3
Plant Trial Methodology
Once the decision is made to advance this work to plant
trial, it is necessary to develop an appropriate plant moni-
toring protocol that allows for the collection of both pulp
chemical and metallurgical data before and after to conver-
sion to high chrome grinding media.
Pulp Chemical Data
The collection of pulp chemical data means that a techni-
cian visits site for up to 10 days before and 10 days after
the conversion to complete a number of pulp chemistry
surveys. Each pulp chemical survey involves the collection
of pH, Eh, dissolved oxygen, oxygen demand, temperature
measurements and samples for EDTA extraction for copper
and iron, from the following process streams:
• Ball mill discharge
• Ball mill cyclone underflow
• Ball mill cyclone overflow
• Rougher feed and
• Rougher tailings.
This data provides information about how the pulp
chemistry changes as the grinding environment is altered
with the change from forged steel to high chrome grinding
media.
Metallurgical Data
To assess the metallurgical performance with the con-
version from forged to high chrome grinding media the
mass balanced plant shift data are utilized. The shift data
generally provides information about:
• Throughput
• Particle size distribution
• Feed grades
• Final concentrate grades
• Final recoveries and
• Reagent consumptions.
In some instances, staged data is also available, which
allows for an examination of where the metallurgical gains
occurred (i.e., during roughing and/or cleaning). Once the
data has been made available it is reviewed, and (in consul-
tation with site personnel) cleaned by omitting those shifts:
• That are three standard deviations away from the
mean using the standardized residuals method11
• With major down time (i.e., less than 22 hours oper-
ating) and
• With unusual operational activities (e.g., reagent tri-
als or different ore types).
The cleansed data are analysed using time series and
‘cusum’ plots to observe variations in performance with
time. Quantitative statistical techniques (the Students
t-test, comparison of regression lines, and multiple variable
regression analysis) are utilized to determine the magnitude
of any improvement to the metallurgical performance.
Generally, between three and six months’ worth of plant
data before and after the conversion is used in this analysis.
Final Analysis and Economic Evaluation
The regression modelling for final concentrate grade and
recovery will provide an estimate of the metallurgical ben-
efit that can be attributed to the change in grinding media
alloy. Ultimately, this improvement in metallurgy is linked
back to changes in pulp chemistry. Further, it is possible to
reduce reagent consumption with the new pulp chemical
regime so evidence of these reductions is sought. These data
are combined with the reduction in media wear to yield an
economic evaluation of what a change in grinding media
composition means financially.
CASE STUDIES
Newmont Cadia Operations
The Ridgeway deposit is located 3 kilometres northwest of
Cadia Hill at a depth of nominally 500 metres, in central
western New South Wales, Australia. This porphyry cop-
per-gold deposit has an average head grade of 0.37 percent
copper (as chalcopyrite) and 0.7 g/t of gold.
Laboratory test work indicated that changing from
forged steel to high chrome grinding media would see a
shift to more oxidizing pulp potentials, a significant increase
in the dissolved oxygen content and a large decrease in the
EDTA extractable iron through reduced corrosion rates12.
A 1.7 percent increase in copper recovery was observed
when using the more electrochemical inert grinding media.
Based on these results and an expectation that the media
consumption would be reduced a plant trial was conducted
in the Ridgeway concentrator.
The plant trial produced increases in the copper and
gold recoveries of 1.0 and 2.1 percent, respectively based
on regression modelling12. The plant subsequently reverted
back to forged steel and the system was monitored to deter-
mine what would happen. Once back on forged steel it was
noted that the copper recovery decreased by 1.1 percent,
with indications that the gold recovery also decreased, but
there is statistical uncertainty due to the differences in gold
head grade which arose because of the time frame involve
in conducting this trial. This trial was repeated and similar
improvements in copper and gold recovery observed.
Plant Trial Methodology
Once the decision is made to advance this work to plant
trial, it is necessary to develop an appropriate plant moni-
toring protocol that allows for the collection of both pulp
chemical and metallurgical data before and after to conver-
sion to high chrome grinding media.
Pulp Chemical Data
The collection of pulp chemical data means that a techni-
cian visits site for up to 10 days before and 10 days after
the conversion to complete a number of pulp chemistry
surveys. Each pulp chemical survey involves the collection
of pH, Eh, dissolved oxygen, oxygen demand, temperature
measurements and samples for EDTA extraction for copper
and iron, from the following process streams:
• Ball mill discharge
• Ball mill cyclone underflow
• Ball mill cyclone overflow
• Rougher feed and
• Rougher tailings.
This data provides information about how the pulp
chemistry changes as the grinding environment is altered
with the change from forged steel to high chrome grinding
media.
Metallurgical Data
To assess the metallurgical performance with the con-
version from forged to high chrome grinding media the
mass balanced plant shift data are utilized. The shift data
generally provides information about:
• Throughput
• Particle size distribution
• Feed grades
• Final concentrate grades
• Final recoveries and
• Reagent consumptions.
In some instances, staged data is also available, which
allows for an examination of where the metallurgical gains
occurred (i.e., during roughing and/or cleaning). Once the
data has been made available it is reviewed, and (in consul-
tation with site personnel) cleaned by omitting those shifts:
• That are three standard deviations away from the
mean using the standardized residuals method11
• With major down time (i.e., less than 22 hours oper-
ating) and
• With unusual operational activities (e.g., reagent tri-
als or different ore types).
The cleansed data are analysed using time series and
‘cusum’ plots to observe variations in performance with
time. Quantitative statistical techniques (the Students
t-test, comparison of regression lines, and multiple variable
regression analysis) are utilized to determine the magnitude
of any improvement to the metallurgical performance.
Generally, between three and six months’ worth of plant
data before and after the conversion is used in this analysis.
Final Analysis and Economic Evaluation
The regression modelling for final concentrate grade and
recovery will provide an estimate of the metallurgical ben-
efit that can be attributed to the change in grinding media
alloy. Ultimately, this improvement in metallurgy is linked
back to changes in pulp chemistry. Further, it is possible to
reduce reagent consumption with the new pulp chemical
regime so evidence of these reductions is sought. These data
are combined with the reduction in media wear to yield an
economic evaluation of what a change in grinding media
composition means financially.
CASE STUDIES
Newmont Cadia Operations
The Ridgeway deposit is located 3 kilometres northwest of
Cadia Hill at a depth of nominally 500 metres, in central
western New South Wales, Australia. This porphyry cop-
per-gold deposit has an average head grade of 0.37 percent
copper (as chalcopyrite) and 0.7 g/t of gold.
Laboratory test work indicated that changing from
forged steel to high chrome grinding media would see a
shift to more oxidizing pulp potentials, a significant increase
in the dissolved oxygen content and a large decrease in the
EDTA extractable iron through reduced corrosion rates12.
A 1.7 percent increase in copper recovery was observed
when using the more electrochemical inert grinding media.
Based on these results and an expectation that the media
consumption would be reduced a plant trial was conducted
in the Ridgeway concentrator.
The plant trial produced increases in the copper and
gold recoveries of 1.0 and 2.1 percent, respectively based
on regression modelling12. The plant subsequently reverted
back to forged steel and the system was monitored to deter-
mine what would happen. Once back on forged steel it was
noted that the copper recovery decreased by 1.1 percent,
with indications that the gold recovery also decreased, but
there is statistical uncertainty due to the differences in gold
head grade which arose because of the time frame involve
in conducting this trial. This trial was repeated and similar
improvements in copper and gold recovery observed.