Characterisation of Pb/Zn Tailings and Drainage Waters to Inform Post-Closure Water Treatment Strategies

Both the tailings and associated leachates should be characterised to predict contaminant levels and identify suitable remediation strategies for appropriate closure planning of tailings management facilities (TMFs). Tailings and associated drainage waters from a modern Pb/Zn site were characterised to determine contaminants of possible concern for discharge. The potential for constructed wetlands to provide suitable treatment of tailings waters was assessed over a 10 month period. Tailings were slightly alkaline (pH 8.3), with high net neutralising capacity (578 kg CaCO3/t), very high level of neutralising carbonate minerals (ca. 60%), and low sulphide content (< 5%). Metal content was Zn (2430 mg/kg), Pb (1900 mg/kg), As (620 mg/kg), Sb (80 mg/kg), Ni (50 mg/kg), and Cr (30 mg/kg). The pH dependent leaching demonstrated the potential for higher amounts of metals to be released under acidic conditions (pH < 5), although this would be most unlikely given the very high NP/AP ratio. Drainage waters were net neutral (pH 7.7) but exceedance of surface water directive levels was observed for sulphate, Sb, and Zn. Constructed wetland treatment demonstrated effective Zn and Sb to achieve limit values. Sulphate levels remained high and exceeded the 250 mg/L limit values. Mn values in the wetland effluent exceeded influent levels. Further evaluation of the constructed wetland treatment option is warranted to achieve sufficient treatment of the neutral pH discharge to levels suitable for discharge.

Automated summary

Both the tailings and associated leachates were characterized to predict contaminant levels and identify suitable remediation strategies for appropriate closure planning. It was found that the tailings had slight alkaline properties, high net neutralizing capacity, and high levels of neutralizing carbonate minerals, while having low sulphide content. The constructed wetland treatment demonstrated effective removal of zinc and antimony, but the sulphate levels remained high.