Selective recovery of copper from mine tailings using a green leaching agent

The growing demand for Critical and Strategic Raw Materials (CRMs, SRMs) and the limited availability of primary resources in Europe have renewed regulatory and scientific interest in mine waste and tailings as secondary raw material sources (European Critical Raw Materials Act 2023; Hool et al. 2024). Accordingly, efficient and environmentally sustainable extraction technologies are necessary to minimize both environmental impact and processing costs (Whitworth et al. 2022). Among emerging solutions to conventional acidic leaching, glycine has been attracting attention as a non-toxic and biodegradable amino acid capable of forming stable complexes with calcophile elements under alkaline conditions and low temperatures, enabling low-cost, possible industrial applications for recovering precious and critical metals from mine waste and tailings (O’Connor et al. 2018; Barragán-Mantilla et al. 2024; Eksteen et al. 2018). This study investigated the application of glycine leaching as a green chemical approach for the recovery of copper from fine-grained historical tailings samples from the Fenice–Capanne mine, Tuscany, Italy.

Historical tailings samples were preliminarily characterised in terms of granulometry, geochemical and mineralogical composition using multiple methodologies, such as ICP-MS, HH-XRF, SEM-EDS and SEM-MLA for the definition of metal grades and the identification of metal-bearing minerals. Batch leaching tests were conducted using a glycine solution under controlled conditions, including alkaline pH, a constant liquid-to-solid ratio, and progressively increasing leaching times. The performance of glycine as a lixiviant was evaluated in terms of metal extraction efficiency and selectivity using HH-XRF on solid residues and ICP-OES on leaching liquors. Particular focus was addressed on Cu and associated Zn extraction. As a term of comparison, the same samples were leached using sulphuric acid leaching.

Preliminary results indicated that glycine leaching enabled the selective extraction of Cu and minor Zn while limiting the dissolution of Fe, and competitive recovery rates when compared to traditional sulphuric acid leaching. It highlighted its potential as an environmentally friendly leaching agent. The outcomes of this study could contribute to the assessment of sustainable options for the recovery of CRMs and SRMs from mine tailings within a sustainable and circular economy approach.