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The aim of this study is the recovery of gold, copper, silver, and palladium from waste printed circuit boards (PCBs) by sequential adsorption with waste orange peel (OP)-derived bio-sorbents. First of all, adsorption tests on the gold and silver model solutions were carried out using native orange peels and modified orange peels by different methods in order to increase the adsorption capacity. These included saponification with sodium hydroxide, hydroxypropylation with propylene oxide, crosslinking with sodium trimetaphosphate and sodium tripolyphosphate, and acidification with citric acid. The optimum adsorption conditions were determined. Gold and silver adsorption was found appropriate to the Freundlich isotherm and pseudo-second-order model for isotherm and kinetic studies, respectively. After this, model solutions including gold, copper, silver, and palladium were prepared and the adsorption efficiencies were examined in the presence of different metals. Finally, waste printed circuit boards were pyrolyzed in a fixed bed stainless steel reactor to obtain an only-metal-containing solid product. Next, leaching of metals from the solid product was performed. For the last stage, adsorption studies on the leach solution were carried out under optimum conditions. As a result, 67.07% gold, 85.77% copper, 97.05% silver, and 75% palladium were adsorbed in total.

The sequential adsorption of gold, copper, silver, and palladium from pyrolysis solid product leach solution of waste PCBs