Leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution

Abstract

The leaching behavior of metals such as copper, zinc, lead and tin from waste printed circuit boards (PCBs) has been investigated using electro-generated chlorine in hydrochloric acid solution. The experiments were carried out by employing two different reactors: (a) a combined reactor facilitated with simultaneous Cl2 generation and metal leaching, and (b) a separate metal leaching reactor connected with the anode compartment of a Cl2 gas generator. Leaching efficiency in two reactors was compared for recycling of valuable metals from the PCBs. It was observed that the leaching rate of the metals increased with increase in current density, temperature and time in both reactors. The copper leaching rate gradually diminished when its dissolution was around 20 and 25% in the combined and separate reactor, respectively, which may be attributed to a decrease in surface area of copper with leaching time and the formation of CuCl(s) on the surface. The leaching efficiency of copper was found to be lower in the combined reactor than that of the separate reactor. The dissolution kinetics of copper with electro-generated chlorine followed empirical logarithmic law controlled by surface layer diffusion. The leaching mechanism of copper was further corroborated by SEM-EDS study of the residue. The activation energy for copper leaching in the combined and separate reactors was calculated to be 24.5 and 20.7 kJ/mol, respectively in the temperature range 298–323 K.