Environmental risk of mining - Environmental Deterioration and Contamination: Problems and their Management - page 125

The result was a spill of about 100,000 m 3 of liquid and suspended waste con-
taining about 50-100 tonnes of cyanide, as well as copper and other heavy metals.
The contaminated spill traveled into the Sasar, Lapus, Somes, Tisza and Danube rivers
before reaching the Black Sea about 4 weeks later. Some 2,000 km of rivers in the
Danube's water catchment area were affected by the spill. The breach in the Aurul
Dam was partially caused by heavy rains and rapidly melting snow that made the
water level in the pond rise. There were no plans to deal with such a rise in water level
or catch overflow wastewater and the newly engineered dam system failed under these
circumstances. A completely closed operation with no discharge to the environment
was thus not possible (UNEP & OCHA Report, 2000).
6.4 The red mud catastrophe at the Ajka bauxite
processing plant
A catastrophic release of red mud from a bauxite waste (tailings) settling pond occurred
at MAL Zrt. processing plant at Ajka, northwestern Hungary in October 2010.
Failure of the dam wall in an active tailings pond led to the release of approximately
800,000 m 3 red mud. Figures 5.4 and 5.5 show the red mud containing cell and the
broken dam as well as the village houses after the accident. Red mud is a highly alkaline
thixotropic material comprising mainly iron oxides and NaOH. Minor amounts of
other potential contaminants such as cadmium, chromium, nickel, arsenic, lead and
vanadium occur in the Ajka red mud. The released red mud streamed with high velocity
and swept away bridges, cars and unfortunately led to human casualties: 10 people died
in the huge mud flood. It flooded three villages, thousands of hectares of agricultural
land downstream the tailings pond and caused intense environmental damage. Fish
kills were observed by the Hungarian authorities in the Torna Creek and high pH and
sediment loadings were propagated downstream through tributaries of the Danube
River. As a first response risk reducing measure, gypsum (CaSO 4 *2H 2 O) and acetic
acid were added into the surface waters in an attempt to neutralize the alkaline surge
(Gruiz, 2010). The desiccated red mud was removed from the flooded soils, but the
infiltrated alkali increased the sodium concentration in the soils significantly. A case
study of the Ajka red mud spill is presented in Volume 5, Chapter 4 of this topic series.
Figure 5.4 View of the broken dam of cell N o 10 from inside (left) and from outside (right).