Recovery of Noble metal elements from effluents of the semiconductor industry as nanoparticles, by dielectric barrier discharge (DBD) plasma treatment

Abstract

The fabrication of semiconductor products for the microelectronic industry requires the deposition of thin noble metal layers (e.g. Au-Sn and Pd) by means of processes involving fluid baths that contain metal ions (e.g. electrowinning and electroless plating). After several cycles, the plating solutions are used up and must be replaced, generating large volumes of discarded solutions containing precious metals. The metals (Au and Pd) are recovered either by electrowinning, a slow batch process, or by the use of toxic molecules (e.g. cyanides). This study demonstrates the possibility of using an atmospheric plasma technology to recover Au and Pd from these solutions, which provides a faster and greener process. Plasma discharges are generated at the surface of the solutions, causing ions to precipitate as nanoparticles. The treatment (few minutes only) allows the recovery of >95% gold, and >60% palladium. The process separates Au (NPs) from Sn ions (remaining in solution), as confirmed by elemental analysis and XPS. Particle size distributions of the nanoparticles recovered through the process suggests that as-synthesized nanoparticles could integrate value-added products (e.g. catalyst industry). Overall, the use of plasma technology could open several possibilities for the recycling of metals contained in solutions discarded from the semiconductor industry.