title: Direct extraction of palladium and silver from waste printed circuit boards powder by supercritical fluids oxidation-extraction process.
abstract: The current study was carried out to develop an environmental benign process for direct recovery of palladium (Pd) and silver (Ag) from waste printed circuit boards (PCBs) powder. The process ingeniously combined supercritical water oxidation (SCWO) and supercritical carbon dioxide (Sc-CO2) extraction techniques. SCWO treatment could effectively enrich Pd and Ag by degrading non-metallic component, and a precious metal concentrate (PMC) could be obtained, in which the enrichment factors of Pd and Ag reached 5.3 and 4.8, respectively. In the second stage, more than 93.7% Pd and 96.4% Ag could be extracted from PMC by Sc-CO2 modified with acetone and KI-I2 under optimum conditions. Mechanism study indicated that Pd and Ag extraction by Sc-CO2 was a complicated physiochemical process, involving oxidation, complexation, anion exchange, mass transfer and migration approaches. Accordingly, this study established a benign and effective process for selective recovery of dispersal precious metals from waste materials.
authors.affiliation: Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Kang
authors.initials: K
authors.lastname: Liu
authors.affiliation: Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: fszhang@rcees.ac.cn.
authors.forename: Fu-Shen
authors.initials: FS
authors.lastname: Zhang
keywords: Precious metals; Recovery; Supercritical fluid extraction; Supercritical water oxidation; Waste printed circuit boards