Recovering Rare-Earth Elements (REE) from Waste Electrical and Electronic Equipment (WEEE): Metal Speciation in Pyrometallurgical Processing

Professor Shih, Kaimin   (Principal Investigator (PI))

42

2021-01-01

614675

Recovering Rare-Earth Elements (REE) from Waste Electrical and Electronic Equipment (WEEE): Metal Speciation in Pyrometallurgical Processing

Quantitative XRD, Rare Earth Elements, Thermal Processing, Waste-to-Resource, WEEE

EnvironmentalOthers - Civil Engineering, Surveying, Building and Construction

Engineering (E)

17208120

General Research Fund (GRF)

2020

On-going

1) A comprehensive waste characterization work will be conducted to understand the detailed chemical compositions of the waste electric and electronic equipment (WEEE) components, such as waste fluorescent powder, computer hard disks, and neodymium magnets in mobile phones. The focus will be on the search and quantification of the rare-earth elements (REE) of neodymium (Nd), yttrium (Y), and lanthanum (La) metals. The project work will then carry out extensive thermal treatments to observe the interactions of REEs with various component matrices under various thermal processing schemes (temperature profile, treatment time, and reduction/oxidation atmosphere). 2) The crystal phases in which metals are hosted largely determine the material reactivity and the mobility of metals, and the identification of REE-hosted phases in the thermally treated samples also critically indicates the REE reaction mechanisms at various thermal transformation stages. X-ray diffraction analysis can be used to probe the signals of various crystal phases in the samples, and thus this proposed project will first use X-ray diffraction analysis to identify REE-hosted phases in the thermally reacted samples. Moreover, our unique quantitative X-ray diffraction (QXRD) analysis method (the Rietveld refinement method using the fundamental parameter approach and amorphous content quantification through internal standards) will then report the quantities of REE-hosting phases in products via high-resolution X-ray diffraction data. 3) The Rietveld structural refinement technique and the electron diffraction pattern analysis can provide lattice parameters, cation distributions, and crystal sizes of the thermally treated samples. After identifying the reaction mechanisms of the REE with the associated component matrices, sintering additives may often be incorporated into the thermal treatment processes to induce or enhance preferred reaction pathways. For this reason, the roles of sintering additives will also be explored by observing their influences on the crystal structural parameters of the REE-hosting phases and their effects on promoting the metal speciation behavior. 4) The separability and extractability of REE from the thermally processed WEEE components will be evaluated by electron microscopic microstructure analyses and solution leaching experiments. To quantify the metal extractability and reaction selectivity, various levels of leaching experiments will be implemented to observe the metal release efficiencies under various chemical extraction conditions. After leaching experiments, the leached samples will be subjected to the characterizations of surface-sensitive analytical tools, including atomic force microscopy and X-ray photoelectron spectroscopy, to elucidate the reaction pathways and release behavior of REE. 5 Optimized pyrometallurgical processes will be generated to achieve the desired nano- and micro-structural features for the intermediate and final products in REE recovery. Our precise controls of REE speciation and grain boundary features will be based on the unambiguous understanding of the reaction mechanisms, phase compositions, metal distributions, and crystalline characteristics obtained in the above procedures. The overall benefits of reducing the use of extraction chemicals, shortening the processing time, and reducing energy consumption will be evaluated and compared with the conventional hydrometallurgical approaches. The material properties and stabilization strategies for the processing residues will also be provided to eliminate secondary pollution.