Natural wetlands treating mine drainage
Woodcutters Mine, Northern Territory, Australia
Since mining began in 1984, excess water from the Woodcutters lead-zinc mine has been discharged into a small, intermittent creek (Woods and Noller, 1995).
Mine dewatering initially produced in excess of 35 ML/day (ca. 25,000 L/min), but now produces up to 10 ML/day (ca. 7000 L/min). The mine drainage is discharged into a 150 x 2,000 m channel. This constant inflow caused large stands of cattails (Typha orientalis) and sedges (Eleocharis spp.) to develop naturally (see Photo 1).
Photo 1. J. Milne, Northern Territory Dept. Mines & Energy, Australia.
The saline, carbonate-rich discharge is buffered against acidification from the oxidation of sulphides in the ore and the waste rock. However, it contains elevated concentrations of cadmium, manganese, lead and zinc.
Soon after the wetland developed, mine workers noticed that concentrations (and total loads) of these metals were reduced in the wetland by 95% or better, to below acceptable environmental standards (Noller et al., 1994). Data from the mine are shown in below. Ammonia and nitrate are also reduced as water flows through the wetland.
Metal concentrations (ppb) in discharge from Woodcutters Mine.
| Sampling point |
As |
Cd |
Cu |
Mn |
Pb |
Zn |
| Wetland inflow (0.0 km) |
5 |
63 |
1.4 |
600 |
12 |
6,900 |
| Mid-point (0.8 km) |
3 |
63 |
1.7 |
580 |
7.3 |
5,600 |
| Wetland discharge (2.0 km) |
1 |
7.8 |
0.6 |
17 |
<0.2 |
1,700 |
Annual loads of sulphate in and out of the natural wetland in Woodcutters Creek
Annual loads of cadmium in and out of the natural wetland in Woodcutters Creek
Annual loads of lead in and out of the natural wetland in Woodcutters Creek
Annual loads of zinc in and out of the natural wetland in Woodcutters Creek
I'd like to thank my colleague Peter Woods, Senior Environmental Scientist at ERA Ranger Mine, for providing me with the photograph of Woodcutters Creek and much information on wetlands in Australia
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