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Dangerous mines

Dangerous mines a study conducted on the burying of waste by the mining industry states that the practice could lead to acid contamination of the soil.

A team led by John Harries and his colleagues at the Australian Nuclear Science and Technology Organisation in Sydney looked at 317 active and abandoned mines throughout the country. Their study found that 54 of them contained significant amounts of waste that could lead to acid contamination. A further 62 mines with smaller amounts of waste were also a cause for concern, they said.

Harries said that open-cast and underground mining often exposes large amounts of pyrite and other sulphide minerals to the air, which accelerates their oxidation. Once oxidised to sulphates, they will form an acid in water that can severely damage plant and animal life if it leaks from the mine. In some areas it is impossible for any aquatic life to survive in rivers, said Harries.

Usually, the waste is simply buried under the soil and rocks, while vegetation is allowed to grow on top. But according to team member Graham Taylor, that is not the long-term solution. He warns that the rainfall can easily wash the acid into the environment, and that it can bring with it dissolved heavy metals.

Taylor says that the risk would be significantly reduced if waste were properly treated while mines were still active. Rehabilitating abandoned sites cost at least us $50,000 per hectare. On the other hand, the cost of an active mine is about a third of that. Canada deals with the problem of acid waste by placing them at the bottom of fresh water lakes, where they cannot be oxidised.

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