Investigations on Mineral Liberation by Transgranular and Intergranular Fracture after Milling


Investigations on Mineral Liberation by Transgranular and Intergranular Fracture after Milling

Leißner, T.; Hoang, D. H.; Rudolph, M.; Heinig, T.; Bachmann, K.; Schubert, H.; Peuker, U. A.

In comminution minerals can be liberated by random fracture of particles into smaller fragments or by detachment along phase boundaries. These two mechanisms represent borderline cases. When ores get crushed and milled the liberation of minerals is achieved to some extent by both mechanisms. This article describes a method to determine the extent of transgranular and intergranular fracture of minerals based on 2-dimensional liberation analysis from automated mineralogy.
The approach uses the non-biased surface information like phase specific surface area (PSSA), phase specific free surface (PSFS) and phase specific locked surface (PSLS) of minerals and their change through comminution. The parameters are discussed related to the normalized grain size, which is the ratio of mineral grain size of the milled product to mineral grain size of the feed material. Finally the amount of transgranular and intergranular fracture can be calculated using the phase specific surface parameters.
An apatite ore (sedimentary origin), a rare earth mineral containing nepheline-syenite and a porphyry-copper ore (both igneous origin) were ground to different fineness using a ball mill. Based on the mineral liberation analysis (MLA, device FEI Quanta 650 MLA-FEG) of feed and products, the extent of phase boundary fracture on the surface exposure of the minerals is studied.
It is found, that the extent of transgranular and intergranular fracture on surface exposure differs for different types of ores. For sedimentary rocks, intergranular fracture (detachment) plays a major role in the liberation of the minerals (cf. Fig. 1 a). Surface exposure of minerals from the nepheline-syenite (cf. Fig. 1, b) has to be discussed more differentiated. Feldspar shows a small percentage of detachment on surface exposure whereas the aegirine is liberated in equal proportions by both mechanisms.
The presented method of liberation analytical calculations using phase specific surface information will be useful for the better understanding of ore specific fracture events with different comminution strategies. Consequently, it will lead to a more economical way to successfully liberate minerals by the energy intense processes of comminution.

Keywords: Mineral liberation analysis; preferential breakage; transgranular fracture; intergranular fracture; random fracture; grain boundary fracture

  • Contribution to proceedings
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016 - Conference Proceedings, Quebec: CIM/ICM, 978-1-926872-29-2

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Publ.-Id: 24043