Metal species indicate the potential of constructed wetlands for long-term treatment of metal mine drainage

Experimental peat-based wetlands at the former Bell Copper Mine (Smithers, B.C., Canada) removed copper from low strength (0.3-1.0 ppm, pH 6-8) and high strength (35-50 ppm, pH 3) copper-contaminated mine drainage. Copper species retained in wetlands sediments were quantified as a means to assess the long-term potential of these wetlands for treating mine drainage. Previous microbial and chemical analyses had indicated that sulphide was biologically generated in these wetlands, and mineralogical analysis confirmed that copper sulphides were present in wetland sediments. However, sequential leaching of these sediments showed that copper was predominantly in organically-bound and oxide-bound phases, with a smaller proportion present as sulphides. The available data suggest that much of the copper was retained as sulphides when low strength mine drainage was applied to the wetlands.