How to pull gold out of old computers and cell phones SAFELY
Flinders University
| Gold recovered from electronic waste in the Flinders University study. Credit: Flinders University |
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
Sustainability, the 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 tons 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 vapors. 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 tons 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.
