Canadian Mining Journal

Feature

Thermophiles: Metal extraction’s newest workforce

If there is one thing the mining industry doesn't do quickly, it's to change. So it's no surprise that only now are mining companies showing a lot of interest in a technology that's two decades old--b...


If there is one thing the mining industry doesn’t do quickly, it’s to change. So it’s no surprise that only now are mining companies showing a lot of interest in a technology that’s two decades old–bioleaching.

Bioleaching of minerals is the safe, environmentally benign use of naturally-occurring suphur- and ironeating bacteria–thermophiles–to aid in the extraction of precious and base metals from sulphide ores and concentrates.

While BacTech Enviromet Corp. is the only purely publicly traded company currently focused on the development and commercialization of proprietary bioleaching technology, the technology itself has been around since the 1980s, developed by a group of scientists from King’s College, London, UK, who were working in Western Australia.

In addition to their relatively harmless effect on the environment, thermophiles are easily found in abundance in acidic environments produced by the oxidation of sulphur–in and around hot springs, volcanic regions and other sulphide-rich areas. The thermophile culture is robust, thriving in sulphuric acid environments with high dissolved metal concentrations under the high ambient temperatures found in many remote mining locations.

Bioleaching speeds up the normal oxidation process by about 500,000 times. Compared with traditional smelting or roasting, bioleaching is a fundamentally efficient and relatively benign way to burn off sulphides, requiring much smaller plants.

Here’s how the process works. Both chemical and biological forces work together to oxidize the metal sulphide to form acid-soluble sulphides. Precious metals, which are not soluble, remain with the residue. Iron, arsenic and base metals such as copper, cobalt and zinc, pass into solution. To recover base metals such as copper, the solution can be separated from the residue and treated with conventional processing methods (such as solvent extraction/electrowinning) prior to neutralization. The residue generated through the process may contain precious metals exposed by the bacterial oxidation, which can be recovered by cyanidation or carbon-in-pulp (CIP).

Bioleaching’s application as a pre-cyanidation/CIP treatment of gold ores has already been proven commercially, beginning with the Youanmi Deeps gold project in Western Australia. More recently, BacTech signed an agreement appointing the Laizhou Gold Metallurgy (LGM) plant of Shandong province in the People’s Republic of China as the exclusive marketing and sales agent for its gold bioleaching technology for China, Korea, Siberia and Mongolia. Laizhou is the third refractory gold plant employing BacTech/Mintek technology. The LGM plant produces 65,000 ounces of gold per year, and LGM has already committed to doubling the capacity.

BacTech is confident that its technology will catch on. The company’s primary target for bioleaching is the US$7-billion-plus per year copper industry. In addition to the lower capital and operating costs (about US$0.40 per pound of LME-grade copper vs. the industry average US$0.65), bioleaching offers a number of other significant advantages:

the process can simultaneously handle a complete range of copper ore minerals

the potential to recover accessory precious metals, thereby increasing the overall value of the concentrate

the process can treat lower-grade concentrate at minimal extra cost

there are no harmful gas emissions

the production of metal on-site in an integrated operation eliminates the need for transportation of concentrates, and

the plants can be built as small as 15,000 tonnes per annum.

The demonstration of BacTech/Mintek’s technology for copper is underway in Monterrey, Mexico. BacTech and Mintek are equity partners (45%) in a bio-oxidation feasibility plant built and funded by Industrias Peoles S.A. de C.V., the world’s largest silver producer and a significant producer of lead, zinc and gold. The Mexican plant will produce 1 tonne of copper per day from concentrates provided by Peoles and other producers in the Zacatecas region of Mexico. Based on a positive feasibility study (due February 2002), the partnership will build a bio-leaching plant in Mexico that will produce between 25,000 and 30,000 tonnes of copper per annum. The plant’s cost is estimated at US$50 million.

Article by Alison Morrow, telephone 416-763-3002.

For more information on BacTech Enviromet Corp., please visit http://www.bactech.com, or phone Ross Orr at 416-777-0001.


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