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Metal and solute transportation through a
wetland at a Lead Zinc Mine, Northern Territory, Australia This
paper presents an evaluation of historical data for metal and solute transport from
underground dewatering through a wetland at the Woodcutters lead-zinc mine in the Northern
Territory, Australia. Groundwater aquifers drain into the underground workings that were
then pumped into an ephemeral stream, which was developed as an extended wetland system,
dominated by Typha sp. The tropical monsoonal climate comprising an extended wet
season from December to April gave flow to the creek system. Only dewatering contributed
flow during the dry season. The significant metal contaminants were antimony, cadmium,
copper, lead and zinc and the major components of solutes magnesium and calcium sulfates.
Retardation ratios for each metal relative to sulfate showed attenuation of all metals by
the wetland system except for some copper under high creek flow conditions. Measurement of
electrical conductivity by continuous logger at the inlet and the outlet of the wetland
showed that solutes were higher at the outlet compared to the wetland inlet. This anomaly
was attributed to the addition of solutes from tailings seepage to the wetland system.
Comparison of the loads of solutes revealed a higher load at the inlet indicating that
some loss of salts occurred within the wetland. The characteristics of carbon in water
were investigated and revealed that inorganic carbon was derived essentially from
dewatering and seepage whereas organic carbon was added to the water column from the
wetland vegetation. Generally there was a reduction in metal load for wetland inlet
compared to that downstream. The efficiency of the wetland system was considered to be
high and presents a model system for treating mine wastewater containing such metal
impurities. |
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