Electrochemical Ironmaking for Green Steel: Turning Low-Grade Ore into High-Purity Iron

Abstract

Listen

Translate article

The production of steel accounts for approximately 7% of global carbon dioxide emissions, the majority of which is produced during the conversion of iron ore to iron metal (“ironmaking”). Conventional ironmaking predominantly utilizes blast furnaces which melt iron ore with coal and other minerals to produce crude steel. The effort to decarbonize is pressuring high emissions processes, like ironmaking, to transition to low-carbon alternatives. To achieve this goal, Electra has developed an acidic electrolysis-hydrometallurgical ironmaking process (Figure 1) that operates at low temperatures (~ 60C)(1). Contemporary solutions geared towards reducing emissions associated with the blast furnace ironmaking route involve combining reformed natural gas in a ‘direct reduced iron’ reactor (NG-DRI) to reduce iron ore to metallic iron. The NG-DRI path only moderately reduces carbon emissions relative to the blast furnace, about 35%. The next generation DRI technology instead utilizes hydrogen as the reductant gas (H2-DRI), which has the potential to significantly reduce emissions as long as the hydrogen is produced via electrolysis using renewable electricity sources. However, a major drawback to the DRI ironmaking process is that it cannot process impurities present in lower-grade ores, unlike the blast furnace approach which can removal impurities through “slag”, a byproduct of smelting that contains a mixture of metal oxides. Thus, DRI methods must either use high-grade ores (> 67% iron oxide), perform upstream beneficiation of low-grade ores, or add an additional downstream smelting step to remove impurities via slag. The latter two approaches incur significant cost, CO2 emissions, and waste. The diminishing availability of high-grade ores preferred by blast furnaces and required by DRI methods represents a significant challenge associated with these routes. A recent report by the International Iron and Metallics Association expects shortages in high-grade ore by the early 2030s(2). As the world supply of high-grade ore dwindles, new technologies are required to tap into lower-grade and, ideally, already mined waste feedstock. Electra’s ironmaking technology is capable of dissolving a range of iron ore grades in acid and extracting iron metal in a manner most similar to conventional copper or zinc electrowinning at around 60C(1). By dissolving iron ore in solution, traditional hydrometallurgical separations processes such as solids precipitation routes or solvent extraction can be employed to remove the principal impurities (Al2O3, SiO2, and P) present in low-grade ores. If removed with enough selectivity, these byproducts can also be valorized, further reducing the auxiliary carbon footprint of mining new materials. Electra’s impurity removal process is critical to electrodeposition of high-purity iron from leached ore solution. This presentation will focus on Electra’s electrowinning process and detail the impact of common iron ore impurities on the quality of electrodeposited iron. The presence of Al3+ and PO4 3- in plating catholyte, specifically, results in incorporation of these elements into the deposited iron via precipitation. These elements are particularly detrimental for steel production in the downstream electric arc furnaces. Reducing Al3+ and PO4 3- content to below ≈ 1 mM in solution eliminates impurity incorporation and results in iron purity of ≈ 99% as measured by LECO combustion analysis and acid digested ICP-OES. Other common ore impurities (Mg, Na, Mn) are ‘bystanders’ and do not negatively impact iron deposition, permitting build-up in the catholyte and eventual removal via a bleed stream. (1) Pham, et al. (2022) 2-Step Iron Conversion System. US Patent Office No. US11767604B2. (2) International Iron Metallics Association. www.metallics.org/faq.html (Accessed Feb 2024). Figure 1. Schematic that identifies the primary electrochemical and hydrometallurgical processing steps in Electra’s ironmaking technology. Figure 1