Life-cycle assessment of ferromanganese production using biocarbon as reductant and carbon capture and storage

Ferromanganese (FeMn) is an essential alloy whose production relies on metallurgical coke as a reducing agent, leading to hard-to-abate carbon dioxide emissions. The use of biocarbon as an alternative reductant and carbon capture and storage (CCS) are key mitigation strategies of FeMn production, yet their environmental performances are still unexplored. This study evaluates the possible environmental co-benefits and trade-offs of replacing metallurgical coke with biocarbon, with and without CCS, in Norway. The climate impact of FeMn production is 2312 ± 110 kg CO 2 -equivalents per tonne of alloy (mean ± 5th/95th percentiles). Emission reductions are about 57 ± 3.0 % at a full substitution rate and 29 ± 3.7 % at a more realistic substitution rate of 50 %. CCS alone can reduce emissions of 53 ± 4.8 %. The combination of biocarbon with CCS can achieve negative emissions when the biocarbon substitution is higher than 78 %. More efficient material and energy use throughout the value chain is key to maximise climate benefits. The main trade-offs can occur with terrestrial acidification and particulate matter formation, and are mostly due to biomass pyrolysis. A 50 % substitution of the metallurgical coke annually used for FeMn production in Norway requires around 25 % of currently unused forest residues, or 8 % of the today's wood harvest volume. Although some economic and technological barriers remain to be overcome, this study offers an initial quantification of the environmental implications that can be expected from a value chain perspective in connection to local resource availability and technical challenges. • Biocarbon integration can reduce emissions by up to 57 % for a full substitution. • Negative emissions are possible with CCS if biocarbon use exceeds 78 %. • Optimisation of biocarbon value chains is key to maximise climate benefits. • Trade-offs may occur with acidification and particulate matter formation. • Unused forest residues can meet annual biomass demand of Norway's FeMn industry.