Turning Waste into Silver Using Everyday Oils

These mild, green solvents not only dissolve silver efficiently but also allow for easy recycling of the acids themselves, the Chemical Engineering Journal reported.

Recycling silver from electronic and industrial waste is becoming more crucial than ever. As demand for this precious metal grows and natural sources become harder to mine, scientists are racing to develop cleaner, smarter ways to recover it.

“Recycling silver from waste materials is becoming increasingly important for securing the supply of this precious metal. It is highly desirable to design new sustainable separation and recycling strategies to replace current processes that strain the environment,” says Postdoctoral Researcher Anže Zupanc from the University of Helsinki and the University of Birmingham.

Now, researchers from the University of Helsinki and the University of Jyväskylä have introduced a breakthrough recycling technique.

To extract silver safely, the team turned to common fatty acids, such as oleic, linoleic, and linolenic acids. When combined with a 30% solution of hydrogen peroxide, a powerful yet eco-friendly oxidant, these natural oils were able to dissolve silver under mild conditions. In this system, the fatty acids didn’t just act as a liquid medium—they also helped stabilize the dissolved silver ions.

“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.

The results made it possible to explain whether the insolubility of metals is caused by surface passivation or a thermodynamic barrier. Adding ethyl acetate to the silver–fatty acid solution enabled the separation of silver as silver carboxylates from the unreacted fatty acids, which can be recycled. The silver carboxylates were in turn reduced to metallic silver in a light-assisted reduction reactor, an efficient and safe method for separating silver.

“The goal of our research is to develop metal recycling techniques from multi-metal substrates using strategies that are inexpensive, sustainable, and selective by design,” says Professor Timo Repo from the University of Helsinki.

Using fatty acids as solvents has many benefits over using traditional mineral acids and aqueous solutions. In addition to originating in waste material, they are biocompatible, biodegradable, low in acid, and non-volatile. This makes them safe and non-corrosive compared with other acids and organic solvents, enabling recycling and reuse.

Since fatty acids are not water-based, metal compounds can be separated from unreacted reaction mixtures by using ethyl acetate and other antisolvents. This allows for both straightforward metal recovery and the recycling of fatty acids. In addition, the possibility of using 30% aqueous hydrogen peroxide as a green oxidant under mild conditions enables urban mining, that is, separating, for example, silver from keyboards with waste silver plating.

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