As the global demand for gold continues to rise, concerns over environmental pollution caused by toxic chemicals traditionally used in alchemy have emerged. Recently, Australian scientists have developed a cleaner and more viable method of gold refining, utilizing a novel polymer that can efficiently extract gold from ores and electronic waste.
Gold holds not only significant economic value worldwide but also serves as a crucial element in industries such as electronics, medicine, aerospace technology, and others. However, many individuals engaged in artisanal and small-scale gold mining globally use mercury to extract gold or cyanide to refine low-grade gold ores. Their operations often lack supervision, leading to the generation of substantial amounts of toxic substances that pollute the environment and pose health risks.
In addition to traditional ores, electronic waste containing gold, silver, precious metals, or rare earth elements has become an important recycling source. However, conventional recycling methods often utilize strong acids and various chemicals, and improper handling of their waste solutions can also release toxic substances like heavy metals, posing threats to human health and the environment.
To address this issue, a multidisciplinary team of experts in green chemistry, engineering, and physics from Flinders University in Australia has developed a safer and cleaner gold extraction technology. This technology aims to extract gold from ores, electronic waste, and scientific waste materials and replace traditional mercury or cyanide-based methods.
The team has collaborated with experts from the United States and Peru and successfully validated the method on actual ores, hoping to provide a viable alternative for small-scale mines that rely on toxic mercury operations. The research results were published in the journal Nature Communications at the end of June, garnering a high score of over 550 attentions.
At the core of this technology is the use of a low-cost and non-toxic compound called trichloroisocyanuric acid (TCCA). TCCA, widely used for water disinfection, becomes an efficient oxidant that can dissolve gold when activated with halide catalysts like sodium bromide or table salt. This oxidant is then used to extract precious metals from ores and electronic waste.
However, the halogenated TCCA compound cannot selectively dissolve gold alone. Therefore, the team introduced an adsorbent to selectively capture gold. They developed a “new sulfur-rich polymer” adsorbent, made from a copolymer of unsaturated triglycerides and sulfur, which can neutralize the active oxidants in leachate and selectively bind with gold.
Most innovatively, the adsorbent polymer after gold absorption can be recycled back into recoverable monomers through thermal decomposition, simultaneously releasing high-purity gold. This design achieves dual recovery goals for gold and the adsorbent, significantly enhancing the sustainability of gold refining.
Researchers applied this method to electronic waste containing gold and observed promising results. The gold recovery rate reached 86%, with a purity of up to 99.9%. Additionally, copper metal precipitated from the solution could also be reclaimed via electroplating with a recovery rate of 98%.
The team also tested the method on unknown scientific waste materials. Results showed successful adsorption of over 99% of gold by the adsorbent. Using 100 grams of adsorbent, they recovered 6.5 grams of 99.9% pure gold.
Moreover, the experimental team applied the method to ores with trace amounts of gold. More than 80% of the gold was captured by the adsorbent, yielding 0.41 grams of 98.8% pure gold powder after drying and thermal decomposition.
Currently, the team plans to collaborate with mining and electronic waste recycling businesses to further test the method on a larger scale. Researchers suggest that this new technology may offer a hopeful solution for the global gold rush and the escalating crisis of electronic waste, reducing the number of toxic wastes generated by mining. Furthermore, this method has the potential to transform the industry structure of artisanal miners and recyclers.
Justin Chalker, the head of the Charlk Laboratory in the Faculty of Science and Engineering at Flinders University, emphasized the innovation of the research, including the extraction of a novel rec…
“We are thankful for the support from the industry and environmental organizations in turning our laboratory discoveries into a larger-scale demonstration of gold recovery technology.”
Dr. Thomas Nicholls, a researcher at the Faculty of Science and Engineering at Flinders University funded by the Discovery Early Career Researcher Award (DECRA), elaborated on the newly developed gold adsorbent. He stated, “The newly developed gold adsorbent utilizing ultraviolet light to create a sulfur-rich polymer is a sustainable adsorbent. Once the gold is recovered, the polymer itself can also be recycled and reused, further enhancing the sustainability of the method.”