Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE EXTRACTION OF VALUABLE METALS
This invention relates to the recovery of one
or more valuable metals, such as gold, copper, nickel,
molybdenum and manganese, from matter contalning such
metals. Such matter may be in the form of ores or
glacial deposits or in the form of tailings, slimes,
calcined ores, or other discarded materials which have
already-been processed ln so~e way, but which it is.now
economically viable to re-process.
It is commonplace for freshly mlned ores, and
materials from mine dumps which are to be further
treated, to be transported for comparatively large
distances, such as several miles, to a processing
plant. The ore of dump material is usually most
conveniently transported as a slurry through suitable
pipelines. When the slurry reaches the processing
plant it is subJected to leaching and subsequent
extraction in specially designed apparatus. The
overall cost of providing pipelines ls high, especially
as it is often necessary to carry out at least the
leaching process at elevated temperatures.
According to this invention, in a process for
recovering valuable metal from matter containing such
metal in which the matter is caused to pass in the form
of a slurry through a pipeline, one or more reagents
are supplied to the pipellne so that leaching
conditions prevail in at least part of the pipeline and
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the desired valuable metal is recovered at a recovery
plant downstream of the pipellne.
Preferably, the matter ls caused to pass
through the pipeline by in~ection of steam and/or
heated compressed alr or other gases into the plpeline,
a method whlch provldes both motlvatlng force and heat
without the presence of moving parts, as ln
conventional pumps. However, especially when heat is
not required for leaching~ conventional pumping means
may be used. ~n the case of alr, the addltlonal
advantage is gained of a source of oxygen for oxidation
where leaching condltions are advantaged;
alternatively, even stronger oxidlslng gases can be
used where needed, e.g. chlorine. Similarly, a motive
force of a neutral or reducing gas, e.g. H2S can be
used.
The material should be reduced to a suitable
particle size to allow lts transport through a pipeline
in slurry form, for example to a particle size of less
than 350 u, more preferably less than 180 u. The
liquid used to slurry the material being processed is
preferably a non-corrosive component of the leaching
reagent, such as water or brine. More corrosive or
environmetally ob~ectional components of the leaching
reagent, such as dilute n~tric acid mixed with
sulphuric acid, or cyanide, are then added further down
the pipeline so that as much as posslble of the
plpellne is sub~ected only to non-corroslve fluids.
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Envlronmentally ob~ectionable material, such as
cyanide, is in~ected in totally enclosed conditions.
The steam and/or compressed air may be
in~ected at the upstream end of the pipeline and/or at
one or more inJection points along the length of the
pipeline. If desired, a separation stage can be
provided adjacent the upstream end of the pipeline for
removing soluble metal values, while allowing the
remainder of the slurry to pass along the pipeline for
leaching.
While the use of any conventional leaching
agent within the pipeline is contemplated, such as
cyanide or thiourea, preferred leaching agents comprise
a source of halide ions and an oxidising agent, such as
nitric acid up to 35% with salt solutlon of 10% NaCl.
Any suitable method may be used to recover the desired
valuable metals from the leach liquor.
According to a further aspect of the
invention, extraction of the valuable metal from the
leach liquor may also be carried out in the pipeline
simultaneously with, or downstream of, the leaching.
Further pre~erred features of the invention
will now be described with reference to the
accompanying flow diagram.
The diagram shows a slurry head 2 feeding
slurry to a pipeline 4 which transports slurry to a
processing plant 6. The slurry head 2 is conveniently,
although not necessarily, ad~acent a mine supplying ore
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from which valuable metals are to be extracted, or near
a dump containing previously processed tailings,
slimes, partially calcined ores, etc., which are worth
processing further, The material to be processed, if
necessary, is ground, for example by ball milling, to a
sufficiently small particle size to allow its transport
as a slurry. This particle size will depend on the
nature of the material being processed and the size of
the pipeline used for transportation. In general, to
prevent settling of the slurry in the pipeline, it is
desirable to have a particle size less than 350 u, more
preferably less than 170 to 180 u. If desired sand, or
other suitable material may be introduced to the
pipeline with the material to be processed so that
attrition occurs as a result of turbulence within the
pipeline to give a material of fine particle size
which can be more readily leached. Examples of
materials which can be advantageously treated in this
way are calcined ores.
~9 Care must be ta~en that a material for
attrition, such as coarse sand, does not adversely
affect the materials present in the pipeline, such as
an absorbent (e.g. carbon) for the leached products.
While attrition may occur throughout the pipeline, it
may be more convenient to provide a special section for
attrition, such as coarse sand or hard sintered
ceramic pellets. The section may be suitably llned to
resist wear and may have a reduced diameter to increase
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turbulence.
The ground material is slurried with a non-
corrosive component of the leach liquor, such as brine.
Quantitles of liquld are ad~usted to give a suitable
speed and volume of flow through the pipeline. The
usual solids content of flowable slurries is in the
range of 40 to 60 per cent by weight but higher and
lower pulp densities are possible.
~he slurry enters pipeline 4 and is
transported along the pipeline by the motive force
provided by in~ection of steam and/or hot air from
in~ection point 8. While in~ection point 8 is shown at
the upstream end of the pipeline, it may be positioned
downstream of the slurry head 2 and one or more
additional in~ection points 10 may be provided along
the pipeline.
The pipeline 4 is of any suitable material to
withstand the materials passing through, for example
synthetic materials, such as polyvinyl chloride (which
can withstand considerable pressure within the pipe~
or mètal tubes lined with synthetic materials.
Different sections of the pipeline may be made of
different materials. Thus, the initial section, in
contact only with a brine slurry, may be o~ cheap
material, such as asbestos cement. The pipeline may be
of any desired length, for example up to several miles,
or comparatively short. If the slurry head and
processing plant are close together, the pipeline may
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be labyrinthine or splralled to give a longer resldence
time, The pipeline may vary ~n diameter, for example
from 4 to 12 inches. It may be buried under~round
to conserve heat. If necessary, for the leaching
process, additional heat may be supplied at one or more
selected places, for example by electrical heating or
steam ~acket.
The steam and/or hot air, for example
supplied from a pressure in~ector with a venturi at a
pressure of 8 to 10 atmospheres, provides motive force
for transporting the slurry along the pipeline, also
heats the slurry to give the correct temperature for
leaching and additionally helps to maintain sufficient
agitation wlthin the pipeline to promote the leaching.
A suitable minimum speed of slurry is of the order of 4
to S ft./sec. and a suitable overall throughflow is of
the order of 25 tons per hour, although higher values
are, of course, possible.
As the brine slurry passes through the first
portion of pipeline 4, some soluble metal salts
containing the desired metal will be extracted into the
brine. In order to recover these soluble metal-
containing materials, a separatlng tank 12 is
positioned, for example, about 200 yards along the
pipeline and the soluble extract withdrawn for recovery
of the deslred metals while the slurry itself continues
to flow along the pipeline, optionally with further
addition of brine.
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At one or more convenient points 14, so as to
allow sufficlent residence time for leaching ln the
pipeline, for example from half to one hour, the
remaining component or components of the leachlng
reagent are added. Suitable leaching components are
oxidising agents, such as a mixture of dllute nitric
and sulphuric acids. Of course, other leaching agents,
such as sodium cyanide in an alkaline medium, can be
employed and liquids other than brine can be used to
slurry the feedstock material, such as halides or a
hypohalite (for example sodium hypochlorite). A
mixture of leaching agents may be used, concurrently or
consecutively, such as the use of sodium hypochlorlte
followed by the use of an acid leaching agent. It may
be possible to leach certain materials, such as
calclned ores, under relatively mild conditions,
for example using only hot brine to release up to two
thirds of the gold values present in a starting
material.
The processing plant 6 at the downstream end
of the pipeline can contain any suitable apparatus for
extracting and recovering the desired metals from the
leach liquor. Thus, for example, the leach liquor and
pulp may be introduced to a separating vessel 16 and
the leached unwanted pulp withdrawn on line 18 while
the separated liquor passses to one of two absorpt$on
vessels 20 ~illed with an absorbent for the desired
metals, such as cellulose chaff, activated carbon or
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diatomaceous earth, The metals are then recovered from
the absorbent in recovery unit 22. Two vessels 20 are
provlded so that one can be stripped while the other is
being loaded.
If the metal being recovered is suitable it
is possible for not only the leaching but also the
extraction to take place within the pipeline 4. Thus,
for example, an absorbent with an active surface, such
as cellulose chaff, activated carbon or diatomaceous
earth, or specially formuiated resins, may be
introduced at one or more points to the pipellne before
or after the introduction of leaching agent, such as
acid, at 14. The absorbent, belng lighter than the
slurry, wlll tend to lie above the slurry, but the
sufficlent agitatlon ln the pipeline will cause mixing
to enable the desired leached metal values to be
extracted by the absorbent. The absorbent carrying the
desired metal can be separated at the end of the
pipeline from the unwanted pulp by a screen or other
suitable means.
A further example lies in the recovery of
gold, where a speclfic extractant for gold, such as
Rhodamine B, can be introduced at one or more points
along the pipellne wlth, for example, a further
extraction stage introduced where the Rhodamine B
carrying the gold values is taken up by a suitable
solvent, such as methyl isobutyl ketone or diisobutyl
ketone. Alternatively, the solvent may also be added to
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the pipeline, suitably in a widened section to
accommodate the additlonal flow volume.
It will be appreciated that the process
described above has several advantages. Thus, the
pipeline between the supply of ore and the processing
plant is being used for the dual purpose of transport
and as a leaching vessel and, possibly, as an
extraction vessel also. This reduces the cost of
equipment. The use of steam and/or hot air provides
both motive power for the slurry and heat to promote the
leaching reaction but does not interfere with the
reaction or cause corrosion. The use of steam is
particularly valuable when used for the processing of
difficult ores, such as sulphidic ores.
The leaching reagents suggested above
minimise corrosion problems, especlally when a non-
corosive agent, such as brine, is used to slurry the
feedstock material and the oxidising agent, such
as dilute nitric acid, added later in the pipeline.
As a pipeline may readily be buried
underground, expensive insulation costs can be avoided.
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