Mining metal: how plants are tapping into critical minerals

Cobalt and lithium are key components in electric vehicle and battery storage infrastructure, meaning that global demand for these metals will increase as the world builds infrastructure for renewable sources of energy. According to Dr Philip Nkrumah from the University of Queensland’s (UQ’s) Sustainable Minerals Institute, cobalt consumption is projected to rise each year by 8–10% despite the likelihood of supplies being geologically limited by 2050.

Clean technologies rely on minerals, principally cobalt, nickel, lithium, copper, aluminum, silver and rare earths. A 2019 study by the UTS Institute for Sustainable Futures (ISF) found that shifts to renewable energy would cause metal requirements to rise dramatically, requiring new primary and recycled sources. The study, funded by US non-profit organisation EarthWorks, highlighted that cobalt, lithium and rare earths are the metals of most concern for increasing demand and supply risks, with batteries for electric vehicles being the most significant driver of accelerated minerals demand.

“The industry needs to identify additional sources,” Dr Nkrumah said.

“Australia is one of the world’s leading mineral resources nations with a number of mines around the country generating large quantities of processed mining wastes.

“These wastes, often stored in tailings facilities, contain valuable metals including cobalt, and represent some of the largest untapped resources globally,” he explained.

To address the need for more sustainable ways to source metals, Dr Nkrumah has been investigating the recovery of scarce metals in mining waste using native plants’ metal-absorbing functions, developing the phytomining technology at the Centre for Mined Land Rehabilitation. Phytomining involves harvesting metals from the living tissue of a group of plants known as hyperaccumulators, which retain metals in high concentrations after absorbing them through their roots.

The resource recovery strategy will create additional revenue streams and offers a sustainable solution to supply-related issues that the critical mineral industry is going to face moving forward.

“Phytomining is an innovative solution because it complements the global supply chain for critical minerals like cobalt while promoting the circular economy by utilising mining waste,” Dr Nkrumah said.

“Some species of plants can contain up to 1% of cobalt or 4% of nickel in their shoots, translating to more than 25% metal in their ash, which is dubbed ‘bio-ore’. The high purity of bio-sourced metals makes them especially suited for applications in the electrochemical industry, like producing rechargeable batteries,” he explained.

Intensive screening efforts in global herbaria led to the discovery of more than 100 hyperaccumulator plants new to science. Fieldwork at Queensland’s MMG Dugald River Mine discovered zinc hyperaccumulation in the native legume Crotalaria novae-hollandiae, which opens up the possibility of zinc phytomining in the future.

Image credit: ©stock.adobe.com/au/Juulijs