Selective Extraction of Gold from Strong Acid E-waste Leachate Through H+-Triggered Cascade Reaction of Thiolated β-Cyclodextrin

Abstract

Recycling precious metals from the increasing amount of electronic waste (e-waste) is of great significance for the sustainability of strategic metal resources. However, there are rarely reports of technologies that can efficiently and highly selectively recover precious metals from strong acid e-waste leachates. Herein, we demonstrated a simply synthesized thiolated β-cyclodextrin (T-CD) that can recover gold with high selectivity from strong acidic medium. The material has an exceptional adsorption capacity, approaching 1890.98 mg gold/g of adsorbent, and a superior selectivity coefficient of about 5×104 for gold from multi-metal coexistence solutions at pH 2. Sulfhydryl groups, as the adsorption sites, are capable of selectively enriching gold to T-CD surfaces. Simultaneously, the acetal of T-CD can be hydrolyzed into hemiacetal by the initiation of H+ in acidic solution with a more energetically favorable reaction barrier (TS = -3.38 eV) than that in neutral solution (TS = 5.36 eV). Further, the serial transformation process of carbon structure and gold valence state (Au3+ to Au) induced by redox reaction of acetal carbon were confirmed by XPS and DFT. In addition, T-CD shows a remarkable ability to extract gold directly from actual complex waste printed circuit board leachate, which facilitates the recycling of the acidic solution up to five times. The concept of H+-assisted enhancement of adsorbent performance provides a new guidance for the direct recovery of rare and precious metals from strongly acidic actual wastewater.