Synthesis and Characterization of Noble Hydrogel Beads of Amino Functionalized Reduced Graphene Oxide for Selective Extraction of Gold from Electronic Waste

For a sustainable future, the rapid increase in the use of electrical and electronic devices necessitates new technologies and methods for the recovery and recycling of electronic waste. The selective extraction of gold from e-waste was achieved using amine-functionalized reduced graphene oxide impregnated in calcium alginate matrix (NH2-rGO-Ca-Alg). The NH2-rGO-Ca-Alg hydrogel beads were characterized using SEM-EDS, XRD, Zeta potential, ATR-FTIR and Raman spectra. Highly efficient gold extraction (above 96% absorption of gold at pH ranges 2-4) was evaluated in batch sorption investigations. The sorption of gold using NH2-rGO-Ca-Alg beads requires an equilibrium contact time of 24 h. Using the Langmuir isotherm model, the maximal sorption capacity of the NH2-rGO-Ca-Alg beads was determined to be 12.48 mg g-1. From the kinetic study, sorption was observed to follow a second-order pseudo kinetic equation. Experimental observation of intraparticle diffusion revealed that gold sorption on the NH2-rGO-Ca-Alg beads takes place in three stages. Additionally, gold was leached from a junk solid-state detector using aqua regia, and the NH2-rGO-Ca-Alg beads demonstrated highly effective and selective gold extraction from the leached solution. The elemental spectra of the NH2-rGO-Ca-Alg beads after gold sorption shows gold peaks and uniform distribution of gold on the bead surface was observed using elemental mapping.