Silver cementation mechanism for leaching silicon solar cells in nitric acid

Abstract

Silicon solar panels are often overlooked in e-waste recycling technology, even though they contain precious silver (Ag). In order to help meet future global Ag demands and prevent contamination of the environment, all the Ag from end-of-life modules must be recovered instead of landfilled. The most mature Ag recycling recipes use high concentration nitric acid (HNO₃) solutions often in combination with heating and agitation. After the Ag is leached, chemical precipitation or electrochemistry is used to recover metallic Ag. However, the process of Ag leaching in the HNO₃ system with competing elements from silicon solar cells is not well understood. In this paper, we investigate the thermodynamics governing Ag leaching in low-concentration HNO₃ without agitation or heating to expand fundamental knowledge in support of Ag recovery efforts from end-of-life solar panels. ICP-OES is used to quantify the amount of Ag leached in the HNO₃ solution over time. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) are used to study the changes on the silicon solar cell surface. Our results suggest when trace tin (Sn) is used in solar cell fingers, it causes Ag to cement in dendritic form.