XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 249
and non-heating phases causes stress around grain bound-
aries leading to preferential breakage around, and libera-
tion of, heating phases. Microwave-induced fractures can
significantly reduce ore competency and enhance mineral
liberation, leading to reduced comminution energy require-
ments, increased primary grind size, increased throughput
and increased recovery, among other indirect benefits such
as reduced grinding media and liner wear, and coarse tail-
ings generation.
The technology is now at the stage where commer-
cial deployment can be considered and this paper reviews
routes to maximise the commercial and carbon reduction
benefit of this technology. In particular, we consider the
impact of induced fractures on conventional grinding/flo-
tation circuits, on the performance of leach systems and on
new flowsheets with the potential to deliver paradigm shift
in carbon emissions from mineral processing circuits.
MICROWAVE PROCESSING IN THE
MINING INDUSTRY
Early Studies and the Importance of Mineralogy
Research into microwave treatment of ores began in the
late 1970s and early 1980s with measurements of dielectric
properties and heating rates of minerals in low power (3
kW), low intensity multimode applicators, such as those
used in domestic kitchen microwaves (Chen et al. 1984
Church et al. 1988 McGill et al. 1987, 1988 Walkiewicz
et al. 1988, 1991). These studies identified which minerals
heated readily and demonstratedw that microwave treat-
ment could be used to induce fracture and significantly
reduce the energy required for comminution.
The use of multimode applicators for experimenta-
tion on ore samples persisted until the early 2000s when
researchers first began using high intensity single-mode
cavities with higher power generators (up to 15 kW)
(Kingman et al. 2000a, 2004a, 2004b Sayhoun et al. 2005)
to increase heating rates. These studies demonstrated that
higher microwave power density could achieve a similar or
better degrees of fracture at significantly lower microwave
specific energy (EMS) inputs.
The role of mineralogy was investigated in the 2000s
and 2010s numerically (Ali and Bradshaw 2009, 2010,
2011 Jones et al. 2005, 2007 Wang et al. 2008 Wang and
Djordjevic 2014 Whittles et al. 2003) and experimentally
at high power density (Batchelor et al. 2015, 2016a Giyani
2023 Kingman et al. 2000b Ure 2017). These studies
demonstrated that mineralogical properties are related to
the development and propagation of induced fractures,
specific microwave energy input, microwave power density
and the subsequent reduction in required comminution
energy and improvement in valuable mineral liberation.
The relevant mineralogical properties include:
• Modal abundance of heating phases
• Grain size distribution of heating phases
• Mechanical strength of heating and non-heating
phases
• Thermal expansion coefficient of heating phases
• Dissemination of heating phases (e.g., veins, cluster-
ing, finely disseminated, etc)
• Association of heating and non-heating phases (plus
valuable and gangue phases)
• Textural consistency of the ore and prevalence of
amenable fragments
• Fragment size
Importantly, the adoption of single-mode cavities
enabled a route to scale-up in the minerals industry for
the first time by significantly reducing residence times (1
s) and allowing for effective microwave treatments at eco-
nomically feasible energy inputs (5 kWh/t) through the
use of high power density microwave treatments.
State of the Art
Microwave treatment of ores has been researched on a vari-
ety of commodities over the past few decades by numer-
ous authors in the laboratory at 2.45 GHz microwave
frequency (maximum power 30 kW), but until recently,
had not been demonstrated at a scale relevant to the min-
ing industry. A large-scale system (in the order of 100 t/h)
required high microwave power (in the order of 100 kW),
a bespoke microwave applicator design and a means to reli-
ably transport the ore to give economically feasible specific
microwave energy inputs (in the order of 1 kWh/t).
100 kW microwave generators are already commer-
cially available off-the-shelf at 896 MHz in the UK. The
applicator was designed in-house at The University of
Nottingham by electromagnetic design experts and com-
prised a single-mode cavity with patented microwave emis-
sion containment apparatus (called chokes). The materials
handling method was selected with assistance from materi-
als handling experts Jenike &Johanson Ltd. The key cri-
teria for a materials handling system to be integrated with
a continuous large-scale microwave applicator includes the
following:
• Small plant footprint (while also considering plant
height)
• Suitable materials of construction (electrical proper-
ties, mechanical properties, wear, etc)
• Low complexity (moving parts, support structures,
etc)
and non-heating phases causes stress around grain bound-
aries leading to preferential breakage around, and libera-
tion of, heating phases. Microwave-induced fractures can
significantly reduce ore competency and enhance mineral
liberation, leading to reduced comminution energy require-
ments, increased primary grind size, increased throughput
and increased recovery, among other indirect benefits such
as reduced grinding media and liner wear, and coarse tail-
ings generation.
The technology is now at the stage where commer-
cial deployment can be considered and this paper reviews
routes to maximise the commercial and carbon reduction
benefit of this technology. In particular, we consider the
impact of induced fractures on conventional grinding/flo-
tation circuits, on the performance of leach systems and on
new flowsheets with the potential to deliver paradigm shift
in carbon emissions from mineral processing circuits.
MICROWAVE PROCESSING IN THE
MINING INDUSTRY
Early Studies and the Importance of Mineralogy
Research into microwave treatment of ores began in the
late 1970s and early 1980s with measurements of dielectric
properties and heating rates of minerals in low power (3
kW), low intensity multimode applicators, such as those
used in domestic kitchen microwaves (Chen et al. 1984
Church et al. 1988 McGill et al. 1987, 1988 Walkiewicz
et al. 1988, 1991). These studies identified which minerals
heated readily and demonstratedw that microwave treat-
ment could be used to induce fracture and significantly
reduce the energy required for comminution.
The use of multimode applicators for experimenta-
tion on ore samples persisted until the early 2000s when
researchers first began using high intensity single-mode
cavities with higher power generators (up to 15 kW)
(Kingman et al. 2000a, 2004a, 2004b Sayhoun et al. 2005)
to increase heating rates. These studies demonstrated that
higher microwave power density could achieve a similar or
better degrees of fracture at significantly lower microwave
specific energy (EMS) inputs.
The role of mineralogy was investigated in the 2000s
and 2010s numerically (Ali and Bradshaw 2009, 2010,
2011 Jones et al. 2005, 2007 Wang et al. 2008 Wang and
Djordjevic 2014 Whittles et al. 2003) and experimentally
at high power density (Batchelor et al. 2015, 2016a Giyani
2023 Kingman et al. 2000b Ure 2017). These studies
demonstrated that mineralogical properties are related to
the development and propagation of induced fractures,
specific microwave energy input, microwave power density
and the subsequent reduction in required comminution
energy and improvement in valuable mineral liberation.
The relevant mineralogical properties include:
• Modal abundance of heating phases
• Grain size distribution of heating phases
• Mechanical strength of heating and non-heating
phases
• Thermal expansion coefficient of heating phases
• Dissemination of heating phases (e.g., veins, cluster-
ing, finely disseminated, etc)
• Association of heating and non-heating phases (plus
valuable and gangue phases)
• Textural consistency of the ore and prevalence of
amenable fragments
• Fragment size
Importantly, the adoption of single-mode cavities
enabled a route to scale-up in the minerals industry for
the first time by significantly reducing residence times (1
s) and allowing for effective microwave treatments at eco-
nomically feasible energy inputs (5 kWh/t) through the
use of high power density microwave treatments.
State of the Art
Microwave treatment of ores has been researched on a vari-
ety of commodities over the past few decades by numer-
ous authors in the laboratory at 2.45 GHz microwave
frequency (maximum power 30 kW), but until recently,
had not been demonstrated at a scale relevant to the min-
ing industry. A large-scale system (in the order of 100 t/h)
required high microwave power (in the order of 100 kW),
a bespoke microwave applicator design and a means to reli-
ably transport the ore to give economically feasible specific
microwave energy inputs (in the order of 1 kWh/t).
100 kW microwave generators are already commer-
cially available off-the-shelf at 896 MHz in the UK. The
applicator was designed in-house at The University of
Nottingham by electromagnetic design experts and com-
prised a single-mode cavity with patented microwave emis-
sion containment apparatus (called chokes). The materials
handling method was selected with assistance from materi-
als handling experts Jenike &Johanson Ltd. The key cri-
teria for a materials handling system to be integrated with
a continuous large-scale microwave applicator includes the
following:
• Small plant footprint (while also considering plant
height)
• Suitable materials of construction (electrical proper-
ties, mechanical properties, wear, etc)
• Low complexity (moving parts, support structures,
etc)