Sustainable Recovery of Cu and Sn from Problematic Global Waste: Exploring Value from Waste Printed Circuit Boards

Abstract

There is a continuous quest for “mining” electronic waste for valuable materials. Currently, e-waste is either disposed of in landfills or transported often to underdeveloped nations where the materials are either disassembled mechanically or incinerated. These processes, unfortunately, can result in toxic pollutants, like dioxins, furans, and lead, contaminating air, soil, and water. In this study, a new pathway, based on thermal micronizing (TM), is used for the controlled transformation of metals present in waste printed circuit boards (PCBs) into value-added tin and copper-based alloys. This fast heating process in a reducing atmosphere recovered tin-based alloy at 500 °C and copper-based alloy at 1000 °C from the waste PCB. Low-temperature heat treatment, short heating times, and decrease in process steps made it possible to remove the lead with tin-based alloy effectively. This prevented the lead evaporating to the atmosphere or diffusing in solid copper of waste PCBs due to the low solubility of lead in copper. After removing the tin-based alloy, the thermal transformation of waste PCBs at 1000 °C facilitated the formation of copper-based alloy droplets, leaving behind the PCB residue. Tin-based alloy is known to be soldering material, and copper is known to be a highly conductive element in electrical applications. Recovered tin-based alloy demonstrated an increased ultimate tensile strength of ∼30% compared to a standard Sn-9%Zn solder alloy. The recovered copper demonstrated ∼80% of IACS (International Annealed Copper Standard) conductivity which makes it favorable for application in various electrical appliances. This simple, low-cost approach opens the opportunity for e-waste processing in the industrial or informal sectors with minimal toxic emissions and encouraging safety.