Recovery of high purity secondary silver from waste Ag/Cu electrical contacts

In this study, a strategy was developed to directly recover high-purity Ag and other metals (especially Cu) from WECs to reduce the leaching of precious metals and promote the leaching of Cu and other metals. The results of SEM, EDS, XRD and ICP-OES clearly suggested that Ag and Cu were effectively released from WECs below 0.15 mm size, which contributed to the regulation of metals crystal types. The zero-valent copper from WECs was changed by roasting to form CuO and Cu2O, and the suitable samples of roasting at 400 degrees C for 3 h were confirmed experimentally. After the leaching processing under H2SO4 (1 M) and H2O2 (30%), the roasted particles were directly obtained, including Ag with 99.53 wt.% purity and more than 99.99% recovered, and Cu, Sn, Ni and Zn extracted by 99.67%, 90.71%, 73.05% and 99.32%, respectively. However, the unroasted particles would generate lower grade of Ag because other metals (e.g. Cu, Sn, Ni and Zn) were difficult to be leached from WECs. The leaching solution primarily included Cu ions (98.3%) and a little of the nickel (0.83%) and tin (0.86%) ions, which could recover copper by evaporation crystallization to form CuSO4 (99.48 wt. %). The reaction mechanism of the process could be concluded that the copper state was transformed by mechanical separation and roasting to promote the leaching of various metals from Ag. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.