Elsevier

Minerals Engineering

Volume 157, 1 October 2020, 106550
Minerals Engineering

The extended drop weight testing approach – What it reveals

https://doi.org/10.1016/j.mineng.2020.106550Get rights and content

Highlights

  • The new ExDWT was used to measure the breakage potential (A × b) of rock particles.

  • Multidimensional definitions of particle size generate higher (softer) A × b.

  • Diametrally oriented cores give higher A × b values than irregular shaped particles.

  • Ore heterogeneity is the main source of breakage variability measured by the ExDWT.

  • The JKDWT and ExDWT methods give statistically equivalent values of mean A × b.

  • Uncertainty in the mean A × b estimate was up to five times less with the ExDWT.

Abstract

The heterogeneous nature of orebodies introduces large uncertainties into all quantitative evaluations, process design and process predictions. Measuring the extent of the variability of ore competence will allow the design process to account for variation in process performance through a quantitative knowledge of its uncertainties related to ore hardness.

The conventional JKMRC drop-weight test (JKDWT) establishes the relationship between input energy (Ecs) and product fineness (t10) from which the breakage potential parameter A × b can be estimated, by combining the broken progeny of groups of particles. A new method, the Extended Drop Weight Test (ExDWT), has been developed which is applied to individual particles and is therefore capable of capturing breakage heterogeneity at high resolution. This paper explores a number of features of the new method, based on breakage tests on individual particles from several different rock types.

The results showed that more accurate descriptions of particle size resulted in higher (softer) A × b values which suggests that the standard method may have been over-estimating rock competence. Regular-shaped cores broken diametrally were found to have higher (softer) A × b values than axially broken cores and irregular shaped particles. These tests also suggested that the true ore intrinsic heterogeneity is the main source of breakage variability measured by the ExDWT. The mean A × b values determined by the ExDWT showed no statistical difference to those determined by the standard JKDWT method, but the standard deviation of the estimate was much lower.

The results have demonstrated the potential of the new method for capturing the inherent heterogeneity of individual ore particles. Such information could be used to populate multi-component models of comminution.

Section snippets

Introduction and background

The problems which mineral engineers confront in designing, optimising and operating mineral processing plants arise mainly from the heterogeneity of the feedstock (the ore). Unlike in manufacturing, in which all inputs are generally uniform and stable, concentrators have to deal with the exact opposite, and it is this reality which makes mineral processing uniquely challenging. It is therefore important to understand and manage this heterogeneity so as to learn how to manage it for best

Sample mass

The ExDWT quantifies the breakage potential of individual particles in a given sample of ore. It involves measuring three particle properties:

  • Particle Mass

  • Residual height of DWT after breakage

  • Fragmentation (tn, where common values for ‘n’ are 2, 4, 10, 25, 50 and 75)

The mass of each particle is measured before breakage. Variation in the mass of particles within a size fraction affects the specific energy received per particle which is further described in Faramarzi et al. (2018b). This type of

ExDWT method with a single size fraction

The standard t10 is estimated based on the standard t10 sizet10(Std)’. In this approach, the geometric mean is assumed as the same for all the particles within a size fraction:GMstd=T×Bwhere T and B are the upper and lower sizes of a given size fraction, respectively and GM is the geometric mean. It should be noted that the t10(std) represents the passing size in this context. In this paper, tn value refers to the degree of breakage, and tnØ represents its characteristic size. As an example,

A more general definition of the ‘t10 size’

The initial size of an irregular particle can be defined in a number of ways, depending on the purpose (Napier-Munn, 2014). In this paper only particles of a narrow size fraction –22.4 + 19 mm are considered. Here we determine the effect of five different definitions of the parent size of each particle and assess the impact on the t10 percent passing defined in the context of that estimate of parent size. These definitions are as follows:

  • 1.

    Standard t10 size,t10(Std)’ – It is estimated based on

Conclusions

The ExDWT approach to testing the competence of rock particles estimates the benchmark A × b value using data from a large number of individual particles and the newly proposed concept of a tn-family per particle. This contrasts with the standard JKDWT method which fits the model to 15 data points, each one being the average response of several particles in a given size interval, and uses the traditional concept of the tn-family for a group of particles. The ExDWT breakage testing approach

CRediT authorship contribution statement

Farhad Faramarzi: Conceptualization, Investigation, Methodology, Formal analysis, Validation, Writing - original draft, Writing - review & editing. Tim Napier-Munn: Supervision, Writing - review & editing. Robert Morrison: Supervision, Writing - review & editing. Sarma S. Kanchibotla: Supervision.

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgements

The authors would like to acknowledge The University of Queensland and JKTech Pty Ltd. for sponsoring this research, and we also gratefully acknowledge Barrick Cortez Gold Mine for supplying ore samples. We also thank the reviewers for many useful comments and suggestions which have been incorporated into the paper.

References (35)

  • L. Tavares et al.

    Single-particle fracture under impact loading

    Int. J. Miner. Process.

    (1998)
  • L.M. Tavares et al.

    Modeling of particle fracture by repeated impacts using continuum damage mechanics

    Powder Technol.

    (2002)
  • L. Vogel et al.

    Determination of material properties relevant to grinding by practicable labscale milling tests

    Int. J. Miner. Process.

    (2004)
  • S.E.A. Awachie

    Development of Crusher Models Using Laboratory Breakage Data

    Julius Kruttschnitt Mineral Research Centre

    (1983)
  • F. Bourgeois et al.

    Low-impact-energy single particle fracture

    Comminution, Theory Pract. Ed: Kawatra

    (1992)
  • Brown, D., Private comminution, and JKMRC internal reports....
  • A. Bye

    Case studies demonstrating value from geometallurgy initiatives

  • Cited by (0)

    View full text