Development of techniques for recycling waste metals and polymers into value-added materials

New_sustainable_materials_and_processes

Deriving materials from waste reduces the level of extraction of natural raw materials from nature and consequent damage to the environment. Recovery of the materials from waste is also less energy intensive in comparison with the natural resource mining. Here we have analysed the metal content of an old electrical circuit board (PCB). This was obtained from a computer as part of electronic waste (E-waste) to investigate the possibility of utilizing E-waste as a new resource for producing metal alloys directly from waste. Results indicated the presence of three major metallic elements Cu, Pb and Sn. In addition, SEM-EDS analysis confirmed the presence of Pb-Sn based soldering material in the chosen PCB boards. High temperature heat treatment of this sample at 900ºC for 30min shows the formation of Cu-Sn alloy of composition Cu-40%Sn and separation of Pb as Pb-Sn alloy of composition Pb-0.05%Sn. Based on the results of this study PCB can be considered as a potential source for metal alloys.

The rapid consumption and obsolescence of electronics has resulted in e-waste being one of the fastest growing waste streams worldwide. Printed circuit boards (PCBs) are among the most complex e-waste, containing significant quantities of hazardous and toxic materials leading to high levels of pollution if landfilled or processed inappropriately. However, PCBs are also an important resource of metals including copper, tin, lead and precious metals; their recycling is appealing especially as the concentration of these metals in PCBs is considerably higher than in their ores. This article is focused on a novel approach to recover copper rich phases from waste PCBs. Crushed PCBs were heat treated at 1150 ⁰ C under argon gas flowing at 1 L/min into a horizontal tube furnace. Samples were placed into an alumina crucible and positioned in the cold zone of the furnace for 5 min to avoid thermal shock, and then pushed into the hot zone, with specimens exposed to high temperatures for 10 and 20 min. After treatment, residues were pulled back to the cold zone and kept there for 5 min to avoid thermal cracking and re-oxidation. This process resulted in the generation of a metallic phase in the form of droplets and a carbonaceous residue. The metallic phase was formed of copper-rich red droplets and tin-rich white droplets along with the presence of several precious metals. The carbonaceous residue was found to consist of slag and _30% carbon. The process conditions led to the segregation of hazardous lead and tin clusters in the metallic phase. The heat treatment temperature was chosen to be above the melting point of copper; molten copper helped to concentrate metallic constituents and their separation from the carbonaceous residue and the slag. Inert atmosphere prevented the re-oxidation of metals and the loss of carbon in the gaseous fraction.