An interdisciplinary team of experts in green chemistry, engineering and physics at Flinders University in Australia has developed a safer and more sustainable approach to extract and recover gold from ore and electronic waste.
Explained in the leading journal Nature Sustainabilitythe gold-extraction technique promises to reduce levels of toxic waste from mining and shows that high purity gold can be recovered from recycling valuable components in printed circuit boards in discarded computers.
The project team, led by Matthew Flinders Professor Justin Chalker, applied this integrated method for high-yield gold extraction from many sources – even recovering trace gold found in scientific waste streams.
The progress toward safer and more sustainable gold recovery was demonstrated for electronic waste, mixed-metal waste, and ore concentrates.
“The study featured many innovations including a new and recyclable leaching reagent derived from a compound used to disinfect water,” says Professor of Chemistry Justin Chalker, who leads the Chalker Lab at Flinders University’s College of Science and Engineering.
“The team also developed an entirely new way to make the polymer sorbent, or the material that binds the gold after extraction into water, using light to initiate the key reaction.”
Extensive investigation into the mechanisms, scope and limitations of the methods are reported in the new study, and the team now plans to work with mining and e-waste recycling operations to trial the method on a larger scale.
“The aim is to provide effective gold recovery methods that support the many uses of gold, while lessening the impact on the environment and human health,” says Professor Chalker.
The new process uses a low-cost and benign compound to extract the gold. This reagent (trichloroisocyanuric acid) is widely used in water sanitation and disinfection. When activated by salt water, the reagent can dissolve gold.
Next, the gold can be selectively bound to a novel sulfur-rich polymer developed by the Flinders team. The selectivity of the polymer allows gold recovery even in highly complex mixtures.
The gold can then be recovered by triggering the polymer to “un-make” itself and convert back to monomer. This allows the gold to be recovered and the polymer to be recycled and re-used.
Global demand for gold is driven by its high economic and monetary value but is also a vital element in electronics, medicine, aerospace technologies and other products and industries. However, mining the previous metal can involve the use of highly toxic substances such as cyanide and mercury for gold extraction – and other negative environmental impacts on water, air and land including CO2 emissions and deforestation.
The aim of the Flinders-led project was to provide alternative methods that are safer than mercury or cyanide in gold extraction and recovery.
The team also collaborated with experts in the US and Peru to validate the method on ore, in an effort to support small-scale mines that otherwise rely on toxic mercury to amalgamate gold.
Gold mining typically uses highly toxic cyanide to extract gold from ore, with risks to the wildlife and the broader environment if it is not contained properly. Artisanal and small-scale gold mines still use mercury to amalgamate gold. Unfortunately, the use of mercury in gold mining is one of the largest sources of mercury pollution on Earth.
Professor Chalker says interdisciplinary research collaborations with industry and environmental groups will help to address highly complex problems that support the economy and the environment.
“We are especially grateful to our engineering, mining, and philanthropic partners for supporting translation of laboratory discoveries to larger scale demonstrations of the gold recovery techniques.”
Lead authors of the major new study – Flinders University postdoctoral research associates Dr Max Mann, Dr Thomas Nicholls, Dr Harshal Patel and Dr Lynn Lisboa – extensively tested the new technique on piles of electronic waste, with the aim of finding more sustainable, circular economy solutions to make better use of ever-more-scarce resources in the world. Many components of electronic waste, such as CPU units and RAM cards, contain valuable metals such as gold and copper.
Dr Mann says: “This paper shows that interdisciplinary collaborations are needed to address the world’s big problems managing the growing stockpiles of e-waste.”
ARC DECRA Fellow Dr Nicholls, adds: “The newly developed gold sorbent is made using a sustainable approach in which UV light is used to make the sulfur-rich polymer. Then, recycling the polymer after the gold has been recovered further increases the green credentials of this method.”
Dr Patel says: “We dived into a mound of e-waste and climbed out with a block of gold! I hope this research inspires impactful solutions to pressing global challenges.”
“With the ever-growing technological and societal demand for gold, it is increasingly important to develop safe and versatile methods to purify gold from varying sources,” Dr Lisboa concludes.
Fast Facts:
Electronic waste (e-waste) is one of the fastest growing solid waste streams in the world. In 2022, an estimated 62 million tonnes of e-waste was produced globally. Only 22.3% was documented as formally collected and recycled.
E-waste is considered hazardous waste as it contains toxic materials and can produce toxic chemicals when recycled inappropriately. Many of these toxic materials are known or suspected to cause harm to human health, and several are included in the 10 chemicals of public health concern, including dioxins, lead and mercury. Inferior recycling of e-waste is a threat to public health and safety.
Miners use mercury, which binds to gold particles in ores, to create what are known as amalgams. These are then heated to evaporate the mercury, leaving behind gold but releasing toxic vapours. Studies indicate that up to 33% of artisanal miners suffer from moderate metallic mercury vapor intoxication.
Between 10 million and 20 million miners in more than 70 countries work in artisanal and small-scale gold mining, including up to 5 million women and children. These operations, which are often unregulated and unsafe, generate 37% of global mercury pollution (838 tonnes a year) – more than any other sector.
Most informal sites lack the funding and training needed to transition towards mercury-free mining. Despite accounting for 20% of the global gold supply and generating approximately US$30 billion annually, artisanal miners typically sell gold at around 70% of its global market value. Additionally, with many gold mines located in rural and remote areas, miners seeking loans are often restricted to predatory interest rates from illegal sources, pushing demand for mercury.
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