Hydrometallurgical processing of waste multilayer ceramic capacitors (MLCCs) to recover silver and palladium

Abstract

Present paper reports an application oriented approach to recover precious metals such as silver (Ag) and palladium (Pd) from multilayer ceramic capacitors (MLCCs) of waste printed circuit boards (PCBs). These capacitors are being widely used in modern electronic gadgets to provide advance features as well as to enhance their performance. Due to the generation of large amount of e-waste as well as the loss of precious metals, a sincere R&D effort has been made to develop a process for the recovery of Ag and Pd from waste MLCCs. Initially, the MLCCs were depopulated from the PCBs by de-soldering using thermal treatment. Further, the depopulated material was pulverised to get homogeneous fine powder of MLCCs, which contained 0.14% Pd, 1.08% Ag, 1.76% Cu and 11.1% Ni. First of all Ni was removed/recovered selectively using two stages of leaching at optimized condition i.e. 2 M HCl, temperature 75 °C and pulp density 100 g/L. The obtained leached residue was washed, dried and further leached to get 99.99% Ag and Pd both in solution using 4 M HNO3, temperature 80 °C, pulp density 100 g/L and mixing time 1 h. From the obtained leach liquor, salt of Ag (purity 99.99%) was selectively recovered/precipitated using KCl. Further, Cu was extracted from the Ag depleted solution using LIX 84IC leaving Pd in the raffinate, which was evaporated to get pure Pd salt. The developed flow-sheet has potential to be commercialized after scale up trials.