Among the environmental scars left behind by mining are heaps of waste known as tailings. They sit in exposed piles, are buried or are deposited in ponds and lakes. The danger comes from sulfide tailings which over time leak acid and arsenic into local water supplies. It’s ugly.
Enter bioleaching, a 20-year-old technology developed in 1986 by S. African concern Gold Fields Limited. Bioleaching breaks down sulfide tailings, separating the remaining valuable metals from the ore and making the residue benign. Bioleaching can also also remove sulphur from coal whose sulphur dioxide byproduct when burned creates the acid rain that has killed so many lakes and forests.
Gold Fields BIOX process uses three tongue-twisting bacteria occurring in nature - “thiobacillus ferrooxidans, thiobacillus thiooxidans and leptospirillum ferroxidans” - to free gold and other “occluded” metals from sulfide tailings. In short, nature’s bacteria devours tailings, spits out the remaining precious metals and leaves behind a relatively benign residue known as ferric arsenate.
Some companies are focusing on bioleaching to clean up the environment.
Our motto is “our bugs eat rocks,” says Ross Orr, CEO of Toronto-based BacTech Mining Corp. BacTech’s 65 varieties of bacteria which Orr calls “Thermophiles” and “Mesophiles” are heated in a half dozen stainless steel tanks to break down sulfides tailings in 5-6 days instead of what takes 15-20 years in nature. Orr speaks endearingly of the bacteria.
“They are non–unionized and work 24 hours a day. We given them right temperature and nutrients such as sodium and potassium. We get them into an excited state for 24 hours a day instead 2-3 hours a month in nature,” he says. “Basically, we are speeding up nature.”
Dangerous byproducts of tailings are often contained by draining off water laced with arsenic. “They bury them and hopefully piping will drain off the water which is treated. Or they’ll build a dam around them. It’s putting a BandAid on the problem,” says Orr.
Bioleaching is the product of a much more regulated and environmentally-aware mining industry which for decades left behind destruction and mountains of dangerous waste.
“We’re moving from pyro-metallurgy (such as smelters) to hydro metallurgy meaning reactions taking place in an aqueous solutions. The common thing about smelters is that we don’t build them any more,” says Orr. Word is NASA’s Apollo astronauts visited Sudbury, Ontario because a smelter there had so deforested the area, its geology was similar to the moon’s.
The proposed BacTech Cobalt, Ontario bioleaching plant for tailings retreatment will cost about $25 million to build and consists of six stainless steel tanks where the concentrate is constantly agitated as rock eating bacteria does its thing. A plant can process about 200,000 tons of tailings annually, which given the millions of tons of tailings around the world is a drop in the bucket.
BacTech bioleaching plant
Now, Orr wants BacTech, which has been financially challenged of late, to split into two companies, one that focuses on gold extraction and another to rectify environment problems.
“We think the environmental opportunity is much bigger than gold,” he says. With an estimated 10,000 arsenic generating tailing sites in Canada and the U.S. alone, indeed, that would seem to be the case. The video below does an excellent job of explaining bioleaching.
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