862 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
differences in performances and many systems have appli-
cation limitations.
The paper discusses a range of technologies successfully
implemented in the minerals sector in well over a dozen
commodities that have proven advantageous with benefits
illustrated through selected case studies.
TECHNOLOGIES
There are many technologies that claim to be ideal for bulk
material quality measurement, however, there are few that
demonstrate the requirements to meet truly representa-
tive measurement according to sampling principles. Rocks
are highly heterogeneous and quality varies significantly
between them as well as within them. Quality can also vary
by particle size depending on mineral breakage character-
istics, hence a surface analysis of some particles in a parcel
or flow is very likely to be unrepresentative of that com-
plete flow in most commodities. Technologies are ideally
fully penetrative of the material as presented to the sen-
sor, designed to provide an unbiased analysis, and measure
continuously to provide compositional averages over short
time increments, or small parcels, to maximize the poten-
tial for effective responses.
Three types of measurement on conveyed flows are the
focus of the paper and these are:
• multi-elemental measurement
• moisture measurement
• fragmentation measurement
The techniques are explained and typical applications and
benefits discussed, and potential applications mentioned.
Other technologies can penetrate but may have application
limitations as they may measure only one mineral (such
as magnetic resonance) or only certain parameters (such
as natural gamma) or relative atomic densities that do not
directly indicate either elements or minerals through lim-
ited depths (x-ray transmission). There are several moisture
measurement techniques (such as near infrared) that sense
the surface of flows only and this is rarely representative
of the underlying material. The author is unaware of any
penetrative fragmentation analysis technique.
Elemental analysis using PGNAA
Prompt Gamma Neutron Activation Analysis (PGNAA)
has been applied to conveyed flows successfully, mainly in
coal and cement (limestone) applications for quality moni-
toring and control, since the 1990s. The minerals industry
commenced practical implementation in the early 2000s
in iron ore quality measurement. The application history
of PGNAA in the minerals industry is discussed in more
detail elsewhere (Kurth 2016).
PGNAA utilizes a neutron source, commonly
Californium-252, usually located under the conveyed
flow, which emits neutrons moderated to lower energies
to improve neutron “capture” by elemental nuclei. The full
cross section of the conveyed flow passes through a zone
of neutron flux, and gamma ray spectra unique to each
element are emitted by most elements instantaneously fol-
lowing neutron “capture.” An array of high performance
detectors, such as bismuth germanium oxide, senses emit-
ted gamma energies from conveyed material and accu-
mulates a response over a measurement time appropriate
for the application. Measurement times of 30 seconds to
two minutes are used in high specification GEOSCAN
PGNAA system (Figure 1) and longer times are application
dependent.
The average response weighted by tons is reported to
the plant control system and any required responses imple-
mented. Elements from carbon upwards in atomic number
can be measured, although some elements do not respond
or have insufficient response for accurate measurement. Up
to twenty elements can be reported simultaneously if they
occur at measurable concentrations although most applica-
tions require fewer than ten.
PGNAA is unaffected by belt speed, mineralogy, par-
ticle size, material segregation, moisture or dust and mea-
sures through the full conveyed profile continuously to
provide representative analysis. Flow rates of under 100
tph to over 12,000 tph are currently measured. No two
PGNAA systems available have the same specification and
hence performance differences are significant, and few have
proven successful in minerals applications. High specifica-
tion systems, such as GEOSCAN designed to require no
external isolation zone around the analyzer, are unique in
their ability to measure:
• Accurately over short measurement times
• Less responsive elements at high precisions (such as
carbon, phosphorus, aluminum, magnesium, etc.)
• Selected trace elements directly in conveyed flows
(such as gold and silver)
• Under certain conditions (such as on conveyor belts
containing steel cords or high chlorine content, or
elements such as sodium, potassium and chlorine in
potash)
Applications
Representative real time data from PGNAA is available
from conveyed flows, normally after primary crushing
differences in performances and many systems have appli-
cation limitations.
The paper discusses a range of technologies successfully
implemented in the minerals sector in well over a dozen
commodities that have proven advantageous with benefits
illustrated through selected case studies.
TECHNOLOGIES
There are many technologies that claim to be ideal for bulk
material quality measurement, however, there are few that
demonstrate the requirements to meet truly representa-
tive measurement according to sampling principles. Rocks
are highly heterogeneous and quality varies significantly
between them as well as within them. Quality can also vary
by particle size depending on mineral breakage character-
istics, hence a surface analysis of some particles in a parcel
or flow is very likely to be unrepresentative of that com-
plete flow in most commodities. Technologies are ideally
fully penetrative of the material as presented to the sen-
sor, designed to provide an unbiased analysis, and measure
continuously to provide compositional averages over short
time increments, or small parcels, to maximize the poten-
tial for effective responses.
Three types of measurement on conveyed flows are the
focus of the paper and these are:
• multi-elemental measurement
• moisture measurement
• fragmentation measurement
The techniques are explained and typical applications and
benefits discussed, and potential applications mentioned.
Other technologies can penetrate but may have application
limitations as they may measure only one mineral (such
as magnetic resonance) or only certain parameters (such
as natural gamma) or relative atomic densities that do not
directly indicate either elements or minerals through lim-
ited depths (x-ray transmission). There are several moisture
measurement techniques (such as near infrared) that sense
the surface of flows only and this is rarely representative
of the underlying material. The author is unaware of any
penetrative fragmentation analysis technique.
Elemental analysis using PGNAA
Prompt Gamma Neutron Activation Analysis (PGNAA)
has been applied to conveyed flows successfully, mainly in
coal and cement (limestone) applications for quality moni-
toring and control, since the 1990s. The minerals industry
commenced practical implementation in the early 2000s
in iron ore quality measurement. The application history
of PGNAA in the minerals industry is discussed in more
detail elsewhere (Kurth 2016).
PGNAA utilizes a neutron source, commonly
Californium-252, usually located under the conveyed
flow, which emits neutrons moderated to lower energies
to improve neutron “capture” by elemental nuclei. The full
cross section of the conveyed flow passes through a zone
of neutron flux, and gamma ray spectra unique to each
element are emitted by most elements instantaneously fol-
lowing neutron “capture.” An array of high performance
detectors, such as bismuth germanium oxide, senses emit-
ted gamma energies from conveyed material and accu-
mulates a response over a measurement time appropriate
for the application. Measurement times of 30 seconds to
two minutes are used in high specification GEOSCAN
PGNAA system (Figure 1) and longer times are application
dependent.
The average response weighted by tons is reported to
the plant control system and any required responses imple-
mented. Elements from carbon upwards in atomic number
can be measured, although some elements do not respond
or have insufficient response for accurate measurement. Up
to twenty elements can be reported simultaneously if they
occur at measurable concentrations although most applica-
tions require fewer than ten.
PGNAA is unaffected by belt speed, mineralogy, par-
ticle size, material segregation, moisture or dust and mea-
sures through the full conveyed profile continuously to
provide representative analysis. Flow rates of under 100
tph to over 12,000 tph are currently measured. No two
PGNAA systems available have the same specification and
hence performance differences are significant, and few have
proven successful in minerals applications. High specifica-
tion systems, such as GEOSCAN designed to require no
external isolation zone around the analyzer, are unique in
their ability to measure:
• Accurately over short measurement times
• Less responsive elements at high precisions (such as
carbon, phosphorus, aluminum, magnesium, etc.)
• Selected trace elements directly in conveyed flows
(such as gold and silver)
• Under certain conditions (such as on conveyor belts
containing steel cords or high chlorine content, or
elements such as sodium, potassium and chlorine in
potash)
Applications
Representative real time data from PGNAA is available
from conveyed flows, normally after primary crushing