Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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"A Method for the Treatment of Ore Material"
FIELD OF THE INVENTION
[0001] The present invention relates to a method for treating ore material
with
electromagnetic energy to form micro-channels.
BACKGROUND ART
[0002] In mineral processing microwave heating has been used for the pre-
treatment of
ore materials in order to increase valuable mineral recovery. Microwave
heating offers a
number of advantages over conventional heating such as, rapid heating,
material
selective heating and volumetric heating. However, the problem with the use of
microwave energy in mineral processing arises from the fact that uncontrolled
levels of
microwave exposure causes unwanted changes in the minerals and undesirable
changes in the ore materials themselves.
[0003] For example, WO 03/102250 proposes the use of pulsed microwave energy
treatment of ores to facilitate the subsequent processing of ores based on the
differences in thermal expansion of the minerals within the ore, to form micro-
cracks
throughout the ore structure. However, one of the main problems of micro-crack
formation within the ore materials is that the micro-cracks tend to weaken the
ore
materials. Weakening of the ore materials can lead to unstable heaps for heap
leaching.
Structurally weak ore materials are also problematic with respect to heap
leaching, as
the potential for the ore material to break into smaller particles exists.
These small
particles affect the percolation of the leach solution through the heap, as
they can
collect in the spaces between the larger particles, preventing the flow of
leach solution
through the entire heap.
[0004] The use of pulsed microwave energy as disclosed in WO 03/102250
requires
significantly high electric field strengths due to very short durations of
microwave energy
exposure. The use of high electric field strengths may result in a situation
where
excessive microwave energy causes dielectric breakdown or arcing of the heated
ore
materials.
[0005] The preceding discussion of the background art is intended to
facilitate an
understanding of the present invention only. This discussion is not an
acknowledgement
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or admission that any of the material referred to is or was part of the common
general
knowledge as at the priority date of the application.
[0006] Each document, reference, patent application or patent cited in this
text is
expressly incorporated herein in their entirety by reference, which means that
it should
be read and considered by the reader as part of this text. That the document,
reference, patent application or patent cited in this text is not repeated in
this text is
merely for reasons of conciseness.
[0007] Throughout the specification and claims, unless the context requires
otherwise,
the term "microwave energy" is understood herein to mean electromagnetic
radiation
that has frequencies in the range of 100-10,000 MHz.
[0008] Throughout the specification and claims, unless the context requires
otherwise,
the term "radio frequency energy" is understood herein to mean electromagnetic
radiation that has frequencies in the range of 1 -1 00 MHz.
[0009] Throughout the specification and claims, unless the context requires
otherwise,
the word "comprise" or variations such as "comprises" or "comprising", will be
understood to imply the inclusion of a stated integer or group of integers but
not the
exclusion of any other integer or group of integers.
DISCLOSURE OF THE INVENTION
[0010] In accordance with the present invention, there is provided a method
for treating
an ore material with electromagnetic energy, the method comprising the steps
of:
agglomerating the ore material;
irradiating the ore material with electromagnetic energy;
thereby heating the liquid in the ore material;
vapourising at least a portion of the liquid in the ore material;
forming micro-channels in the ore material; and
acid leaching the ore material.
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[0011] Advantageously, irradiation of the ore material results in localised
heating of the
liquid present within the ore material, forming micro-channels. Without being
limited by
theory, it is believed that the radiation heats the liquid volumetrically
forming vapour.
The vapour forces its way to the surface of the ore material resulting in the
formation of
the micro-channels.
[0012] Advantageously, the micro-channels assist the percolation of the leach
solution
through the ore material and increases leaching rates and recoveries.
[0013] In the context of this invention, the term electromagnetic energy, is
understood to
mean electromagnetic radiation that has frequencies in the range of 1-10,000
MHz,
being either microwave energy or radio frequency energy.
[0014] Advantageously, the use of radio frequency energy may provide increased
heating efficiency compared to microwave energy due to higher electrical
conductivity in
the water at lower frequencies.
[0015] The term ore material may encompass unprocessed or processed ores
including
crushed ore particles, cakes of crushed ore particles or agglomerated ore
particles.
[0016] It will be appreciated that the method of the present invention is
particularly
suited to multiphase ore material wherein the phases have different dielectric
properties
and wherein the bulk of the ore material has low dielectric property.
[0017] It will be appreciated that the ore material contains liquid.
Preferably, the liquid
contains ions.
[0018] Preferably, the liquid content within the ore material is about 5
w/wcY0 to about 30
w/wcYo.
[0019] In one form of the invention, the method comprises the further step of:
crushing the ore material to provide ore particles,
prior to the step of:
agglomerating the ore material.
[0020] The step of crushing the ore material may be performed using tools
known in the
art including ball mills, crushers, hammer mills.
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[0021] Preferably, the ore particles have an average diameter of less than 5
cm.
[0022] Preferably, the step of agglomerating the ore material is carried out
in a solution
of acid and water.
[0023] In one form of the invention, the method comprises the further step of:
agglomerating the ore material in a solution of acid and water;
prior to or after the step of;
irradiating the ore material with electromagnetic energy.
[0024] Without being limited by theory, it is believed that the step of
agglomerating the
ore material in the solution of acid and water causes the particles to bind
together to
form larger particles termed herein, agglomerates.
[0025] Advantageously, agglomerating the ore material in the solution of acid
and water
results in retention of some liquid within the agglomerates.
[0026] Preferably, the liquid content in the agglomerates is +/- 10% w/w.
[0027] By careful control of the step of irradiating the ore material with
electromagnetic
energy, it is possible to heat the liquid in the ore material in preference to
the ore
particles. Advantageously, this results in little or no change to the
structural integrity of
the ore material, despite the formation of the micro-channels.
[0028] Advantageously, both heap stacking and leaching benefit from the
structural
integrity of the ore materials with micro-channels remaining substantially
unaltered. The
Applicant envisages that, advantageously, this can result in agglomerates of
increased
strength and integrity, enabling heaps to be stacked higher and with greater
stability
than under conventional practise.
[0029] Preferably, the acid is provided in the form of sulphuric acid.
[0030] Preferably, the solution of acid and water used in the step of;
agglomerating the ore particles in a solution of acid and water,
contains up to 50 kg of sulphuric acid per dry tonne of ore particles.
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[0031] It will be appreciated that the amount of sulphuric acid in the
solution of acid and
water may vary depending on the actual mineral composition of the ore
particles, the
moisture content of the ore particles and other factors.
[0032] The ore particles preferably are agglomerated for an amount of time
that may
vary from an hour to several days, depending on the extent of agglomeration
required.
It will be appreciated that the amount of time required to achieve suitable
agglomerates
will be dependent on the ore composition, agglomerate size, liquid content
within the
agglomerates and other factors.
[0033] Without being limited by theory, it is believed that as the agglomerate
is made
smaller higher power densities (Watts/m3 in the liquid phase) will be required
due to
greater heat losses and easier mass transport behaviour due to the fact that
surface
area to volume ratio is much higher in smaller particles than larger ones. The
larger the
agglomerate, the more resistance there is to mass transport, therefore the
higher the
temperature reached in the liquid phase (superheating) and the greater the
number of
channels. In small agglomerates the liquid gets to the surface more easily so
it needs to
be heated much more quickly than in larger agglomerates. However, if the power
density is too high, the agglomerate may blow apart. Consequently, power
density must
be controlled depending on the agglomerate size and also the liquid content.
[0034] In one form of the invention, the method comprises the further step of:
curing the ore material;
after the step of:
agglomerating the ore particles in a solution of acid and water;
or during the step of:
irradiating the ore material with electromagnetic energy.
[0035] Without being limited by theory, the curing step gives the agglomerates
strength
even with the included micro-channels. The heating of the agglomerates during
microwave treatment and consequent drying effectively result in a degree of
curing of
the agglomerates. The strengthening of the agglomerates through curing enables
higher heap stacking and compensates for any loss in strength due to the micro-
channels which are formed.
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[0036] Preferably, the ore material that includes the agglomerates formed in
the step of:
agglomerating the ore particles in a solution of acid and water,
are fed as a bulk flow of material down a pipe to a troughed or flat conveyor
to an
electromagnetic treatment assembly to be irradiated with electromagnetic
energy.
[0037] The electromagnetic treatment assembly is any assembly that can support
a
homogenous electric field distribution that is sufficiently high to heat the
liquid content
contained within a sufficient portion of the ore material. Preferably
'sufficient portion' in
this context refers to >90 % of the ore material. The assembly will comprise
an
electromagnetic generating source, such as a microwave generator.
[0038] In one form of the present invention, the step of:
irradiating the ore material with electromagnetic energy,
comprises the movement of the ore material through an applicator or cavity.
Alternatively, the step of:
irradiating the ore material with electromagnetic energy,
comprises exposing the ore material to the electromagnetic energy in batch
mode.
[0039] Advantageously, the movement of the agglomerates past an
electromagnetic
energy zone as a bed on a conveyor or a moving bed of agglomerates in a tube,
pipe or
other enclosed structure, facilitates the homogenous irradiation of the
agglomerates
with electromagnetic energy.
[0040] Preferably, the agglomerates pass the electromagnetic energy zone on a
conveyor as a bed of agglomerates.
[0041] The step of:
irradiating the ore material with electromagnetic energy,
comprises exposure with a continuous or pulsed source of radio frequency
energy.
[0042] Irradiating the ore material preferably comprises creating a power
density ranging
between 1x105 to 1x1012 w/m3 in the liquid phase of the ore material. It will
be
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appreciated that the power density employed will be dependent on at least the
form of
the ore material, liquid content in the ore material, the size of the ore
material, the mass
in any cavities of the ore material, the dielectric properties or conductivity
of the liquid,
the frequency of the applied electromagnetic energy radiation and the duration
of
electromagnetic energy irradiation.
[0043] It will be appreciated that the step of;
irradiating the ore material with electromagnetic energy,
includes controlling the electric field strength of the electromagnetic energy
and/or the
duration of electromagnetic energy irradiation to ensure the ore material is
not overly
exposed to electromagnetic energy, to minimise undesirable heating of the
agglomerates. Undesirable heating of the agglomerates may result in, the
formation of
micro-cracks that will weaken the agglomerates and/or sintering of the
agglomerates
that will alter the chemical properties of the minerals present with the
agglomerates.
[0044] Preferably, the ore material is irradiated with continuous source of
electromagnetic energy for less than about 10 seconds.
[0045] Preferably the average diameter of the ore material is substantially
unaltered by
the step of;
irradiating the ore material with electromagnetic energy.
[0046] The step of:
acid leaching the ore material,
is preferably conducted using at least one of the following, sulphuric acid
(H2SO4) or
ferric acid (H2Fe04) or a combination of both.
[0047] In one form of the present invention, the step of;
acid leaching the ore material,
is followed by a further step of;
recovering metal values from the pregnant liquor solution from the step of
acid
leaching the ore material with electromagnetic energy.
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[0048] In accordance with the present invention, there is provided an ore
material
comprising micro-channels, wherein the micro-channels are formed by the
preferential
heating of the liquid in the ore material.
[0049] Preferably the ore material comprising micro-channels is a copper,
nickel or
uranium-containing ore.
[0050] Preferably, the ore materials comprising micro-channels may be made
from a
starting material that includes the ore, ore particles, agglomerates formed
from ore
particles or any other form of ore material that has a liquid content.
BRIEF DESCRIPTION OF DRAWINGS
[0051] The present invention will now be described, by way of example only,
with
reference to the following figure in which:
[0052] Figure 1 is a schematic flow sheet of a method for treating an ore
material with
electromagnetic energy, in accordance with the first embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0053] Figure 1 shows a schematic flow sheet of a method for treating an ore
material
with electromagnetic energy in accordance with the first embodiment of the
present
invention, comprising the steps of:
crushing 14 of the ore 12;
agglomerating 16 the crushed ore particles;
irradiating 18 the agglomerates with electromagnetic energy;
acid leaching 20 the agglomerates irradiated with electromagnetic energy; and
recovering 22 the metal values.
[0054] In one embodiment of the invention, a uranium ore 12 is supplied to a
primary
crusher and is crushed 14 to a particle size less than 5 cm.
[0055] In an agglomeration step 16, the crushed uranium ore particles are
mixed with a
solution of sulphuric acid and water to agglomerate the particles, as known by
those
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skilled in the art. The agglomerates after leaching have a liquid content in
the range of
about 5 w/w% to about 30 w/w% and more specifically a liquid content of +/-
10% w/w.
[0056] The agglomerates are fed as a bed to an electromagnetic energy
treatment
assembly to be irradiated with electromagnetic energy 18, by way of a conveyor
or
chute under vertical flow 24. The electromagnetic energy treatment assembly
may be
provided in the form of a microwave treatment assembly. The microwave
treatment
assembly includes a source in the form of a microwave generator that generates
microwaves. The bed of agglomerates on the moving conveyor pass a microwave
energy zone, which is created by the microwave generator. The moving
agglomerates
are exposed to a continuous source of microwave energy with electric field
strength
sufficient enough to create a power density ranging between 1x105 to 1x1012
w/m3 in
the liquid phase of the ore material for lOs or less. The operating
conditions, such as
the electric field and the duration of microwave energy exposure, are selected
to ensure
that the microwave treatment causes only localised heating of the liquid
content within
the agglomerates.
[0057] The microwave energy exposure cures the agglomerates and heats the
liquid in
the agglomerates, forming vapour. The vapour forces its way to the surface of
the
agglomerates resulting in the formation of micro-channels in the agglomerates.
[0058] The agglomerates irradiated with microwave energy are stacked in heaps
with
heights ranging between 20 m to about 50 m for subsequent leaching 20. The
leach
solution, which is a sulphuric acid solution is applied to the top or upper
surface of the
heaps and allowed to percolate through the heap. The micro-channels formed
during
the irradiation step assist the percolation of the leach solution through the
agglomerates, thereby to increase leaching rates and recoveries. The
percolated
solution is collected at the bottom of the heaps as the pregnant leach
solution (PLS).
The PLS may be recycled to the heap, collected for the recovery of metal
values or a
combination of both. For the recovery 22 of metal values standard processes
that are
known in the art are employed.
Modifications and variations such as would be apparent to the skilled
addressee are
considered to fall within the scope of the present invention.
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