New research shows that magnesium and other metals in mine waste can be dissolved and recovered thanks to acid-producing bacteria. Researcher Nathan van Wyk believes that the method has great potential for reducing environmental pollution, extending the life of mines and providing raw materials for industry.
Image Credit: Linnaeus University
Each year, more than three billion tons of metal are produced for use in various products. However, the metal content of ores has decreased with exploitation, which has made it more difficult to access the metals. This has resulted in increased metal prices and more harmful wastes. In addition, there is an increased demand for so-called rare earth elements, which are found in very low concentrations, which can also generate a lot of mine waste.
The mine waste is often dumped in large piles at the mine. It is an environmental hazard, because metals in the waste can leach into groundwater, and some chemical used in metals extraction can also cause pollution. But the waste also presents an opportunity.
– The waste still contains significant quantities of metal and also several other useful metals. So if we can get the metals out of the waste, we can both reduce environmental pollution and extract more raw materials, says Nathan van Wyk, researcher in Ecology.
Acid Dissolution
In his doctoral thesis, Nathan has investigated how the metals can be extracted from the waste using acids produced by bacteria. The wastes he examined were mainly bauxite residues, a mineral that contains aluminium and is used in aluminium production, and several wastes that are residues from magnesium production.
The research shows that the acids extracted close to 100% of the magnesium from the magnesium-rich waste. And when it comes to the bauxite residues, the acids extracted several metals: 68% of aluminium, 80% of calcium, and 59% of titanium, and also some rare earth elements; 42% of yttrium.
“Acid dissolution of mine waste is a promising way to make use of valuable resources. It reduces the amount of waste, protects nature, creates raw materials for industry and extends the life of the mines. And also advances ‘green’ technology while providing jobs. There are many advantages to this method, rather than just leaving the waste behind” says Nathan.
The Remains Can be Used as Concrete
A positive side effect of the method is that any residual material can be combined with cheap additives to produce a type of rapid curing concrete.
“With the waste from our process, we can make construction material, like concrete. Our concrete doesn’t need to be calcinated (an energy intensive process) during production as the energy had already been spent. Over 7% of all the energy used in industry globally is used for the production of concrete and cement. So by using this waste we can achieve zero solid waste, and reduce global energy consumption, to a degree” says Nathan.
Nathan believes that the acid dissolution method needs some development to achieve large-scale production, but lab scale work reveals an elegant and effective process, and he hopes it will be implented by the mining industry in the future.
“We have developed a new technology that has several applications within the mining industry. Through this technology, we can create mining operations into a zero-waste facility” says Nathan.