Developing protocols for XCT scanning of dense mineral ore samples with applications to geology and minerals processing
Thesis (PhD)--Stellenbosch University, 2020.
ENGLISH ABSTRACT: X-ray computed tomography (XCT) is a non-destructive technique capable of producing 3Dmineralogical and textural information from drill cores. The discrimination between mineralogical information of the drill cores was optimised by using the developed linear attenuation coefficient data bank that can automatically provide linear attenuation coefficient information. The discrimination between the minerals was further optimised by using the determined optimal scanning parameters. XCT technique is most effective when scanning low density samples or minerals with low linear attenuation coefficients. However, when scanning high density samples, the technique suffers from the lack of X-ray penetration which results in beam hardening. Beam hardening affects the true representation of mineralogical and textural information and this leads to the misrepresentation of the mineralogical and textural information. Beam hardening is not easily quantifiable because its impact on the sample information is not uniform and can result in a loss of sample information. To address this, it was proposed to use an aluminium standard when scanning high density samples which acted as a standard in order to quantify the degree of beam hardening in each slice of the sample volume. The aluminium standard sample not only quantified the degree of beam hardening but also determined the optimal sample size for scanning where no sample information is lost. The optimal sample size for scanning was determined to be 4mm when scanning samples with SG > 3. Even though the impact of beam hardening was minimised when using the optimal sample size the degree of beam hardening still affected the discrimination between minerals. This lead to the development of a simplified dual energy method in order to optimise the discrimination between minerals that are affected by beam hardening and result in high levels of noise within the images. The developed simplified dual energy method uses a combination of scanned volume data volume together with the simulated image. This combination has an advantage over the traditional dual energy method that uses two scanned volume data which is more time consuming. The simplified dual energy method effectively discriminated mineralogical information with no artefacts as compared to the traditional dual energy method which result in edge artefacts. The utilisation of the aluminium standard and the simplified dual energy method resulted in the reliable quantification of porosity information and 3D chalcopyrite grain size distribution (GSD). The quantified porosity information was largely in agreement with QEMSCAN results which show the importance of using the aluminium standard when scanning high density ore samples. The quantified 3D chalcopyrite GSD had a similar trend to the 2D QEMSCAN data but with coarser GSD as expected. This shows the effectiveness of the developed simplified dual energy method to optimise the discrimination of chalcopyrite in dense ore mineral samples. The reliable quantification of porosity and chalcopyrite information is important in minerals processing. Porosity is a component of texture and it is of relevance to physical processing where chalcopyrite is important in terms of inherent rock strength, its breakage, liberation properties and establishing geometallurgical units. The reliable quantification of the textural information using XCT shows that the technique can be adopted and adapted to any ore type with even more complex textures or mineralogies.
AFRIKAANSE OPSOMMING: Geen opsomming