Mining waste alchemy: Transforming tailings into valuable metals

New research highlights a breakthrough in recovering valuable metals like magnesium and other metals from mine waste using acid-producing bacteria. According to researcher Nathan van Wyk, this innovative approach is promising to reduce environmental pollution, extend mines' operational lifespans, and supply critical raw materials for industrial use.

Globally, over three billion tons of metals are produced annually for various products. However, as ore grades decline due to extensive mining, accessing these metals has become increasingly challenging. This has driven up metal prices and generated larger volumes of harmful waste. Furthermore, the rising demand for rare earth elements—often present in low concentrations—adds to the challenge by creating substantial mine waste in the extraction process.

Mine waste is often dumped in large, open piles at mining sites, creating serious environmental risks. Metals in the waste can leach into groundwater, fine particles can be carried by the wind and spread contaminants, and the chemicals used in metal extraction can pollute the surrounding environment.

However, this waste also holds untapped potential. It still contains significant quantities of valuable metals. An ecology researcher, Van Wyk, explains that extracting these metals can simultaneously tackle two problems: reducing environmental pollution and generating additional raw materials.

The dissolution of acid

In his doctoral thesis, van Wyk explored the extraction of metals from industrial waste using bacteria-generated acids. The primary waste materials studied included bauxite residues—a byproduct of aluminium production—and various wastes from magnesium manufacturing.

The research demonstrated impressive results, with the bacterial acids successfully extracting nearly 100 per cent of the magnesium from magnesium-rich waste. The acids effectively solubilised multiple metals for bauxite residues: 68 per cent of aluminium, 80 per cent of calcium, and 59 per cent of titanium. Additionally, significant quantities of rare earth elements were recovered, including 42 per cent of yttrium.

Bauxite residue, rich in iron and aluminium, is produced by extracting alumina from bauxite, typically through the Bayer process. The composition of bauxite residue depends on the source and the extraction process.

Van Wyk said, "Acid dissolution of mine waste is a promising way to use valuable resources. It reduces waste, protects the environment, generates raw materials for industry, and extends the life of mines. It also advances 'green' technology while providing jobs. There are many advantages to using this method instead of just leaving the waste behind."

The remains can be used as concrete

A notable benefit of this method is its ability to use residual material. This material can be transformed into rapid-curing concrete when combined with cost-effective additives.

Van Wyk added, "With the waste from our process, we can produce construction materials, like concrete. Our concrete doesn't need to be calcinated (an energy-intensive process) during production, as the energy has already been spent."

"Over 7 per cent of all the energy used in industry globally is used for producing concrete and cement. So, by using this waste, we can achieve zero solid waste from magnesium mining and reduce global energy consumption to a degree."

"We have developed a new technology with several applications within the mining industry. This technology can turn some mining operations into a zero-waste facility."

Image credit: AZO Mining; iStock

Information credit: Physics.org