Speciation and quantitation of precious metals in model acidic leach liquors, theoretical and practical aspects of recycling

Waste printed circuit boards are a major source of strategic materials such as platinum group metals since they are used for the fabrication of technological devices, such as hard drive discs, capacitors, and diodes. Because of the high cost of platinum, palladium, and gold (> 25 k€/kg), an economic and environmental challenge is their recycling from printed circuit boards that represent around 2% weight of electronic equipment. Hydrometallurgical treatments allow the recovery of these metals in solution, with a high recovery rate for a leaching liquor made of thiourea in hydrochloric acid. So as to develop an efficient recycling process from this leach liquor, one requires the speciation of these strategic metals, as well as their extraction and quantitation in the mixture. For this purpose, platinum, palladium, and gold were dissolved in model leach liquors made of hydrochloric acid and thiourea at low concentration. The identification of metal complexes was determined as a function of thiourea concentration (between 10 μmol/L and 10 mmol/L) by the combination of UV-visible spectrometry, cyclic voltammetry, and for the first time capillary electrophoresis. The electrokinetic method was then applied for the quantitation of trace metal analyses in leach samples from waste printed circuit boards reprocessing, demonstrating its applicability for industrializable recycling applications. Graphical abstract