Monitoring gravitational and particle shape settling effects on MLA sampling preparation


Monitoring gravitational and particle shape settling effects on MLA sampling preparation

Heinig, T.; Bachmann, K.; Tolosana-Delgado, R.; van den Boogaart, K. G.; Gutzmer, J.

Epoxy blocks for automated mineralogy typically contain unsorted material from feeds, concentrates or tailings of the processing chain. In these cases, accuracy and precision of SEM-based analytics not only depend on stable measurement parameters and conditions but also on sample preparation. The major aim of sample preparation is the production of representative specimen mounts to generate valid information about the given samples. However, experiences in preparation indicate an influence on the analytic results of many factors such as resin type, resin viscosity, mineral grain density, grain shape and sample material/resin ratio.
This study aims at evaluating the influence of different material/resin ratios on the representativity of a mineral sample. In order to investigate possible gravitational and shape related settling effects during sample preparation, the use of homogenized Zinnwaldite ore is suitable as it provides sample material with a heterogeneous mineral composition, mineral density (Quartz – Topaz), grain shape (Mica – Quartz) and grain size. Eight specimens were prepared with equal weight aliquots of the same ore material, with increasing resin amount. These polished epoxy mounts were analyzed three times with the Mineral Liberation Analyzer (MLA) at Helmholtz Institute Freiberg for Resource Technology (HIF) to evaluate their difference in modal mineralogy, grain sizes and grain shapes. Each sample was analysed as usual on the XY plane, then polished a bit and measured again on a deeper XY plane; and finally the samples were cut along the YZ plane, remounted and measured again, thus capturing a plane orthogonal to the classical measurement plane.
First visual inspection indicates a connection between the amount of resin and the appearance of gravitational and shape related settling effects. The effects such as fractionating of grains by size and density or specific orientation of elongated grains became stronger the more resin was used. These aspects are statistically tested by comparing the frequency distributions of intersection segments between grains and families of lines (random in the XY planes, 9 equally spaced lines in the case of YZ plane observations), a way to circumvent Stereological degeneration effects. Results suggest a range of material/resin ratio that is suited for sample preparation of this particular ore type, by showing no statistical deviations between the distributions on the XY and YZ planes, hence no or very small gravitational or shape related settling effects.

  • Contribution to proceedings
    Annual Conference of the International Association of Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the Annual Conference of the International Association of Mathematical Geosciences, 978-3-00-050337-5

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Publ.-Id: 21792