Abstract
A green approach was introduced to regenerate Sn-Pb solder from waste printed circuit boards (PCBs). For this purpose, waste Al-based heat sinks were used as cementing agent to precipitate Sn and Pb from pregnant leach solution (PLS) obtained from the dissolution of waste PCBs in HCl. 97 % and 94.9 % of Sn and Pb were recovered, respectively, under optimum conditions at Al powder size of 300 μm, Al dosage of 1.516 g/l and reaction time of 15.41 min. Thermodynamic analysis was performed to predict the effect of temperature on the main reactions relevant to the cementation process. The structure of the Sn-Pb cement changed as function of temperature, leading to enhancement of the cementation rate via improving cathodic area. Kinetic modeling indicates that product layer diffusion is the rate limiting step for Sn and Pb cementation. However, the reaction mechanism shifted to chemical reaction control at high temperatures. The results of solder characterization indicated that the melting point of solder was 184.76 °C. The electrical resistivity and conductivity of the recovered pure alloy were measured to be 34.73 μΩ-cm and 2.88 × 106 Sm−1, respectively. The characterization revealed that the regenerated product is adequate as an alternative solder alloy.
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