Simple process for the recovery of gold metals and palladium(II) compound from aqua regia etching solutions of printed circuit boards by chemical reduction and precipitation

Abstract

Printed circuit boards (PCBs) contain precious metals like gold and palladium. After pretreatment, PCBs are dissolved with aqua regia to recover precious metals. Reduction and precipitations experiments were done to recover gold metal and palladium(II) compound from PCB etching solutions which contained Au(III), Pd(II), Al(III), Cu(II), Fe(III), Ni(II), Sn(II), and Zn(II). In the first step, Au(III) ions were chemically reduced to gold metal using ascorbic acid without changing the acidity of the solution. The optimal conditions for the reduction were 1.5 for the molar ratio of ascorbic acid to Au(III) at room temperature for 30 min. Then, PdI₂ was recovered from the filtrate by using NaI as a precipitant. The optimal conditions for this precipitation were a NaI/Pd(II) molar ratio of 7 at room temperature for 60 min. The purity of the gold metal and PdI₂ was verified by measuring the composition of the solution after dissolving with aqua regia. A simple process was proposed to recover gold metal and PdI₂ powders with 99.9% purity from the etching solutions of PCBs at room temperature.