The Elements of Innovation Discovered

Organic solvents for urban metal mining

Metal Tech News - May 27, 2024


University of Helsinki used organic solvents to selectively recover gold, silver, and copper from old circuit boards and solar panels.

Researchers develop increasingly sustainable methods for dissolving precious metals like gold, silver and copper from recycled e-waste.

With a surprising assortment of solvents you can pick up at the local store, researchers at the University of Helsinki have developed sustainable dissolution methods that have successfully extracted gold, silver, and copper from e-waste.

The massive amount of unrecycled waste from computers, printers and cell phones, video game consoles, TVs, batteries, appliances and other discarded electronics large and small are an important source of precious metals to supplement traditional mining.

Electronics and batteries are usually designated as hazardous waste. The extraction methods for recycling e-waste currently in industrial use – coined urban mining – consume too many chemicals and water, or too much energy while requiring additional processes to avoid being detrimental to the environment.

The method of grinding up and roasting mixed materials into black mass is particularly dangerous for its labor, expensive to automate, and isn't a good trade for the environmental toll, however minimized.

In developing countries, valuable metals are to this day extracted by hand from landfills – often by underage and impoverished locals – under inhumane conditions.

Even though newer, more advanced hydrometallurgical processes are safer and able to dissolve noble metals, there is a lot of water use and the result is metal mixtures that require further processing.

The findings of Catalysis and Green Chemistry research group headed by Professor of Chemistry Timo Repo at the University of Helsinki have been published in the journal Angewandte Chemie International Edition. The article describes a three-stage process where copper, silver and finally gold are each individually dissolved from electronic waste. This way, metals can be selectively separated from a mix of plastics, ceramics and other materials, yielding pure metals. In addition, the solvents are recyclable.

Researchers at the university tested organic solvents on crushed circuit boards, successfully extracting the gold and copper, while silver was separated from crushed old solar panels – particularly interesting results due to solar panels being high-volume products whose recycling opportunities have been subpar.

Riitta-Leena Inki

Anže Zupanc with container of circuit board scraps being dissolved in an organic solvent.

"In this study, we used what are known as deep eutectic solvents, liquids, that are made from substances that are solid in room temperature and under normal pressure, such as choline chloride-also used in poultry feed-and urea, as well as other safe organic compounds," said Anže Zupanc, a postdoctoral researcher at the University of Helsinki.

Deep eutectic solvents are renewable and in many cases biodegradable with applications in chemical reactions, catalysis and extraction techniques. Lactic acid and hydrogen peroxide were used in the study as well.

"An important result was that the solvents could be reused, putting the principles of green chemistry into practice," Repo notes.

Recovering precious metals and critical minerals from the global e-waste feedstock has the potential to become a lucrative niche industry in the short term, one which – it is hoped – will die out as better recycling infrastructure, more thoughtful product engineering and less planned obsolescence are adopted.


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