Determining transition metal ion concentration and valence state in lead silicate glasses using paramagnetic resonance spectroscopy

Groep: EMR

Promotors: Freddy Callens (EMR) en Kim Verbeken (Faculty of Engineering and Architecture, Dept. of Materials, Textiles and Chemical Engineering)

Begeleiding: Henk Vrielinck (DiSC-EMR) en Inge Bellemans (Faculty of Engineering and Architecture, Dept. of Materials, Textiles and Chemical Engineering)

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Spent industrial and automotive catalysts and electronic scrap are becoming an important resource of precious metals, e.g. gold, silver, platinum, palladium, and rhodium. Umicore is a global materials technology and recycling group. It generates precious metals from complex waste streams and industrial by-products. These metals are separated from each other by a combination of pyro-, hydro- and electrometallurgical processes. Within the pyrometallurgical processes, molten phases at high temperatures (500-1600°C) are encountered: metal alloys, slags (mixture of metal-oxide compounds) and mattes (mixture of metal-sulfide compounds). Liquid slags play a crucial role in modern pyrometallurgical processes during the production and recycling of many metals. The properties of this molten metal oxide phase have a large impact on the overall efficiency and kinetics of these processes. In particular, the valence state of the iron (Fe2+ or Fe3+) in the slag is of interest, because it influences the distribution of elements between alloy and oxide phases.

 

Recently, we have shown that electron microscopy (energy dispersive X-ray spectroscopy, SEM-EDX) and electron paramagnetic resonance (EPR) present a promising combination for determining the iron oxidation state concentrations in model systems for slags containing high concentrations of heavy metals, in particular Pb [1]. The aim of this master thesis is to consolidate and to extend the conclusions of this previous study. EPR measurements will be performed on lead silicate glass pieces containing various concentrations of Fe3+ (without Fe2+, the glasses change color with Fe3+ concentration, see Figure 1) and on fine powders of this material in two microwave frequency bands. These glasses are model systems for slags and are obtained by quenching liquid mixtures of PbO, SiO2 and FexOy from their liquid phase. Various characteristics directly measured on the spectra (total intensity, spectral line width, intensity ratio of certain resonance lines) will be evaluated for their ability to determine the Fe3+ concentration in a reliable and robust way. The added value of advanced simulations of these spectra in the determination of concentration will also be assessed. Simulations of EPR spectra for glasses with considerable Fe3+ concentrations present various challenges, due to the wide variety of nearest environments of the Fe3+ ions in the glass and the interactions between them.

Figure 1 : Lead silicate glasses with a PbO/Fe2O3 weight ratio of 70/30 and increasing Fe3+ concentration (0 – 7 weight%), taken from [1].
Figure 1 : Lead silicate glasses with a PbO/Fe2O3 weight ratio of 70/30 and increasing Fe3+ concentration (0 – 7 weight%), taken from [1].

This thesis is performed mainly in the Electron Magnetic Resonance group of the Department of Solid State Sciences (Faculty of Sciences), in close collaboration with the Sustainable Materials Science research group of the Faculty of Engineering and Architecture.

 

[1] V. Cnockaert et al. J. Non-Crystalline Solids (2020), accepted for publication

 

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