POLLUTION: Abandoned Mines, Acid Mine Drainage, and the Promise of Bioleaching

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Abandoned Mines, Acid Mine Drainage, and The Promise of Bioleaching by Christiana Moffa

The worldwide damage caused by abandoned mines is widespread. The magnitude of the problem is considerable, especially in countries with a long history of mining, where toxic chemicals leach into the surrounding areas.

The Abandoned Mine Problem

There are tens of thousands of sites around the world that contain mining-related arsenic and other substances. The effects of such contamination include polluted water, contaminated land, air pollution, loss of useful groundwater and land, and significant negative health consequences to humans and animals living in the area. More than a century of mining has left many areas around the world filled with highly-toxic materials and known carcinogens.

The issue is so widespread across the globe, and has been going on for so long, that the exact extent of the contamination is unknown and a complete list of affected sites remains unavailable. Studies of various geographic locations and anecdotal evidence, however, provide a robust understanding of the contamination and public health problem.

According to the US Environmental Protection Agency, there are approximately 420,000 abandoned mines, over 13,000 of which are categorized as "abandoned mines with potential environmental hazard," in the states of California, Arizona and Nevada alone.

Acid Mine Drainage

This process during which the sulfides contained in the tailings react with the atmosphere to create an acidic solution that expands to the surrounding area, is called "acid mine drainage." This long-term neglect has left many areas around the world severely polluted with known toxins.

A specific example of the toxic impact of unregulated mining can be seen in Thailand. The effect on human health related to arsenic poisoning in a southern province of Thailand was first recorded in 1987. This area, the Nakhon Si Thammarat Province, has a long history of bedrock and alluvial mining, producing significant amounts of waste products such as ores containing arsenopyrite. In 1994, an international group studied the extent of the impact on the surrounding aquifer systems in the area. The team discovered that the local drinking water contained 500 times the World Health Organization's potable drinking guidelines for dissolved arsenic. One thousand people were treated for skin problems by the late 1990's.

Bioleaching and Environmental Remediation Efforts

Until recently, little was done to address the negative environmental consequences of global progress toward modernization and an industrial economy. In some regions, no remediation efforts have been taken.

Bioleaching is a ground-breaking, eco-friendly technology for the mining area remediation process. An added benefit of bioleaching, in addition to stabilizing arsenic and capturing heavy metals, is that it oxidizes sulfides in the tailings, thereby eliminating a major source of acid mine drainage. The technology also recovers precious and base metals from the tailings for sale to market. In other words, bioleaching is an environmental clean up solution that can also create a profit.

Bioleaching uses naturally occurring bacteria, harmless to both humans and the environment, to oxidize the contained sulfides and separate metal from the difficult-to-process tailings. In the process, toxic elements such as arsenic are stabilized. The tailings created by bioleaching are benign, and zero environmental damage occurs as a result of the process. An added bonus is its ability to recover valuable metals such as silver, cobalt and nickel that remain in the tailings.

The author is a consultant to BacTech, a publicly-traded Canadian company that is pioneering environmental remediation efforts to offset the contamination caused by abandoned mines. For more information about BacTech's proprietary bioleaching technology, visit http://www.bactech.com/green/Overview.asp or call 416-813-0303.

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