Doctor of Philosophy
Faculty of Engineering
Tanner-Jones, Jeffrey John, An investigation of the microwave-stimulated reduction of oxides of refractory metals, Doctor of Philosophy thesis, Faculty of Engineering, University of Wollongong, 2010. http://ro.uow.edu.au/theses/3649
The experimental programme of this thesis project was designed to explore the potential of microwave-stimulated reduction of refractory metal minerals in both "mine concentrate" mineral form and in the "pure" oxide mineral form. Representing the five refractory metals titanium, zirconium, hafnium, niobium and tantalum, the core minesite-derived minerals selected were rutile, ilmenite, zircon and the tantalite-like mineral wodginite, all oxidic minerals, whilst the "pure" standard oxides selected were TiO2 , ZrO2 , HfO2 , Nb2O5 and Ta2O5. By like means, the minerals of these groups were reduction-processed utilising an innovative plasma technique whose applications and methods are described herein. It was found that, across the range of microwave-stimulated reduction of core refractory metal minerals, both concentrate minerals and pure oxide minerals could be effectively reduced to metallic phases.
Fundamental in this study was that the experimental programme should identify reduction capabilities, alternative extraction route possibilities and process options; this was a keystone study of microwave reduction applied to obdurate minerals. As such, the intention of the study was to underpin further-stage initiatives in advancing microwave-stimulated extractive pyrometallurgy and allied applications. To this end, across the scope of experimentation, the reduction of refractory metal oxides to realise metallic product by means of elementary reduction processes whilst employing such basic reduction procedures suggested the potential for extractive processing routes leading to commercial-grade metal products – outcomes parallel and equivalent to those of conventional routes.
Whilst reduction directly from the metal oxide represents neither a new reduction strategy nor a new production route, the direct microwave-stimulated reduction of thermochemically obdurate refractory metal oxides is novel. Incorporating both carbothermic and metallothermic means of reduction across the experimental programme, the microwave-stimulated reduction method devised was used throughout the core programme of experimental reduction exercises. Being complementary to these core refractory metal results, various instructive "non-core" reduction results are also reported whilst examples of microwave initiated "metal halide" reduction afford comparability with the conventional Kroll and Hunter industrial production processes.
Ultimately, in this foundation project, it was considered that sufficient tangible evidence was accumulated during broader characterisation and analyses of reduction product specimens to contend that essentially pure metal was produced transiently under the experimental conditions before the onset of "over-processing" that produced solid solution and metallic compound phases. And further, system deficiencies and exothermic contributions aside, that refractory metals of good purity can be efficiently reduced from their stable oxide minerals under an extractive metallurgical regime utilising microwave-stimulation to supply the external (or "applied") energy into the system so initiating and sustaining – and generally integral with – its non-equilibrium plasma environment.