Separation of Au(III) and Pd(II) from the Etching Solutions of Printed Circuit Boards by Chemical Reduction and Oxidative Precipitation

Abstract

ABSTRACT Printed circuit boards contain gold and palladium. The first step in the recovery of gold and palladium from PCBs is to dissolve them by etching. In this work, a process was developed to recover gold metal and palladium compound from the etching solution containing Al(III), Cu(II), Fe(III), Ni(II), Sn(II) and Zn(II). Gold metal powders with 99.3% purity were recovered from the solutions by chemical reduction with hydrazine at room temperature within 30 mins when the molar ratio of hydrazine to Au(III) was 3. Hydrazine was more effective than sodium borohydride in reducing Au(III). Then Pd(II) could be recovered from the filtrate after separation of Au(III) by either precipitation or oxidative precipitation. When 0.3 M NaI was employed as a precipitant, PdI2 and CuI were co-precipitated from the filtrate, while Pd and Sn ions were co-precipitated during oxidative precipitation by adding 0.54 M NH4Cl as a precipitant and 0.3 M NaClO3 or 0.3 M NaIO3 as an oxidizing agent at room temperature for 30 min and a stirring speed of 500 rpm. It was possible to suppress the co-precipitation of Sn ions by adjusting the concentration of NaIO3. (NH4)2PdCl6 powders with 99.8% purity were recovered within 30 mins from the filtrate by oxidative precipitation with 0.1 M NaIO3 when the molar ratio of NH4Cl to Pd(IV) was 5. The purity of the gold metal and palladium compound thus recovered was verified by measuring the composition of the solution after dissolving them with aqua regia.