Upgrading Low-Grade Iron Ore via Biomass/NaOH-Assisted Heat Treatment

This study evaluated the production of reduced iron and gangue removal from iron ore which is containing gangue levels exceeding those typically imported into Japan (denoted as low-grade iron ore), using NaOH and glycerol (Gly) as biomass. In particular, the optimal conditions (raw material ratio, temperature, and holding time) for a high gangue removal and production of reduced iron were explored, and the formation of valuable products (hydrogen and organic acids) was investigated in detail (experimental conditions: 0.24 g of iron ore, particle size of 50–3500 μm, 2.582 g of GL, 1.096–2.19 g of NaOH (NaOH:C₃H₈O₃ = 1~2:1 mol ratio), temperature of 200–300 °C, holding time of 0–60 minutes). Consequently, the optimal conditions within the range of this work for gangue removal were found to be: iron ore with a particle size of < 1000 μm, Gly/NaOH mol ratio of 1/1.25, temperature of 240 °C, and holding time of < 30 minutes. Under these optimum conditions, the gangue removal rate was 50 pct for Si, 90 pct for Al, and 90 pct for P. Almost all the iron oxide species in the ore were reduced to metallic iron during the process. Moreover, the gas produced during the reaction was mostly hydrogen, with lactic and formic acids as the by-products. This method produces reduced iron with reduced gangue components, hydrogen, and organic acids at low temperatures.