Pyrite is one of the most persistently problematic components
Associate Professor Dr Liza Forbes works at the Julius Kruttschnitt Mineral Research Centre at The University of Queensland’s Sustainable Minerals Institute.
She’s tackling one of the biggest challenges in mineral processing — separating pyrite, or ‘fool’s gold’, from copper-bearing minerals — in order to recover most of the base metal and reduce the amount lost to tailings.
‘Pyrite is the world’s most ubiquitous base metal sulphide mineral. It’s also one of the most persistently problematic components of base metal processing operations, including copper, lead and zinc,’ Dr Forbes said.
‘The earlier we can remove pyrite, the more we can mitigate its harmful effects on base metal recovery and the overall environmental impact of the process.’
The processing of pyrite has major economic implications for mineral processing as it greatly affects base metal recoveries and concentrate quality, which then presents challenges for smelting operations.
Advance Queensland Industry Research Fellowship
In 2020, Dr Forbes received a $300,000 Advance Queensland Industry Research Fellowship to produce and test possible solutions.
What she has come up with so far has produced some good insight into how the problem might be solved — but there is still more work to be done.
She has been working closely with one of the world’s largest resource companies — Glencore — at their Mount Isa Copper Operation.
One of the major stages for recovering copper from mined ore is known as mineral flotation.
In this process, minerals are mixed with water and placed in vessels called flotation cells. The mineral/water mixture is then treated with chemical reagents that modify the surface properties of certain minerals in a way that makes them attach to air bubbles.
These mineral-laden bubbles then ‘float’ to the surface of the cell, where they are collected for further processing.
Unfortunately, the nature of pyrite is such that it also readily attaches to the surface of air bubbles. This creates competition between pyrite and copper minerals for available bubble surfaces.
This results in large amounts of copper being lost to tailings – the uneconomic materials left over after processing.
Pyrite’s valuable products
‘If we get the pyrite out early, it becomes a valuable resource used to produce industrial sulphuric acid,’ Dr Forbes said.
Sulphuric acid is used in the manufacture of fertilisers, pigments, dyes, drugs, explosives and detergents, as well in petroleum refining.
‘Pyrite can also contain other valuable metals – specifically cobalt in the case of this study. Therefore, recovering pyrite early creates a possibility of recovering additional value from the ore.’
Cobalt is seen as one of the key commodities of the green economy. In 2021, cobalt-containing batteries accounted for three-quarters of the global electric vehicle market.
Another motivation to solve the pyrite processing dilemma is that as high-grade ore deposits worldwide are being depleted, there is increasing demand to process low-grade ores, which are often rich in pyrite, to extract the valuable metals they contain.
Copper demand up 30% by 2030
According to the Australian Government’s Department of Industry, Science, Energy and Resources, the global demand for copper is expected to rise to over 30% by 2030, driven by renewables, construction, energy and transport.
Dr Forbes says that initially, the project team thought that they would be able to rely on a chemical reagent treatment pathway to improve the separation of pyrite and the valuable base metal.
‘This was shown to be an untenable strategy for the Mount Isa ore, because of its inherent geochemistry.’
Like all good scientists, Dr Forbes didn’t let that defeat her. She and her team learned and moved on.
Pyrite texture
Their focus turned to the texture of pyrite. Pyrite can have a variety of textures depending on the conditions under which it was formed.
‘The main benefit of the work was not the proposed treatment strategy, but rather the increased understanding of what makes pyrite behave the way it does — where pyrite is characterised as a function of its texture,’ Dr Forbes said.
She says the next step is extending this study to other ore bodies and other commodities.
‘We’re also working on creating automated pyrite texture identification and classification systems that will allow plant personnel to better identify and predict problematic pyrite behaviour in their ores.’
Senior Glencore Zinc Project Metallurgist Roxanne O’Donnell said for her the most intriguing part of the work has been the identification of pyrite textures being linked to flotation performance.
‘This is cutting-edge research’
‘The research the Julius Kruttschnitt Mineral Research Centre is doing will assist in providing a better understanding of the impacts of pyrite textures and how they can be identified.
‘This will have impacts on mining operations worldwide and hopefully spur the creation of mineral texture identification tools that will assist in understanding the complicated mineralogy of the feeds that impact on flotation performance,’ Ms O’Donnell said.
‘Until you know what potential problems are in your feed, you can’t create treatment strategies to combat them.’
Find out more about the Advance Queensland Industry Research Fellowships.
Last updated: 16 May 2024