Tailings Disposal - Mining and the Environment: From Ore to Metal - page 719

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Maximize the settling rate and density of settled tailings solids, and minimize the time
required to achieve this density;

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Facilitate recovery and re-use of tailings liquid;

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In cases where the facility poses a potential threat to wildlife or livestock, remove the
threat or prevent access; and

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Facilitate rehabilitation of the facility after tailings discharge is complete.

As with waste rock storages, there may be a trade-off between competing objectives; e.g.
minimizing the footprint of the facility involves higher retention structures and thicker
tailings accumulations, which may reduce stability and make rehabilitation more difi cult.

CASE 18.3
Tailings Spill at Baia Mare, Romania, 2000

The tailings storage facility at Baia Mare, designed for 'zero
discharge', became probably one of the most publicized tail-
ings spills to date. The scheme at Baia Mare involved rework-
ing of former mine wastes including the construction of a
new impoundment and a new effi cient processing plant that
would accept all tailings removed from the old impoundments.
At the new tailings storage facility an outer perimeter
bank 2 m high was built from old tailings which also
served to anchor the HDPE liner that covered the entire
90 ha storage area. About 10 m inside the perimeter,
starter dams were built to heights of between 2 and about
5.5 m. Cyclones mounted along the crest of the starter
dams accepted the tailings piped from the new processing
plant, discharging the coarser fraction on to the down-
stream side to fi ll the space to the perimeter dam, and
raise the whole dam, with the main volume of fi ne tailings
slurry being discharged into the impoundment. Cyanide
was used in the new processing plant for the extraction of
gold, so that the tailings and water in the new impound-
ment contained considerable amounts of cyanide.
The fi rst discharge into the impoundment was in March
1999, and during the summer everything worked well
although the delivered tailings did not contain quite as
much coarse material as had been envisaged and the rate
of height increase of the dams was lower than intended.
During the winter, however, the temperature fell below zero,
freezing the cyclones. Tailings from the processing plant were
warm enough to keep the operation working, but there was
no further height increase for the dams because the cyclones
were out of action.
Precipitation during September to January fell as rain
and snow on the whole area of the impoundment. This
extra water was stored in the impoundment causing the
level to rise under the now thick layer of ice and snow.

On 27th January there was a marked change in the
weather. The temperature rose above zero and 37 mm of
rain fell. The ice and snow covering melted and the dams,
where they were only starter height, were lower than the
developing water level. On 30th January 2000, a section
overtopped, washing out a breach 25 m long. An estimated
100,000 m 3 of mud and wastewater with a 126 mg/litre
cyanide load entered through
dewatering channels into the Lapus River, a tributary to
the Szamos river and from there into the Tisza river and
the Danube upstream of Belgrade and fi nally entered the
Black Sea.
A very large number of fi sh were killed with serious con-
sequences for the fi shing industry for a time. The Hungarian
authorities estimated the total fi sh kill to have been in
excess of one thousand tonnes. Water intakes from the rivers
had to be closed until the toxic plume had passed.

The concept of a closed system in which none of the
process water should escape into the environment should have
been excellent, with the new tailings impoundment completely
lined with plastic sheeting and provision for the collection of
any seepage. While in principle this was a worthy objective,
both in environmental and economic terms, the design in
each case contained no provision for the emergency discharge
of excess waters when overfl ow threatened. Without specifi c
provision for avoiding overfl ows, such 'zero discharge' systems
are not suitable for use in meteorological conditions of heavy
and intense precipitation, nor had the problems of working at
low temperatures been addressed. The scheme was one that
could have worked well in the hot and dry conditions found
in some parts of Australia and South Africa.

Source: BMTF (2000) and BRGM (2004)
Photo: The Mineral Policy Centre