A new technology, dubbed MinPET, which 
 is used to detect, image and sort diamonds in kimberlite and has its roots in medical nuclear physics, has been taken through a substantial part of the research and development phase by engineering company Bateman Engineering.

Experiments using a technology demonstrator have further established the scientific and technological viability of the project.

The company reports that preliminary tests on kimberlite indicate that, with MinPET, more than 99 % of the rock could be rejected as waste, thus offering the potential for significant savings in both capital costs for new mines and operating costs for new and existing ones.

The two main technological components of the system, the development of which is being undertaken by the University of Johannesburg in partnership with Bateman, are found 
routinely in modern well-equipped hospitals. 
The first is an analogue of positron emission tomography (PET) used in hospitals for medical imaging.

In the MinPET system, PET has been reformatted as a mineral sorting technique. The diamond in the host kimberlite rock is represented by a high concentration of localised carbon seen against a homogenous background of carbon- and oxygen-containing molecules.

The temporary PET radioactivity of the carbon is initiated by irradiation using a high-energy photon beam of the kimberlite rock. The other major component is, therefore, an electron accelerator that provides the photon source for the transient activation of the PET isotopes within the host rock. These transient PET isotopes indicate the occurrence of a diamond-bearing rock in real time for an online rock stream. Tests have shown that transmuting only a tiny fraction of the carbon in the kimberlite is enough to have sufficient PET activity for detection while ensuring that no detectable radiation damage occurs in the diamonds owing to the MinPET system.

Since the proportion of rock particles containing diamonds is very low, with the current technology, a ton or more of ore must be pro-
cessed to extract only a few carats of diamonds.

In the MinPET system, kimberlite will be coarse-crushed to rocks of about 10 cm in diameter. They are then photon-irradiated to induce the transient PET activity. A hold hopper allows time for the only interference, oxygen, to decay out. The planar PET detector then implements a fast, statistical quasi-imaging decision algorithm. The material is withdrawn from the holding hopper and fed onto a conveyor belt running at about 2 m/s. The throughput rate can be up to 1 000 t/h. 
Diamondiferous kimberlite is removed and the barren rock stream does not require 
further processing.

Professor Friedel Sellschop, of the University of the Witwatersrand, first identified the 
potential of MinPET for diamond recovery and this was confirmed in laboratory tests by the university between 2000 and 2004. The programme is now in the pilot testing phase to 
determine critical operating parameters, such as detection periods and sensitivity.

In practical application, it is envisaged that MinPET could be installed underground with the crushing system for the selection of rock near the source and disposal of barren material 
underground, or immediately after a surface primary crusher for early diversion of the waste material to the tailings.