Constructing a cationic pyridine for the highly selective and efficient recovery of gold from waste printed circuit boards

Recovering gold from rich waste printed circuit boards (WPCBs) resource are of great significance to gold development and utilization. In this paper, cationic pyridine polymers with different configurations were designed and synthesised for highly selective and efficient recovery of gold from a WPCB leaching solution. The structures and performances of the cationic pyridine polymers were analysed using a 4-aminopyridine polychloromethylstyrene (4-AP/PCMS). The results indicate that the 4-AP/PCMS performed well in an acidic environment, including in the 5 % aqua regia solution. Gold adsorption on the 4-AP/PCMS followed pseudo-second-order kinetics and Langmuir isotherm models, suggesting that chemisorption occurred via a single-layer mechanism with a maximum loading capacity of 437.68 mg/g. Further, Au(III) adsorption on the 4-AP/PCMS involved electrostatic interactions and reduction between pyridine and AuCl4-. After five adsorption-desorption cycles, the adsorption rate remained above 99 %, whereas in actual leaching solutions it reached 92.24 %. All five pyridine polymers demonstrated outstanding Au(III) selectivity over binary and multicomponent solutions containing Cu(II), Ni(II), Co(II), Zn(II), Fe(III), Cd(II), and Mg(II), benefitting from the cationic pyridine skeleton. Contact patterns between the cationic pyridine polymers and AuCl4- considerably affected the gold loading capacity, and a single-point contact was found to be favourable for gold adsorption. These results indicated that cationic pyridine polymers are promising for recovering gold from WPCB leaching solutions.