Zero Metal Discharge from Electronic Waste Treatment: Control Metal Speciation in Glass-Ceramics

Professor Shih, Kaimin   (Principal Investigator (PI))

42

2019-01-01

2022-06-30

632421

Zero Metal Discharge from Electronic Waste Treatment: Control Metal Speciation in Glass-Ceramics

E-Waste, Glass-Ceramic, Hazardous Metals, Leaching Behavior, Quantitative XRD

EnvironmentalWater

Engineering (E)

17203418

General Research Fund (GRF)

2018

Completed

1) This project aims to control metal speciation and distributions of Cr, Cu, Pb and Zn by thermal reactions to enhance the metal recovery and stabilization of e-waste residue. The main challenge is the identification of metal hosting phases derived from the complicated matrix reactions in e-waste residue. High resolution X-ray diffraction and electron diffraction skills will be the keys to reveal the reaction processes among different metal hosting phases and to utilize the partitioning of glass and ceramic phases to separate target metals; 2) Based on the high resolution X-ray diffraction data, atomic structure models needed for quantitative X-ray diffraction analysis will be constructed for the start-of-the-art Rietveld refinement analyses (fundamental parameter approach and precise amorphous content quantification with internal standards) to quantify the metal distributions in the systems. Our new technical development of combining the Rietveld refinement results and the elemental information from transmission electron microscopy will further quantify metal occupancy ratios in the different coordination positions of the crystalline and glass phases; 3) The stability of target metals in their hosting phases is closely related to the crystal parameters. The modeling of Rietveld structural refinement and the measurement by electron diffraction technique will provide the lattice parameters, cation distributions, crystal sizes, defects, and impurities of the metal phases generated from thermally treating the e-waste residue with different glass-ceramic precursors. The roles of sintering additives will also be evaluated to observe their influences on the crystal structures of metal hosting phases and their effects on the promotion of metal speciation in glass-ceramics; 4) Metal extractability and immobilization effects will be quantified by phase separation outcomes and leaching experiments. Characterization tools targeting on probing surface and interfacial reactions, such as small-angle X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy, will further delineate the metal leaching behavior and reaction pathways. The relationship between the glass-ceramic microstructures and the resulting grain boundary features will be investigated by high resolution electron microscopy (FESEM and HRTEM) to assist the control of metal release and incorporation behavior; 5) The preferred nano- and micro-structural features will be designed for the intermediate and final products in e-waste recovery and immobilization processing. With the unambiguous understanding of the reaction mechanisms, phase compositions, metal distributions, and crystalline characteristics in this study, the control of metal speciation and grain boundary features will provide new opportunities for reaching more reactive sites and larger available surfaces to optimize metal recovery efficiency and stabilization effect.