Selective recovery of noble metals from electronic waste leachates via coral-like adsorbents

Coral-like adsorbents (BCTC@PEI) with polyethyleneimine backbones and a crosslinked network are engineered to selectively recover gold, palladium, and platinum, from synthetic E-waste leachates. These adsorbents exhibit high maximum adsorption capacities (q_max) according to the Langmuir isotherm: 2405, 1084, and 1153 mg/g for Au, Pd, and Pt, respectively (at 25 °C). The adsorption processes fit well with the pseudo-second-order kinetics (R² > 0.99), with rapid equilibrium (t_e) achieved within 5 and 10 min for Au and Pd, respectively. The coral-like morphologies and macroporous structure facilitate intraparticle diffusion, resulting in a bulk diffusion-controlled kinetics. By combining experimental design and systematic characterizations, the adsorption mechanism is confirmed to involve synergetic forces, including electrostatic, chelation, and redox interactions (excluding redox interactions for Pd recovery). Furthermore, a significant separation factor (10³–10⁶) is realized among noble metals and competing metals, with effective adsorption (>89 % recovery) maintained over eight regeneration/reuse cycles. Over 90 % of Au recovery is also realized with real E-waste leachates. With their high adsorption capacity, rapid kinetics, high selectivity, and robust stability, these coral-like adsorbents hold great potential for selectively recovering noble metals from E-waste leachates.