Kojovic, T.

Shi, F.

University of Queensland eSpace

Update on the JKRBT (JKMRC Rotary Breakage Tester) 
T. Kojovic and F. Shi 
University of Queensland, JKMRC, QLD
Introduction, Background and Objectives 
The long history of comminution studies at the 
JKMRC has included the development of 
laboratory testing procedures, to provide material 
characterisation data that are used in conjunction 
with machine specific data in modelling and 
simulation (Napier-Munn et al, 1996). The key 
developments include: 
• Twin Pendulum  
• Drop Weight tester (DWT) 
• Automated Linear Impact Comminution 
Evaluator (ALICE)  
• Short Impact Load Cell (SILC)  
The DWT is an established and globally accepted 
impact characterisation device, and has become 
one of the standard impact tests for AG/SAG 
milling ore characterisation. The DWT apparatus 
and its associated data reduction technique were 
developed so that the relationship between 
specific energy input and resultant product size 
could be determined (see Equation 1): 
( )EcsbeAt .10 1 =    (1) 
where t10 is a size distribution ‘fineness’ index 
defined as the progeny percent passing one tenth 
of the initial mean particle size, Ecs is the specific 
comminution energy (kWh/t), and A and b are the 
ore impact breakage parameters determined from 
DWT results. The index A*b has become well 
known in the mining industry as a reliable 
indicator of impact ore hardness, and essentially 
describes the rate at which fines are produced 
(t10) for a set amount of specific energy (Ecs). 
The t10-Ecs relationship and A*b parameters are 
used in size-reduction-modelling for crushers and 
mills in the JKSimMet mineral processing 
simulator (Wiseman and Richardson, 1991).  
Since all tests using the DWT, SILC (Bourgeois 
and Banini, 2002), or the Hopkinson bar are 
conducted on single rock specimens positioned 
manually on the anvil or flat surface, they are both
time consuming and expensive. For the test to 
remain practical the rock samples being tested are 
limited to 10 – 30 pieces for each size fraction, 
which inevitably throws into question the 
statistical validity of the derived ore 
characteristics. Recent developments in DEM of 
milling have revealed that small energy impacts 
occur much more frequently than high energy 
impacts (Djordjevic et al, 2004). As such it 
appears a new requirement in breakage testing 
will be the characterization of incremental 
breakage at small impact energies. However, 
testing of repetitive impacts at small energies 
using the DW tester is very time-consuming and 
hence impractical. Research into finding a rapid 
breakage characterization device was clearly 
warranted in an effort to overcome these 
limitations. 
The concept of using kinetic energy to crush rocks 
seemed like a viable alternative for rapid breakage 
characterization, since it no longer requires the 
positioning of rock specimens manually on the 
anvil. Industrial applications of this concept are 
found in Vertical Shaft Impact (VSI) crushers and 
laboratory pulverizers, which employ a rotor-
stator impacting system. However, both of these 
devices are employed merely for particle size 
reduction, not for breakage characterization, as the 
exact amount of energy applied in the process is 
not well controlled or measured. However, the 
JKMRC found that VSI crushers can be modelled 
from first principles, allowing useful simulations 
(e.g. effect of rotor speed) to be carried out with 
only the basic design data on the machine and 
rock characteristics required (Kojovic, 1996; 
Djordjevic et al, 2003). This suggests that the rock 
characteristics may be inferred from the product 
of the VSI, if the amount of energy applied in the 
process can be precisely controlled and measured. 
In response to the body of evidence supporting the 
use of kinetic energy, in 2005 the JKMRC 
comminution research team led by Shi and 
Kojovic decided to thoroughly investigate the 
feasibility of using the kinetic energy concept for 
particle impact breakage characterization. A 
prototype Rotary Breakage Tester (JKRBT), with 
a rotor diameter of 360 mm, was designed and 
manufactured by the JKMRC pilot plant 
workshop team (Figure 1). The operating system 
consists of a vibrating feeder, a rotor-stator 
impacting device with its drive system, and an 
operation control unit. Like the DWT, the JKRBT 
also requires the ore particles be pre-sized into 
narrow fractions. Particles of the selected size are 
fed into the rotor-stator impacting system via a 
vibrating feeder. 
Figure 1:  Photograph of the prototype JKRBT device, with 
rotor-stator showing through the inspection window. 
Methodology / Experimental Technique 
The JKRBT uses a rotor-stator impacting system, 
in which particles gain kinetic energy while they 
are spun in the rotor. They are then ejected and 
impacted against the stator, causing particle 
breakage. The specific energy of each impact in 
the JKRBT, Ecs, is defined as the kinetic energy 
Ek per particle mass m: 
2
2
5.0
5.0
i
ik V
m
Vm
m
E
Ecs ===  (2) 
Since the particle mass does not affect the specific 
energy in this type of impact breakage device, the 
Ecs becomes solely dependent on the impact 
velocity Vi. The research team has shown that the 
specific energy of impact can be accurately and 
precisely controlled in the JKRBT. They also 
confirmed that the actual impact velocity in 
practice is less than theoretical, requiring the 
JKRBT to be calibrated first to achieve precise 
breakage energy levels.  The calibration is 
machine specific and can be programmed into the 
JKRBT control system to allow the user to enter 
the required specific energy directly, or it can be 
tabulated in the JKRBT Operating Manual as pre-
set speeds which can be entered manually to 
achieve a desired specific energy level. 
Key Results / Findings 
The JKRBT overcomes some of the limitations of 
existing impact tests such as a lack of precision of 
the energy input, the amount of time required to 
run individual tests and the difficulties in testing 
the smallest particles.  To date, comparative 
breakage tests using the prototype JKRBT device 
and the traditional JKMRC Drop Weight Tester 
showed that the two devices generate the identical 
breakage–energy relationship for the same ore of 
the same size, as shown in Figure 2.  
0
5
10
15
20
25
30
35
40
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Ecs (kWh/t)
t 1
0
 (
%
)
DWT
RBT
RBT repeat
Model Fit
Figure 2:  Comparison of t10 vs. Ecs relation determined by 
the JKRBT and DWT. 
Statistical analysis indicates that the two testing 
methods can generate statistically similar 
breakage parameter A*b values, as illustrated in 
Figure 3 which compares the A*b values of 16 ore 
types determined by industrial JKRBT and DWT 
respectively. This analysis accounts for the 
difference in contact points and strain rates 
between the DWT and JKRBT. 
0
20
40
60
80
100
120
140
160
180
200
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Data set
A
x
b
 v
a
lu
e
s
Figure 3:  Comparison of breakage parameters A*b 
determined by the JKRBT and DWT (10% error bars on 
DWT result).  
The very positive feedback received from mining 
companies to the JKRBT has prompted the 
JKMRC to further validate the device through a 
formalized experimental test program on 
professionally designed and manufactured JKRBT 
machines. The validation project started in March 
2007 with the first industrialised unit installed and 
commissioned at Anglo Research in 
Johannesburg, South Africa. Barrick, BHP 
Billiton, Rio Tinto and Teck Cominco have also 
signed up to participate in the project. The current 
status and site deployment is as follows: 
• Anglo Research (Crown Mines, South Africa) 
x 2 machines 
• Barrick Gold (JKtech, Brisbane) - 12 months 
agreement 
• BHP-Billiton (Newcastle Technology Centre, 
Australia) 
• Rio Tinto (Kennecott, USA) 
• Teck Cominco (Trail, Canada) 
Figure 4 shows a diagram of the industrialised 
JKBRT, designed and manufactured by Russell 
Mineral Equipment (RME). 
Figure 4:  The first industrialised JKRBT installed at Anglo 
Research in South Africa. 
Unlike the prototype device, the industrialised 
JKRBT can be opened for easy access to clean the 
breakage chamber. The lid is operated by an 
electronically driven linear actuator. The counter-
weight at the back of the lid is designed to prevent 
the lid from falling down by gravity should the 
electronic system fail while the lid is opening or 
closing. The industrialised JKRBT employs a 
rotor 450 mm in diameter, and can treat particles 
from 1 to 45 mm, at specific energy levels from 
0.001 to 3.8 kWh/t. The use a rotary feeder has 
provided a simple feeding system that also offers 
an effective noise suppression mechanism, 
reducing the noise to below 85dB at the highest 
operating speed. 
It is worth noting that the new breakage model 
developed by the JKMRC (Shi and Kojovic, 
2007) enables the user to accurately match the 
DWT derived breakage parameters, A and b, from 
JKRBT data on four (13.2 to 45 mm) instead of 
the standard five DWT size fractions (13.2 to 63 
mm). The model and application of JKRBT 
concept to ore testing has been patented by The 
University of Queensland. 
Highlights / Benefits 
Feedback from Anglo Research has indicated 
higher productivity and better repeatability by the 
first commercial JKRBT when compared with the 
Drop Weight Tester.  The results to date look very 
promising and suggest the JKRBT will provide a 
powerful and easy to use tool for rapid ore 
breakage characterisation to the mining industry. 
Tests have confirmed the device offers a rapid 
method for determining the hardness of drill core 
samples within the context of the AMIRA P843 
geometallurgical project. For comparative testing, 
Walters and Kojovic (2006) found the JKRBT 
appears to be the best choice, followed by SMC 
and PLT.  
Some of the key features of the JKRBT are: 
• Treats many more particles – hence can 
generate statistically more valid results 
• Wide particle size range (1.4 – 45 mm), wide 
energy range (0.001 – 3.9 kWh/t) 
• Rapid characterisation (1/8 - 1/10 of DWT 
time confirmed by Anglo Research) 
• Accurately and precisely control energy 
• Excellent reproducibility 
Conclusions and Future Direction 
A new rapid breakage characterization testing 
device, the JKRBT, has been developed by the 
JKMRC. A detailed study using a prototype 
machine confirmed the concept of using
controlled kinetic energy to characterize ore 
particle breakage, prompting a comprehensive 
validation using an industrialized JKRBT, 
professionally designed and fabricated by Russell 
Mineral Equipment (RME). The validation project 
will be completed in 2008, with commercial 
release expected in early 2009. 
Application of the prototype JKRBT in 
geometallurgical testing with the AMIRA P843 
GeM project has confirmed the JKRBT device 
offers a rapid and consistent method for 
determining the hardness of drill core samples.  
The JKRBT has the potential to revolutionize ore 
testing, with applications in laboratory impact 
breakage characterisation of rock samples, drill 
cores, coal and other materials. Automation with 
lab image sizing technology like the Camsizer 
would further enhance its productivity. It also 
stands poised to significantly advance the process 
control of comminution circuits since it is readily 
adaptable to on-line ore hardness measurement. 
This concept will be explored in the current P9O 
project. 
Acknowledgements 
The research and development of the JKRBT has 
been funded by The University of Queensland, 
JKMRC, JKTech, AMIRA/P9N Project, and 
Centre for Sustainable Resource Processing 
(CSRP).  In-kind support from Anglo Research 
staff during the commissioning of the first 
industrial JKRBT unit is greatly appreciated. 
References 
1. Bourgeois, FS and Banini, GA, 2002. A Portable load 
cell for in-situ ore impact breakage testing. Int. Journal 
of Mineral Processing. 65, 31–54. 
2. Djordjevic, N, Shi, F and Morrison, RD, 2003. Applying 
discrete element modelling to vertical and horizontal 
shaft impact crushers. Minerals Engineering 16: 983-
991. 
3. Djordjevic, N., Shi, F. and Morrison, R., 2004.  
Determination of lifter design, speed and filling effects 
in AG mills by 3D DEM.  Minerals Engineering, 17, 
1135-1142. 
4. Kojovic, T., 1996. Vertical shaft impactors: predicting 
performance, Quarry Aust Jrnl, Vol 4, No 6, pp35-39 
5. Napier-Munn, T.J., Morrell, S., Morrison, R.D., and 
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operation and optimisation.  ISBN 0 646 28861.  Julius 
Kruttschnitt Mineral Research Centre. 
6. Shi, F. and Kojovic, T. 2007.  Validation of a model for 
impact breakage incorporating particle size effect. Int. 
Journal of Mineral Processing, 82, 156-163.  
7. Van Latum, LA, 1985. The evaluation, 
conceptualization and development of single particle 
breakage testing apparatus. Masters Thesis 
(unpublished), Technical University of Delft, 
Netherland.  
8. Walters, S., and  Kojovic, T., 2006. Geometallurgical 
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Update on the JKRBT (JKMRC Rotary Breakage Tester)

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Update on the JKRBT (JKMRC Rotary Breakage Tester)

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