A new technique developed at the University of Helsinki uses fatty acids, hydrogen peroxide and visible light to dissolve and recover silver from waste, offering a safer alternative to conventional cyanide-based recycling.
Researchers in Finland have demonstrated a new method for recycling silver that avoids the use of cyanide and other harsh chemicals, potentially offering a safer and more sustainable route for recovering the metal from waste products.
The process, developed by a team at the University of Helsinki, uses simple organic molecules related to those found in everyday vegetable oils, combined with visible light, to dissolve silver and then convert it back into solid metal ready for reuse. The study has been published in the Chemical Engineering Journal.
Silver demand continues to rise due to its widespread use in electronics, solar panels and other clean technologies. However, only around 20% of global silver supply currently comes from recycling, with most recovered through mining.
A safer approach to silver recovery
The research was led by postdoctoral researcher Anže Zupanc, whose work focuses on cleaner methods for metal recovery that align with circular economy principles. Traditional silver extraction and recycling often relies on cyanide leaching, a process that has been used for more than a century but carries significant environmental and health risks.
With regulatory pressure increasing around cyanide use, the team set out to design a method that could recover silver efficiently while reducing toxicity and environmental impact.
Instead of strong mineral acids, the researchers used fatty acids – simple organic acids commonly found in plant-based oils – to dissolve metallic silver under mild conditions.
Dissolving silver with organic acids
In laboratory tests, pieces of silver metal were placed in a solution containing fatty acids and hydrogen peroxide. The hydrogen peroxide acted as an oxidising agent, gradually converting silver on the metal surface into positively charged ions that dissolved into the liquid.
Under these conditions, the solution was able to hold up to 4.6% of its own weight in dissolved silver. The team also recorded dissolution rates of up to 1.62 moles of silver per square metre of metal surface per hour.
As the silver entered the solution, it formed compounds known as silver carboxylates, created when metal ions bind to the acid groups in the fatty acids. By adding ethyl acetate, the researchers caused these compounds to crystallise, allowing the silver-containing material to be separated while the unused acids were recovered for reuse.
Using light to recover metallic silver
To convert the dissolved silver back into solid metal, the team exposed the silver carboxylate crystals to visible light inside a reactor. Two compact fluorescent lamps, each rated at 30 watts and emitting wavelengths between 400 and 650 nanometres, were used to drive the reaction.
This photoreduction process turned the silver ions back into metallic silver particles, which could then be filtered out and collected. Throughout the process, hydrogen peroxide served as the oxidant and broke down into water and oxygen, leaving no persistent chemical residues.
The result was a closed-loop system in which both the silver and the organic acids could be reused.
Potential for urban mining
The researchers see the technique as particularly relevant for “urban mining” – the recovery of valuable metals from discarded consumer products rather than newly mined ore.
In experiments, the team applied the method to waste materials such as silver-coated plastics used in computer keyboard connections. These components typically combine thin silver layers with polymers and other metals, making recovery challenging.
According to the researchers, the process was able to selectively dissolve silver while leaving most base metals behind.
Zupanc said recycling silver from waste streams is becoming increasingly important as demand grows and supply risks increase.
Relevance for clean technologies
Silver plays a critical role in photovoltaic solar panels, where silver-based pastes are used to conduct electricity. Industry data shows that silver consumption in solar technologies reached around 193.5 million ounces (approximately 5.5 million tonnes) in 2023, continuing an upward trend.
As economies electrify, silver is increasingly viewed as a critical material vulnerable to supply disruptions. While the new method is not intended to replace mining entirely, the researchers argue it could help reduce pressure on primary resources by capturing silver that would otherwise be lost in waste.
If adapted for larger-scale equipment and diverse waste streams, the technique could support more automated recycling of silver-rich components at the end of their life, reducing environmental impacts and improving material security.
The study is published in Chemical Engineering Journal.
