Dielectric Properties of Minerals and Ores and the Application of Microwaves for Assisted Comminution and Ore Sorting

Upon exposure to microwave radiation, most valuable minerals heat very well, while in general, gangue minerals do not. This selective heating leads to differential thermal expansion across phase boundaries and causes microfractures, which can improve liberation and reduce ore competency. During ore sorting, the heat signature is detected using infrared sensors to accept or reject valuable or gangue rock, respectively. A comprehensive literature review identified research gaps in the field of microwave-assisted comminution and ore sorting and found that developments have been limited by complexities associated with scaling up from bench- to pilot-scale. Dielectric properties were measured on key sulphide and silicate minerals and select ores at various frequencies and temperatures using the cavity perturbation technique. In combination with data from the literature, experimental data were used to ascertain which minerals could be defined as highly microwave-amenable phases (HMAPs). Bench-scale microwave heating experiments were completed on 42 ores. These data were then combined with the total wt.% HMAPs and the ore dielectric property data to create a database that can be used to predict the bench-scale heating behaviour of any ore based on the wt.% HMAPs. High-power microwave tests were done on select ores, which were subsequently ground using the SAGDesign test, and the degree of liberation of valuable minerals was obtained via QEMSCAN® (quantitative evaluation of minerals by scanning electron microscopy). Microwave treatment increased mineral liberation from most ores but reduced the competency of only a few ores. Massive sulphide ores could not be treated on the pilot-scale system given their very high conductivities, which caused severe arcing. A study on a Cu porphyry ore found that an upper boundary exists for the power density, above which the ore will experience excessive arcing. Bench-scale microwave infrared and conductivity sorting tests on a Cu-Ni ore found general agreement between rock conductivity and its overall sortability. Optimization tests were completed to determine the limitations of the pilot-scale system. Recommendations for high-power microwave treatment include microwave pulsing, quenching, and treatment of iron ores.

Department dc:contributor.department

Materials Science and Engineering

Year dc:date.issued

2023

Author dc:creator

• Forster, John

Advisor dc:contributor.advisor

• Bobicki, Erin R

• comminution
• liberation
• microwaves
• minerals
• permittivities
• sorting

Handle dc:identifier.uri

http://hdl.handle.net/1807/126914

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/126914