A method has emerged to efficiently adsorb and recover gold, a valuable precious metal, from discarded electronic waste. Alireza Abbaspourrad, a professor at Cornell University in the U.S., noted on the 3rd that he has developed a technology that can recover over 99.9% of the gold contained in electronic waste without using toxic substances.
The precious metal extraction industry, referred to as "urban mining," is gaining attention for its potential to generate significant added value. However, there has been a concern over the use of toxic substances during the metal extraction process, which causes environmental pollution.
According to the International Electronics Waste (WEEE) Forum, 62 million tons of electronic waste were disposed of worldwide in 2022. The amount of electronic waste is projected to rise to 82 million tons by 2030. However, only 20% of this waste is recycled. Most discarded electronic waste is treated through incineration or landfilling. In this process, heavy metals such as lead, mercury, and cadmium contained in electronic products can leak and cause environmental pollution.
The research team has newly developed a material that efficiently adsorbs gold from electronic waste. The material, known as Tetra-thiophene-COF (TTF-COF), uses sulfur (S) atoms in its composition and features a covalent organic framework (COF). COF has a porous structure with many tiny holes on its surface, composed of robust covalent bonds and is known to be non-toxic. TTF-COF can strongly bind to gold ions while forming almost no bonds with other metals, allowing for efficient gold capture.
The research team verified the gold recovery rate of TTF-COF using discarded computer central processing units (CPUs). After disassembling the CPUs, they scraped off the metallic film from the surface and dissolved it in a special solution. Then, they placed TTF-COF in the metallic solution and allowed it to react for one hour before retrieving it.
The concentration of recovered gold was calculated by comparing the gold concentration in the solution before and after adding TTF-COF. As a result, it was found that 99.9% of the gold, which was initially present at a concentration of 251.03 mg per liter in the solution, disappeared after adding TTF-COF. This indicates a successful adsorption and separation of most of the gold present in the electronic waste. In contrast, the amounts of copper and nickel decreased by 5.5% and 2.1%, respectively, while almost no other metals were found to be mixed in.
The research team also succeeded in recovering over 98% of the gold adsorbed on TTF-COF. Even after 16 uses, the adsorption efficiency remained above 88%, confirming its economic viability.
The research team said, "Previously, toxic chemical substances had to be used to recover gold from electronic waste. However, the method developed this time allows for the efficient recovery of gold using an adsorbent without harmful substances."
The industrial sector is currently developing electronic waste into a new industrial area known as "urban mining." The idea is to extract precious metals from discarded electronic products, similar to mining gold ore. For example, 1 million mobile phones contain approximately 24 kg of gold, 16,000 kg of copper, 350 kg of silver, and 14 kg of palladium, among other precious metals. It is estimated that the total value of precious metals in discarded electronic waste amounts to about $57 billion (approximately 84 trillion won) each year. However, for the urban mining industry to thrive, it is necessary to secure technology that can economically and efficiently separate precious metals from electronic waste.
The research team has also developed industrial catalysts using the recovered gold from electronic waste. This utilizes the characteristic of carbon dioxide (CO₂), which contributes to global warming, to strongly bond with the COF. When TTF-COF captures carbon dioxide from the atmosphere and reacts at 50 degrees Celsius, it produces propiolic acid. Propiolic acid serves to inhibit the corrosion of steel and is utilized in the steel industry.
Professor Abbaspourrad expects that this method will help solve the environmental pollution issues caused by electronic waste and could also replace the expensive carbon dioxide conversion catalysts that use silver or platinum. He stated that it will lead to sustainable development by replacing mining for precious metals.
The research results were introduced in the international journal "Nature Communications" on the 30th of last month.
Reference Material
Nature Communications (2024), DOI: https://doi.org/10.1038/s41467-024-55156-3