Masters Degrees (Chemical Engineering)

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Browsing Masters Degrees (Chemical Engineering) by Author "Attah-Kyei, Desmond"

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    Investigating the use of printed circuit board leach residue as reductant in pyrometallurgical operations
    (Stellenbosch : Stellenbosch University, 2019-04) Attah-Kyei, Desmond; Akdogan, G.; Dorfling, C.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: In recent years, there has been an increase in the generation of waste electrical and electronic equipment (WEEE) due to the advancement of technology. In addition to the environmental benefits of recycling electronic waste (e-waste), it also provides certain economic value. Printed circuit board (PCB) is the main focus of electronic waste because of the inherently high value of contained metals such as gold, silver and copper. Hydrometallurgical processes, consisting of several leaching stages, are often the most preferred option for the recovery of metals from PCB waste. However, hydrometallurgy does not address the issue of non-metallic PCB fractions that may end up being dumped at landfill sites or incinerated. It is important to reduce the environmental impact and gain value from both the metallic and non-metallic fractions of PCB waste. Several options for treatment of the non-metallic fraction including material recycling, where the residue may be used as inclusions in concrete or asphalt materials with minimal processing or chemical recycling, where chemicals and fuels are produced from the residue using techniques such as pyrolysis exist. Due to the complex composition of PCB leach residue, recovery by thermal treatment is likely to be the most feasible process route from technical and economical perspectives. In this study, the utilisation of the non-metallic PCB waste fraction as reductant in primary metal smelting operations and solid state reduction was investigated. The organic component as well as the ash composition of the PCB were characterised using Fourier transform infrared spectroscopy (FTIR) and X-ray fluorescence spectroscopy (XRF) respectively. Proximate analysis on the PCB revealed the ash and volatile matter contents being 40.1% and 44.8%, which is higher than coal used in reductive smelting operations. The elemental analysis showed carbon and oxygen content of 30.43% and 20.72% respectively. Thermodynamic modelling of chromite and iron smelting were performed using various blends of PCB and coal. The models showed that PCB residue might be used to partially replace the conventional reductants. The study revealed that in chromite smelting the optimal blend contains around 20 wt% PCB residue, with energy savings of 200 kWh/t of ore to achieve the same metal recovery. Laboratory-scale experiments simulating solid state reduction of hematite (Fe2O3) was also performed using various blends of PCB and graphitic carbon. The tests were carried out in a Differential Scanning Calorimeter (DSC) from ambient temperature to 1200℃ as well as in Single particle reactor (SPR) at 900℃ and 1000℃. The product of each test was analysed using scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The degree of reduction calculated from the mass lost during the test showed that PCB acts as better reductant at lower temperatures. However, at higher temperatures the advantage shift towards carbon.