Although rare earth minerals and copper get a lot of attention related to the energy revolution, silver is a quiet workhorse whose value has gone up more than 500 percent during the past 20 years.
Many uses: Silver’s uses go beyond jewelry and cutlery to include solar panels, those lovely defrost lines on your back car window, switches, TV screens, and printed circuit boards.
Recycling is cyclical: Although 15–20 percent of used silver is recycled, that amount can vary widely depending on silver prices and the source of the recycled silver.
Much like oil and gas, the commodity pricing of silver determines the activity around it, and that includes recycling, though extraction efficiency also plays a role.
Low-hanging fruit: As you can imagine, melting down jewelry (especially higher-purity pieces) is one of the easier processes that will get a higher volume of silver out and might march on regardless of price.
Something like a solar panel, though, where the prize is less voluminous and harder to extract, is a different story.
How it works: The more engrained the silver is in the original material, the harder it is to extract.
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The process is more expensive as more corrosive chemicals and environmentally invasive techniques might be needed.
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The yield might be lower as silver makes up a smaller percentage of the overall material.
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Materials that are left behind can require more complicated and expensive mitigation techniques.
What’s new: Even without the price increase, the need for an effective and environmentally friendly recycling technique is clear, and a team from the University of Helsinki and the University of Jyväskylä thinks they’ve found a way to extract silver using readily available materials: cooking oil, hydrogen peroxide, and light.
What they did: Researchers combined some of the most commonly used fatty acids—oleic, linoleic, and linolenic—with a 30-percent H2O2 solution to dissolve silver into fatty acids. The fatty acids acted as a medium and stabilizing ligands for silver ions.
The silver carboxylates were then reduced to metallic silver in a light-assisted reduction reactor.
Sticking point: Metals are generally insoluble, and understanding the reason helped unlock the method.
A thermodynamic barrier or surface passivation can be the cause of the insolubility, and the computational models led the team to try different concentrations of hydrogen peroxide, catalysts, and temperature profiles to find the best combination to extract silver.
What they are saying: “Computational chemistry enabled us to understand the solubility of metals by investigating the effect of solvents on the thermodynamics of dissolution,” says Professor Karoliina Honkala from the University of Jyväskylä.
What they found: Adding ethyl acetate to the silver–fatty acid solution enabled the separation of silver—as silver carboxylates—from the unreacted fatty acids.
The result was an efficient and safe method for separating silver, opening the door to a more environmentally friendly and sustainable recycling method. Even the fatty acids can be recycled after the process.
Future work: Scaling up is the next step, but it is not without its barriers: Mass and heat transfer in the three-phase system need to be figured out, and the selectivity, which is time-dependent, needs to be better controlled…perhaps by some intrepid geoscientists well-versed in chemistry.
To read a press release about the discovery, go here, and for the journal article, go here.
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