Gold contained in discarded electrical or electronic devices can be selectively separated from the rest of the metals
It is estimated that 7% of all world’s gold is found in the printed circuit boards of electrical devices which will be wasted if not retrieved at the end of their life cycle. The good news is that scientists at Edinburgh University developed a new method of extracting the precious metal contained in waste electrical and electronic equipment (WEEE) such as mobile phones. Gold can be separated from the mixture of metals by extraction into toluene from an aqueous HCl solution; a simple and efficient method that does not use toxic chemicals like cyanide (used by other current processes), that can be hazardous to health. Their work, published in August in the journal Angewandte Chemie, was funded by EPSRC and could help salvage some of the estimated 300 tonnes of gold used in electronics each year.
In order to extract the gold, printed circuit boards are first placed in a mild acid, so that all of their metal parts are dissolved. Then, a primary amide contained in an oily toluene solvent is added, which is capable of extracting gold selectively from the mixture of other metals. According to the head researcher Professor Jason Love, gold is retrieved from the chemical mixture with water. “After separation of the oily phase from the acid one, washing the oily phase with water transfers the gold into the water phase for electro-winning,” he told The Engineer. “We have to do this a couple of times to ensure complete phase transfer, but each wash step is very quick.” It is interesting that 85% of gold contained on old circuit boards is extracted on just the first pass, however Prof. Love says that these extractions are repeated several times to ensure complete recovery of the desired metal. “We want to look into developing a whole process to satisfy a possible circular economy theme,” he added.
In any case, this is a fundamental chemical understanding gained, which should be taken into account at the development of large-scale metal-recovery processes.
Source: The Engineer