Recovery of Au and Pd from the etching solution of printed circuit boards by cementation, solvent extraction, reduction, and precipitation

Printed circuit boards (PCBs) contain precious metals like Au and Pd. Therefore, it is important to recover these metals from waste PCBs. A process was developed in this work to recover pure Au powders and Pd compounds from the aqua regia etching solution of waste PCBs. Au(III) and Pd(II) were separated by cementation with Cu powder from the etching solutions containing Al(III), Cu(II), Fe(III), Na(I), Ni(II), Sn(II) and Zn(II). The Au and Pd metals present in the cemented Cu were dissolved together with Cu by the mixture of HCl and NaClO. Au(III) was separated from the leaching solution of the cemented Cu by solvent extraction with Cyanex 272. Then pure Au powders were recovered from the thiourea stripping solution by chemical reduction with hydrazine. In order to recover Pd(II) from the raffinate after extraction of Au(III), Pd(II) was oxidized to Pd(IV) by adding NaClO3 and then pure Pd compound ((NH4)2PdCl6) was recovered by precipitation with NH4Cl. Optimum conditions of these steps were obtained at room temperature. The purity of the recovered Au and Pd compound was higher than 99%.