Decontamination and revalorization of Cu–Co polluted mine spoil heaps through magnetic soil washing

Many historical copper and cobalt mining operations were abandoned before the implementation of modern mining and environmental regulations, leaving behind large volumes of unmanaged mine tailings with elevated metal concentrations in forms of spoil heaps. Today, these sites represent both a source of soil contamination and a potential secondary resource of critical and strategic raw materials.

This research explores the application of magnetic soil washing as an innovative strategy for the reclamation of these Cu–Co contaminated mine soils and tailings, while simultaneously exploring their potential revalorization within a circular economy framework. Soil washing is an ex-situ decontamination process based on concentrating pollutants into a smaller fraction of soil, leaving the matrix with a lower content of pollutants.

Particularly, the high-mountain Texeo copper–cobalt mine (Asturias, Spain) was studied as a representative example of such legacy mining facilities. The area hosts a sulphide-rich geological setting, where copper and cobalt mineralization is mainly associated with iron-bearing phases derived from hydrothermal processes.

Here, a systematic soil sampling campaign was first conducted to assess the spatial extent and intensity of metal contamination. After this preliminary campaign, two large samples from areas with high (>1500 ppm of Cu; > 230 ppm of Co) and low (>600 ppm of Cu; > 60 ppm of Co) concentrations were selected and gathered. Afterwards, laboratory-scale remediation tests were carried out using wet high-intensity magnetic separation (WHIMS) for two soil fractions: coarse-sandy (2000-500 µm) and silt/clays (<500 µm).

Magnetic soil washing was applied to these two particle-size fractions to assess the partitioning of Cu- and Co-bearing phases between magnetic and non-magnetic products. The process aims to concentrate metal-rich phases into a reduced volume, facilitating their potential recovery, while decreasing contaminant levels in the bulk soil material to support its reclamation. The results were also reinforced with a mineralogical analysis of samples through X-Ray Diffraction and SEM-BSE imagery.

Preliminary results reveal a pronounced preferential concentration of Cu and Co in the magnetic fractions, particularly within the fine-grained material, reflecting their strong association with iron-rich sulphide and oxide phases. The resulting non-magnetic products exhibit a marked reduction in metal content, supporting the technical feasibility of magnetic soil washing to decouple environmental risk from resource value. These findings position magnetic separation as a promising, non-chemical and potentially scalable remediation pathway capable of transforming contaminated mine spoil heaps from environmental burdens into strategic secondary resources.