Promoting Circular Economy in Cast Iron Production Through Co-charging of Mill Scale–Biochar Agglomerates and Scrap in an Induction Furnace

For ferrous foundries, sustainability is becoming an essential goal to preserve their competitiveness in producing cast iron. Among the possibilities applicable to the iron and steel industry, the charging of alternative iron sources inside the furnaces could represent an effective approach. Following the paradigms of recycling metallurgical residues and the valorization of non-fossil carbon sources, this study examined the use of mill scale–biochar agglomerates as a complementary iron source for producing gray cast iron in induction furnaces. The effect of the agglomerates co-charging (7 wt.% of the total charge) was hence evaluated based on the melt evolution, process yields, and casting product characteristics. The results highlighted the possibility of recovering more than 90 wt.% of the iron contained in the mill scale without affecting the metallic yield (94.6 wt.%) and maintaining the slag production within acceptable levels (2.2 wt.%). Furthermore, the properties of the produced cast iron resulted compliant with those of unalloyed cast iron. Nevertheless, interactions between the agglomerate components and the melt were observed. Compared to the chemical composition of the charged scrap cast iron, the elemental concentrations of carbon, silicon, manganese, and chromium increased in the produced cast iron due to the transfer of these elements from the biochar and mill scale to melt. Similarly, the formation of a diopside-based slag was associated with the introduction of calcium into the melt by biochar. Overall, the results suggested that mill scale, when agglomerated with biochar, can be used as a complementary iron source in the foundry industry.