252 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
which could achieve mass flow with a 50 mm (2 in.) top
size for the ore under test at up to 150 t/h. It is readily seen
that as the flow path diameter increases, the throughput
increases rapidly.
It is apparent that careful consideration must be given
to the flow path diameter, particle top size, throughput, ore
properties and microwave power input when designing a
large-scale microwave treatment system for an industrial
application. For example, a large porphyry copper mine
may require several 1,000 t/h modules, which would
require some additional development, or a relatively small
gold mine may require one 200 t/h module, which is
already at demonstrated scale.
MICROWAVE PROCESSING
APPLICATIONS AT SCALE
Comminution
Microwave treatment requires a relatively dry material,
given water is an excellent microwave heater, thus micro-
wave treatment must be performed before wet milling.
Previous unpublished work has indicated that usual mois-
ture contents of run of mine (ROM) material are not pro-
hibitive to microwave treatment, but it may represent a
reduction in energy efficiency if excessively wet. So, weather
patterns and stockpile protection may also need consider-
ation in various locations and seasons.
Previous studies have shown that coarser particles tend
to yield greater reductions in ore competency attributed to
the particles being more likely to contain a greater propor-
tion of constrained microwave-heating phases, with a lower
proportion of exposed surface microwave-heating miner-
alisation, and fewer barren fragments. This suggests that
microwave treatment should be performed at as coarse a
size as possible.
Given the SAG mill feed top size of many mining oper-
ations, SAG mill feed is a natural place to consider plac-
ing a microwave system. If there are secondary and tertiary
crushing stages between ROM and the SAG mill in existing
flowsheets, these may also be considered as potential loca-
tions. If the required throughput and flow path diameter
do not match with the feed top size, then additional crush-
ing and/or bypass screening may be needed, as illustrated in
Figure 3. The same applies if rod mills are used in the circuit
or ultra-fine grinding and regrind mills prior to recovery.
Microwave treatment may also be targeted at specific
points in a flowsheet. A location that is often considered
is the pebble crusher feed, illustrated in Figure 4, to help
increase the capacity of the installed crusher and SAG
mill with difficult to process materials. The pebble crusher
stream is screened, largely free of water and also has a much
lower throughput than the SAG mill and may be an easier
place to demonstrate microwave treatment at existing scale
for large operations.
The primary goal of microwave treatment of ROM or
primary crusher product is to reduce ore competency at
the secondary, tertiary and pebble crushers (e.g., decrease
Bond Impact Crushing Work Index, CWi), SAG mill (e.g.,
increase A*b parameter) and ball mills (i.e., reduce Bond
Work Index, BWi). A reduction in ore competency would
equate to reduced energy requirement for a fixed through-
put, or an increased throughput for fixed energy input. In
other words, to reduce the specific energy requirement.
Given the energy required for comminution increases
exponentially as particle size decreases, the greatest direct
energy reduction savings may be realised around the ball
mill. However, this requires residual microwave-induced
fractures that have not been exhausted through crushing
and SAG milling.
As previously mentioned, coarser particles tend to
exhibit a greater propensity for microwave-assisted break-
age, but standard metallurgical testing methods are some-
what limited at very coarse particle sizes. It was proposed
SAG Mill
ROM/Crush
MW
Screen
-XXmm
SAG Mill
ROM/Crush
MW
Crush
-XXmm
Figure 3. Microwave system primary location options for
typical circuits
SAG Mill
Screen
U/S
Crusher
O/S
MW
ROM/Crush
Figure 4. Microwave system in targeted location
+XXmm
which could achieve mass flow with a 50 mm (2 in.) top
size for the ore under test at up to 150 t/h. It is readily seen
that as the flow path diameter increases, the throughput
increases rapidly.
It is apparent that careful consideration must be given
to the flow path diameter, particle top size, throughput, ore
properties and microwave power input when designing a
large-scale microwave treatment system for an industrial
application. For example, a large porphyry copper mine
may require several 1,000 t/h modules, which would
require some additional development, or a relatively small
gold mine may require one 200 t/h module, which is
already at demonstrated scale.
MICROWAVE PROCESSING
APPLICATIONS AT SCALE
Comminution
Microwave treatment requires a relatively dry material,
given water is an excellent microwave heater, thus micro-
wave treatment must be performed before wet milling.
Previous unpublished work has indicated that usual mois-
ture contents of run of mine (ROM) material are not pro-
hibitive to microwave treatment, but it may represent a
reduction in energy efficiency if excessively wet. So, weather
patterns and stockpile protection may also need consider-
ation in various locations and seasons.
Previous studies have shown that coarser particles tend
to yield greater reductions in ore competency attributed to
the particles being more likely to contain a greater propor-
tion of constrained microwave-heating phases, with a lower
proportion of exposed surface microwave-heating miner-
alisation, and fewer barren fragments. This suggests that
microwave treatment should be performed at as coarse a
size as possible.
Given the SAG mill feed top size of many mining oper-
ations, SAG mill feed is a natural place to consider plac-
ing a microwave system. If there are secondary and tertiary
crushing stages between ROM and the SAG mill in existing
flowsheets, these may also be considered as potential loca-
tions. If the required throughput and flow path diameter
do not match with the feed top size, then additional crush-
ing and/or bypass screening may be needed, as illustrated in
Figure 3. The same applies if rod mills are used in the circuit
or ultra-fine grinding and regrind mills prior to recovery.
Microwave treatment may also be targeted at specific
points in a flowsheet. A location that is often considered
is the pebble crusher feed, illustrated in Figure 4, to help
increase the capacity of the installed crusher and SAG
mill with difficult to process materials. The pebble crusher
stream is screened, largely free of water and also has a much
lower throughput than the SAG mill and may be an easier
place to demonstrate microwave treatment at existing scale
for large operations.
The primary goal of microwave treatment of ROM or
primary crusher product is to reduce ore competency at
the secondary, tertiary and pebble crushers (e.g., decrease
Bond Impact Crushing Work Index, CWi), SAG mill (e.g.,
increase A*b parameter) and ball mills (i.e., reduce Bond
Work Index, BWi). A reduction in ore competency would
equate to reduced energy requirement for a fixed through-
put, or an increased throughput for fixed energy input. In
other words, to reduce the specific energy requirement.
Given the energy required for comminution increases
exponentially as particle size decreases, the greatest direct
energy reduction savings may be realised around the ball
mill. However, this requires residual microwave-induced
fractures that have not been exhausted through crushing
and SAG milling.
As previously mentioned, coarser particles tend to
exhibit a greater propensity for microwave-assisted break-
age, but standard metallurgical testing methods are some-
what limited at very coarse particle sizes. It was proposed
SAG Mill
ROM/Crush
MW
Screen
-XXmm
SAG Mill
ROM/Crush
MW
Crush
-XXmm
Figure 3. Microwave system primary location options for
typical circuits
SAG Mill
Screen
U/S
Crusher
O/S
MW
ROM/Crush
Figure 4. Microwave system in targeted location
+XXmm