Using rock’s naturally occurring bacteria to extract metal from ore isn’t nearly as experimental or futuristic as some people might think. Neri Botha, an extractive metallurgist with the Research Productivity Council (RPC) in Fredericton, N.B., says the technique, known as bioleaching, is primed to be ready for prime time in the mining industry.
“The technology is ready,” she says, “but the commercialization is lagging behind. What is needed is the right opportunity where the obstacles necessitate the process, making it worth taking on any perceived risk, due to the process being relatively novel. Government support for the environmentally friendlier process could also help,” she adds.
Bioleaching has been around at least since 1000 BC when the Romans and Phoenicians utilized the process to recover copper from streams passing through ore bodies. It was first used commercially in a South African gold mine in 1986. As a South African-trained professional engineer, Botha has kept a close watch on developments in this area since her days at the University of Pretoria, where a course in hydrometallurgy first sparked her interest in this novel process.
Bioleaching works, Botha explains, “by utilizing certain microorganisms to accelerate the rate of dissolution of sulfide minerals using their enzymes. These microorganisms, known as mesophiles or moderate thermophiles, could be isolated from mine water, or from ores, or from sulphur-bearing hot springs etc.”
Genomics plays a critical role in helping sort out the identities of the microorganisms, and Botha has been researching genomics applications for the mining industry for many years, with ongoing support from Genome Atlantic.
She explains that in the mining industry, bioleaching’s economic and environmental advantages – particularly in gold mining, but also in nickel, cobalt and copper mining – are spurring intense interest.
The reason for this is the depletion of conventional high-grade reserves. The situation, she says, has created a need to treat lower grade ores as well as re-treat old tailing sites to extract residual metals. Bioleaching makes those propositions not only doable but economically feasible. For tailing sites, bioleaching presents opportunities to unlock their value as well as to remediate them with the added bonus of producing no atmospheric pollution. The technique also boasts low capital and operating costs.
RPC, New Brunswick’s provincial research institution where Botha has worked since 2012, is considered an important centre of bioleaching expertise in the world’s scientific community. That expertise has developed in conjunction with the institution’s mandate to engage in industry-driven applied research. RPC has been involved in various types and phases of bioleaching projects in over 30 countries since 1989.
Currently, RPC is assisting on a primary copper bioleaching project now under development with an Ontario based engineering firm. In addition, the institution is working on a chalcopyrite bioleaching project in Zambia and on a cobalt research project in the United Kingdom (CoG3). Other research projects in progress, Botha says, concern “the gold extraction process for Newfoundland ores and we are also involved with Rare Earth Element Research.”
The U.K. project, CoG3, is particularly prestigious. The focus is on safeguarding the supply of cobalt, a metal critical to advanced technology, for such things as batteries and superalloys. The project, led by the National History Museum in the U.K., involves a research consortium of six universities, three research institutes and eight industrial partners. RPC is part of the technical advisory committee.
Bioleaching is a “proven technology,” says Botha, “especially in the gold industry and for secondary copper minerals as well as other metals.” When it comes to gold, she says bioleaching is “uniquely situated to assist in the extraction of problematic ores containing locked gold.” The metal can be locked for physical or chemical reasons or it can be trapped in the ore’s sulphide lattice. Bioleaching could potentially unlock it.
“Certain minerals still present challenges though, such as chalcopyrite,” she pointed out. Chalcopyrite is the brassy yellow mineral in which copper is commonly found. It tends to form passivating or unreactive layers of oxides on its surface,” she said, “These layers limit the recovery of copper at temperatures and redox conditions suitable for microbial culturing.” She adds, “significant research has thus gone into this and the world’s first primary copper bioleaching plant is currently being built, incorporating RCP findings.”
Once this new plant is running, she foresees bioleaching becoming standard for copper extraction within a few years. As secondary copper minerals and high-grade ores continue to deplete, she says, the bulk of the world’s unexploited copper reserves are becoming increasingly less economic to mine by conventional means.
In many cases, bioleaching, with some help from genomics, presents an irresistible solution, which Botha expects will make it a mainstream mining technology very soon.