The Recovery Of Precious Metals From Electronic Wastes

The recovery of electronic wastes has been a global issue because electronic wastes with a large quantity are both hazardous and valuable. Especially, the recovery of precious metals is the major economic driving force for recycling electronic wastes.The unique character that precious metals are widely used as coating/plating in electronics was attention paid to and the principle that lead possesses good collector properties with respect to precious metals was utilized to recover precious metals from electronic wastes. Central processing unit (CPU), a significant electronic component with a high gold content, was taken in experiment. CPU was pre-processed by centrifugal separation, solder smelting and vacuum pyrolysis to separate the pins from the base plates. The dissolution behaviors of Au and the base metals of the pins (Cu and Ni) in Pb were discussed according to the phase diagrams. The lead extraction was carried out using immersion method and the effects of extraction temperature and extraction time on the extraction efficiency was studied.Results showed the pins could be separated from the base plates by the solder smelting and the vacuum pyrolysis while the centrifugal separation failed in separating the pins from the base plates at oil temperature of240℃and rotating speed of800rpm. The gold-plated layer of the pins was intact by the solder smelting method. Meanwhile, the solder smelting method had advantage in high productivity and the simplicity of the equipment and the operation. The separation of the pins and the recovery of the organic compositions could be realized at one step by the vacuum pyrolysis method. When the vacuum pyrolysis was carried out at300-400℃, the gold-plated layer of the pins remained intact relatively. Also, a low pyrolysis oils yield was obtained and the composition of the pyrolysis oils was relatively simple. Good results were achieved in the recovery of Au by lead extraction.97.2%of Au from the pins was extracted into lead melt at extraction temperature of500℃and immersion time of60min. Meanwhile, the dissolution ratios of Cu and Ni in lead were just1.77%and0.52%, respectively.