Cage-like amine-rich polymeric capsule with internal 3D center-radial channels for efficient and selective gold recovery

Abstract

With the ever-increasing demand for electronics, recovering precious metals from secondary sources such as electronic waste is both environmentally and economically attractive. However, a challenge still remains in how to realize the highly selective and efficient recovery of a particular metal of interest. Here, a novel cage-like amine-rich polymeric capsule (APC) with internal 3D center-radial pore channels was prepared through a solvent-exchange method to efficiently separate gold from secondary sources. A thin shell of APC allows the gold ions to penetrate well into the APC inside, and the amine-rich surface in the interior hierarchical pore structure selectively reduces the gold ions to nanocrystals in the presence of interference ions (recovery selection ratio of Au/Cu = 9,103, Au/Ni = 15,172, and Au/Zn = 3,240). Moreover, the thin shell of APC enhances recovery stability by preventing the release of the gold nanocrystals to the exterior, and also by preventing clogging of the internal 3D center-radial pore channels in the presence of various suspended solids such as metallic, hydrophobic, and hydrophilic nanoparticles that may exist as impurities in the gold recovery process. Consequently, the APC adsorbent achieved a gold recovery ratio of ∼ 99%, maintained even after 10 cycles of repetitive adsorption/desorption. Thus, the APC offers a pragmatic way possible to address intrinsic drawbacks of conventional nano- and micro-sized adsorbents such as low recovery stability after use, selectivity for gold ion, and low tractability.