Recovery of lead from the solder of waste printed circuit boards

Abstract

Environmentally benign method for the removal of lead from waste Printed Circuit Boards (PCBs) is presented in this paper which is an innovative recycling technique for the emancipation of metals from PCBs using organic swelling followed by selective leaching of lead from the separated layer of epoxy resin. Present paper is a part of above work, which mainly deals with the leaching of lead from the epoxy resin residue, which is the outer layer of printed circuit boards obtained after the metal layer separation recovery of copper metal. Leaching experiments were carried out with nitric acid to see the dissolution behaviour of lead from flat particles of pure lead metal pieces of size 5–10 mm and fresh solder (Pb = 47.36% and remaining tin) of 5 mm cylindrical particle size under varying process parameters viz. acid concentration, temperature, time etc. The results show that 99.99% dissolution was achieved from pure lead metal with 0.4 M nitric acid in 45 minutes at 90°C. However, selective leaching of lead was obtained up to 99.99% from the solder with 0.2 M nitric acid in 120 minutes at 90°C. The kinetic model in case of solder was found to follow “chemical reaction control dense constant size or shrinking spheres” i.e. 1-(1-X)1/3 = Kct rate model. Remaining tin from the residue could be leached out using hydrochloric acid. The metal free epoxy resin residue could be utilized or disposed off safely without affecting the environment.