Characterisation of copper mine tailings for environmental stability from the Copperbelt Province, Zambia

Copper mine tailings are a source of potentially toxic elements (PTEs). These pose long-term environmental risks, particularly where storage facilities are not rehabilitated. This study compares the physical, chemical, and leaching properties of copper tailings from a site with a soil cover and from an open facility in Zambia's Copperbelt Province. Physical characteristics included organic matter content, specific gravity, particle size distribution, and mineralogy. Chemical characterisation focused on total elemental concentrations. Leaching behaviour was evaluated using the field leaching test (FLT), toxicity characteristic leaching procedure (TCLP), and the synthetic precipitation leaching procedure (SPLP). Covered tailings showed greater buffering capacity due to elevated dolomite and calcite. In contrast, uncovered tailings consisted mostly of quartz (60%) and had higher concentrations of labile elements. These included copper (4470 mg/kg), zinc (12 mg/kg), chromium (12 mg/kg), arsenic (2 mg/kg), and lead (7 mg/kg). The uncovered tailings exhibited greater copper leachability, with estimated annual leachate loads of 1 tonne/year under mild (SPLP) environmental conditions. Covered tailings released far less Cu (0.004 tonnes/year) and showed enhanced stability due to reduced oxidation and improved acid neutralisation. However, increased zinc mobility was observed, likely due to ion exchange and complexation facilitated by higher carbonate content. The findings show that applying a soil cover limits elemental leaching and improves stability, but the effect is element-specific. These results provide important data for future mine waste rehabilitation and risk-mitigation studies in Zambia and other mining-impacted regions.