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This dissertation, Stabilization Mechanisms of Cadmium Wastes Using Ceramic Precursors by Minhua, Su, 苏{27424a}华, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Stabilization Mechanisms of Cadmium Wastes Using Ceramic Precursors Submitted by SU MINHUA For the degree of Doctor of Philosophy at The University of Hong Kong in August 2015 Cadmium (Cd) compounds existed in the waste streams, such as waste sludge, ash, slag and flue gas, cause significant risks to the environment and biota. To control and reduce the considerable releases of Cd from such waste streams is of great importance. This study aimed at the mechanistic study of stabilizing the simulated Cd-bearing wastes by sintering with the low-cost and attainable ceramic precursors (γ-Al O, SiO, α-Fe O, Fe O, 2 3 2 2 3 3 4 kaolinite and mullite) and fundamental understanding of the leaching performance of the product phases. As a waste-to-resource strategy, beneficially using sewage sludge ashes to incorporate cadmium oxide was also investigated. Besides, an in-line capture and stabilization (ILCS) process for the removal of vaporized CdO in the simulated flue gas was conducted and evaluated. Mixtures of cadmium oxide (CdO) and the tested precursors with various Cd/Al, Cd/Si or Cd/Fe molar ratios were fired at the corresponding temperatures (600-1000 C) for 3 h. X- ray diffraction (XRD) technique was employed to monitor and quantify the phase transformations. XRD results qualitatively demonstrated Cd could be crystallochemically incorporated into CdAl O, CdSiO, Cd SiO, Cd SiO, CdAl Si O and CdFe O phases. 4 7 3 2 4 3 5 2 2 8 2 4 5 The incorporation reactions were strongly controlled by the treatment temperature. An unambiguous understanding of the product structure details (e.g., lattice parameters, atomic positions, bond lengths and bond angles) is essential to ensure the phase quantification capability of XRD technique. Therefore, the crystal structure details of the CdAl4O7, which were unreported, were successfully solved and refined with Rietveld refinement analysis of the XRD data. According to the structure refinement results, the stabilization efficiencies were quantified and expressed as a transformation ratio (TR) with optimized processing parameters, such as the treatment temperature and dwell time. Since metal stabilization effect is one of the most important factors affecting the potential reuse of the products, a series of constant-pH leaching test (CPLT) was conducted. Even considering the factors involved in the sample surface area and metal loading, a remarkable reduction in Cd leachability could be achieved by forming different Cd-hosting crystalline products, particularly for CdFe2O4 spinel phase. The leaching behavior of all the tested phases was addressed by CPLT and X-ray photoelectron spectroscopy (XPS) results. Furthermore, to accomplish the waste-to-resource strategy, the sewage sludge ashes were prepared and successfully employed to incorporate Cd into crystalline products. Moreover, the waste sludge from spent Ni-Cd batteries enriched a great amount of Cd and Ni was stabilized via the formation of ferrite spinel solid solutions. Finally, the vaporized CdO were fully captured and well stabilized into CdFe2O4 spinel showing the good capability of this novel in-line capture and stabilization technique for flue gas detoxification. The overall outcomes obtained in this study demonstrated a promising strategy to stabilize hazardous cadmium into crystalli

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