After millennia as the world’s most precious substance, gold plays a practical role today in n electronics, says inorganic chemist Wendy Lee Queen, due to “its highly efficient electrical properties and corrosion resistance, which are unmatched by any other metal.”
But there has never been a lot of gold around:
… despite intensive efforts throughout history to extract gold from the Earth, best estimates suggest that to date only 190,000 metric tonnes of this precious metal have been mined, an amount that will surprisingly fit into a cube of approximately 20 metres on each sideWendy Lee Queen, “Could mining gold from waste reduce its great cost?” at Aeon
So the electronics industry is now competitive with both the religious world and the jeweler for gold. It takes only forty cell phones to use up one gram of the stuff. But, Queen says, it takes a ton of mined ore to produce that gram.
No surprise then that we are starting to hear about “urban mining”—picking valuable minerals out of discarded electronics. Queen notes that, though recycling is only beginning to catch on in many places, a metric ton of recycled laptop circuit boards can yield 40 to 800 times as much gold as the ore. The next step is to develop an economically viable recovery process. And chemists working on the problem, like Steven Foley, say that’s not easy:
There are two current industry standards for removing gold from electronic scraps. The first is pyrometallurgy, which burns the gold off using high temperatures. This method is energy intensive, cost prohibitive and releases dangerous gases, like dioxins.
The second is hydrometallurgy in which leaching chemicals like cyanide solution or aqua regia—Latin for king’s water, which is a mixture of concentrated nitric acid and hydrochloric acid—are used, a process Foley called “expensive, very toxic and completely non-recyclable.
“The environmental effects of current practices can be devastating,” said Foley.University of Saskatchewan, “Sustainable technique recovers gold from e-waste cheaply” at phys.org
Foley and others are working at developing new processes, particularly processes that can leach gold without the risk of heavy-duty contaminants escaping.
One source estimates the potential recovery of valuable metals:
For every 1 million cell phones that are recycled, the following amounts of precious metals can be recovered:
16,000 kg of copper
350 kg of silver
34 kg of gold
15 kg of palladiumBenedette Cuffari, “Extracting Gold from E-Waste” at AZO Cleantech (October 26 2017)
So gold remains “the pot at the end of the rainbow” but now it is also “the coating on astronaut vizors” (LiveScience). It is “the least reactive of all metals” (Nature, 1995), hence its industrial value. Yet a financial guide admits, “part of the reason that gold has always had value lies in the psychology and nature of the human experience.”
Quantify that, if you will.
In any event, we can’t afford to run short of the stuff, which is why research continues into economically feasible means of recycling the gold from our departed electronics.
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