1507
Extensive Validation of New Rock Test Using the Hardgrove Mill
with Torque Measurement for the Determination of the Bond
Ball Mill Work Index
Mauricio Guimarães Bergerman
University of São Paulo, Department of Mining and Petroleum Engineering, Laboratory of Mineral Processing
Norman B. Keevil Institute of Mining Engineering, University of British Columbia
Giovanni Pamparana, Bern Klein
Norman B. Keevil Institute of Mining Engineering, University of British Columbia
Homero Delboni Jr
University of São Paulo, Department of Mining and Petroleum Engineering, Laboratory of Mineral Processing
ABSTRACT: Grinding ores in conventional ball mills demands high energy consumption, resulting in relatively
high operating costs in a typical mineral processing industrial plant. Whether in the initial stages of a project
or during its operation, conducting tests to determine the processing circuit’s energy consumption throughout
the life of the mine is necessary to reduce such high operating costs. Traditional tests used to define the energy
consumption in grinding are relatively time-consuming and require significant amounts of sample, e.g., 8 -10
kilograms, which is not always available in the initial stages of a project or geometallurgical studies. The present
study used a modified Hardgrove test that requires only approximately 50 g to estimate the Bond Ball Mill
Work Index -BBMWI. This test involves the measurement of the torque using a fixed sample volume with a
–3.35+0.60 mm feed size to determine the size-specific energy from grinding with a Hardgrove mill. The results
indicated that for a set of 130 samples tested, the average error associated with the predicted BBMWI was within
±6%. The proposed test, with its accuracy and efficiency, has potential applications not only in geometallurgical
studies but also in other scenarios where relatively small samples are available, thereby broadening its utility in
the mineral processing industry.
Keywords: Geometallurgy, Bond Ball Work Index, Comminution, Hardgrove mill.
INTRODUCTION
Comminution is an important operation in ore processing
and is widely used in mining (Lynch, 1977). Significant
demand for increasingly finer grinding has been seen in the
industry over the past few decades to achieve the required
mineral liberation for the concentration and metallurgical
stages, which has significantly increased the comminution
circuits’ energy consumption (Bergerman &Delboni Jr,
2020 Jankovic, 2003). Concern over the energy consump-
tion during the comminution processes is evident as these
processes account for a large percentage of energy con-
sumption in the mineral industry (Administration, 2009
Ballantyne et al., 2012 Ballantyne &Powell, 2014 Curry
et al., 2014 Herbst et al., 2003).

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Extracted Text (may have errors)

1507
Extensive Validation of New Rock Test Using the Hardgrove Mill
with Torque Measurement for the Determination of the Bond
Ball Mill Work Index
Mauricio Guimarães Bergerman
University of São Paulo, Department of Mining and Petroleum Engineering, Laboratory of Mineral Processing
Norman B. Keevil Institute of Mining Engineering, University of British Columbia
Giovanni Pamparana, Bern Klein
Norman B. Keevil Institute of Mining Engineering, University of British Columbia
Homero Delboni Jr
University of São Paulo, Department of Mining and Petroleum Engineering, Laboratory of Mineral Processing
ABSTRACT: Grinding ores in conventional ball mills demands high energy consumption, resulting in relatively
high operating costs in a typical mineral processing industrial plant. Whether in the initial stages of a project
or during its operation, conducting tests to determine the processing circuit’s energy consumption throughout
the life of the mine is necessary to reduce such high operating costs. Traditional tests used to define the energy
consumption in grinding are relatively time-consuming and require significant amounts of sample, e.g., 8 -10
kilograms, which is not always available in the initial stages of a project or geometallurgical studies. The present
study used a modified Hardgrove test that requires only approximately 50 g to estimate the Bond Ball Mill
Work Index -BBMWI. This test involves the measurement of the torque using a fixed sample volume with a
–3.35+0.60 mm feed size to determine the size-specific energy from grinding with a Hardgrove mill. The results
indicated that for a set of 130 samples tested, the average error associated with the predicted BBMWI was within
±6%. The proposed test, with its accuracy and efficiency, has potential applications not only in geometallurgical
studies but also in other scenarios where relatively small samples are available, thereby broadening its utility in
the mineral processing industry.
Keywords: Geometallurgy, Bond Ball Work Index, Comminution, Hardgrove mill.
INTRODUCTION
Comminution is an important operation in ore processing
and is widely used in mining (Lynch, 1977). Significant
demand for increasingly finer grinding has been seen in the
industry over the past few decades to achieve the required
mineral liberation for the concentration and metallurgical
stages, which has significantly increased the comminution
circuits’ energy consumption (Bergerman &Delboni Jr,
2020 Jankovic, 2003). Concern over the energy consump-
tion during the comminution processes is evident as these
processes account for a large percentage of energy con-
sumption in the mineral industry (Administration, 2009
Ballantyne et al., 2012 Ballantyne &Powell, 2014 Curry
et al., 2014 Herbst et al., 2003).

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1508 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Accurately predicting energy consumption is essen-
tial to correctly operating and optimizing comminution
circuits. Also, comminution circuit design is typically a
significant part of any capital investment in a new process
plant. In the case of ball mill-based circuits, the Bond test
is commonly used to design and optimize circuits (Bond,
1960 Mcivor, 2015 Morrell, 2019), the result of which is
referred to as Bond Ball Mill Work Index (BBMWI). Based
on Bond’s method, sizing and optimizing the operation
of mills includes determining the ore grindability using a
standardized laboratory test, calculating the BBMWI, and,
once the particle size distributions resulting from the indus-
trial operation and their respective F80 and P80 are known,
calculating the specific energy (SE) required for a given
grinding application. The test should be carried out with
a closing screen aperture that provides a P80 index close
to what would be expected on an industrial scale (Global
Mining Guidelines Group, 2021 Lynch, 2015). Various
correction factors were proposed to adjust the energy con-
sumption based on the BBMWI, the most common ones
being those defined by Bond, 1961 and later by Rowland
Junior, 2002.
Notwithstanding the test’s limitations, as discussed in
detail by several authors (Amelunxen et al., 2016 Lynch,
2015 Morrell, 2019 Tavares et al., 2012), this is the most
widely used test globally to calculate a ball mill’s energy
requirements (Lynch, 2015 Mcivor, 2015). Determining
the BBMWI requires approximately 8 to 10 kg of material
and around 8 hours of work by a suitably experienced tech-
nician (Yap et al., 1982). If wet sieving is used, the amount
of time will substantially increase. The precision of the
test was evaluated by different authors (Angove &Dunne,
1997 Bailey et al., 2009 Heiskari et al., 2018 Kaya et
al., 2002 Mosher &Tague, 2001 Weier &Chenje, 2018),
indicating differences of up to 10% between the higher and
the lower values for the same sample in other laboratories.
This is important when evaluating a BBMWI test result or
a simplified test.
For a robust comminution circuit design, it is impor-
tant to conduct sufficient BBMWI tests to understand the
ore deposit variability and make sure that the hardness
domains are understood. As such, there can be a challenge
in obtaining sufficient sample mass, time to conduct, and
the cost of testwork. Also, in some cases, the required mass
and time to carry out the test can be excessive, for example,
when developing geometallurgical models (David, 2014)
and for the evaluation of the impact of laboratory scale tests
in a comminution circuit (José Neto et al., 2019 Klein et
al., 2010 Li et al., 2019).
Several authors have proposed different tests and adap-
tations to the original Bond test to meet the need for tests
that predict the BBMWI using a small mass (M. Bueno et
al., 2023 Guimarães Bergerman et al., 2023 Nikolić et
al., 2021). The proposed methods provide a prediction that
ranges from 1.8% to 16%. All these tests are unquestion-
ably significant advances for obtaining BBMWI predictions
with less mass and time requirements. Most tests, how-
ever, still require a mass of approximately 500 to 2000 g.
Although smaller than the mass necessary for the standard
Bond test, such a mass may still be challenging to obtain in
certain cases, including determining the BBMWI in sam-
ples for geometallurgical studies and laboratory scale test
products, such as in the evaluation of preconcentration and
its impacts in comminution. Few of the reviewed options
are commercially available, such as MiniBond (Aminpro,
2023), Geopyora (Bueno et al., 2021 Matus et al., 2020),
HIT (Bergeron et al., 2017 Kojovic, 2016 Kojovic et al.,
2019), and ModBond (SGS, 2023).
Another research approach to predict BBMWI uses
the Hardgrove mill developed by Ralph Hardgrove in 1932
(Beke, 1981 McIntyre &Plitt, 1980 Prasher, 1987), which
is used to determine the energy consumption for comminu-
tion operations for coal pulverization for power generation
(Limited, 1998). The test emulates the operation of a con-
tinuous coal pulverizer at a batch scale. Several authors have
criticized this method, as summarized in papers published
by Sanders, 2007, 2005, 2003. Despite the reservations, it
is still accepted as the primary reference worldwide when
designing coal mills (Limited, 1998). When developing his
test, Bond himself published correlations between BBMWI
and HGI (Bond, 1961 Bond, 1954). Various authors have
obtained good results using the Hardgrove mill to predict
the BBMWI (Bilen, 2021 Hower et al., 1992 Kogut et al.,
2021 McIntyre &Plitt, 1980 Mucsi, 2008 Mucsi et al.,
2011, 2019), with prediction errors below 6%. Although
this is a standard test in the coal industry, it has been
performed differently in the literature. Agus and Waters,
1972 proposed changing from a fixed 50 g mass to a fixed
volume. This is an important change given the ore den-
sity variations, which can lead to a varying filling level in
the grinding chamber. Although this modified test has not
been adopted as a standard by the coal industry, it was used
in different studies that sought to correlate the BBMWI
with the HGI, such as those conducted by McIntyre and
Plitt, 1980, Hower et al., 1992, and Mucsi, 2008.
Furthermore, the original test developed by Hardgrove
assumes that the energy applied for grinding is constant,
regardless of the material, since the test does not measure

Previous Page Next Page

Extracted Text (may have errors)

1508 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Accurately predicting energy consumption is essen-
tial to correctly operating and optimizing comminution
circuits. Also, comminution circuit design is typically a
significant part of any capital investment in a new process
plant. In the case of ball mill-based circuits, the Bond test
is commonly used to design and optimize circuits (Bond,
1960 Mcivor, 2015 Morrell, 2019), the result of which is
referred to as Bond Ball Mill Work Index (BBMWI). Based
on Bond’s method, sizing and optimizing the operation
of mills includes determining the ore grindability using a
standardized laboratory test, calculating the BBMWI, and,
once the particle size distributions resulting from the indus-
trial operation and their respective F80 and P80 are known,
calculating the specific energy (SE) required for a given
grinding application. The test should be carried out with
a closing screen aperture that provides a P80 index close
to what would be expected on an industrial scale (Global
Mining Guidelines Group, 2021 Lynch, 2015). Various
correction factors were proposed to adjust the energy con-
sumption based on the BBMWI, the most common ones
being those defined by Bond, 1961 and later by Rowland
Junior, 2002.
Notwithstanding the test’s limitations, as discussed in
detail by several authors (Amelunxen et al., 2016 Lynch,
2015 Morrell, 2019 Tavares et al., 2012), this is the most
widely used test globally to calculate a ball mill’s energy
requirements (Lynch, 2015 Mcivor, 2015). Determining
the BBMWI requires approximately 8 to 10 kg of material
and around 8 hours of work by a suitably experienced tech-
nician (Yap et al., 1982). If wet sieving is used, the amount
of time will substantially increase. The precision of the
test was evaluated by different authors (Angove &Dunne,
1997 Bailey et al., 2009 Heiskari et al., 2018 Kaya et
al., 2002 Mosher &Tague, 2001 Weier &Chenje, 2018),
indicating differences of up to 10% between the higher and
the lower values for the same sample in other laboratories.
This is important when evaluating a BBMWI test result or
a simplified test.
For a robust comminution circuit design, it is impor-
tant to conduct sufficient BBMWI tests to understand the
ore deposit variability and make sure that the hardness
domains are understood. As such, there can be a challenge
in obtaining sufficient sample mass, time to conduct, and
the cost of testwork. Also, in some cases, the required mass
and time to carry out the test can be excessive, for example,
when developing geometallurgical models (David, 2014)
and for the evaluation of the impact of laboratory scale tests
in a comminution circuit (José Neto et al., 2019 Klein et
al., 2010 Li et al., 2019).
Several authors have proposed different tests and adap-
tations to the original Bond test to meet the need for tests
that predict the BBMWI using a small mass (M. Bueno et
al., 2023 Guimarães Bergerman et al., 2023 Nikolić et
al., 2021). The proposed methods provide a prediction that
ranges from 1.8% to 16%. All these tests are unquestion-
ably significant advances for obtaining BBMWI predictions
with less mass and time requirements. Most tests, how-
ever, still require a mass of approximately 500 to 2000 g.
Although smaller than the mass necessary for the standard
Bond test, such a mass may still be challenging to obtain in
certain cases, including determining the BBMWI in sam-
ples for geometallurgical studies and laboratory scale test
products, such as in the evaluation of preconcentration and
its impacts in comminution. Few of the reviewed options
are commercially available, such as MiniBond (Aminpro,
2023), Geopyora (Bueno et al., 2021 Matus et al., 2020),
HIT (Bergeron et al., 2017 Kojovic, 2016 Kojovic et al.,
2019), and ModBond (SGS, 2023).
Another research approach to predict BBMWI uses
the Hardgrove mill developed by Ralph Hardgrove in 1932
(Beke, 1981 McIntyre &Plitt, 1980 Prasher, 1987), which
is used to determine the energy consumption for comminu-
tion operations for coal pulverization for power generation
(Limited, 1998). The test emulates the operation of a con-
tinuous coal pulverizer at a batch scale. Several authors have
criticized this method, as summarized in papers published
by Sanders, 2007, 2005, 2003. Despite the reservations, it
is still accepted as the primary reference worldwide when
designing coal mills (Limited, 1998). When developing his
test, Bond himself published correlations between BBMWI
and HGI (Bond, 1961 Bond, 1954). Various authors have
obtained good results using the Hardgrove mill to predict
the BBMWI (Bilen, 2021 Hower et al., 1992 Kogut et al.,
2021 McIntyre &Plitt, 1980 Mucsi, 2008 Mucsi et al.,
2011, 2019), with prediction errors below 6%. Although
this is a standard test in the coal industry, it has been
performed differently in the literature. Agus and Waters,
1972 proposed changing from a fixed 50 g mass to a fixed
volume. This is an important change given the ore den-
sity variations, which can lead to a varying filling level in
the grinding chamber. Although this modified test has not
been adopted as a standard by the coal industry, it was used
in different studies that sought to correlate the BBMWI
with the HGI, such as those conducted by McIntyre and
Plitt, 1980, Hower et al., 1992, and Mucsi, 2008.
Furthermore, the original test developed by Hardgrove
assumes that the energy applied for grinding is constant,
regardless of the material, since the test does not measure

1506 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The authors believe this is the first test of its kind that com-
bines coarse particle breakage with sensor amenability. This
test can be economically done on dozens of samples as a
precursor to proceeding to larger mass, performance testing
(pilot runs) currently being offered by sorter manufactur-
ers. As an added advantage, all work is completed by an
independent laboratory—as is the case for other forms of
metallurgical testwork.
It is SRK’s objective to progress toward an industry
standard test protocol so that data can be shared and bench-
marked between projects at different levels of study. This
test procedure can be done by any competent metallurgi-
cal laboratory or research facility with the associated testing
apparatuses and the XRT sensor response can be replicated
using the same unit or alternative XRT sensor. There is no
licensing fee and the protocol is made public in order to
achieve an industry standard.
The SRK test protocol provides estimates of coarse
breakage and metal deportment on samples before they
are crushing and prepared for downstream testing. This is
the only opportunity to evaluate representative samples for
early-stage studies. Test costs are designed to be as economi-
cal as possible (e.g., including limited number of assays) to
allow as many samples to be tested as possible.
For existing operations, larger samples can be collected
using crushing/screening plants for stockpiles or sampling
primary crusher product streams. In addition, AG/SAG
mill pebbles and crushing circuit coarse streams can be
assessed using this protocol. With a growing database of
results, SRK will pursue methods to include pre-concentra-
tion results as part of geometallurgical modelling programs.
REFERENCES
CRC ORE, 2022, Grade Engineering. www.crcore.org.au
/solutions/grade-engineering (viewed Dec 2023).
Dance, A. 2022. Opportunities for Pre-Concentration:
Development of a Lab-Scale Evaluation Test, SME
Annual Conference &EXPO, Salt Lake City, Feb 27 to
Mar 2, 2022.
McCarthy, B. 2019. Exploiting Heterogeneity: Improving
Head Grade and Project Value, World Gold 2019
Conference Proceedings, Perth, pp 430–440.
Saskatchewan Research Council, 2023, Sensor-based
Sorting. www.src.sk.ca/services/sensor-based-sorting
(viewed Dec 2023).
SimSAGe, 2024. HIT—Portable Device for Rapid
Hardness Index Testing. www.simsage.com.au/hit-2/
(viewed Dec 2023).
SMC Testing, 2024. Technical Information. www.smc
testing.com/about/technical-information (viewed Dec
2023).
Source: SRK 2024
Figure 11. Simulated pre-concentration flowsheet from SRK protocol (manganese sample)

Previous Page Next Page

Extracted Text (may have errors)

1506 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The authors believe this is the first test of its kind that com-
bines coarse particle breakage with sensor amenability. This
test can be economically done on dozens of samples as a
precursor to proceeding to larger mass, performance testing
(pilot runs) currently being offered by sorter manufactur-
ers. As an added advantage, all work is completed by an
independent laboratory—as is the case for other forms of
metallurgical testwork.
It is SRK’s objective to progress toward an industry
standard test protocol so that data can be shared and bench-
marked between projects at different levels of study. This
test procedure can be done by any competent metallurgi-
cal laboratory or research facility with the associated testing
apparatuses and the XRT sensor response can be replicated
using the same unit or alternative XRT sensor. There is no
licensing fee and the protocol is made public in order to
achieve an industry standard.
The SRK test protocol provides estimates of coarse
breakage and metal deportment on samples before they
are crushing and prepared for downstream testing. This is
the only opportunity to evaluate representative samples for
early-stage studies. Test costs are designed to be as economi-
cal as possible (e.g., including limited number of assays) to
allow as many samples to be tested as possible.
For existing operations, larger samples can be collected
using crushing/screening plants for stockpiles or sampling
primary crusher product streams. In addition, AG/SAG
mill pebbles and crushing circuit coarse streams can be
assessed using this protocol. With a growing database of
results, SRK will pursue methods to include pre-concentra-
tion results as part of geometallurgical modelling programs.
REFERENCES
CRC ORE, 2022, Grade Engineering. www.crcore.org.au
/solutions/grade-engineering (viewed Dec 2023).
Dance, A. 2022. Opportunities for Pre-Concentration:
Development of a Lab-Scale Evaluation Test, SME
Annual Conference &EXPO, Salt Lake City, Feb 27 to
Mar 2, 2022.
McCarthy, B. 2019. Exploiting Heterogeneity: Improving
Head Grade and Project Value, World Gold 2019
Conference Proceedings, Perth, pp 430–440.
Saskatchewan Research Council, 2023, Sensor-based
Sorting. www.src.sk.ca/services/sensor-based-sorting
(viewed Dec 2023).
SimSAGe, 2024. HIT—Portable Device for Rapid
Hardness Index Testing. www.simsage.com.au/hit-2/
(viewed Dec 2023).
SMC Testing, 2024. Technical Information. www.smc
testing.com/about/technical-information (viewed Dec
2023).
Source: SRK 2024
Figure 11. Simulated pre-concentration flowsheet from SRK protocol (manganese sample)