This study focuses on the recovery of valuable metals, specifically silver (Ag) and palladium (Pd),
from copper-containing sludge (with copper content less than 20 per cent) generated during PCB
processing and from spent petrochemical catalysts used in vapour decomposition during oil refining
processes. The present results indicate that an increase in the mixing ratio of alumina-based spent
catalyst leads to a decrease in the recovery rate of Ag and Pd. The recovery rates for Ag and Pd
range from 84 per cent to 96 per cent and 80 per cent to 98 per cent, respectively. This trend is
attributed to the increased emulsification of copper droplets containing Ag and Pd in the slag. The
emulsification is caused by the decrease in the settling velocity of the copper droplets due to the
increased viscosity of the slag as well as by the decrease in the slag-metal interfacial tension due to
an increase in sulfur content at higher mixing ratio of spent catalyst.