals, Trans-Urals, and North and Central Kazakhstan are presented. The study used Cu-(Fe)-sulfides as indicator minerals. Cu-(Fe)-S minerals in slags [...] Read more.

In the paper, the results of an investigation into trace elements found in slag sulfides from 14 archaeological Bronze Age settlements of the Cis-Urals, Trans-Urals, and North and Central Kazakhstan are presented. The study used Cu-(Fe)-sulfides as indicator minerals. Cu-(Fe)-S minerals in slags are primarily represented by covellite and chalcocite, as well as by rarer bornite and single chalcopyrite grains. Slag sulfides formed relic clasts and neogenic droplets of different shapes and sizes. Supergenic ores in the Bronze Age in Urals and Kazakhstan played a significant role in the mineralogical raw material base. In sulfides, the main indicator elements, Fe, Co, Ni, As, Se, Te, Sb, Ag, Pb, and Bi, are important markers of copper deposit types. Sulfides from olivine Cr-rich spinel containing slags of Ustye, Turganik are characterized by As-Co-Ni high contents and confined to copper deposits in ultramafic rocks. Olivine sulfide-containing slags from Kamenny Ambar, Konoplyanka and Sarlybay 3 are characterized by Co-Se-Te assemblage and confined to mafic rocks. Glassy sulfide-containing slags from Katzbakh 6, Turganik, Ordynsky Ovrag, Ivanovskoe, Tokskoe, Bulanovskoe 2, Kuzminkovskoe 2, Pokrovskoe, Rodnikovoe, and Taldysay are characterized by Ag-Pb-(Ba)-(Bi) assemblage and confined to cupriferous sandstone deposits. High As, Sb, Sn, and Ba contents found in slags can be seen as indicators of alloying or flux components in primary copper smelting. These include samples from Ustye, Katzbakh 6, Rodnikovoe, and Taldysay sites, where high Ba and As slag contents are identified. The compilation of a database with a broad sample of sulfide compositions from Bronze Age slags and mines in the Urals and Kazakhstan will permit the further identification of ore types and raw materials associated with a particular deposit. Full article

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15 pages, 5172 KiB

Open AccessArticle

The Influence of Slag Tapping Method on the Efficiency of Stabilization Treatment of Electric Arc Furnace Carbon Steel Slag (EAF-C)

by Davide Mombelli, Andrea Gruttadauria, Silvia Barella and Carlo Mapelli

Minerals 2019, 9(11), 706; https://doi.org/10.3390/min9110706 - 14 Nov 2019

Cited by 10 | Viewed by 4656

Abstract

Studies 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 [...] Read more.

Studies 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. Full article

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14 pages, 7265 KiB

Open AccessArticle

Multi-Analytical Characterization of Slags to Determine the Chromium Concentration for a Possible Re-Extraction

by Liesbeth Horckmans, Robert Möckel, Peter Nielsen, Frantisek Kukurugya, Christine Vanhoof, Agnieszka Morillon and David Algermissen

Minerals 2019, 9(10), 646; https://doi.org/10.3390/min9100646 - 22 Oct 2019

Cited by 19 | Viewed by 5449

Abstract

The CHROMIC project (effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials) aims to recover chromium from steelmaking and ferrochrome slags to regain valuable resources and simultaneously reduce potential environmental impacts. To develop the recovery flowsheets [...] Read more.

The CHROMIC project (effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials) aims to recover chromium from steelmaking and ferrochrome slags to regain valuable resources and simultaneously reduce potential environmental impacts. To develop the recovery flowsheets and reliably calculate metal recovery, an accurate assessment of chromium concentration and distribution is essential. Therefore, model streams were thoroughly characterized using a combination of analytical techniques. In all materials, chromium is present in distinct but often small spinel phases, intergrown with other minerals and showing a considerable zonation in Cr content with higher amounts in the cores. The small size of the Cr-rich particles makes recovery by mineral processing challenging. Measured chromium content was found to differ largely based on the chemical dissolution method applied. The analysis of insoluble residues and comparison with a standard reference material evidenced that standard acid dissolution procedures based on HCl/HNO₃/HBF₄ and HNO₃/HF/H₂O₂ are insufficient to fully dissolve spinel structures, leading to severe underestimations of chromium content. A sodium peroxide treatment is required for a full dissolution of spinels. This is noteworthy, since most of the legislation for the reuse of slags is currently based on acid dissolution methods. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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16 pages, 1854 KiB

Open AccessArticle

Properties of Inorganic Polymers Produced from Brick Waste and Metallurgical Slag

by Athanasia Soultana, Aikaterini Valouma, Georgios Bartzas and Konstantinos Komnitsas

Minerals 2019, 9(9), 551; https://doi.org/10.3390/min9090551 - 12 Sep 2019

Cited by 22 | Viewed by 4728

Abstract

This paper explores the alkali activation potential of brick wastes and metallurgical slags. Inorganic polymers (IPs) were produced using an alkaline medium consisting of sodium hydroxide and sodium silicate solutions and the optimum synthesis conditions were determined. In this context, the variable parameters, [...] Read more.

This paper explores the alkali activation potential of brick wastes and metallurgical slags. Inorganic polymers (IPs) were produced using an alkaline medium consisting of sodium hydroxide and sodium silicate solutions and the optimum synthesis conditions were determined. In this context, the variable parameters, such as solid to liquid (S/L) ratio, curing temperature (60, 80 and 90 °C) and ageing time (7 and 28 days) on the compressive strength and the morphology of the produced IPs were investigated. Specimens produced under the optimum synthesis conditions were subjected to high temperature firing and immersed in distilled water and acidic solutions for various periods of time, in order to assess their durability and structural integrity. The results showed that the IPs produced using a mix ratio of 50 wt % metallurgical slag and 50 wt % brick wastes, cured at 90 °C and aged for 7 days obtained the highest compressive strength (48.9 MPa). X-ray fluorescence analysis (XRF), particle size analysis, Fourier transform infrared spectroscopy (FTIR), mineralogical analysis (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and thermogravimetric (TG) analysis also confirmed the optimum microstructural characteristics and the chemical reactions that took place during synthesis. The overall results of this study indicate that the co-valorization of different waste streams, which are produced in large quantities and cause environmental problems if not properly managed, is a viable alternative for the production of binders or secondary construction materials with higher added value. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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24 pages, 7454 KiB

Open AccessArticle

Prospective (Bio)leaching of Historical Copper Slags as an Alternative to Their Disposal

by Anna Potysz and Jakub Kierczak

Minerals 2019, 9(9), 542; https://doi.org/10.3390/min9090542 - 9 Sep 2019

Cited by 36 | Viewed by 4749

Abstract

The aim of this study was to evaluate the feasibility of (bio)hydrometallurgical methods for metal extraction from historical copper slags. Two types of slags (amorphous slag—AS, and crystalline slag—CS) were subjected to 24 to 48 h of leaching with: (i) Sulfuric acid at [...] Read more.

The aim of this study was to evaluate the feasibility of (bio)hydrometallurgical methods for metal extraction from historical copper slags. Two types of slags (amorphous slag—AS, and crystalline slag—CS) were subjected to 24 to 48 h of leaching with: (i) Sulfuric acid at 0.1, 0.5, and 1 M concentrations at 1%, 5%, and 10% pulp densities (PDs); and (ii) normality equivalent (2 N) acids (sulfuric, hydrochloric, nitric, citric, and oxalic) at pulp densities ranging from 1% to 2%. Bioleaching experiments were performed within 21 days with Acidithiobacillus thiooxidans accompanied by an abiotic control (sterile growth medium). The results demonstrated that the most efficient treatment for amorphous and crystalline slag was bioleaching at 1% PD over 21 days, which led to extraction of Cu at rates of 98.7% and 52.1% for AS and CS, respectively. Among the chemical agents, hydrochloric acid was the most efficient and enabled 30.5% of Cu to be extracted from CS (1% PD, 48 h) and 98.8% of Cu to be extracted from AS (1% PD, 24 h). Slag residues after leaching were characterized by strong alteration features demonstrated by the complete dissolution of fayalite in the case of CS and the transformation of AS to amorphous silica and secondary gypsum. Based on this study, we conclude that amorphous slag is a more suitable candidate for potential metal recovery because of its generally high susceptibility to leaching and due to the generation of residue significantly depleted in metals as the end product. The inventory of economically relevant metals showed that 1 ton of historical copper slag contains metals valued at $47 and $135 for crystalline and amorphous slag, respectively, suggesting that secondary processing of such materials can potentially be both economically and environmentally viable. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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19 pages, 5138 KiB

Open AccessArticle

Investigation of Possible Leaching Control Mechanisms for Chromium and Vanadium in Electric Arc Furnace (EAF) Slags Using Combined Experimental and Modeling Approaches

by Simone Neuhold, André van Zomeren, Joris J. Dijkstra, Hans A. van der Sloot, Peter Drissen, David Algermissen, Dirk Mudersbach, Susanne Schüler, Thomas Griessacher, Johann G. Raith, Roland Pomberger and Daniel Vollprecht

Minerals 2019, 9(9), 525; https://doi.org/10.3390/min9090525 - 30 Aug 2019

Cited by 22 | Viewed by 4358

Abstract

In this study, possible leaching control mechanisms for Cr and V in electric arc furnace slags were investigated by using a multi-methodological approach. Aside from chemical and mineralogical bulk analyses, special emphasis was given to surface investigations of the slags prior to and [...] Read more.

In this study, possible leaching control mechanisms for Cr and V in electric arc furnace slags were investigated by using a multi-methodological approach. Aside from chemical and mineralogical bulk analyses, special emphasis was given to surface investigations of the slags prior to and after leaching. In addition, pH dependence leaching tests were performed and the obtained data were evaluated with hydrogeochemical models. Investigations revealed that Cr and V are mainly bound in spinel and wuestite as well as minor amounts of olivine. Spinel and wuestite do not dissolve during water leaching for 48 h, whereas, depending on the composition of olivine, this phase either dissolves and releases V and Cr congruently, or does not dissolve but may hydrate. Melilite may also hydrate, but neither V nor Cr were detected in this phase. It appears that leached V is subsequently adsorbed onto these newly hydrated phases. The combination of the applied methods further showed that the abundance of calcium silicates, spinel, and wuestite is influenced by the FeO/SiO₂ and CaO/SiO₂ ratio in the slag. Therefore, it is assumed that the leaching of V and Cr can be minimized by changing these ratios to favor the formation of Fe bearing calcium silicate and spinel instead of wuestite. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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26 pages, 3604 KiB

Open AccessArticle

Geochemical Characterization of Iron and Steel Slag and Its Potential to Remove Phosphate and Neutralize Acid

by Nadine M. Piatak, Robert R. Seal II, Darryl A. Hoppe, Carlin J. Green and Paul M. Buszka

Minerals 2019, 9(8), 468; https://doi.org/10.3390/min9080468 - 31 Jul 2019

Cited by 21 | Viewed by 7292

Abstract

Iron and steel slags from legacy and modern operations in the Chicago-Gary area of Illinois and Indiana, USA, are predominantly composed of Ca (10–44 wt. % CaO), Fe (0.3–28 wt. % FeO), and Si (10–44 wt. % SiO₂), with generally lesser [...] Read more.

Iron and steel slags from legacy and modern operations in the Chicago-Gary area of Illinois and Indiana, USA, are predominantly composed of Ca (10–44 wt. % CaO), Fe (0.3–28 wt. % FeO), and Si (10–44 wt. % SiO₂), with generally lesser amounts of Al (<1–15 wt. % Al₂O₃), Mg (2–11 wt. % MgO), and Mn (0.3–9 wt. % MnO). Mineralogy is dominated by Ca ± Mg ± Al silicates, Fe ± Ca oxides, Ca-carbonates, and high-temperature SiO₂ phases. Chromium and Mn concentrations in most samples may be environmentally significant based on comparison with generic soil contaminant guidelines. However, simulated weathering tests suggest these elements are present in generally insoluble phases making their use in water treatment applications possible; however, the generation of high pH and alkaline solutions may be an issue. As for possible water treatment applications, batch and flow-through experiments document effective removal of phosphate from synthetic solutions for nearly all slag samples. Air-cooled fine fractions (<10 mm) of modern slag were most effective; other types, including modern granulated, modern air-cooled coarse fractions (>10 mm), and legacy slag removed phosphate, but to a lesser degree. An additional water treatment application is the use of slag to neutralize acidic waters. Most slag samples are extremely alkaline and have high net neutralization potentials (NNP) (400–830 kg CaCO₃/t), with the highest approximately equivalent to 80% of the neutralization potential of calcite. Overall, phosphate removal capacity and NNP correlate positively with total Ca content and the dissolution of Ca minerals facilitates secondary Ca phosphate formation and consumes acid during hydrolysis. Utilizing locally available slag to treat waste or agricultural waters in this region may be a higher value alternative than use in construction, potentially offsetting restoration costs to degraded legacy areas and decreasing steel manufacturers’ current waste footprint. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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25 pages, 9265 KiB

Open AccessArticle

Geometallurgical Characterization of Non-Ferrous Historical Slag in Western Tasmania: Identifying Reprocessing Options

by Anita Parbhakar-Fox, Sarah Gilmour, Nathan Fox and Paul Olin

Minerals 2019, 9(7), 415; https://doi.org/10.3390/min9070415 - 5 Jul 2019

Cited by 9 | Viewed by 4995

Abstract

Pyrometallurgical processing of ore from the Zeehan mineral field was performed intermittently between 1896 and 1948, primarily recovering Pb, Ag and Cu. While Zn recovery was attempted at the time, it was unsuccessful using the available technology. Consequently, Zn reported to the slag [...] Read more.

Pyrometallurgical processing of ore from the Zeehan mineral field was performed intermittently between 1896 and 1948, primarily recovering Pb, Ag and Cu. While Zn recovery was attempted at the time, it was unsuccessful using the available technology. Consequently, Zn reported to the slag during the smelting process. Today, the former smelter site consists of two large slag piles (North and South). Using a range of techniques (including X-ray diffractometry, scanning electron microscopy, laser ablation inductively coupled plasma mass spectrometry, and static testing) the geometallurgical and geo-environmental properties of these slag materials (n = 280) were determined. The South and North piles contain on average 15% and 11% Zn, respectively. A range of complex mineral phases were identified, and are dominated by glass, silicates (i.e., monticellite–kirschsteinite and hardystonite), oxides (gahnite and hercynite) and minor sulfides (sphalerite and wurtzite). Microtextural examinations defined nine mineral phases (Glass A, Silicates A to D, Oxides A and B, Sulfides A and B). Zn was concentrated in Sulfide A (26%), Glass A (24%) and the Silicates (43%), while Pb was concentrated in Oxide B (76%), with Sulfide B host to the highest Ag (45%) and Cu (65%). Considering this, recovery of Zn using conventional hydrometallurgical processes (i.e., sulfuric acid leaching) is suitable, however the application of unconventional biohydrometallurgical techniques could be explored, as well re-smelting. These slag materials are classified geo-environmentally as potentially acid forming, with leachate concentrations of Zn, Pb consistently above ANZECC (2000) aquatic ecosystem 80% protection guideline values, and, for the majority of samples, exceedances of Cu, Ni and Cd were also measured. Considering these findings, reprocessing of these historic slags for Zn extraction may provide an economically feasible management option for rehabilitating this historical site. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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19 pages, 24884 KiB

Open AccessArticle

Slags as Evidence for Copper Mining above Casaccia, Val Bregaglia (Central Alps)

by Hans-Rudolf Wenk, Rong Yu, Nobumichi Tamura, Duri Bischoff and Walter Hunkeler

Minerals 2019, 9(5), 292; https://doi.org/10.3390/min9050292 - 12 May 2019

Cited by 1 | Viewed by 5617

Abstract

Slags from the remote Mota Farun locality above Casaccia (Val Bregaglia, Swiss Alps) have been analyzed with scanning electron microscopy, X-ray powder diffraction and microfocus synchrotron X-ray diffraction to determine mineralogical composition and microstructures. Non-magnetic slag samples are largely composed of euhedral and [...] Read more.

Slags from the remote Mota Farun locality above Casaccia (Val Bregaglia, Swiss Alps) have been analyzed with scanning electron microscopy, X-ray powder diffraction and microfocus synchrotron X-ray diffraction to determine mineralogical composition and microstructures. Non-magnetic slag samples are largely composed of euhedral and dendritic iron-rich olivine in a glassy matrix. Locally there are zones with globular inclusions rich in bornite ((Cu₅Fe)S₄) and locally metallic copper. Some regions display dendritic pentlandite ((Fe,Ni)₉S₈). Magnetic samples are mainly composed of fayalite (Fe₂SiO₄) and wüstite (FeO), with minor magnetite (Fe₃O₄). The mineralogical composition indicates that slags were the product of copper smelting. The slag compositions and morphologies are analogous to slags described from the Oberhalbstein (Graubünden, Switzerland) and the Trentino Alps (Italy) which are attributed to metallurgical exploitations of the Late Bronze Age. While the origin of the ore could not be determined, it may be related to ore deposits of chalcopyrite in greenschists and serpentinites in the vicinity, such as Alp Tgavretga (Septimer Pass) and Val Perossa (Val Bregaglia). Full article

(This article belongs to the Special Issue Metallurgical Slags)

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19 pages, 4232 KiB

Open AccessArticle

Understanding Heterogeneity of a Slag-Derived Weathered Material: The Role of Automated SEM-EDS Analyses

by Anna Pietranik, Jakub Kierczak, Rafał Tyszka and Bernhard Schulz

Minerals 2018, 8(11), 513; https://doi.org/10.3390/min8110513 - 8 Nov 2018

Cited by 18 | Viewed by 3921

Abstract

Slag heaps over years may evolve into complexly weathered zones, which are a challenging material for analyses as they contain phases from numerous sources and at different stages of weathering. However, the weathered zones are important parts of slag heaps, because they contain [...] Read more.

Slag heaps over years may evolve into complexly weathered zones, which are a challenging material for analyses as they contain phases from numerous sources and at different stages of weathering. However, the weathered zones are important parts of slag heaps, because they contain both primary and secondary phases enriched in metal(oid)s that may become soluble under specific conditions. The weathering reactions related to metal release or precipitation may be recorded in a heavy mineral fraction as the fraction contains predominately minerals with elevated toxic elements concentrations. Therefore, an automated SEM analysis on a polished section of included heavy mineral particles was applied in this paper for a rapid recognition of phases in a complex setting and their classification into detrital, primary and secondary phases. The approach was applied to a slag heap in Świętochłowice (Upper Silesia, Poland) and it consisted of analyzing magnetic and non-magnetic heavy mineral fractions from three distinct horizons noted A, B and C. Materials had been previously interpreted as being sourced from the heap itself (lowermost horizon C) and from artificially added materials used later for superficial site remediation (upper horizons A and B). Instead, automated SEM analysis demonstrated that horizon C is derived from the slag heap weathering, horizon B is derived predominately from the artificially added materials, whereas horizon A is a mixture of the B and C horizons. Additionally, when slag particles in horizons A and C are compared, the lowermost horizon C contains more slag-derived secondary phases, whereas horizon A contains more primary slag phases. Therefore, horizon A remains the most prone to releasing toxic elements because, considering its position as the uppermost horizon, it can be submitted to climatic solicitation (fast water circulation). Full article

(This article belongs to the Special Issue Metallurgical Slags)

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11 pages, 3880 KiB

Open AccessArticle

Stability of Chromium in Stainless Steel Slag during Cooling

by Qing Zhao, Chengjun Liu, Longhu Cao, Xiang Zheng and Maofa Jiang

Minerals 2018, 8(10), 445; https://doi.org/10.3390/min8100445 - 11 Oct 2018

Cited by 24 | Viewed by 3693

Abstract

The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling [...] Read more.

The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling process is still poorly understood. In this work, the phase composition and chromium distribution of SS slag from different quenching temperatures were experimentally studied, and the stability of chromium-bearing phases was evaluated using standard leaching tests. The results indicated that dicalcium silicate and spinel phases had formed in the molten slag at 1600 °C, while the dicalcium silicate disappeared and the phases of merwinite and melilite precipitated when the temperature decreased from 1600 to 1300 °C (at a rate of 5 °C/min). During this cooling process, the chromium migrated from other phases into the spinel, significantly suppressing the chromium elution. The leaching results also demonstrated that the potential chromium-bearing phases of glass, dicalcium silicate and merwinite are unstable and are presumably the main source of chromium release. The treated SS slag meets the requirements for the utilization of chromium-bearing slag in the cement and brick industries. Full article

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10 pages, 4336 KiB

Open AccessArticle

Effect of Lime on Stability of Chromium in Stainless Steel Slag

by Qing Zhao, Chengjun Liu, Longhu Cao, Xiang Zheng and Maofa Jiang

Minerals 2018, 8(10), 424; https://doi.org/10.3390/min8100424 - 26 Sep 2018

Cited by 22 | Viewed by 4172

Abstract

The stabilization of chromium is of great importance to the use of stainless steel slag (SSS), and the influence of lime on the stability of chromium is currently unclear. In this work, the variation of phase transformation and chromium distribution with slag basicity [...] Read more.

The stabilization of chromium is of great importance to the use of stainless steel slag (SSS), and the influence of lime on the stability of chromium is currently unclear. In this work, the variation of phase transformation and chromium distribution with slag basicity (CaO/SiO₂) were investigated experimentally, and the leaching ability of chromium was evaluated. Results showed that chromium-bearing phases were glass, dicalcium silicate (C₂S), spinel, and periclase, while the degree of enrichment of chromium in these phases was found to be closely related to the basicity. The optimal basicity obtained in this research was 1.5, with the chromium mainly present in the stable spinel and exhibiting the lowest leaching ability. The product layer structure of unmelted lime was studied as well, showing a periclase layer and a Ca₂SiO₄ layer. Some CaCr₂O₄ had formed in the periclase layer, which is potentially hazardous for the environment and living organisms. Full article

(This article belongs to the Special Issue Metallurgical Slags)

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