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

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.

Pilot Tests of Pre-Reduction in Chromium Raw Materials from Donskoy Ore Mining and Processing Plant and Melting of High-Carbon Ferrochromium

“…The great difference has been also observed in comparison with the data described in [7]. Referring to this study, the specific energy consumption during the remelting of pre-reduced product of 65% in DC furnace was 2.67 MW•h/t of high-carbon ferrochromium.…”

“…It has been observed that the utilization of a metalized product, derived from enriching metal concentrates in slag and varying in quality within the charge of the ore-smelting furnace, results in decreased specific energy consumption for melting ferroalloys, alongside an increased furnace capacity. Consequently, the introduction of partially or fully reduced material into the ore-smelting furnace for remelting purposes will reduce specific energy consumption for ferrochromium melting and enhance its capacity [3][4][5][6][7][8][9][10][11][12][13].…”

“…Different ratios of chromium to iron in various chromite types must be considered when selecting the pre-reduction technology. Figure 2 illustrates the relationship between chromium reduction degree and iron reduction degree for Kazakhstan chromites based on data described in [7].…”

Treatment of chromium (VI) waste solutions with clay-based adsorbents after reduction with acid mine drainage

“…The cyclone and furnace dusts are sent to the slimes dam. The dried clay from the slurry is the slimes dust (du Preez et al, 2023). These dusts are classified as hazardous wastes by the US Environmental Protection Agency, as they contain hexavalent chromium, Cr(VI) (Sedumedi et al, 2009).…”

From Segmentation to Classification: A Deep Learning Scheme for Sintered Surface Images Processing

“…Iron and steel metallurgy, as a typical process industry in the traditional manufacturing sector, contributes significantly to both infrastructure development and economic growth [1]. In order to achieve the objectives of high-quality, high-yield, and lowconsumption iron and steel manufacturing, the iron ore sintering process offers raw materials for the subsequent blast furnace ironmaking process, which is a crucial preliminary step for contemporary iron and steel smelting [2]. A poor and inconsistent quality of sintered ore can severely impact the blast furnace smelting process, resulting in, for example, unstable working conditions, poor iron quality, and other smelting product quality losses.…”