Hierarchical recovery of gold and silver from secondary resources using D-cysteine-functionalized activated carbon: High capacity, selectivity, and economic feasibility

High-performance adsorbents have attracted considerable research interest in the recovery of precious metals. Nevertheless, existing adsorbents suffer from poor adsorption performance, low economic feasibility, and ambiguous mechanisms. Herein, an eco-friendly coconut shell activated carbon (AC) modified with chiral amino acid was first developed for precious metals recovery. D-cysteine-modified AC (AC-(D)SH) exhibited extraordinary adsorption capacities of 3783.8 mg/g for Au(Ⅲ) and 2076.6 mg/g for Ag(Ⅰ), with prominent regenerability and excellent selectivity. Combined experimental characterizations and theoretical calculations confirm that reductive and coordinative adsorption act as the dominant adsorption mechanisms. A novel selective desorption-functional group grafting method was presented to quantitatively distinguish the contribution of the two mechanisms and individual functional groups (−SH or –NH 2 ) to total adsorption capacity. Specifically, thiourea/nitric acid-mediated desorption was used to discriminate the contributions from coordination and reductive adsorption, whereas stepwise grafting of single −SH or –NH 2 onto AC permitted the quantification of their separate adsorption performance. Moreover, AC-(D)SH accomplished the recovery of high-purity metallic Au (99.32%) and Ag (99.99%) from real waste CPUs and spent solar panels, respectively, and achieved stepwise Au/Ag recovery from copper anode slime. This work thus offers a design strategy for chiral amino acid-functionalized adsorbents, a quantitative approach for evaluating adsorption contributions, and an economical protocol for Au and Ag recovery from secondary resources.