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Date of Award
Master of Science in Materials Science and Engineering (MS)
College, School or Department Name
Department of Materials Science and Engineering
The goal of these experiments was to induce cracking in ore particles using MW energy for improved communition behavior of ore material by thermal expansion of MW absorbing phases to increase metallic mineral liberation. The material used for experiments was from a metallic sulfide ore deposit located in Michigan’s Upper Peninsula composed of peridotite (olivine + pyroxene) rock with Fe-Cu-Ni sulfide minerals pyrrhotite, chalcopyrite, and pentlandite containing minor concentrations of precious metals (PGM’s) and inclusions of Fe-Cr-Ti spinel oxide minerals disseminated throughout the mineralization. Rapid heating in ore particles was mainly attributed to the high absorption capabilities of magnetic phase’s pyrrhotite, Ni-pyrrhotite, and Fe-Cr-Ti oxide minerals.
MW exposure of ore particle caused differential thermal expansion of constituent phases producing macro and microscopic cracks in ore particles. The production of sulfur gas and subsequent weight loss in samples was also reported. Imaging of samples using scanning electron microscope (SEM) in back scatter electron mode (BSE) shows fracturing originating at metallic mineral phases and continuing throughout the host rock matrix. Ball milling experiments showed increased grindability of MW treated ore particles and an overall decrease in the work index compared with as-received material. MW treated ore particles passed through a roll crusher showed an increase in metallic bearing minerals reporting to coarser size fractions then as-received material.
In the presence of MW field, it was observed that sulfide ore particles exposed to open atmosphere can electrically arc during sulfide oxidation generating plasma. The plasma reaction is highly exothermic creating high local temperatures that melts constituent phases. The formation of a flux-type solution comprised of metal sulfides droplets dispersed in silicate melt was observed. Multiple flecks of gold were observed to be nucleated on metal sulfide droplets as indicated by electron dispersive spectroscopy (EDS) during SEM beam probing.
Andriese, Matthew D., "MICROWAVE ASSISTED COMMUNITION OF SULFIDE ORE", Master's Thesis, Michigan Technological University, 2015.