Spent coffee grounds (SCGs): Thermal transformation and application in sustainable iron production

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Copyright: Biswal, Smitirupa
The iron and steel industry is one of the prominent industrial sectors in the world since steel is a vital material with a wide range of applications in our daily lives. There will be a gradual improvement in the living standards, infrastructure and economic growth of developing nations with time. All these will necessitate the demand for steel, and it is essential to meet the same but in an environmentally friendly and sustainable way. The ferrous industries are associated with various issues like extensive greenhouse gas emissions, energy-intensive processes and heavy reliance on fossil fuels and natural resources. At the same time, concern regarding waste generation and its management is taking up the momentum and calls are being made for recycling and green recovery. Reuse of waste materials in the manufacturing process could make the industries circular economy resilient. The Ph.D. research work is based on this notion and involves a novel approach of utilizing a bio-based waste material called spent coffee grounds (SCGs) for application in ironmaking. The research work involved the use of SCGs to produce iron from iron oxide as an alternative to coal/coke. Thermal transformation study of SCGs were carried out in the temperature range of 400 °C to 900 °C. The transformed sample obtained at 400 °C, called T-SCGS (transformed-spent coffee grounds), was preferred for the reduction study in the research work due to presence of optimal amount of volatile matter and fixed carbon. This observation was further validated with better high temperature reduction performance in comparison with metallurgical coke (MC) and SCGs (as-received form). Detailed study regarding solid-state (800-1200 °C) and molten-state (1550 °C) reduction processes were carried out with no-flux and fluxed composite pellets of iron oxide and T-SCGs. Use of T-SCGs for iron recovery from electric arc furnace (EAF) slag was also studied. T-SCGs have both hydrogen and carbon in their molecular structure and reaction of in-situ hydrogen with iron oxide will release the by-product of H2O therefore, helping in reduction of CO2 emissions. Hydrogen is known to be a kinetically better reducing agent than carbon thus, improving reaction efficiency and decreasing energy consumption. Overall, the waste source of SCGs when transformed to a suitable form has the potential to be used as an alternative to coal/coke for sustainable iron production such as in solid-state direct reduction as well as smelting reduction processes and also aiding in the novel concept of circular economy.
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PhD Doctorate
UNSW Faculty
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