Recycling of Mill Scale Into High‐Purity Iron Through Hydrogen‐Based Reduction

Steel production generates various by‐products. Among them, mill scale stands out as an iron oxide‐rich residue from the casting and hot rolling processes, representing approximately 2% of all global steel output. However, mill scale is also often contaminated with other types of impurities, including metallic and non‐metallic ones, which makes the recycling process into a high‐purity product a challenge. This study investigates two hydrogen‐based reduction techniques, viz., solid‐state direct reduction (DR) and hydrogen plasma smelting reduction (HPSR), as a low‐carbon alternative for mill scale recycling. The influence of different temperatures and exposure times to gaseous hydrogen during direct reduction provides valuable information regarding phase transformation kinetics. Specifically, local chemical segregation of impurities, such as Mn, retards the full conversion of wüstite into sponge iron. This work demonstrates a 92% reduction rate of wüstite into metallic iron after 180 min of reduction via DR. Conversely, reduction via HPSR achieves a similar reduction rate, that is, 91% in only 20 min of the experiment. The obtained results shed light on the feasibility of recovering mill scale through hydrogen‐driven emerging techniques, thus minimising the generation of waste sub‐products during steel production.