An efficient method for tin recovery in waste printed circuit boards: Ultrasonic coupled composite organic acid system

Waste printed circuit boards are abundant in Sn and possess significant recycling potential. In this study, an ultrasonic coupled composite organic acid system was proposed to enhance the leaching of Sn from waste printed circuit boards. The composite organic acid system was constructed with citric acid as leaching agent and ascorbic acid as reducing agent to promote the conversion leaching of multivalent Sn ions. On this basis, the shock wave and high-speed micro-jet generated by the ultrasonic cavitation effect continuously impact the surface of Sn, accelerating the mass transfer rate at the solid–liquid interface, and effectively strengthening the leaching process of the Sn. The influence of ultrasonic intensity, leaching conditions and compound concentration of composite organic acid on the leaching effect of Sn was investigated. When the leaching agent concentration is 0.80 mol/L and the reducing agent concentration is 0.20 mol/L, the composite organic acid system has excellent reduction and leaching properties for Sn ions. When combined with the ultrasonic power of 96 W, the leaching rate of Sn is the highest (89.03 %). The cavitation mechanism of ultrasonic waves significantly enhances the Sn leaching process, increasing the leaching rate by over 15 %. And kinetic analysis revealed that the tin leaching process conformed to the pseudo-first-order model in the progressive conversion model, with an apparent activation energy of 64.37 kJ/mol. This study reveals the leaching mechanism of Sn by ultrasonic coupling composite organic acid system and provides a novel method for the efficient leaching of Sn from WPCBs.