Flinders University researchers have discovered a unique class of recyclable sulphur polymers that can recover precious metals and heavy metals from e-waste and gold mine tailings.
As technology evolves at a breakneck pace, the lifecycle of electronic devices has become alarmingly short. With 1 in 3 Australians upgrading their smartphones every 2 years or sooner, and the pandemic-driven surge in computer purchases, the volume of electronic waste (e-waste) has skyrocketed. Surprisingly, 7% of the world’s gold is currently sitting in disused electronics, yet only about 20% of e-waste is effectively recycled. This presents both a significant environmental challenge and a golden opportunity.
E-waste is a rich source of precious metals, such as gold and copper, and heavy metals. In addition, the processing of gold ore in traditional gold mining creates waste material known as mine tailings that still contain trace amounts of gold. These piles of slag also harbour other valuable metals, presenting a dual opportunity for recovery and environmental remediation.
Prof Justin Chalker’s team at the Institute for Nanoscale Science and Technology, in a project led by Dr Thomas Nicholls and Dr Jasmine Pople, is pioneering a new class of tri-sulfide polymers to enhance recovery of metals from solutions. These polymers are synthesised using elemental sulphur (S8), a byproduct of petroleum refining, so the sulphur is both cheap and abundant. The resulting polymers boast a high affinity for precious metals due to their high sulphur content and numerous S-S bonds.
The high affinity of S-S bonds for metal ions makes these polymers excellent ion sponges.
Gold ions adhere to the sulphur atoms in the polymer, allowing for selective recovery. The monomer can be modified to change selectivity; for example, a water-soluble poly(trisulfide) with a carboxylic acid modification can act as a copper sorbent.
Additionally, these polymers can be tailored to bind to mercury, a common pollutant used to process gold ore.
Even the way these polymers are created is an improvement. They use electrochemically initiated polymerisation, which involves the electrons circulating in an electrochemical cell activating the monomer building blocks, triggering a polymerisation chain reaction in which the polymer precipitates from solution. By avoiding hazardous chemical initiators and high temperatures (this system works at room temperature), this method is much safer.
Access to ANFF-SA’s electrochemical characterisation equipment has enabled the researchers to perform detailed analysis of the starting monomers, determine the optimal polymerisation conditions and monitor reactions in real-time. This support has been crucial in refining the polymerisation process.
Tri-sulphide polymers can be converted back to their original monomers through the process of thermal depolymerisation. The monomers can then be removed from the system, leaving behind purified gold.
This method not only recovers valuable metals but also allows the polymers to be recycled and reused, creating a sustainable, closed-loop system.
This innovative approach aligns with UN Goal 12 – Responsible Consumption and Production. Traditional polymer waste poses significant environmental and health risks, as mechanical recycling often leads to structural degradation and downcycling. The breakdown of traditional polymers like polyethylene creates particles that persist in the environment. In contrast, these sulphur polymers can be recycled without such degradation, reducing the environmental impact and promoting sustainable practices.
The strategy of converting excess elemental sulphur from the petroleum industry into useful monomers and polymers, coupled with the recovery of gold from e-waste, offers a promising solution to reduce the need for environmentally damaging open-pit gold mining. By embracing these advanced recovery methods, we can mitigate the environmental impacts of both e-waste and traditional mining, paving the way for a more sustainable future.
Post-publication update:
Since the original release of this article, further developments have been published that underscore the significance of this research:
- A peer-reviewed study in Nature Sustainability has validated the efficacy of these tri-sulfide polymers in selectively recovering gold and copper from complex waste streams, demonstrating scalability and industrial relevance.
- A Flinders University news article highlights the broader environmental applications of these polymers, including mercury remediation and their potential role in circular economy models.
- In The Conversation, Dr Justin Chalker provides a compelling overview of how this technology could revolutionise e-waste recycling globally, offering insights into the socio-economic and environmental benefits of adopting sulphur polymer-based recovery systems.
Published 15 October 2024 in ANFF’s 2024 Casebook ‘ANFF NEXT‘
Posted 1 July 2025
