Low temperature optimization of copper recovery from e-waste.

Abstract

The purpose of the report is to provide a detailed investigation on the recycling of copper from waste electronic Printed Circuit Boards (PCBs). The roles played by leaching agent, temperature, time, particle size, and hydrogen peroxide (parameters) towards the recovery of copper are also explored. Other objectives include investigating the type of material being studied by performing a sieve analysis, investigating the effects of different leaching agents, and use of TGA to characterise the electronic waste (e-waste). PCBs recycling does not only address the issue of finite resources but also serves as an alternative way of obtaining resources (urban mining) with minimal harm to the environment compared to traditional mining. In this study, e-waste recovery has three major steps, the liberation of materials from e-waste, characterization of e-waste, and hydrometallurgical processing. E-waste recycling also helps tackle the problem of landfilling and pollution and is the fastest rising waste source is electronic waste and electronic waste processing for metal recovery is a recycling technique, and it creates job opportunities. From the analysis of the particle size distribution, the coefficient of curvature was 2.56, and the coefficient of uniformity was 2.91, this indicates that the PCBs are not well distributed. This limits the study in that not sufficient size classes (there were significant differences in size classes) were represented in the PCBs. Furthermore, the thermogravimetric analysis (TGA) found that the ash content within the PCB increases with an increase in size class. When comparing the acid mediums under which the PCBs were leached, it was seen that; nitric acid conditions bring about more dissolution of the target metals. Under nitric acid conditions, copper, iron, and nickel fractions dissolved were 0.2391, 0.0047, and 0.0006 respectively. Under sulphuric acid and hydrogen peroxide, copper, iron and nickel metal fractions dissolved were 0.17568, 0.00364, and 0.00046 respectively. However, nitric acid was not explored beyond preliminary runs because of its hazardous nature (it was used to investigate more parameters that are paramount to e-waste processing); it is more toxic than sulphuric acid with hydrogen peroxide. Aqua regia is a highly corrosive combination of nitric acid and hydrochloric acid and has been used to fully dissolve metals within PCBs. This allowed for the recovery of copper from the leaching processes to be determined, the maximum recovery of copper was found under using the central composite design with conditions: hydrogen peroxide at 18 volume%, the temperature at 300C, time at 120 minutes, and the particle size of 0.75mm. Amongst the parameters, hydrogen peroxide volume percentage was found to be the most significant parameter. The recovery of copper was found to be 36.1%.