Promoting pyrometallurgical slags as a critical metal resource: Geometallurgy and leaching behaviour with environmentally benign solvents.

Pyrometallurgical slags are solidified waste products generated during the smelting of metals. These materials predominantly consist of finely crystalline or glassy silicate and oxide minerals but may also contain small inclusions of native metals or metal sulfides, reflecting the composition of the original smelted ore, such as tin (Sn), copper (Cu), lead (Pb), or silver (Ag). Over time, weathering processes can lead to the formation of secondary oxide and carbonate minerals.
Historically produced slags, which were generated through inefficient smelting and slag separation processes, often retain high metal concentrations, sometimes ranging from a few percent to over 10% for base metals and tens to hundreds of parts per million (ppm) of silver or gold. These concentrations exceed modern ore values, suggesting that historical slags represent a potentially valuable metal resource if efficient recovery methods can be developed. However, little is known about the critical metal content of slags. Given that historical smelters processed less refined ores than modern operations, it is likely that some historical slags contain significant amounts of critical metals, such as antimony (Sb), bismuth (Bi), and tellurium (Te).
Reprocessing of these slags presents several challenges. The distribution of metal-bearing phases is poorly understood, oxidation of metal particles varies, and certain metals, such as zinc (Zn), tend to partition into the silicate phase. While pyrometallurgical reprocessing is an option, it requires high energy input and may not be feasible in locations where smelting infrastructure no longer exists. Alternatively, hydrometallurgical approaches using solvents such as sulfuric acid may be considered, but challenges such as gelation of certain slags and the difficulty of recovering silicate-hosted metals can limit their effectiveness.
This project aims to develop an innovative approach to the reprocessing of historical slags. A geometallurgical workflow...