Characterising tensile strength and elastic moduli of altered igneous rocks at comminution scale using the Short Impact Load Cell

Abstract

The primary breakage properties of rocks such a strength (σ) and elastic moduli (i.e. Young's modulus (E) and Poisson's ratio (ѵ)) are not usually characterised at comminution scale. Traditional comminution tests such as the Bond Work Index grinding test and the Drop Weight Test are used for describing the breakage behaviour of different ores. Nevertheless, these tests do not decouple the ore characteristics from the mode of breakage. The primary breakage properties control the initiation and propagation of fractures in rocks and exert control over the resultant progeny of breakage events when the rock is stressed. However, how these properties change as the particle size decreases in comminution is not clear yet. This work explores the change of primary breakage properties and the derived quantities estimated using the Short Impact Load Cell (SILC) (e.g. apparent stiffness and mass-specific fracture energy) within a particle size relevant to ball milling, using a suite of real ores.The results of this work show that the median values of strength in populations of cylindrical (minicore) particles do not vary with size within the range size studied (3–30 mm) for all the ore types studied. In contrast, the stiffness and the mass-specific fracture energy derived from the primary breakage properties data show a size dependency for all of the ore types in agreement with Weibull's weakest link theory. The degree of variation of the primary breakage properties has also been studied over a range of particle sizes. The results show that this degree of variation tends to increase for some of the rocks as the particle size decreases, but the variation is size-independent for other rock types. These results align with previous results in the literature that indicate the size independency of tensile strength in small samples but are contrary to earlier researchers' findings that suggest that the variance decreases with size. The ore dependent nature of the primary breakage properties found in this work requires further research. Understanding the behaviour of the primary breakage properties in a comminution context might help to characterise the comminution potential of ores better, as well as to develop characterisation and modelling techniques that are more responsive to the ore characteristics.