Page 67 from: March 2016
67March 2016
I N T H E L A B O R A T O R Y . . .
Global demand for gold fell 2% last year whereas an increase of
5% is anticipated for the current year
by GFMS analysts at Thomson Reuters.
While the precious metal remains popu-
lar among consumers, the fact is that
mine supply is forecast to keep falling
together with worldwide jewellery
fabrication. In such a volatile market,
recycling is likely to play an even more
important role.
This is especially true in the USA where
citizens generated over 3.4 million tons
of e-scrap in 2012, according to the US
Environmental Protection Agency. A total
of 1 million tons or 29.2% was recycled
that year, up from 25% in 2011.
The recycling of one million mobile
phones can yield around 24 kg (53 lb)
of gold. Indeed, it is said that one tonne
of personal computer scrap contains
more gold than that recovered from 17
tonnes of gold ore.
It is against this backdrop that asso-
ciate professor Stephen Foley and his
research team at the University of Sas-
katchewan in Canada undertook work
which they believe has the potential to
‘change the gold industry’ – not least
because mining for gold requires large
amounts of sodium cyanide.
Nature-friendly solvent
‘We use one of the most mass-produced
chemicals – acetic acid,’ Foley explains.
‘At 5% concentration, it’s plain table
vinegar. We use a minute amount of
an acid and an oxidant to finish our
solution.’ The chemistry expert goes on
to describe this solution as the most
nature-friendly solvent next to water.
In essence, the new technique achieves
gold extraction under ‘very mild’ condi-
tions. Furthermore, the solution is said
to dissolve gold at ‘the fastest rate ever
recorded’. In fact, all gold is stripped
from circuits in around 10 seconds while
leaving other metals intact. When time
savings are factored in with lower lev-
els of toxicity, the researchers claim this
solution might ‘revolu¬tionise’ the gold
industry as well as the recycling industry.
Tricky to dissolve
Gold is a tricky metal to dissolve,
according to Foley, because it is one of
the ‘least reactive’ chemical elements.
‘That is why artefacts discovered from
3000 years ago still have gold on them,’
he observes. The main advantage of the
new approach over existing recycling
processes is that the team’s solution
is ‘gold selective’ – in other words, it
dissolves only gold and not the other
metals found in printed circuit boards
such as copper, nickel, iron and cobalt.
Aqua regia dissolves everything, Foley
points out, but then the gold still needs
to be extracted from the solution and
the other metals. In this case, the final
solution gets saturated ‘very quickly’.
It has been calculated that it costs
US$ 1520 to extract 1 kg of gold using
aqua regia, leaving 5000 litres of waste,
whereas it costs only US$ 66 to produce
1 kg of gold using the method devised
at the University of Saskatchewan. In
addition, this would leave just 100 litres
of waste that can be reused ‘over and
over again’.
Potentially ‘devastating’
Foley says the world produces more
than 50 million tons of electronic waste
every year and the volume is rising
because new technologies effectively
cut short the lifespan of what were once
must-have devices. And he also believes
a large proportion of this e-scrap ends
up in landfills, largely because the recy-
cling industry is still playing catch-up.
The two current industry standards
for removing gold from electronic
scrap require some serious improve-
ment, Foley adds, as pyrometallurgy
is energy-intensive, cost-prohib¬itive
and releases dangerous gases while
hydrome¬tallurgy is expensive, very
toxic and a ‘completely non-recyclable’
process. The latter relies on leaching
chemicals like cyanide solution oraqua
regia – the environmental impacts of
which ‘can be devastating’, he insists.
The next step for Foley and his team
– which includes research associate
Loghman Moradi and PhD student Hiwa
Salimi – is to move the process into large-
scale applications for recycling the pre-
cious metal from gold-bearing materials.
The researchers are eager for progress
and have announced they are actively
looking for industry partners.
By Kirstin Linnenkoper
Every month, Recycling International highlights a promising recycling-related research project with a global, technical, economic or social impact.
If you know of an innovative recycling-related research project that merits coverage in this section of the magazine, contact: [email protected]
For more information,
contact Stephen Foley at:
[email protected]
RESEARCH
LED BY
PIONEER
gold re
cycling
University of S
askatchewan
Stephen Foley
New golden age
for recycling?
A research team at Canada’s University of
Saskatchewan has discovered ‘a simple, cheap and
environmentally benign solution’ for extracting gold
from e-scrap in a matter of seconds. Their hope is that
this breakthrough will prove to be a game-changer for
the precious metals sector.
The new solution is capable
of dissolving gold at ‘the
fastest rate ever recorded’.
