Synergistic effects of ultrasonic and pH adjustment on sustainable gold bioleaching from waste printed circuit boards

Gold (Au) recovery from waste printed circuit boards (WPCBs) is a growing focus in sustainable resource management, with bioleaching emerging as an environmentally friendly alternative to conventional methods. However, its efficiency remains limited. This study investigates the enhancement of Au bioleaching from WPCBs using Chromobacterium violaceum through the combined application of ultrasonic treatment and alkaline conditions. Initial findings confirm that ultrasonic irradiation significantly improves Au recovery, primarily by accelerating the reaction between cyanide and Au, with minimal influence on bacterial activity or WPCB structure. Kinetic analysis further revealed that the process follows a hybrid mechanism governed by both diffusion and surface reaction control when applying ultrasonic during Au bioleaching. Alkaline conditions were also found to enhance cyanide production by C. violaceum, further contributing to improved leaching performance. Under optimized conditions, Au recovery reached 37.8 ± 6.5 %, compared to 10.9 ± 2.3 % without ultrasound. These results highlight the potential of ultrasonic treatment and pH adjustment as practical strategies to improve the efficiency and scalability of bioleaching processes.