Copper Recovery from Smelting Slags by Glycine Leaching: Influence of Slag Mineralogy and Ferromanganese Crusts

Copper smelting slags represent a growing environmental and metallurgical challenge due to their large volumes and their content of unrecovered critical metals such as copper. Although conventional treatment relies mainly on acidic leaching, more sustainable hydrometallurgical routes are required to valorise these residues. In this study, an alternative copper extraction process is proposed based on alkaline glycine complexation and the use of ferromanganese crusts as an unconventional oxidising agent. Leaching tests were performed using two slags (A and B) at ambient conditions. Copper recoveries up to 59.7% (slag A) and 25.7% (slag B) were achieved at 1 M glycine without external oxidants. The addition of ferromanganese crusts (1:1 and 2:1) resulted in marginal increases (up to 61.1% and 29.1%, respectively), attributed to the limited oxidative performance of MnO2 at near-neutral pH. The results demonstrate that glycine is a viable lixiviant for copper recovery from slags at room temperature and highlights, for the first time, the use of naturally occurring Fe–Mn crusts as oxidants in alkaline leaching systems. This work contributes to the development of more sustainable valorisation strategies for metallurgical slags and offers a basis for future optimisation of alkaline complexation routes.