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(2020)ThesisElectronic waste (e-waste) has become an urgent issue in digitally dependent world, owing to the unprecedented use of electronic devices, and this has compelled the world to develop new techniques to recycle such wastes. Printed Circuit Boards (PCBs), one of the most complex components of e-waste, contain different metallic, polymeric, and ceramic components. Recycling of waste PCBs (WPCBs) is a critical issue from both aspects of hazardous waste management and recovery of valuable resources. Direct transformation of e-wastes into value-added materials helps to conserve resources and at the same time prevents the environmental impacts of conventional disposal. Consequently, during the course of this project, the primary purpose was improving the recycling of WPCBs by valorizing and transforming them into high value-added products, such as nanostructured alloy and nanopowders. Regarding the zero-waste approach, eight separate phases were followed: In phase 1, a mechanical-physical separation method for recovery of metallic elements of WPCB without any chemical or/and thermal processes was introduced. Two milling stages were applied to enhance the liberation degree, followed by a physical flotation process for enrichment. In phase 2, solid-state mechanical alloying was used to directly convert crushed WPCB to a homogenous nanostructured alloy (Cu79-Zn13-Fe3-Sn3-Ni1). The nanopowder was successfully applied in nanofluid application. In phase 3, an effective statistical tool was taken to optimize the recovery of metal content (i.e., Cu, Fe, Zn, Pb, Ni, Sn, and Al) embedded in crushed WPCB using a leaching agent without any additive or oxidative agent. In phase 4, the polymeric residue left from the leaching process was used as the source of carbon in the reduction of iron oxide from electric arc furnace (EAF) slag in steelmaking. Hence, two problematic and complex waste streams were successfully converted to a clean alloy. In phase 5, Sn content of the leaching solution was directly transformed into high surface area t-SnO2 nanoparticles (NPs). The synthesized NPs successfully removed dye pollutants from simulated industrial wastewater. In this way, one waste material was used to remove another. In phase 6, using ion-exchange (adsorption/desorption) technique, heavy metals (Cu, Zn, Ni, and Pb), and Al were selectively recovered and separated. In phase 7, the Cu content of the leaching solution was electrodeposited as trilayer thin films for energy storage (supercapacitor) and energy harvesting (renewable solar water splitting) applications. Finally, in phase 8, the environmental and economic impacts of the thin film production process assessed using Life Cycle Assessment (LCA) approach.
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(2022)ThesisThe iron and steel industry is one of the prominent industrial sectors in the world since steel is a vital material with a wide range of applications in our daily lives. There will be a gradual improvement in the living standards, infrastructure and economic growth of developing nations with time. All these will necessitate the demand for steel, and it is essential to meet the same but in an environmentally friendly and sustainable way. The ferrous industries are associated with various issues like extensive greenhouse gas emissions, energy-intensive processes and heavy reliance on fossil fuels and natural resources. At the same time, concern regarding waste generation and its management is taking up the momentum and calls are being made for recycling and green recovery. Reuse of waste materials in the manufacturing process could make the industries circular economy resilient. The Ph.D. research work is based on this notion and involves a novel approach of utilizing a bio-based waste material called spent coffee grounds (SCGs) for application in ironmaking. The research work involved the use of SCGs to produce iron from iron oxide as an alternative to coal/coke. Thermal transformation study of SCGs were carried out in the temperature range of 400 °C to 900 °C. The transformed sample obtained at 400 °C, called T-SCGS (transformed-spent coffee grounds), was preferred for the reduction study in the research work due to presence of optimal amount of volatile matter and fixed carbon. This observation was further validated with better high temperature reduction performance in comparison with metallurgical coke (MC) and SCGs (as-received form). Detailed study regarding solid-state (800-1200 °C) and molten-state (1550 °C) reduction processes were carried out with no-flux and fluxed composite pellets of iron oxide and T-SCGs. Use of T-SCGs for iron recovery from electric arc furnace (EAF) slag was also studied. T-SCGs have both hydrogen and carbon in their molecular structure and reaction of in-situ hydrogen with iron oxide will release the by-product of H2O therefore, helping in reduction of CO2 emissions. Hydrogen is known to be a kinetically better reducing agent than carbon thus, improving reaction efficiency and decreasing energy consumption. Overall, the waste source of SCGs when transformed to a suitable form has the potential to be used as an alternative to coal/coke for sustainable iron production such as in solid-state direct reduction as well as smelting reduction processes and also aiding in the novel concept of circular economy.
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(2022)ThesisPlastic revolutionised the world, but meantime generates a substantial amount of waste plastics. However, plastics are generally non-biodegradable and hence remain in the environment for a very long time. Most plastics are not discarded properly, these wastes either end up in the landfills or left in the environment which can end up in water systems including oceans. Alternatively, plastics are burned to remove from premises or to recover energy. Today it is well established that if waste plastics are not deal properly, they can pose a great risk to both the people and the environment and at the same time a lot of valuable materials will be lost. However, only a small percentage of waste plastic is currently recycled due to the limitations of recycling and reprocessing technology, which requires massive infrastructure and normally is not economically feasible and environmentally sustainable. To overcome these challenges, several easy-to-operate and less cost incentive processes have been evaluated throughout this PhD project. This project first began by investigating the effect of reprocessing on polymer, which is important to develop efficient and effective recycling processes. At the next step a simple process that required fewer steps has been developed to utilise waste hard plastics as feedstock to produce new plastic products whilst retaining the original properties and colour of input waste plastics. Then, two novel processes have been demonstrated for another two types of problematic waste plastic (fishing net and flexible plastic packaging). In the final part of this research, three-dimensional (3D) printing, an advanced method of manufacturing, has been employed to transform waste plastics from toys into products. All produced plastics from the proposed methods showed good mechanical performances as virgin material. Life cycle assessment indicated that the processes could reduce greenhouse gas emission, fossil fuel depletion and ecotoxicity. Considering the conclusions of this project, different methods demonstrated in this thesis can manage and transform a wide range of waste plastics (from hard to soft) into high-quality plastics. They are not limited to the case studied waste plastics rather they have the potential to deal with other similar kinds of waste plastic. Overall, this research will create value for waste plastics, and in turn, speed up their collection and recycling.