Feedstock types in Sustainable Metallurgy

Feedstock: from ores to “urban” resources

Sustainable metallurgy starts with a broader, more complex palette of feedstocks: primary ores, secondary scrap, tertiary re‑mined wastes, and even biological and organic materials used as reductants or bio‑accumulators. Primary feedstock spans high‑grade oxides and sulfides through to fine, low‑grade, and banded ores, whose higher gangue contents and complex mineralogy demand new direct‑reduction and slag‑engineering strategies to maintain thermodynamic selectivity and acceptable kinetics. Secondary feedstock includes everything from clean in‑house runaround scrap to heavily mixed post‑consumer scrap, with large gradients in composition, form factor, and contamination, which drive the need for “sink alloys” and scrap‑acceptor alloys that can absorb specific impurity vectors without property loss.

Tertiary feedstock, often referred to as “urban feedstock”, covers deposited industrial residues such as red mud, steelmaking slags, flue dusts, and mine tailings that can be re‑mined to recover base and critical metals. Because these materials are already mined and partially processed, their embodied energy and effective ore grade can surpass those of primary resources, provided that re‑mining routes are carefully optimized so that the CO₂ emissions associated with collection, transport, and processing do not exceed the sustainability gains. Biological and organic feedstocks—bio‑leaching bacteria, super‑accumulator plants, and organic wastes used as reductants—provide additional levers, especially for low‑grade ores and contaminated soils, but must be deployed in ways that do not compete with food production.