Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR SELECTIVE ACID LEACHING NICKEL AND COBALT FROM A MIXED
HYDROXIDE INTERMEDIATE
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for the sulphuric acid leaching of an
impure nickel
containing intermediate, to produce a solution containing substantially all of
the nickel and a
major portion of the cobalt and a solid residue containing substantially all
of the manganese
originally in the intermediate.
In particular, the process relates to the processing of a mixed hydroxide
intermediate,
preferably a nickel-cobalt-manganese-magnesium hydroxy-sulphate intermediate,
which
may also contain zinc and copper. Such intermediates are also known as Mixed
Hydroxide
Product (or Precipitate) or "MHP" or as referred to herein as a "mixed
hydroxide
intermediate".
Description of the Related Art
Recovery of nickel as an intermediate product for subsequent refining to a
metallic product is
well established, with mixed sulphide mattes from smelting operations and
mixed sulphide
precipitates from leaching operations being common examples.
Precipitation of intermediates from sulphuric acid leaching liquors as
hydroxides and
hydroxy-sulphates has been under consideration over an extended time period,
as
discussed for example in U.S. Patents 1,091,545, USP 2,899,300 and USP
3,466,144 and
Canadian Patent 618,826.
Nickel containing intermediates produced by addition of an alkali reagent are
commonly
referred to as mixed hydroxide precipitates (or products) or MHP, particularly
when they
contain significant quantities of cobalt and manganese and minor quantities of
zinc and
copper, as when they are derived from nickel laterite acid leach solutions or
nickel sulphide
acidic pressure oxidation leach solutions. In addition, if using magnesia as
the precipitating
agent, they typically contain some unreacted magnesium.
Such mixed hydroxide
intermediates typically contain 3% to 5% sulphur in the form of sulphate (9 to
15% sulphate),
so can more properly be termed a mixed hydroxy-sulphate or basic sulphate.
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Patent Application AU 2013904693 in the name of BHP Billiton SSM Development
Pty Ltd
summarises a number of ammonia leached based refining processes for mixed
hydroxide
intermediates. These processes are generally selective for nickel and cobalt
over
manganese. However, it has been found that mixed hydroxide intermediates
undergo a
number of phenomena, collectively known as "ageing", which reduce the
extraction of nickel
and cobalt in ammonia leaching processes and leads to a leach residue that is
difficult to
filter.
Patent Application WO 2012100293 in the name of The University of Queensland
describes
a process for selectively leaching nickel from MHP, while retaining cobalt in
the leach
residue solids. The process described in this application seeks to leach
nickel from MHP,
whilst preventing substantial leaching of cobalt and incidentally manganese.
This process
suffers from several disadvantages, including:
1. Cobalt, a valuable co-product of nickel refining, reports to the leach
residue, so
requiring separate re-leaching and separation from manganese.
2. Nickel-Cobalt separation is not perfect and there is significant cross
contamination of
these elements.
The present invention aims to overcome one or more of the difficulties or
disadvantages
identified in the prior art documents.
A reference herein to a patent document or other matter which is given as
prior art is not to
be taken as an admission that that document or matter was known or that the
information it
contains was part of the common general knowledge as at the priority date of
any of the
claims.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a process for the
selective leaching of
nickel and cobalt from a mixed hydroxide intermediate that has been produced
from the
processing of a nickel ore or concentrate also containing manganese, the
process including
the steps of:
a) providing a mixed hydroxide intermediate and forming a mixed hydroxide
intermediate slurry;
b) treating the mixed hydroxide intermediate slurry with an oxidizing agent
to
substantially oxidise the manganese present whilst minimising the oxidation of
cobalt and
nickel; and
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c) either consecutively or simultaneously to the oxidation step, leaching
the oxidised
slurry in an acid sulphate medium to produce a nickel and/or cobalt sulphate
solution
containing substantially all of the nickel and a major portion of the cobalt
and a solid residue
containing substantially all of the manganese in a resultant oxidised leach
slurry.
Preferably, contacting the mixed hydroxide intermediate with the oxidising
agent results in a
substantial portion of the manganese being oxidised to thereby cause it to be
stabilised in
the solid phase while a substantial portion of the nickel and a major portion
of the cobalt are
subsequently dissolved in the following acidic leach step.
Preferably, the oxidising agent has sufficient oxidising potential to oxidise
manganese(II) to
manganese (IV), and is added only in sufficient quantity to minimise oxidation
of cobalt(II) to
cobalt(III).
Suitably, the oxidising agent is selected from the group consisting of
persulphates,
peroxides, peroxymonosulphuric acid (Caro's Acid), sulphur dioxide-air
mixtures, sulphur
dioxide-oxygen mixtures, permanganates, perchlorates, ozone, oxides, oxygen
and chlorine.
Preferably, the oxidising agent is a persulphate.
In one embodiment, the oxidising agent is ammonium, sodium or potassium
persulphate,
hydrogen peroxide or Caro's acid. Ammonium, sodium or potassium persulphate
are
particularly preferred.
Preferably, the process includes the steps of:
(i) determining the stoichiometric amount of oxidising agent to be added to
the mixed
hydroxide intermediate slurry to cause the oxidation of a substantial
proportion of the
manganese; and
(ii) adjusting the amount of oxidising agent determined in step (i) based
on the amount
of manganese, cobalt and nickel that dissolves in step c).
In a preferred form, the acid sulphate medium is sulphuric acid, preferably a
concentrated
sulphuric acid.
An advantage of the process is that the leach residue is easy to filter,
regardless of the
ageing history of the mixed hydroxide intermediate. In a preferred embodiment
other metals
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contained in the mixed hydroxide intermediate may also be leached, for example
zinc and
copper. The process has the advantage of stabilizing the manganese in a solid
phase and
rejecting manganese impurities from the liquor stream prior to the recovery of
the metal
values and producing a leach residue which is readily filtered.
The mixed hydroxide intermediate product may be produced as an intermediate
product in
the processing of both nickel laterite and nickel sulphide materials including
concentrates. It
is also commonly referred to as a mixed hydroxide precipitate (or product), or
MHP, but
herein is referred to as a "mixed hydroxide intermediate".
The mixed hydroxide intermediate may be recovered from a sulphuric acid
leaching liquor
during the processing of a nickel laterite ore. For example, such intermediate
products are
produced when an alkali reagent such as magnesia or lime is used to raise the
pH of an
acidic sulphate solution to precipitate a nickel product as a mixed hydroxide
intermediate.
Such intermediates are also recovered from nickel sulphide acidic pressure
oxidation leach
solutions by the addition of a comparable alkali material.
Typically, a mixed hydroxide intermediate produced from processing a nickel
laterite or
nickel sulphide ore, contains the main elements of interest, namely nickel and
cobalt,
together with variable quantities of metals such as zinc and copper as well as
sulphur in the
form of sulphates, and impurities such as manganese, magnesium, iron and
calcium.
Sodium and chlorine, in the form of chloride, may also be present.
In a preferred embodiment, the process further includes the steps of treating
the resultant
oxidised leach slurry with ammonia and/or ammonia containing liquors to
progressively
convert the nickel and/or cobalt sulphate to nickel and/or cobalt ammine
sulphates in a
neutralised ammine leach slurry.
The neutralised ammine leach slurry may then be subjected to a solid/liquid
separation step
to produce a neutralised ammine leach solution containing substantially all of
the nickel and
a major proportion of the cobalt, and a leach residue containing a major
proportion of the
manganese.
In a preferred embodiment, the neutralised ammine leach slurry is blended with
a ground
nickel matte and/ or mixed sulphide and subjected to an ammonia pressure leach
step with
the addition of air and ammonia to produce an ammonia leach slurry.
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In a further embodiment, the neutralised ammine leach slurry may be blended
with the
ammonia leach slurry after the ground nickel matte and/or mixed sulphide has
been
subjected to the ammonia pressure leach step. This blended leach slurry may
then be
subjected to a solid/liquid separation step to produce an ammonia leach
solution that
contains substantially all of the nickel and a major proportion of the cobalt
together with a
leach residue containing a major proportion of the manganese.
The ammonia leach slurry from the ammonia pressure leach step may be combined
with
either the leach residue and/or the neutralised ammine leach solution and then
subjected to
a solid/liquid separation step to produce an ammonia leach solution and a
further residue
containing a major proportion of the manganese. This neutralised ammine leach
solution
may be combined with the ammonia leach solution to form a blended leach
solution
containing substantially all the nickel and a major proportion of the cobalt
for further
processing.
Copper may be removed from the blended leach solution with the addition of
steam and/or
sulphuric acid and/or sulphur to remove copper as a copper sulphide product.
The blended leach solution may then undergo oxydrolysis where it is oxidised
with air and
heated with steam to remove any remaining thiosulphates and convert
sulphamates to
sulphates.
Nickel may then be recovered from the blended leach solution by hydrogen
pressure
reduction, or other suitable means leaving a nickel depleted reduction end
solution. Cobalt
may be recovered from the nickel depleted reduction end solution by adding a
sulphiding
agent to recover cobalt, residual nickel and/or zinc as a mixed nickel/cobalt
sulfide or
nickel/cobalt/zinc sulphide product. Suitable sulfiding agents include
hydrogen sulphide,
sodium hydrosulphide, sodium sulphide or ammonium sulphide.
In a further embodiment of the invention, a mixed sulphide slurry may be
subjected to a
pressure oxidation step with the addition of oxygen to form a pressure
oxidation leach slurry.
The resultant oxidised leach slurry from the mixed hydroxide intermediate
oxidation step
may be either directly blended into the pressure oxidation step or blended
with the pressure
oxidation leach slurry to produce a blended leach slurry. The resultant
oxidised leach slurry
from the mixed hydroxide intermediate oxidation step may have undergone a
solid/liquid
separation step prior to the addition with the mixed sulfide slurry so as to
first form a
nickel/cobalt sulphate solution and a leach residue. The nickel/cobalt
sulphate solution may
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alternatively be added to the pressure oxidation leach slurry to produce the
blended leach
slurry which may then optionally undergo a solid/liquid separation step to
produce a blended
leach solution and a leach residue prior to further impurity removal and
nickel recovery.
The blended leach solution may be subjected to an iron and copper removal step
with the
addition of an ammonia solution to raise the pH to precipitate the iron as an
iron oxide, and
the addition of a sulphide product or sulphiding agent to precipitate copper
as a copper
sulphide. The iron oxide and copper sulphide may be removed as a residue
following a
solid/liquid separation step.
Zinc may be removed from the blended leach solution by an ion exchange or
solvent
extraction process.
Nickel may be recovered from the blended leach solution by adding an ammonia
solution to
form a nickel ammine solution and subjecting the nickel ammine solution to a
hydrogen
pressure reduction step to produce a metallic nickel product and a nickel
reduction end
solution.
Cobalt may be recovered by first separating the cobalt from the nickel in the
blended leach
solution by solvent extraction or ion exchange and then subjected to a
hydrogen pressure
reduction step or other suitable means to produce a metallic cobalt product
and a cobalt
reduction end solution.
Excess ammonium sulphate is formed through the process and may be recovered by
crystallisation of ammonium sulphate to form ammonium sulphate crystals. The
ammonium
sulphate crystals and/or any ammonium sulphate solution may be recycled to the
step of
neutralising the resultant leach slurry, the ammonia pressure leach step or
the hydrogen
pressure reduction step.
The nickel reduction end solution and the cobalt reduction end solution may be
combined
and treated with a sulphiding reagent in a mixed sulphide precipitation step
to produce a
cobalt/nickel sulphide which may then be recycled to either the pressure
oxidation step or
the iron and copper removal step.
Preferably, both the nickel and cobalt product are metallic nickel and
metallic cobalt
powders.
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A 'major portion' as used herein may refer to greater than 50%, preferably
greater than 60%,
more preferably greater than 70%, even more preferably greater than 80% in
relation,
independently, to both stabilisation of the manganese in the solid phase and
to dissolution of
the nickel and cobalt.
"Substantially all" as used herein, may refer to greater than 90%, preferably
greater than
95% in relation, independently, to both stabilisation of the manganese in the
solid phase and
to dissolution of the nickel and cobalt.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flowsheet of the oxidising, leaching, neutralisation
and solid-liquid
separation phases of the preferred embodiment of the invention.
Figure 2 is a schematic flowsheet where the oxidising and leaching steps have
been
combined into a simultaneous step.
Figure 3 is a schematic flowsheet of a preferred embodiment of the invention
involving
integration into a Nickel Sulphide Matte or Mixed Sulphide Ammonia Pressure
Leach.
Figure 4 is a schematic flowsheet of the product recovery phase of the process
described in
Figure 3.
Figure 5 is a schematic flowsheet of a preferred embodiment of the invention
involving
integration into a Mixed Sulphide Acid Sulphate Pressure Oxidation Leach.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with reference to the accompanying
figures. It is to
be understood that the figures or illustrations of the preferred processes of
the invention
should not be taken as limited to particular features described herein.
First Embodiment: Integration into Nickel Sulphide Ammonia Pressure Leach
As illustrated in Figure 1, mixed hydroxide intermediate 100 is water washed
110 using
desalinated water 120, to remove or partially remove contaminants. These
include
magnesium, calcium, sulphate, chloride, and sodium components. The water wash
can
consist of the washing of a filter cake on a filter, re-pulping of the mixed
hydroxide
intermediate in water to give a "water leach", a combination of these, or
other techniques
such as continuous counter-current decantation. Multiple stages of water
washing have
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been found to be beneficial as has extended leaching times of up to several
days. Multiple
contacts are especially advantageous for calcium removal, as calcium will
continue to leach
out of the mixed hydroxide intermediate, constrained only by its solubility
limit. An additional
benefit of the water wash has been found to be the "fixing" of most of the
remaining
magnesium in the mixed hydroxide intermediate, so that it does not
substantially dissolve in
downstream ammonia leaching operations. The waste wash liquor 130 must be
disposed of
separately to other refinery liquors, so the water washing step is preferably
carried out at the
location where the mixed hydroxide intermediate is produced.
The washed mixed hydroxide intermediate 140 is initially repulped 150 with
repulp liquor 160.
This repulp liquor 160 typically contains 0 to 20 g/L of titratable ammonia
and 0 to 200 g/L of
ammonium sulphate. It may also contain minor amounts of nickel (0 to 5 g/L)
and cobalt (0
to 0.5 g/L). The mixed hydroxide intermediate slurry 170, is oxidised 180
typically using
ammonium persulphate 190. The oxidised repulp slurry 200 is then leached 210
with
sulphuric acid 220. Leaching is carried out preferably at 50 to 60 C for 3 to
4 hours, with a
target terminal pH of 2. Relevant metal extractions are: Nickel: > 95%,
Cobalt: > 80% and
Manganese: < 0.5%. The resultant oxidised leach slurry 230 is neutralised 240,
using
ammonia 250, and ammonia leach liquor 260 to form an ammine leach slurry.
Ammonium
sulphate 270 is also added to stabilise the resulting metal ammines in
solution. The
neutralised ammine leach slurry 280 is subjected to solid-liquid separation
290, to produce a
neutralised ammine leach solution 300 containing substantially all of the
nickel and a major
portion of the cobalt originally in the washed mixed hydroxide intermediate
and a Leach
residue 310 containing a substantial portion of the manganese originally in
the washed
mixed hydroxide intermediate. The solid-liquid separation step may be
thickening, filtration,
or a combination of both and preferably includes a washing step to remove
soluble nickel
and cobalt from the manganese containing leach residue.
An alternative embodiment to this is shown in Figure 2 where the oxidation
step 180 (of
Figure 1) and the leaching step 210 (of Figure 1) are conducted simultaneously
in combined
oxidation and leaching step 210.
Figure 3 shows a further embodiment where the neutralised ammine leach
solution 300 is
forwarded to Leach Liquor Blending 510 where it is blended with nickel matte
or mixed
sulphide ammonia leach liquor 480. Alternatively the neutralised ammine leach
slurry 320
may be sent directly to solid liquid separation 470, or at any suitable point
within the
Ammonia Pressure Leach 430.
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The steps from Copper Boil 530 through to ammonium sulphate crystallisation
720 as shown
in Figure 3 and 4 are carried out in a conventional manner. The blended leach
solution 520
is forwarded to Copper Boil 530. Here copper is precipitated from solution as
copper
sulphide product 560, and titratable ammonia levels are adjusted, by the
addition of steam
540 and sulphuric acid 550, to a ratio of around 2 moles of ammonia per mole
of nickel, in
preparation for nickel reduction. The blended leach solution 570 is forwarded
to Oxydrolysis
580 where it is oxidised with air 590 and heated with steam 600 to remove any
remaining
thiosulphate, polythionate and sulphamate compounds which would otherwise
cause product
contamination. The blended leach solution 610 then flows into Nickel Pressure
Reduction
620, where hydrogen 630 is added in a batchwise manner to an agitated
Autoclave to
produce nickel metal powder. Nickel depleted reduction end solution 640
undergoes powder
¨ solution separation 650. Metallic nickel powder product 660 may be
transformed into other
forms such as briquettes by drying and compacting in a conventional manner.
The nickel
depleted reduction end solution 670 is then treated with a sulphiding reagent
such as
hydrogen sulphide 690 in a mixed sulphide precipitation step 680 to produce a
mixed cobalt-
nickel-zinc sulphide product 700. The barren ammonium sulphate solution 710
passes to
ammonium sulphate crystallisation 720. Steam 730 is used to evaporate the
water for
crystallisation. Crystalliser configurations can include multiple effect
evaporators, vapour
recompression or a combination of both. Ammonium sulphate crystal slurry 740
undergoes
crystal ¨ liquor separation 750 and drying 780. The liquor 760 may be returned
to
crystallisation as shown in Figure 4. Ammonium sulphate crystal is directed to
both product
800 and Ammonium Sulphate Crystal Dosing 790 of Leach liquor.
Further Embodiment: Integration into Mixed Sulphide Acid Sulphate Pressure
Oxidation Leach
With reference to Figure 5, after repulping 150, oxidation 180 and leaching
210, the leached
slurry 230 is subjected to solid-liquid separation 295, to produce a
nickel/cobalt sulphate
solution 305 containing substantially all of the nickel and a major portion of
the cobalt
originally in the washed mixed hydroxide intermediate and a Leach residue 315
containing a
substantial portion of the manganese originally in the washed mixed hydroxide
intermediate.
The nickel/cobalt sulphate solution 305 is forwarded to Leach Liquor Blending
515 where it is
blended with pressure oxidation leach slurry 465 to create a blended leach
slurry 525.
Alternatively the resultant oxidised leach slurry 325 from the mixed hydroxide
intermediate
oxidation step may be sent to the pressure oxidation leach 435, or directly to
Leach Liquor
Blending 515. An optional solid/liquid separation step may occur here to
create a blended
leach solution.
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The steps from Iron and Copper Removal 535 through to ammonium sulphate
crystallisation
725 Figure 5 are carried out in a conventional manner. The blended leach
solution or
blended leach slurry 525 is forwarded to Iron and Copper Removal 535 where
anhydrous
ammonia 545 is added to raise the pH and precipitate iron. Copper is
precipitated as a
sulphide by the addition of nickel-cobalt sulphide 555, or hydrogen sulphide
995. The nickel-
cobalt sulphide may be sourced from the "strip" mixed sulphide precipitation
step 685 carried
out on the pressure reduction end solutions. Discharge from Iron and Copper
Removal 575
undergoes solid / liquid separation 585. The iron oxide / copper sulphide
residue 565 is
typically recycled to recover the contained nickel and cobalt values. The iron
and copper
free blended leach solution 595 undergoes a zinc solvent extraction step 815,
typically using
a phosphorous based extractant such as a phosphoric acid, phosphonic acid or
phosphinic
acid dissolved in a hydrocarbon diluent. Most commonly used extractants are Di-
2-
ethylhexylphosphoric acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl
ester, and bis-
(2,4,4-trimethylpentyl) phosphinic acid. Ammonia 825 is typically added for pH
control in
extraction and sulphuric acid 835 is used to strip the zinc from the loaded
organic extractant,
to produce a zinc sulphate solution 845. A loaded organic wash step is
typically used
between the extraction and stripping steps to remove co-loaded cobalt and
nickel from the
organic.
The zinc free blended leach solution 855 undergoes a cobalt solvent extraction
step 865,
typically using one of the aforementioned phosphorous based extractants
dissolved in a
hydrocarbon diluent. Ammonia 875 is typically added for pH control in
extraction and
sulphuric acid 885 is used to strip the cobalt from the loaded organic
extractant, to produce a
cobalt sulphate solution 1895. A loaded organic wash step is typically used
between the
extraction and stripping steps to remove co-loaded nickel from the organic.
The purified nickel blended leach solution 895 proceeds to nickel reduction
solution
preparation 905, where anhydrous ammonia 915 and ammonium sulphate 925 are
added to
form a nickel annmine solution 615, which is pumped into Nickel Pressure
Reduction 625.
Hydrogen 635 is added in a batchwise manner to an agitated Autoclave to
produce nickel
metal powder. Nickel reduction discharge undergoes powder ¨ solution
separation to
produce a metallic nickel powder product 665 that may be transformed into
other forms such
as briquettes by drying and compacting in a conventional manner. Cobalt
sulphate solution
1895 is treated in a similar manner to the nickel sulphate solution, to
produce cobalt powder
1665 and a cobalt reduction end solution 1675. The nickel reduction end
solution 675 and
cobalt reduction end solution 1675 are combined and treated with a sulphiding
reagent such
as hydrogen sulphide 695 in a mixed sulphide precipitation step 685 to produce
a cobalt-
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nickel sulphide 705. The cobalt-nickel sulphide 705 is typically recycled to
the pressure
oxidation leach 435 or iron and copper removal 535. The barren ammonium
sulphate
solution 715 passes to ammonium sulphate crystallisation 725. Steam 735 is
used to
evaporate the water for crystallisation. Crystalliser configurations can
include multiple effect
evaporators, vapour recompression or a combination of both. Ammonium sulphate
crystal is
directed to both product 805 and Ammonium Sulphate Crystal Dosing 795 of
nickel and
cobalt reduction feed solutions.
Examples
Example 1
Typical assays of mixed hydroxide intermediate feeds are shown in the table
below. In
addition, a typical nickel matte refinery feed and precipitated mixed sulphide
analyses are
provided as leach solutions from these sources will often be blended with the
leach liquor
from the invented process.
TABLE 1
Refinery Feeds Analysis, wt% dry basis
Ni Co Mn Mg Fe Al Ca S Zn Cu
Typical Mixed
47 1.7
2.0 1.5 0.13 0.04 0.09 4.4 0.31 0.03
Hydroxide Intermediate
Aged Mixed Hydroxide
45 1.6
1.7 1.5 0.5 0.07 0.1 3.7 0.27 0.03
Intermediate
Typical Nickel Matte 70.5 0.72 - 3.75 20 -
3.1
= _________________________________________________________________________
Typical Precipitated
55 5 1 35 1 0.1
Mixed Sulphide
Those skilled in the art would understand that the compositions of the feeds
can vary over a
significant range from those presented above.
Mixed hydroxide intermediates can be highly variable in composition. Iron,
aluminium and
silicon levels vary depending on the efficiency of upstream impurity removal
processes.
Manganese and cobalt levels vary depending on their concentration relative to
nickel in the
feed solution to the hydroxide precipitation step, which ultimately reflects
on the ore or
concentrate feed composition to the leaching process upstream of the mixed
hydroxide
precipitation step.
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Nickel matte may have differing levels of iron content, depending on the
extent to which iron
is removed in the smelter converting process. Copper and cobalt levels can
also vary
significantly, depending on the concentrate feed to the smelter and the
converting process
used.
Mixed sulphide precipitates will have varying levels of cobalt, also depending
on the on the
ore or concentrate feed composition to the leaching process upstream of the
mixed sulphide
precipitation step.
Example 2 - First example of leaching MHP
A bench scale test using the process of the invention was carried out as
follows:
1366 grams of "as received" aged mixed hydroxide intermediate, containing 698
grams of
dry solids, of the composition shown in example 1 above was slurried in 802 mL
of deionised
water. The slurry was agitated while 37 grams of ammonium persulphate was
added,
calculated to be the stoichiometric quantity required to oxidise the contained
manganese
from the 2+ to the 4+ oxidation state. Under continued agitation, 503 grams of
98%
sulphuric acid was added to the oxidised slurry to give a terminal pH target
of 2. Leaching
was continued for 8 hours, with the temperature controlled at 60 C. Solid-
liquid separation
was carried out using a laboratory pressure filter, of 0.005 m2 filtration
area, with a feed
pressure of 600 kPag, using a Machery-Nagel MN1672 filter paper as the
filtering medium.
The compositions of the final solution and washed solids were as shown in the
following
Table:
TABLE 2
Ni, g/L Co, g/L Mn, mg/L
Leach Solution 191 5.0 0.5
Ni, % Co, % Mn, %
Washed Solids 5.1 7.4 23.6
A mass balance around the test showed that the nickel extraction was 99%, the
cobalt
extraction was 63% and the manganese extraction was 0.02%
Example 3 Second example of leaching MHP
A bench scale test using the process of the invention was carried out as
follows:
830 grams of "as received" aged mixed hydroxide intermediate, containing 462
grams of dry
solids, of the composition shown in example 1 above was slurried in 1617 mL of
deionised
water. The slurry was agitated while 12.1 grams of ammonium persulphate was
added,
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calculated to be the stoichiometric quantity required to oxidise the contained
manganese
from the 2+ to the 4+ oxidation state. Under continued agitation, 476 grams of
98%
sulphuric acid was added to the oxidised slurry to give a terminal pH target
of 1. Under
continued agitation, leaching was continued for 4 hours, with the temperature
controlled at
80 C. Solid-liquid separation was carried out using a laboratory pressure
filter, of 0.005 m2
filtration area, with a feed pressure of 600 kPag, using a Machery-Nagel
MN1672 filter paper
as the filtering medium. The compositions of the final solution and washed
solids were as
shown in the following Table:
TABLE 3
Ni, g/L Co, g/L Mn, mg/L
Leach Solution 89 3.0 123
Ni, (Y0 Co, % Mn, %
Washed Solids 3.6 3.47 35.4
A mass balance around the test showed that the nickel extraction was 99.7%,
the cobalt
extraction was 92.5% and the manganese extraction was 4.8%.
Example 4 - Combined oxidation and acid leaching of MHP
A bench scale using the process of the invention with a combined oxidation-
acid leach of
aged mixed hydroxide intermediate of the composition shown in TABLE 1 was
carried out as
follows:
830 grams of "as received" aged mixed hydroxide intermediate, containing 462
grams of dry
solids, of the composition shown in example 1 above was slurried in 1617 mL of
deionised
water. The slurry was agitated while 427 grams of 98% sulphuric acid was added
to give a
terminal pH target of 1. After 1 hour, 12.1 grams of ammonium persulphate was
added,
calculated to be the stoichiometric quantity required to oxidise the contained
manganese
from the 2+ to the 4+ oxidation state. Under continued agitation, leaching was
continued for
4 hours, with the temperature controlled at 80 C. Solid-liquid separation was
carried out
using a laboratory pressure filter, of 0.005 m2 filtration area, with a feed
pressure of 600
kPag, using a Machery-Nagel MN1672 filter paper as the filtering medium.
The
compositions of the final solution and washed solids were as shown in the
following Table:
TABLE 4
Ni, g/L Co, g/L Mn, mg/L
_Leach Solution 88 3.0 215
Ni, % Co, % Mn, %
Washed Solids 5.45 2.11 32.4
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14
A mass balance around the test showed that the nickel extraction was 99.6%,
the cobalt
extraction was 95.3% and the manganese extraction was 8.7%.
Comparative Example - Ammonia Leach of Aged MHP
A bench scale ammonia leach of aged mixed hydroxide intermediate of the
composition
shown in TABLE 1 was carried out as follows:
Aged mixed hydroxide intermediate, of the composition shown in Example 1 above
was
leached in an ammonia ammonium sulphate liquor of composition 42 g/L free
ammonia, and
440 g/L ammonium sulphate. Aged mixed hydroxide intermediate addition rate to
the liquor
was 27.5% solids (360 g of dry solids per litre of leach solution). Leaching
was continued for
2 hours, with the temperature controlled at 60 C.
Solid-liquid separation was carried out using a laboratory pressure filter, of
0.005 m2 filtration
area, with a feed pressure of 600 kPag, using a Machery-Nagel MN1672 filter
paper as the
filtering medium. The compositions of the final solution and washed solids
were as shown in
the following Table:
TABLE 5
Ni, g/L Co, g/L Mn, g/L
Leach Solution 63.6 3.0 0.16
Ni, % = Co, % Mn, cYo
Washed Solids 23.2 0.71 3.2
A mass balance around the test showed that the nickel extraction was 76%, the
cobalt
extraction was 83% and the manganese extraction was 5%.
This test illustrates that aged mixed hydroxide intermediate leached in
ammonia solutions
has relatively poor extraction characteristics, compared to the invention.
CA 02949580 2016-11-24
FIGURE 6 is a graphical representation of the manganese and nickel leach
extractions
measured over the range of cobalt extractions referred to in the invention.
10 100
= = = = % = =
= =
9 - = 99
=
8 - 98
=
7 - 97
u 6 - 96 o
i7:7)
w 5 - 95
= r<
c 4 - 94
a)
cis 3 - 93
2
2 - = Mn Extraction
92
=
Ni Extraction =
1 - 91
=
= = = =
=
=
0 == = _________________________________________________ 90
50 60 70 80 90 100
Cobalt Extraction, %
FIGURE 6
Referring to FIGURE 6, this shows that manganese extraction is less than 10%,
even as
cobalt extraction is increased from 55% to over 90%, while nickel extraction
at all times is in
excess of 97%.
Limitations to Addition of Mixed Hydroxide Intermediate
The limits of mixed hydroxide intermediate addition to an ammonia pressure
leach process
depend primarily on economic drivers. As the level of cobalt in refinery feed
increases, an
equivalent mass of nickel is typically not reduced and reports to mixed
sulphide. As a
saleable product, the revenue received for the contained nickel in this stream
is less than if
sold as nickel metal. One variant to overcome this limitation is to add the
cobalt hexamine
precipitation process, as discussed for instance in U.S. Patent 5,468,281,
into the flowsheet.
Zinc may reach an economic limit, as refiners of cobalt-nickel-zinc mixed
sulphide typically
have limits on zinc levels and/or apply penalties for high zinc feeds. This
limitation may be
overcome by producing separate zinc sulphide and mixed sulphide products by a
two stage
sulphiding process.
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16
As the relative quantity of mixed hydroxide intermediate increases, the
ability of the leach
process to produce a nickel leach solution of high nickel tenor may become a
limitation. This
again is an economic rather than a technical limitation, with a wide range of
nickel
concentrations contemplated, for instance, US Patent 6,949,232 stating, "The
leach solution
produced will typically contain from 40 to 110 g/L nickel..."
Thus, within the constraints described above, there is no particular
limitation to the relative
quantity of mixed hydroxide that may be processed.
Advantages of processing the mixed hydroxide intermediate in this manner are:
1. Nickel and cobalt recovery are maximised whilst minimising manganese leach
extraction, to give leach solutions compatible with existing sulphide matte
and mixed
sulphide refineries.
2. A way of dealing with a mixed hydroxide intermediate that has aged, giving
improved
nickel and cobalt recovery, and a leach residue that is readily filterable.
3. Nickel pressure reduction capacity is not compromised because the nickel
concentration is maintained, due to the co-processing of leach solutions.
4. Copper & zinc do not have to be removed from the mixed hydroxide
intermediate
feedstock.
The invention described herein is susceptible to variations, modification
and/or additions
other than those specifically described and it is to be understood that the
invention includes
all such variations, modifications and/or additions which fall within the
spirit and scope of the
above description.
Further patent applications may be filed in Australia or overseas on the basis
of, or claiming
priority from the present application. It is to be understood that the
following provisional
claims are provided by way of example only and are not intended to limit the
scope of what
may be claimed in any such future application.
Features may be added to or omitted from the provisional claims at a later
date so as to
further define or re-define the invention or inventions.
