Impact of biowaste reducers on continuous solar-driven hematite reduction for carbon–neutral co-production of iron and syngas

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Green iron production using bio-reducers and solar energy offers a promising alternative pathway towards carbon–neutral metallurgy. However, the types of raw bio-reducers play an important role in hematite reduction performance. An experimental investigation of continuous hematite reduction with seven agricultural biowastes was conducted in a solar reactor to unravel the impact of bio-reducer types and shapes (pellets and particles) on conversion performance and efficiency at 900–1200 °C. As a result, the most promising biowaste reducers were betel nut, palm oil empty fruit bunch, and beech wood due to their high volatile and carbon content, followed by bagasse, coconut fiber, and particle board. Conversely, rice husk was found to be inappropriate because of low gasification activity due to high ash content. No significant impact of reactant shape between particles and pellets was observed, pointing out that the reactor can accommodate various biomass feedstocks. The syngas yield varied in the range of 23.2–56.9 mmol/g dry_biomass , and simultaneous high-purity iron production was confirmed by XRD and SEM/EDS. High process efficiency was demonstrated with maximum carbon conversion of 83.1%, oxygen conversion of 100%, and energy upgrade factor up to 1.00. The solar-to-fuel energy efficiency reached 13.2% at 1200 °C, highlighting the remarkable conversion performance of waste biomass and solar energy to clean syngas fuel and renewable iron.