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Mine rehabilitation experts from Australia form one of several international
teams eager to win lucrative cleanup contracts from Wismut. Whichever group
or groups tackles the job, the approach will be similar. ‘Much of it is
simply an earth moving exercise. There’s very little subtle science involved,’
says Des Levins, a member of Australia’s Wismut team and head of ore processing
and waste management for the Australian Nuclear Science and Technology Organisation
(ANSTO). The major challenge, he says, is the scale of the cleanup. At its
simplest, the job involves covering up the contaminated tailings to stop
the escape of radioactive radon gas and dispersal of fine particles. It
must also prevent contaminated water from leaching into streams and ground
water.

The first step will be to drain the tailings ponds and clean the water
recovered in a treatment plant. Lime and barium chloride added to the contaminated
water will cause the precipitation of radioactive material, heavy metals
and toxic wastes. The precipitates will be returned to the tailings ponds
and the treated water slowly discharged into a nearby river.

If it has enough cash, Wismut could decide to run the water through
a secondary treatment plant to remove the heavy loading of ore salts, such
as sodium sulphate and sodium chloride, that remain after primary treatment.
The extracted sodium could then be purified for sale or dumped with the
other wastes.

Drying out Wismut’s tailings ponds is expected to take at least a decade.
Drainage is slow because the particles that make up the tailings are small
– a result of the poor quality of the local ore, which had to be finely
ground before uranium could be extracted. In addition, Wismut has promised
the German government that if ore salts are not removed from the water,
the company will not increase the rate at which water is discharged into
already polluted rivers and streams.

The key to disposing of the contaminated solid waste is to protect it
from rain, says Levins. If this is done, there will only be slight leaching
of contaminants into the ground water. A suitable covering would be about
3 metres thick, would slope slightly to drain rainwater and would comprise
layers of clay, gravel and earth. Vegetation on top would prevent erosion.

Levins says an enormous opencast mine near Ronneburg will be harder
to rehabilitate than the tailings ponds. Since mining stopped and there
has been no need to pump water from the deepest excavations, the water table
has started to rise to its natural level, and threatens to flood radioactive
and sulphide-bearing ores in a nearby labyrinth of underground tunnels and
caverns.

Exposed to water and oxygen, the sulphides will gradually oxidise to
sulphuric acid and, along with radioactive particles, could seep out of
the tunnels and into adjacent creeks, says Levins.

Another problem is the remains of ‘in situ leaching’, a method of extracting
the uranium from the ore while it is still underground. Miners crack open
the ore face with explosives then inject an acid solution. The acid dissolves
the uranium from the ore and the resulting acidic solution of uranium is
pumped to the surface. The acid is recycled after the uranium has been separated
from the solution. Leftover acid now threatens to contaminate the rising
water table.

‘There will always been some seepage,’ says Levins. To reduce the risks,
an underground tunnel could be driven downstream of the mine. The tunnel
would act as a barrier, enabling the cleanup crew to monitor seepage and
intercept polluted water for treatment.