Tailings
From Free net encyclopedia
Tailings are the waste left over after removing the gangue from ore. Ore extracted from the earth's crust typically has two components: the ore mineral containing the desired metal, and waste material called gangue.
Tailings and gangue are the uneconomic remainder from mining; as mining techniques and the price of minerals improve it is not unusual for tailings to be reprocessed using new methods or more thoroughly with old methods, perhaps to recover minerals other than those originally mined.
In coal production and oil sands mining, the word 'tailings' refers specifically to fine waste suspended in water and the word 'gangue' is never used.
Effects on the environment
Certain types of extraction methods, like heap leaching for example, leave behind toxic compounds in the tailings. Large-scale operations often leave huge piles of this material on site. Particles of toxic metals blown by the wind or leached by rainfall can contaminate surface water and groundwater. In other cases, tailings are specifically disposed of in bodies of water, rasing the issue of water pollution. A specific method, submarine tailings disposal (STD), is outlawed in the United States via the Clean Water Act, and in most other locations in the developed world. Unfortunately, these standards are not usually established or enforced in the developing world. Transnational mining companies, like Newmont Mining, Placer Dome, Rio Tinto Group and BHP Billiton, have come under attack for operating or planning STD at mines throughout the Asia-Pacific region.
Often, as in the case of riverbed metal extraction, this has buried valuable river-flat soils under the largely worthless and often contaminated tailings. Modern extraction methods have resulted in less damage but land rehabilitation continues to be a major problem and costly consideration.