Measurement of labile metals in acid rock drainage springs,New Zealand: Field application of anodic stripping voltammetry |
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| Institution: | 1. Division of Geosciences and Environmental Engineering, Luleå University of Technology, S-971 87 Luleå, Sweden;2. Division of Sustainable Process Engineering, Luleå University of Technology, S-971 87 Luleå, Sweden;3. ALS Laboratory Group, ALS Scandinavia AB, Aurorum 10, S-977 75 Luleå, Sweden;1. University of Idaho, Department of Geological Sciences, Moscow, ID, USA;2. University of Waterloo, Department of Earth and Environmental Sciences, Waterloo, ON, Canada;3. Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada;4. Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada;5. Canada Centre for Mineral and Energy Technology, Mining & Mineral Sciences Lab, Ottawa, ON, Canada;1. School of Engineering, UBC, Kelowna, BC, Canada;2. Minesite Drainage Assessment Group, Surrey, BC, Canada |
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| Abstract: | Spring waters were analysed in the field by anodic stripping voltammetry, using equipment which is sufficiently portable to be useful in a remote heavily forested area accessible by foot only. The equipment and techniques are capable of producing analyses on site to the μg/L level for labile metals. Field analysis avoids issues of sample storage and transport protocols that limit confidence in laboratory measurements of labile elements. Samples were taken as a feedback to immediate analysis resulting in a fine grid map of the geological site. Acid rock drainage emanates from a New Zealand historic mine site, with elevated concentrations of metals. However, ground water and surface water discharging naturally from mineralised rocks in the same area also have elevated levels of metals. This study quantifies natural metalliferous discharges from a single site, and compares this to the overall metal flux from the mine area. Acid (pH 3) metalliferous springs emanate from colluvium and bedrock in a young (months-old) landslide. Labile Cu, Pb, Zn and Cd are the environmentally most significant metals in the studied area. Labile metal concentrations observed in the natural springs are up to 24 μg/L Cu, up to 50 μg/L Pb, up to 5 μg/L Cd and up to 9 mg/L Zn. Labile Cu and Zn concentrations are similar to laboratory-determined total concentrations, whereas labile Pb and Cd concentrations are generally distinctly lower than total Pb and Cd concentrations. Four different spring water compositions occur within metres of each other: acid metalliferous water with high Pb, acid metalliferous water with low Pb, high Cu, Pb, Zn acid water and high pH water with elevated Cu. High metal concentrations in these waters are readily attenuated by adsorption to Fe oxyhydroxides (HFO), especially when rain raises spring water pH at the surface. Copper, Pb and Cd are >99% adsorbed, and Zn >95% adsorbed, during this rainfall dilution. Natural spring waters have potential to contribute up to 10% of the total Zn flux from the catchment, but negligible proportions of Cu, Pb and Cd. |
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