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Dynamic up-flow percolation tests - a model for mining waste leachate generation

Lookup NU author(s): Dr Hugh Potter


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Column experiments, based on the European standard up-flow percolation test (TS 14405), were applied to waste rock from an abandoned Pb/Zn mine in southwest England. The aim was to investigate the range and magnitude of pollutants transported from mine waste tips to surface watercourses. The dynamic leaching test was chosen to mimic the transport of rainwater through mine spoil, thereby providing a laboratory proxy for field conditions. A range of metals (Cd, Cu, Mn, Pb, Zn) and major ions were determined in the column leachate, covering solid:liquid ratios of 0-10 L kg-1. The highest concentrations of Zn (200 μmol L-1), Cu (17.4 μmol L-1) and Cd (0.70 μmol L-1) in the leachate were observed at low L/S ratios. Leachate concentrations decreased exponentially for most elements, except Pb, which maintained high concentrations (up to 80 μmol L-1) throughout the experiment. Batch extractions with L/S ratios of 2, 5 and 10 L kg-1 were applied to the same material. Concentrations in the supernatant were generally comparable to results from column experiments, but some differences at high L/S were attributed to the dynamic mode of leaching and the resulting higher adsorptive capacity of the solid phase in the column. Concentrations of Zn and Cd determined in shallow groundwater collected at the former mine site were of the same order of magnitude as concentrations obtained from the column experiments at high L/S ratios, showing that the column experiments provide a good approximation of field conditions. However, Pb and Cu concentrations, which showed close agreement between batch and column experiments, were much lower in the field (max. 3.0 μmol L-1 and 1.9 μmol L-1, respectively), probably due to the prevailing higher pH and/or a higher L/S ratio. This discrepancy highlights the limitations of using laboratory experiments to predict pollutant sources at abandoned mine sites.

Publication metadata

Author(s): Turner A, Braungardt C, Worsfold P, Rieuwerts J, Williamson B, Potter HAB

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: 11th International Mine Water Association Symposium

Year of Conference: 2009

Pages: 858-867