New process could lead to “urban mining” for metals

A new process can efficiently recover metals from electronic waste in an energy-efficient manner

Spotted: A new process developed at Rice University can extract valuable metals from electronic waste. This process—called flash joule heating—uses up to 500 times less energy than current methods. Flash joule heating was originally introduced to produce graphene from carbon using sources like waste food. However, the Rice researchers adapted the method to recover minerals like rhodium, palladium, gold and silver from e-waste.

The method works by flash heating the electronic waste to temperatures of 3,400 Kelvin (5,660 degrees Fahrenheit). This high heat vaporises the metals. The gases are then piped from the flash chamber into a cold trap using a vacuum. Once in the cold trap, the metal gases condense back into solid metal. The reclaimed metal mixture in the trap can then be further purified to yield individual metals. 

In addition to retrieving metals from electronic waste, the researchers found that the flash joule reaction reduces the concentration of lead in the charred remains to below 0.05 parts per million. This is a level safe enough for the waste to be disposed of in agricultural soils. Levels of other toxic metals, such as arsenic and mercury, could also be reduced by using additional flashes. As each flash lasts less than a second, this is quick to do. 

Rice chemist James Tour points out that the process could turn a major source of toxic waste into a useful resource. “Here, the largest growing source of waste becomes a treasure,” he said. “This will curtail the need to go all over the world to mine from ores in remote and dangerous places, stripping the Earth’s surface and using gobs of water resources. The treasure is in our dumpsters.”

Currently, less than 20 percent of e-waste is sustainably recycled, and there is a lot of interest from innovators in improving this situation. Here at Springwise, we have seen this take a number of forms, such as the development of a low-cost biodegradable PC and a biodegradable electronic display.