From waste to wonder

MIWATCH research responds to accelerating environmental and industry needs

As global demand for minerals increases, mining companies are developing orebodies with lower grades that produce more mine waste, and the industry is under pressure to protect people and the environment by better understanding what happens to the waste.

Many mine waste dumps contain sulphides (e.g. pyrite and pyrrhotite) that, when exposed to oxygen and water, oxidise to produce sulphuric acid. This forms ‘acid and metalliferous drainage’, which is extremely damaging to groundwater, ecosystems and human health. There is now a growing interest in exploring the possibility for critical (or technology) metals that can be recovered from mine waste, often called a ‘supplementary secondary resource’.

“Once you start looking, you start finding; for example, we’ve identified the potential for a historic tailings storage facility at the Savage River Mine [in Tasmania] to be a significant resource of cobalt, which is a globally sought after critical metal and key battery ingredient,” Associate Professor Parbhakar-Fox said.

“Once you start looking, you start finding; for example, we’ve identified the potential for a historic tailings storage facility at the Savage River Mine [in Tasmania] to be a significant resource of cobalt, which is a globally sought after critical metal and key battery ingredient,” Associate Professor Parbhakar-Fox said.

“These waste streams can be weird and wonderful sources of a whole gamut of critical metals.”

“One site we went to – Phosphate Hill in Queensland – produces ammonium phosphate fertilisers. A by-product is phosphogypsum ‘slime’ that we characterised in the search for rare earth elements.

“We found a significant enrichment of two rare earth elements (erbium and yttrium) hosted in the mineral fluorapatite.”

^{Image credit: Adobe Stock / Janelle}

Results already show industry that new solutions are possible

Associate Professor Parbhakar-Fox said it is encouraging to see industry looking closely at its waste.

“If they do, we can break the source–pathway–receptor chain by recovering additional value and environmental de-risking.”

One major outcome for the team will be feeding this data into the Atlas Australian Mine Waste launched by Geoscience Australia in collaboration with RMIT and MIWATCH, giving industry and the public an idea where critical, base and precious metals are located in mine wastes.

Associate Professor Parbhakar-Fox explained that this interactive, online tool will be very powerful for mining companies undertaking this type of exploration.

“Then companies can start to identify if there is potential for reprocessing, and start building business cases to do that. It’s a win–win in many ways.

“We can demonstrate to industry that they should not rely on existing data on mine wastes from old reports of tailings and grades, but that they must ‘go back, drill it and characterise it’, because minerals evolve over time in mine waste environments. This means any further mineral processing needs to be modified to achieve profitable recoveries.

“We’ve shown the necessity of treating these sites like an ore deposit, because these secondary mine wastes are complex orebodies in themselves,” she said.

“For new mining projects, applying robust sampling methods to fully understand the heterogeneity of waste and using integrated, analytical workflows is how ‘perfect planning will prevent pathetic performance’.

^{Image credit: Adobe Stock / Roel}