Facile recovery of gold from e-waste by integrating chlorate leaching and selective adsorption using chitosan-based bioadsorbent

Abstract

Recovery of gold from electronic wastes, particularly waste printed circuit boards (WPCBs), has received significant attention due to its high gold content and economic value. This study reports a novel method for efficient and selective recovery of gold from WPCBs using an integrated chlorate leaching and chitosan-based bioadsorption. The experimental conditions of the leaching step were optimized, and ∼100 % leaching efficiency of gold could be achieved when 0.5 g of WPCB sample was treated with 12.5 mL (liquid to solid ratio of 25) of a mixture of chlorate (0.2 M) and chitosan (1% w/v) in 2 M HCl at 55 °C for 5 h. The WPCB leachate containing gold and other metal ions (e.g. Cu and Al) was diluted three-fold and then treated with glutaraldehyde-crosslinked chitosan (GCC) beads, achieving selective and complete adsorption of gold at GCC dose of ≥1 g/L. The adsorbed gold on GCC could be fully desorbed by using a thiourea/HCl mixture (each 0.2 M). The high efficiency of gold adsorption-desorption could be maintained up to four successive cycles, signifying long-term reusability of the GCC. As an alternative approach, thermal decomposition of the gold-adsorbed GCC at 650 °C was shown to generate sponge-like gold residue with 97.8 % purity. These results indicated high efficiency of the proposed method for recovering gold from e-waste along with its simple process steps, low chemical usage and low cost.