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Ferrochrome Waste Management—Addressing Current Gaps for Energy and Material Consumption, Carbon Release, and Waste Beneficiation

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Special Issue Editor

Dr. Stephanus Petrus du Preez

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Guest Editor

Hydrogen South Africa (HySA) Infrastructure, Faculty of Engineering, North-West University (NWU), Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520, South Africa
Interests: metallurgy; smelting; waste management; hydrogen energy; material sciences

Special Issue Information

Dear Colleagues,

The modern world would be completely different without stainless steel. Equally so, ferrochrome (FeCr), the primary source of virgin chromium (Cr) units during the production of stainless steel, is of critical importance. FeCr is mainly produced by the energy-intensive carbothermic smelting of chromite ore in submerged arc furnaces (SAFs), and, to a lesser extent, direct-current (DC) arc furnaces. Several solid and gaseous byproducts (considered by industry as wastes) are generated during FeCr production depending on the production route employed, and are typically stockpiled/discarded, released into the atmosphere, or sold as low-value products.

The specific waste management practice used is determined by the physical and chemical properties of the material. It is thus considered a critical aspect that the identified waste be fully characterized if a suitable and effective management strategy is to be developed. An alternative to waste management is the identification of alternative processes that limit the generation of the specific waste material.

The objective of this Special Issue is to identify/characterize the wastes being generated during FeCr production and approaches to either manage such wastes or showcase alternative processes that forego/curve the generation of these wastes. Some of the topics of importance (but not limited to them) include the development of alternative chromite smelting procedures (e.g., assisted reduction and solid-state reduction by gaseous hydrocarbons/hydrogen), low-temperature chromite pelletization (e.g., cold bonding), slimes and slag beneficiation/uses, the utilization/recycling of undersized materials, and Cr (VI) management/mitigation strategies.

Dr. Stephanus Petrus du Preez
Guest Editor

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Keywords

ferrochrome/ferrochromium
solid-state reduction
waste beneficiation
recycling
carbon reduction
metal recovery
cold bonding

Published Papers (2 papers)

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Research

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25 pages, 6740 KiB

Open AccessArticle

The Effect of Pre-Oxidation on the Reducibility of Chromite Using Hydrogen: A Preliminary Study

by Jamey Davies, Merete Tangstad, Eli Ringdalen, Johan Paul Beukes, Dmitri Bessarabov and Stephanus Petrus du Preez

Minerals 2022, 12(7), 911; https://doi.org/10.3390/min12070911 - 20 Jul 2022

Cited by 4 | Viewed by 2204

Abstract

The majority of ferrochrome (FeCr) is produced through the carbothermic reduction of chromite ore. In recent years, FeCr producers have been pressured to curve carbon emissions, necessitating the exploration of alternative smelting methods. The use of hydrogen as a chromite reductant only yields water as a by-product, preventing the formation of carbon monoxide (CO)-rich off-gas. It is however understood that only the Fe-oxide constituency of chromite can be metalized by hydrogen, whereas the chromium (Cr)-oxide constituency requires significantly higher temperatures to be metalized. Considering the alternation of chromite’s spinel structure when oxidized before traditional smelting procedures, the effects on its reducibility using hydrogen were investigated. Firstly, the effect of hydrogen availability was considered and shown to have a significant effect on Fe metallization. Subsequently, spinel alternation induced by pre-oxidation promoted the hydrogen-based reducibly of the Fe-oxide constituency, and up to 88.4% of the Fe-oxide constituency was metallized. The Cr-oxide constituency showed little to no reduction. The increase in Fe-oxide reducibility was ascribed to the formation of an exsolved Fe₂O₃-enriched sesquioxide phase, which was more susceptible to reduction when compared to Fe-oxides present in the chromite spinel. The extent of Fe metallization of the pre-oxidized chromite was comparable to that of unoxidized chromite under significantly milder reduction conditions. Full article

(This article belongs to the Special Issue Ferrochrome Waste Management—Addressing Current Gaps for Energy and Material Consumption, Carbon Release, and Waste Beneficiation)

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Review

Jump to: Research

35 pages, 7929 KiB

Open AccessReview

An Overview of Currently Applied Ferrochrome Production Processes and Their Waste Management Practices

by Stephanus P. du Preez, Tristan P. M. van Kaam, Eli Ringdalen, Merete Tangstad, Kazuki Morita, Dmitri G. Bessarabov, Pieter G. van Zyl and Johan P. Beukes

Minerals 2023, 13(6), 809; https://doi.org/10.3390/min13060809 - 13 Jun 2023

Cited by 3 | Viewed by 4522

Abstract

Ferrochrome (FeCr) is the main source of virgin chromium (Cr) units used in modern-day chromium (Cr) containing alloys. The vast majority of produced Cr is used during the production of stainless steel, which owes its corrosion resistance mainly to the presence of Cr. In turn, stainless steel is mainly produced from Cr-containing scrap metal and FeCr, which is a relatively crude alloy between iron (Fe) and Cr. The production of FeCr is an energy and material-intensive process, and a relatively wide variety of by-products, typically classified as waste materials by the FeCr industry, are created during FeCr production. The type and extent of waste generation are dictated by the smelting route used and the management practices thereof employed by a specific smelter. In some cases, waste management of hazardous and non-hazardous materials may be classified as insufficient. Hazardous materials, such as hexavalent Cr, i.e., Cr(VI), -containing wastes, are only partially mitigated. Additionally, energy-containing wastes, such as carbon monoxide (CO)-rich off-gas, are typically discarded, and energy-invested materials, such as fine oxidative sintered chromite, are either stockpiled or sold as ordinary chromite. In cases where low-value containing wastes are generated, such as rejects from ore beneficiation processes, consistent and efficient processes are either difficult to employ or the return on investment of such processes is not economically viable. More so, the development of less carbon (C)-intensive (e.g., partial replacement of C reductants) and low-temperature pellet curing processes are currently not considered by the South African FeCr smelting industry. The reasoning for this is mainly due to increased operation costs (if improved waste management were to be implemented/higher cost reductants were used) and a lack of research initiatives. These reasons result in the stagnation of technologies. From an environmental point of view, smelting industries are pressured to reduce C emissions. An attractive approach for removing oxygen from the target metal oxides, and the mitigation of gaseous C, is by using hydrogen as a reductant. By doing so, water vapor is the only by-product. It is however expected that stable metal oxides, such as the Cr-oxide present in chromite, will be significantly more resistive to gaseous hydrogen-based reduction when compared to Fe-oxides. In this review, the various processes currently used by the South African FeCr industry are summarized in detail, and the waste materials per process step are identified. The limitations of current waste management regimes and possible alternative routes are discussed where applicable. Various management regimes are identified that could be improved, i.e., by utilizing the energy associated with CO-rich off-gas combustion, employing a low-temperature alternative chromite pelletization process, and considering the potential of hydrogen as a chromite reductant. These identified regimes are discussed in further detail, and alterative processes/approaches to waste management are proposed. Full article

(This article belongs to the Special Issue Ferrochrome Waste Management—Addressing Current Gaps for Energy and Material Consumption, Carbon Release, and Waste Beneficiation)

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