Using Metakaolin to Promote Metal Incorporation under Thermal Conditions: Mechanisms of Copper, Zinc and Lead Incorporation

Professor Shih, Kaimin   (Principal Investigator (PI))

Professor Chan Siu Wai   (Co-Investigator)

Professor Navrotsky Alexandra   (Co-Investigator)

36

2012-11-01

700000

Using Metakaolin to Promote Metal Incorporation under Thermal Conditions: Mechanisms of Copper, Zinc and Lead Incorporation

Calorimetry, Leaching, Metakaolin, Metal Incorporation, XRD

Environmental,Water

Engineering (E)

HKU 715612E

General Research Fund (GRF)

2012

Completed

1) Building on our preliminary findings of metal incorporation enhancement at the metakaolin stage, a systematic analysis of the evolution of metal hosting phases across different temperature and time ranges will be undertaken. By calcining the targeted metal (copper, zinc, lead) compounds with metakaolin under various thermal conditions, this project aims to establish a clear temperature and time range for each metal incorporation mechanism through X-ray diffraction observation. 2) Our expertise in quantitative X-ray diffraction analysis (Rietveld refinement method using the fundamental parameter approach and amorphous content quantification through internal standards) will report the enhancement of target metal incorporation by metakaolin through comparing its efficiency with that of similar oxide and aluminosilicate precursors (alumina, silica, and mullite). An amorphous content quantification protocol employing a more commonly available calcium fluoride internal standard will be also conducted in order to compare the project results to a traditional alumina standard (SRM 676a). This comparison will provide a basis to assist the development of a reliable amorphous content quantification method. 3) Crystalline characteristics (lattice parameters, cation distribution, crystal size, etc.) of metal hosting phases generated from metakaolin and the other oxide/aluminosilicate precursors will be also obtained by Rietveld analysis to evaluate the quality of metal stabilization. Project co-investigator Professor Alexandra Navrotsky, who is a world renowned thermochemist and a member of the U.S. National Academy of Sciences, will analyze the formation enthalpies and surface energies of these phases through her very unique high-temperature oxide melt solution calorimetry technique to further provide direct evidence on metal hosting phase stability. 4) The stabilization effects of incorporated metals in different aqueous environments will be examined by leaching experiments at constant pH (ranging from 2-12), and surface-sensitive characterization tools, e.g. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), will be used to elucidate the metal leaching behavior on the product surface. Project co-investigator Professor Siu-Wai Chan at Columbia University will provide her expertise in analyzing grain boundary features through high resolution transmission electron microscopy (TEM) to confirm the metal leaching behavior observed through spectroscopy. 5) Based on the mechanistic understanding of copper, zinc and lead incorporation by metakaolin, the influences of other operational parameters, such as sample preparation and compositional design, will be delineated to provide an effective control on the reactive crystallization and viscous sintering processes. Such understanding is crucial to determining the nano- and micro-structural features in metal-bearing products and is also a necessity for developing safe and reliable techniques for environmental and industrial applications.