Prospective Life Cycle Assessment Suggests Direct Reduced Iron Is the Most Sustainable Pathway to Net-Zero Steelmaking.

Decarbonizing the steel industry is essential due to its substantial contribution to climate change. This study explores pathways to achieve net-zero CO emissions in the iron and steelmaking industry while minimizing environmental burdens beyond climate change. We conducted a comprehensive attributional life cycle assessment using the net-zero-CO-emissions framework, incorporating both conventional and prospective life cycle assessment methods, to evaluate various decarbonization strategies within the United Kingdom. All value chains were constrained to achieve net-zero CO emissions. Our findings indicate that, under a "current time" scenario, the natural gas-fired direct reduced iron with electric arc furnace is the most favorable option. This is mainly because hydrogen-based direct reduced iron production relies on the UK's current electricity grid, which has a carbon intensity of 293.28 g CO per kWh. As greenhouse gas emissions decrease toward 2050 (approximately 70% for hydrogen-based direct reduced iron), the choice between natural gas and hydrogen will become increasingly region-specific. All net-zero-CO steelmaking case studies perform similarly on human health indicators, while the direct reduced iron with electric arc furnace options have 60-82% lower impacts on the ecosystem end point indicator than the blast furnace basic oxygen furnace routes.