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MEI Online: Environmental Issues: Latest News: January 26th 2004


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:: Mining's Malignant Menace  

It goes by the name acid rock drainage (ARD) and it is one of the most serious and potentially enduring environmental problems of the mining industry. At some mines it is rampant, generating enough acid to dissolve the Eiffel Tower. At others it is like a hidden cancer, one that may eat away at the value of the mine and the reputation of its owners.

Chris Morrissey looks at the threats - and at the steps being taken as counter-measures by Rio Tinto.

ARD results from reactions between oxygen-bearing water and rock-forming sulphide minerals. Oxidation of the sulphides releases sulphuric acid into the water, and also whatever metals are present in the sulphides. Many of the common ore minerals are sulphides and therefore potential acid generators. The main "culprits" are intrinsically valueless iron sulphides such as pyrite and pyrrhotite, which are ubiquitous as minor constituents of many rock types. Unless the acid is neutralized by alkalis dissolved from other rock-forming minerals, there is a risk that acid effluents spiked with potentially toxic metals will, sooner or later, pollute life supporting water courses. Subterranean aquifers may be at much as risk as surface waterways.

Read the rest of the article at www.riotinto.com/library/reviewmagazine/68/article5-1.aspx



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