Environmental and circular economy-based characterisation of abandoned mine wastes in the Odiel River basin (southwestern Spain)

Abstract

The Odiel River basin (southwestern Spain) is severely affected by acid mine drainage resulting from a long history of intensive mining, particularly during the 19th and 20th centuries. This legacy has left numerous abandoned mine wastes scattered across the basin, contributing to widespread contamination of the river system. Many of these materials also contain economically relevant concentrations of critical and high-tech metals. This study evaluates the acid-generation potential of several waste types and provides a preliminary assessment of their suitability for metal recovery. A detailed characterisation was conducted on wastes from 24 abandoned sites, including measurements of surface area, volume, tonnage, acid-generation capacity (via acid–base accounting), and pseudo-total concentrations of 33 elements. Crude sulphide ores, despite their limited volume, exhibit the highest acid generation potential, whereas mixed wastes in dumps pose the greatest environmental risk due to their large tonnage. Roasted pyrite wastes and roasted pyrite ashes are highly enriched in valuable metals, with a preliminary estimated gross recovery value of up to 0.9 billion USD based on the combined contents of the analysed elements. Environmental desulphurisation is proposed as an effective strategy to reduce acidity and enable metal recovery, with the potential to eliminate approximately 80% of the total acidity associated with the studied wastes. Overall, the findings support integrated remediation and resource-recovery approaches consistent with circular-economy principles.