Researchers at the National University of Singapore, working with colleagues from Manchester University and Guangdong University of Technology, have developed a sponge-like material made of graphene oxide and chitosan, that can be used to extract gold from electronic waste. In their recent study, the research team describes how they made their sponge and how well it worked during testing.
Previous research has shown that removing gold, silver and other metals from electronic equipment that is no longer useful, as a way to recycle such materials, is a difficult task that often results in low yields and the generation of a variety of toxic pollutants. In this new work, the team has found a way to remove the gold in a way that is cheaper and cleaner than conventional methods and much more efficient as well.
The scientists chose to work with these materials as both have been used to extract gold from other materials. Also, graphene has a demonstrated ability to absorb ions, and chitosan (a natural biopolymer) is a well-known reducing agent, which in this case was used to catalytically convert gold ions into their solid form.
The two materials were made into a composite by allowing the chitosan to self-assemble on two-dimensional graphene flakes—a process that also resulted in the formation of sites on the material that could bind to gold ions. After the gold ions are absorbed into the graphene, the chitosan converts them into their solid gold state, allowing for easy collection—a process the research team describes as highly efficient.
The team tested their sponge using real e-waste provided by a recycling company. The e-waste came in the form of a solution mixture, which meant it had been ground up with other materials present in the electronic equipment and mixed into a liquid. Measurement prior to treatment showed gold concentrations of 3 ppm.
The newly developed sponge was able to extract approximately 17g/g of Au3+ ions and a little more than 6 g/g of Au+. Such amounts, the team says, are approximately 10 times that of any other known extraction process.