Selective Recovery of Au(III) and Pd(II) from Waste PCBs Using Ethylenediamine Modified Persimmon Tannin Adsorbent

Abstract

The adsorption characteristics of gold and palladium from hydrochloric acidic solutions onto the ethylenediamine-modified persimmon tannin adsorbent (EPPFR) have been investigated. Amine groups was successfully introduced into persimmon tannin resin to prepared this bifuctional adsorbent. Effects of HCl concentration, contact time, metal ions concentration, temperature were studied in detail. The adsorption capacity was strongly affected by HCl concentration. The complete adsorption equilibrium of Au(III) and Pd(II) was reached within 360 and 60min, respectively. The adsorption isotherms were described by the typical monolayer type of Langmuir model, and the maximum uptake capacity was evaluated as 1550.4 and 112.6mg g-1, respectively. The analysis of thermodynamic parameters revealed that the nature of adsorption was feasible, spontaneous and endothermic process. The applicability of adsorptive recovery of Au(III) and Pd(II) was investigated by treating waste printed circuit boards (PCBs) liquor leached with aqua regia, EPPFR can effectively adsorb precious metals but exhibited no affinity towards base metal ions. Characterized by FTIR, XRD, SEM, the adsorption of mechanisms were proposed to be redox and chelation, respectively. The present results suggested this tannin-based adsorbent EPPFR can serve as a potential adsorbent for the recovery of Au(III) and Pd(II) from waste PCBs liquor in hydrochloric acid solutions.