Oxidation of Ferrochrome Slag Using CO2: A Possible O2 Carrier in CLC Process

Global warming and other environmental issues due to the increasing CO<inf>2</inf> in the atmosphere have raised concerns about reducing CO<inf>2</inf> emissions. CO<inf>2</inf> sequestration using Chemical looping combustion (CLC) is a technology with inherent greenhouse gas (CO<inf>2</inf>) separation. This technique involves transferring oxygen from combustion air to fuel without direct interaction using metal oxide as an oxygen carrier. Steel industry waste such as ferrochrome slag consists of transition metal oxides that can be an attractive and inexpensive oxygen carrier for chemical looping combustion. The present work explores the possibility of oxidation of ferrochrome slag, pure Fe turning, and their mixtures using CO<inf>2</inf> in the CLC process. TG experiments were performed using ferrochrome slag, pure Fe turning, and their mixture in varying weight ratios (1:1, 1:2, and 2:1) at 800 °C, 900 °C, and 1000 °C (isothermal and dynamic temperature program) in the presence of 40% CO<inf>2</inf> and 60% Ar gas mixture. The oxidized samples were investigated using SEM–EDS and XRD to analyze the phases and composition. Furthermore, thermodynamic calculations were performed using FactSage 7.1 software to aid the understanding of the oxidation mechanism. The results show that Slag–Fe mixtures gain significant mass due to Fe<inf>3</inf>O<inf>4</inf> spinel formation. In addition, the oxidized Slag–Fe samples also constitute MgAl<inf>2</inf>O<inf>4</inf> spinel with Fe and Cr solubility. The oxidation kinetics is found to increase with temperature and Fe content in the mixtures. The study effectively demonstrates that CO<inf>2</inf> can be utilized for the oxidation of Slag–Fe turning mixtures. Graphical Abstract: [Figure not available: see fulltext.]