Preparation of nano-sized tin oxide powder from waste Pb-free solder by direct nitric acid leaching

Abstract

Nano-sized tin oxide particles were prepared by nitric acid (HNO3) leaching of Pb-free solder containing tin (Sn), silver (Ag), and copper (Cu) as main components. During the nitric acid leaching, Ag and Cu were dissolved whereas Sn was not detected in the leach solution and the leaching efficiencies of Ag and Cu increased with increasing temperature and HNO3 concentration. The precipitates were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The tin precipitate was determined to be tin oxide by XRD and nano-sized particles were observed in the SEM and TEM images. The larger particle size was observed in the leaching condition of slow leaching rate. The purity and particle size of tin precipitate, obtained from the leaching test performed in the 2 mol/L HNO3 solution at 90°C and 400 rpm, were 99.986% and 6.03 nm, respectively.