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A better way to mine gold from old electronics

A better way to mine gold from...
There's gold in dem dar electronics!
There's gold in dem dar electronics!
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There's gold in dem dar electronics!
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There's gold in dem dar electronics!

When you get rid of an old phone or tablet, you're likely to remove your valuable information from it, but what about the valuable materials – like gold – that it contains?

Naturally, such substances are too hard for consumers to retrieve, which might be why, according to the University of Edinburgh (UE), about seven percent of the world's gold supply is currently locked inside of electronics. While removing that gold has heretofore been a highly toxic and inefficient proposition, researchers now think that a new process will make prospecting for gold in electronics heaps more achievable than ever.

Gold is often found on printed circuit boards, particularly under keyboards where its durability is an advantage. According to the UE researchers, about 300 tonnes of the metal are used in electronics each year.

The new process to remove it uses a mild acid as opposed to harsher chemicals such as cyanide or mercury that are currently used to extract gold.

First, printed circuit boards are dissolved in the acid which turns all of the metal in the board to liquid. Then, an oily solvent made from toluene is added, kicking off a process known as solvent extraction. Toluene is an aromatic hydrocarbon commonly found in paint thinners. The toluene solvent pulls the gold free from the other materials in the acid wash where the metal can be recovered and used again. Likewise, the solvent and acid can be reused, cutting down on waste.

"The solvent extraction technique is great in that the recycling of reagents and acid are integral to the process," lead researcher Jason Love of UE's School of Chemistry told New Atlas.

Love also says that it might be possible to extract other metals using the process.

"Once you have dissolved metals in acid, you can use solvent extraction to separate all of them," he said. "So, in principle, we could devise a process that would be able to separate all of the metals in electronic waste, which of course would have environmental and potentially economic benefits, but this would depend on the prices of metals and the cost of the process."

The work Love and his team carried out is part of a student- and staff-led initiative at UE to promote the circular economy, which focuses on the efficient use of materials and their reuse as well.

Source: University of Edinburgh

4 comments
AndySouthern
"Mild" acid to dissolve the metals + Gold?
The whole reason we use Gold in electronics is because it doesn't react with many things. This includes acids. You can use Aqua Regia (a mixture of two acids) to dissolve gold, but this is not by any description "mild". It's this stage of the process I am not believing. Maybe they use Aqua Regia, and then leach the gold out with the other part of the process. But I'm not sure about this. You may be better using Cyonide leaching, just keep a close eye on the pH levels to avoid creating Cyonide gas (that is generally bad...) I am interested and will read up further.
Douglas Bennett Rogers
It looks like the circuit board could also be recycled with this process.
Expanded Viewpoint
Yes, hydrochloric acid and nitric acid (Aqua Regia) are hardly to be considered "mild" acids, unless you compare them to hydrofluoric acid! The gold is only a very thin flash plating to combat corrosion, which would create a loss in the voltage in the circuitry. And since we're only talking about a few volts in those devices, even a slight increase in resistance will make a big difference in power loss. Dissolving ALL of the metal on a PCB is a big waste of time and money. The trails on a PCB are copper, with a coating of solder, sometimes. When the acid dissolves the metal, a chemical reaction is taking place. It's called a Redox (pronounced ree-docks) reaction because one element is being reduced, while the other is being oxidized. ALL chemical reactions except for catalytic ones, are Redox reactions, so unless there is some way to give back those electrons that were taken in the reaction, I don't see how the acid bath could be maintained. Proof of this is take some vinegar and put it into a glass, then pour in some baking soda in small amounts. At first, the reaction will be quite strong, but get weaker and weaker until there is no more reaction. All of the acidity of the vinegar will have been neutralized at that point. And stoichiometry will have been achieved. Unless the toluene has excess electrons that it is willing to give up, I call B.S. on that part of the theory. What I would try is using some solar panels or wind power ('cause it's cheap!) to generate electricity to reverse the plating process. Use a piece of metal with a gold plating on it to attract off the gold from the PCBs fingers and such.
xs400
How about some genetically modified bacteria? They seem to be capable of anything.