Metal recovery from electronic scrap

Researchers at Imperial College London have developed a novel aqueous leaching and electrowinning process for recycling metals including tin, silver gold, lead, copper and palladium from electronic and other scrap material.

In an electrochemical reactor, oxidant species – ultimately chlorine – are generated at a titanium/ruthenium/oxygen anode immersed in acidic aqueous chloride electrolyte, then used in a leach reactor to drive the non-selective oxidative dissolution of the metals from the scrap, which has been shredded to >8mm.

The metals are recovered from solution by electrodeposition at a graphite felt cathode as the counter-reaction for the anodic generation of chlorine. Therefore, the overall process involves inputting electrical energy to move the metals from the scrap to the cathode, resulting in

de-metallised waste.

The scrap used by the Imperial College researchers was made up of printed circuit boards, mother boards, graphic cards and similar parts from discarded personal computers. Rotary shears were used to shred the scrap.

The shredded scrap was leached by electrogenerated chlorine in acidic aqueous solutions of chloride ion activity of =5M using a continuously-stirred tank reactor, produced a multi-metal leach solution, which was found to contain almost all the available metal.

The process is a significant improvement on currently used pyrometallurgical processes, maximising metal recovery with low specific energy consumption, and eliminating the need to treat the noxious gaseous emissions created by pyrometallurgical processes.

Imperial College (020) 7589 5111

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