Rock differentiation using microwave irradiation

This project arose as a result of inefficiencies in the diamond recovery process at Premier Mine. A considerable amount of barren waste rock, gabbro, is mined along with the diamond bearing kimberlite. No automated method exists for separating the kimberlite from the waste rock and a device was required to effect ore sorting on a rock by rock basis. Experimentation with a microwave oven indicated that samples of kimberlite were more attenuative than samples of gabbro. The possibility of using microwave heating for rock differentiation was investigated but was impractical to implement. A study of low power microwave attenuation and reflection measurements was undertaken. Reflection measurements were found to be impractical due to the similar amounts of reflected signal from the different rock types. Microwave signal attenuation through rock samples was studied over a broad frequency spectrum. A detectable difference in signal attenuation was found through the gabbro and kimberlite. The difference in signal attenuation increased with increasing frequency. Different techniques to implement signal attenuation measurements through rock samples were investigated. The passing of rock samples through waveguide structures was found to be impractical in this application. Microwave signal attenuation measurements were successful when rock samples were placed between a transmitting and a receiving antenna. Equipment was designed and constructed with an operating frequency of 35GHz chosen due to the small antenna aperture area and the large attenuation difference at this frequency. Static measurements with this equipment revealed the problems with signal scattering and reflection from some irregularly shaped samples of low loss gabbro. The importance of these phenomenon could only be gauged from dynamic measurements. Dynamic measurements were performed using a laboratory test system with a conveyor belt capable of moving at speeds of up to 5 m/s. It was found that 93% of the kimberlite could be correctly detected whilst rejecting 67% of the gabbro. The system functioned satisfactorily and led to the filing of several patents.

Grantor dc:publisher.institution

Department of Electrical Engineering

Year dc:date.issued

1987

Author dc:creator

• Mercer, Sean R

Advisor dc:contributor.advisor

• Downing, B J

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/9638

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/9638