Mushrooms recover gold out of mobile scrap

April 11, 2014 // By Julien Happich
Gold, silver, copper and many other valuable metals (including rare earth metals) are commonly used in the manufacture of consumer electronics only to end-up into huge piles of electronic waste.

The metals are used get the signal from one chip to another (gold wirebonds, copper traces on printed circuits boards) or to improve contact reliability (gold or silver electrodeposition on connectors), or as minute traces in passive components just to name a few applications.

The e-waste issue is not new, and before it became on the European legislation agenda, it used to be that unscrupulous “recyclers” would ship discarded electronic devices to third world countries where very basic and hazardous metal recovery techniques would be used.

This often includes burning and smelting the metals from cables (toxic fumes including dioxins), or separating gold from burnt PCB ashes using toxic cyanides solutions that then contaminate nearby rivers.

In Europe and the US, several companies have industrialised the recovery of precious metals from e-waste, first crushing the devices and PCB boards, then using various separation methods (magnets to take out the steel, Eddy currents to separate non-ferrous metals from plastic) before smelting again or using toxic chemistries (often sulphuric acid or cyanide solutions) to dissolve the metal particulates and recover them through chemical reactions. The processes are similar, only better managed at industrial scale, but they are still energy intensive and environmentally debatable.

Reportedly, such industrialised processes can yield up to 300 grams of gold per ton of discarded mobile phones, and between 2 and 2.5 kilos of silver. By far, the most aboundant metal in e-waste is copper, making up between 10 and 15% of a mobile phone’s weight.