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In July 2008, we visited the town of Cobalt in northern Ontario to learn about the mining industry's legacy in this once-productive mining camp. What we saw and learned have opened the door to a new application of bioleaching, that being the environmental remediation of polluted tailings and the subsequent recovery of metal for sale to market.
In 1903, silver was discovered in Cobalt and that set off a mining rush similar to the Klondike gold fields. Between 1903 and 1922, over 300 million ounces of silver were produced from 100 mines. Keep in mind, that a mine can be anything from a project with a 1,000 foot shaft, to a hole in the ground made by a lone miner following a silver-rich vein. The grades of some of the veins in this camp reached 1,000 ounces per ton, which allowed for a significant amount of silver to be left behind if it was deemed to be too difficult to recover. In addition, there were very few applications or uses for cobalt metal in those times, and so it was thrown out with the silver tails. Prior to the global recession, cobalt metal traded upwards of $50 per pound compared to historic prices closer to $3 per pound. All of this means that there is considerable value entombed in the tailings of this mining camp and the hard work of blasting and lifting rock to the surface has already been done.
But there is also a big problem associated with the Cobalt tailings... arsenic.
Conventional mineral extraction practices in most mining regions, including the silver and gold projects in Cobalt, involved virtually unregulated processing of the ores, with no disposal control systems for the unwanted rock (i.e., mine tailings). Most tailings in the world contain sulphides, other toxic elements, and where previous technology limitations existed, economically recoverable quantities of precious or other valuable metals. Sulphides readily react with the atmosphere to create an acidic solution referred to as acid mine drainage ("AMD"). This acidic solution is very efficient at liberating certain heavy metals such as arsenic from mine tailings, resulting in pollution of the surrounding watersheds.
An estimated eighteen million tonnes of tailings were left in lakes, on shorelines and in open areas over a large region. These tailings contain high levels of arsenic that have been leaching into local lakes, streams and the drinking water. With the exception of one of the lakes in the area, most of the lakes contain between 0.040 to 6.510 mg/L arsenic, and water wells have reported concentrations as high as 6.97 mg/L. The maximum acceptable concentration for freshwater aquatic life is 0.050 mg/L, and for human consumption, it is enforced by regulation at 0.010 mg/L.
Arsenic toxicity has been linked to cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate, while non-cancerous effects include thickening and discoloration of the skin, stomach pain, nausea, vomiting, diarrhea, numbness in hands and feet, partial paralysis and blindness. Clearly, this is a serious environmental problem that must be cleaned up.
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