Leaching of lead from solder material of waste printed circuit boards (PCBs)

Abstract

Present work is focused on the selective leaching of lead from the soldering material present on the outer layer i.e. epoxy resin of waste PCBs, liberated through a novel pre-treatment technique of organic swelling using n-methyl-2-pyrrolidone. Nitric acid was found as a suitable leachant to dissolve lead. Initially, the effect of temperature, S:L ratio, leaching time and acid concentration on leaching of lead was investigated using fresh solder material containing 47.36% lead and remaining tin. With 0.2 M HNO3 at S:L ratio 1:100 (g/mL) and temperature 90 °C, 99.99% lead was leached in 120 min. Leaching kinetics followed 1−(1−X)1/3=Kct i.e. chemically controlled reaction model with activation energy 26.94 kJ/mol. Validation of lead leaching from solder of liberated epoxy resin of swelled PCBs indicates that 99.99% of lead could be leached out at 90 °C with 0.2 M HNO3 in 45 min. Tin left in the residue of the liberated resin was further leached with 3.5 M HCl at 90 °C for 120 min at S:L ratio 1:20 (g/mL), which dissolve almost 98.74% tin. Then, metal free epoxy resin was washed with water to utilize it or dispose-of safely without affecting the environment.