Palladium recovery from monolithic ceramic capacitors by leaching, solvent extraction and reduction

Palladium finds a remarkable use in electronic devices and catalysts; therefore, an efficient and complete recovery from the containing secondary materials assumes a great relevance. The present paper discusses recovery of palladium (Pd) contained in monolithic ceramic capacitors from waste printed circuit boards (PCBs) of electrical and electronic equipment by hydrometallurgical techniques. Samples, after a milling step, were leached by aqua regia varying the operative conditions. Parameters such as lixiviant concentration, solid/liquid ratio and temperature were investigated. Pd was separated from the leach solution by solvent extraction using Aliquat 336 as an extractant in limonene. This solvent was studied as alternative to the usual ones because it is a renewable organic diluent, with low-toxicity and easily available. After the extraction the organic phase was treated with sodium borohydride to precipitate metallic palladium obtaining a recovery rate of 83% with a purity grade of 98.8%. Based on the results of the present study, a process flow sheet was proposed for industrial implementation.