Note: Descriptions are shown in the official language in which they were submitted.
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PROCESSES FOR EXTRACTION OF NICKEL WITH IRON-COMPLEXING AGENT
FIELD OF INVENTION
[0001] The present invention relates to processes for extracting base metals.
More
specifically, the invention relates to processes for extracting nickel from a
nickel-
containing source material.
BACKGROUND OF THE INVENTION
[0002] Current technology for extracting nickel from various sources includes
pyrometallurgical smelting of sulfide mineral concentrates, hydrometallurgical
leaching of
lateritic deposits in sulfuric acid, and chemical reduction of nickel in
lateritic deposits at
high temperature followed by leaching in ammonia, originally proposed by
Caron, US
Patent No. 1,487,145. Each of these processes suffer from technical or
commercial
drawbacks. For example, smelting involves fine milling and flotation to obtain
a sulfide
mineral concentrate, which is generally shipped to an off-site smelter,
resulting in large
transportation costs. Smelting is also generally not useful for ores
containing high levels
of magnesia. Leaching in sulfuric acid is not economic for highly acid
consuming ore
types, such as ultramafic deposits, due to high acid consumption and the
generation of
large amounts of magnesium and aluminium salts that require disposal. The
Caron process
is highly energy-intensive, due to the requirement for drying and milling the
ore.
[0003] Previous efforts to extract nickel and other base metals alloyed with
iron have
employed alkaline ammoniacal solutions (e.g., US Patent Nos. 3,845,189;
4,069,294;
4,187,281; 4,200,455; 4,229,213; 4,312,841; 4,322,390; 4,328,192; and
6,524,367).
Generally, the alloys were artificially generated from more oxidized minerals
by reduction
at high temperature, rather than from naturally occurring alloy minerals, such
as awaruite.
US Patent, No. 3,984,237, discloses a process for leaching of "low-grade
nickel complex
ore" in alkaline ammoniacal solution at high temperature and pressure in an
autoclave in
the presence of sulfite and carbonate.
[0004] US Patent No. 3,645,454 by Fowler discloses a physical method in which
an
awaruite-rich concentrate is produced from asbestos tailings by magnetic
means, and the
particle size of the awaruite grains increased by ball milling. The awaruite
grains are then
recovered from magnetite and gangue minerals by size-separation. A subsequent
US
Patent by Fowler (No. 3,677,919) describes leaching of a magnetically-produced
awaruite
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concentrate by iodine in a suitable solvent (e.g. methanol) and electrowinning
of nickel
from the same solvent as an alloy with iron.
[0005] US Patent Nos. 2,556,215 and 2,478,942 disclose processes for the
recovery
of iron or nickel, respectively, under high temperatures.
[0006] Niinae et al. disclose ammoniacal leaching of Ni from cobalt-rich
ferromanganese crusts using ammonium thiosulfate and ammonium sulfite as
reducing
agents (Niinae et al., Preferential Leaching Of Cobalt, Nickel And Copper From
Cobalt-
Rich Ferromanganese Crusts With Ammoniacal Solutions Using Ammonium
Thiosulfate
And Ammonium Sulfite As Reducing Agents, Hydrometallurgy 40: 111-121, 1996)
and
Tzeferis et al. disclose microbial leaching of non-sulfide nickel ores
(Mineral leaching of
non-sulphide nickel ores using heterotrophic micro-organisms; Letters in
Applied
Microbiology 18:209-213,1994).
[0007] In many known processes, significant amounts of nickel and cobalt are
not
recovered due to co-precipitation with iron(III), e.g. as Fe(OH)3.
SUMMARY OF THE INVENTION
[0008] In one aspect, the invention provides a process for extracting nickel
from a
source material including nickel and iron (the "nickel-containing source
material"), by
contacting the nickel-containing source material with an aqueous ammonia
solution that
includes an iron-complexing agent under suitable conditions, thus solubilizing
the iron and
extracting a sufficient quantity of the nickel from the nickel-containing
source material.
[0009] The nickel-containing source material may include one or more of an
ultramafic material, an iron-nickel alloy, a nickel sulfide, or an industrial
material. For
example, the nickel-containing source material may include awaruite,
josephinite or
serpentinite, or may include an industrial by-product such as asbestos
tailings. The source
material may be milled to a suitable particle size, for example, up to 300
microns or at
least 80% passing of milled product using a 48-mesh sieve (P-80 48 mesh). It
is to be
understood that, in general, a particle size that may be stirred in a stirred
tank is suitable
for use in a process according to the invention.
[0010] The iron-complexing agent may include a hydroxy-carboxylic acid,
including
but not limited to citric, tartaric, oxalic, glycolic, lactic and malic acid.
In one
embodiment, the iron-complexing agent may include citric acid or a salt
thereof. In
alternative embodiments, the iron-complexing agent may include tartaric or
malic acid or a
salt thereof. It is understood that the concentration of the iron-complexing
agent may be
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varied by a person of skill in the art. Accordingly, the amount of the iron-
complexing
agent may be adjusted as necessary up to its solubility limit. The iron-
complexing agent
may be capable of solubilizing and/or complexing a substantial portion of the
iron present
in the nickel-containing source material.
[0011] In alternative embodiments, the process may also include a sulfur-
containing
reductant, such as thiosulfate, which may be present at a concentration of at
least 0.1 mM
(0.01 g/L S2032 ).
[0012] In alternative embodiments, the suitable conditions may include a pH
that is
weakly alkaline e.g., ranging from about 7.0 to about 9.0 or any value
therebetween, such
as from about 7.5 to about 8.5, or about 8Ø It is understood that the
suitable pH would
depend on the temperature, and may be varied as appropriate by a person of
skill in the art.
[0013] In alternative embodiments, the suitable conditions may include a
temperature
ranging from about 20 C to about 90 C or any value therebetween. The process
may be
carried out at atmospheric pressure.
[0014] This summary of the invention does not necessarily describe all
features of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other features of the invention will become more apparent
from the
following description in which reference is made to the appended drawings
related to
embodiments of the invention wherein:
[0016] FIGURE 1 is a schematic diagram of the chemical processes involved in
awaruite leaching in alkaline ammonia-citrate-thiosulfate solution;
[0017] FIGURE 2 is a graph showing extraction of nickel (circles) and iron
(squares) from milled josephinite (pH 8.00, 50 C, I = 3.0 M, 1.5 M [NH3]total,
75 mM
citrate, 2.0 mM S2032");
[0018] FIGURE 3 is a graph showing the dependence of the initial rate for
nickel
extraction from josephinite at 50 C on thiosulfate concentration (note:
logarithmic
abscissa scale; error bars are one standard deviation in the fit);
[0019] FIGURE 4 is a graph showing the effect of citrate concentration on
final
extraction of nickel (circles) and iron (squares) from milled josephinite at
50 C;
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[0020] FIGURE 5 is a graph showing the extraction of nickel (circles) and iron
(squares) from milled josephinite at 25 C (pH 8.50, I = 3.0 M, 1.5 M
[NH3]total, 100 mM
citrate, 50 mM S2O32-);
[0021] FIGURE 6 is a graph showing a summary of nickel extraction from milled
josephinite at 25 C as a function of citrate and thiosulfate concentration (pH
8.50,1.5 M
[NH3]total, I = 3.0 M);
[0022] FIGURE 7 is a graph showing the extraction of nickel (circles) and iron
(squares) from milled serpentinite-awaruite ore (Sample FP001) (pH 8.00, 50 C,
I = 3.0
M, 1.5 M [NH3]total, 50 mM citrate, 2.0 mM thiosulfate);
[0023] FIGURE 8 is a graph showing nickel extraction from Sample FP226,
indicated as Ni % with respect to total nickel in the Sample, measured by
solution XRF;
standard conditions (pH 8.00, 50 C, 1.5 M [NH3]t tal, 50 mM citrate, 2.0 mM
S2032-; pulp
density 86 g L-1); based on total nickel
[0024] FIGURE 9 is a graph showing extraction of nickel from Sample FP226;
aggressive conditions (3.0 M NH3, 500 mM citrate, 2.0 mM S2032 , pH initially
8.9, 60 C,
160 g L-1 pulp density);
[0025] FIGURE 10 is a graph showing extraction of iron from Sample FP226;
aggressive conditions (3.0 M NH3, 500 mM citrate, 2.0 mM S2032 , pH initially
8.9, 60 C,
160 g L"1 pulp density);
[0026] FIGURE 11 is a graph showing rate constants (double exponential fit) of
nickel (white) and iron (grey) leaching for Sample FP226; aggressive
conditions;
[0027] FIGURE 12 is a graph showing extraction of nickel from Sample FP226;
aggressive conditions without citrate (3.0 M NH3, 2.0 mM S2032 , pH initially
8.6, 60 C,
130 g L"1 pulp density)
[0028] FIGURE 13 is a graph showing extraction of nickel from Sample FP226;
high pH conditions (1.5 M NH3, 2.0 mM S2032 pH 9.00, 50 C, 134 g L-1 pulp
density)
[0029] FIGURE 14 is a graph showing the comparison of the effect of different
leaching conditions on nickel extraction from Sample FP226 (see Table 4 for
conditions);
standard conditions (circles, solid line), aggressive conditions (squares,
dashed line),
aggressive conditions, no citrate (diamonds, dotted line), high pH (triangles,
dashed and
dotted line);
[0030] FIGURE 15a-d are graphs showing the effect of (a) thiosulfate (b)
citrate and
temperature (50 C -- circles, 60 C -- squares, 70 C -- triangles; 80 C -
diamonds) (c)
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ammonia (250 mM citrate) and (d) pH on nickel extraction (1.5 M [NH3]total, pH
9, 5 mM
thiosulfate, 50 mM citrate, 50 C except where noted) for Sample FP226, flask
tests;
[0031] FIGURE 16a-d are graphs showing the effect of (a) thiosulfate (b)
citrate
and temperature (50 C -- circles, 60 C -- squares, 70 C -- triangles; 80 C -
diamonds) (c)
ammonia (250 mM citrate) and (d) pH on iron extraction (1.5 M [NH3]t0 ,, pH 9,
5 mM
thiosulfate, 50 mM citrate, 50 C except where noted) for Sample FP226, flask
tests;
[0032] FIGURE 17 is a graph showing the effect of milling time on nickel
extraction
for 50 mM citrate (grey) and 250 mM citrate (black);
[0033] FIGURE 18 is a graph showing the effect of milling time on iron
extraction
for 50 mM citrate (grey) and 250 mM citrate (black) for Sample FP226, flask
tests;
[0034] FIGURE 19a-b are graphs showing the effects of citrate and thiosulfate
on
extraction of (a) nickel and (b) iron (3.0 M [NH3]total), (100 mM -- circles,
250 mM --
squares, 500 mM -- triangles) for Sample FP226; aggressive conditions;
[0035] FIGURE 20a-b are graphs showing the effects of citrate and [NH3]t tai
on
extraction of (a) nickel and (b) iron (2.0 mM S2032"), (1.5M [NH3]tota- --
circles, 3.0 M
[NH3]total -- squares) for Sample FP226; aggressive conditions;
[0036] FIGURE 21 is a graph comparing extraction using different iron-
complexing
agents (black: nickel, grey: iron); line is nickel extraction from `blank'
test for Sample
FP226, flask tests;
[0037] FIGURE 22 is a graph showing nickel extraction from Sample FP226,
measured by solution XRF; 70 C (pH 9.00 at RT, 1.5 M [NH3]totai, 100 mM
citrate, 5.0
mm S2032-, pulp density 136 g L-1); based on total nickel;
[0038] FIGURE 23 is a graph showing iron extraction from Sample FP226,
measured by solution XRF; 70 C (pH 9.00 at RT, 1.5 M [NH3]total, 100 mM
citrate, 5.0
mm S2032 , pulp density 136 g L-1); based on total iron;
[0039] FIGURE 24 is a graph showing pH change during leaching of Sample FP226
(70 C, pH 9.00 at RT, 1.5 M [NH3]totat, 100 mM citrate, 5.0 mM S2032 , pulp
density 136 g
L-1);
[0040] FIGURE 25 is a graph showing nickel extraction from the Brazilian
nickel
sulfide ore with 100 mM citrate (circles), 50 mM citrate (diamonds) and
without citrate
(squares). All other conditions excepting the citrate concentration were
identical in the
three tests.
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DETAILED DESCRIPTION
[00411 The invention provides, in part, a process for extracting nickel from a
nickel
source or feedstock that includes iron i.e., the nickel-containing source
material, using an
aqueous ammonia solution containing a suitable iron-complexing agent (e.g.,
citrate) and,
optionally, a suitable sulfur-containing reductant (e.g., thiosulfate).
[0042] Without being bound to any particular theory, the processes thought to
be
involved in leaching of the nickel-containing source material, such as a
nickel-iron alloy
particle, are shown in Figure 1 where citrate (or any agent capable of
complexing and/or
solubilizing Fe(III) in an aqueous ammonia solution) may be used to minimize
precipitation of Fe(III), which may inhibit the leaching of nickel, and
thiosulfate (or any
suitable sulfur-containing reductant) may be optionally used to facilitate
leaching of the
nickel. The sulfur-containing reductant may alter the surface of the alloy
particles and
thus enable leaching to occur and the complexing agent may inhibit the
precipitation of the
iron. Silicate minerals are generally inert to this leaching chemistry, and as
such, the
costly dissolution of magnesium and aluminium may be avoided.
[0043] The nickel-containing source material for use in processes according to
the
invention include, without limitation, nickel present in an ore or concentrate
thereof, or in
an industrial concentrate. In alternative embodiments, the nickel-containing
source
material may be obtained from naturally occurring terrestrial sources, such as
ores, or from
extra-terrestrial sources, such as meteorites, or from non-naturally occurring
sources such
as industrial materials. In alternative embodiments, the nickel-containing
source material
or feedstock may also include iron, cobalt, magnesium, manganese, copper or
mixtures
thereof. The nickel content of the ore may vary widely in type and amount,
depending on
the source of the ore. In alternative embodiments, the nickel can be present
both as
awaruite and in silicate minerals, and the nickel fraction in silicate
minerals may not be
extracted according to the processes according to the invention. In
alternative
embodiments, laterites are specifically excluded from sources of nickel for
use according
to the invention.
[0044] In alternative embodiments, the nickel-containing source material can
be a
nickel-iron alloy, a nickel sulfide or a nickel oxide. In alternative
embodiments, the nickel
sulfide can be present in mafic-ultramafic (also known as ultrabasic) rocks,
or as naturally-
occurring nickel-iron alloys.
[0045] In alternative embodiments, the nickel-iron alloy may be awaruite, also
known as josephinite or souesite. In general, awaruite has a variable
composition around
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Ni3Fe, with an isometric crystal system. Awaruite may be present in
serpentinite/asbestos
deposits or in ultramafic rocks. Accordingly, serpentinite/asbestos deposits
or ultramafic
rocks may be used as sources for awaruite. In alternative embodiments, other
nickel-iron
alloys such as kamacite, taenite or tetrataenite may be used. In alternative
embodiments,
wairauite may be used. In general, any nickel-containing material that is
alloyed with iron
and capable of being sulfidized with, for example, thiosulfate to form ammine
complexes,
may be used in processes according to the invention.
[0046] In alternative embodiments, the nickel-containing source material for
use in
processes according to the invention may be an industrial by-product such as
tailings (e.g.,
asbestos tailings).
[0047] In alternative embodiments, the nickel-containing material may be
milled to a
suitable particle size, for example, up to 300 microns or at least 80% passing
of milled
product using a 48-mesh sieve (P-80 48 mesh). It is to be understood that, in
general, a
particle size that may be stirred in a stirred tank is suitable for use in a
process according
to the invention.
[0048] In alternative embodiments, the nickel-containing source material may
be
subjected to known processes for extraction of materials prior to use in
processes
according to the invention.
[0049] The ammonia may be added as a salt, e.g. ammonium sulfate, ammonium
thiosulfate, ammonium citrate, ammonium chloride, ammonium carbonate, ammonium
phosphate, ammonium bromide, ammonium iodide, ammonium sulfite, ammonium
fluoride, ammonium sulfide, etc., and partially converted to ammonia by the
addition of a
base, e.g. ammonia, ammonium hydroxide, sodium hydroxide, etc. In alternative
embodiments, the ammonia may be added as liquid or aqueous ammonia and may be
partially neutralized by citric acid or sulfuric acid.
[0050] A suitable iron-complexing agent may be any agent, such as a di- or tri-
chelating ligand, that is capable of complexing and solubilizing Fe(III) in an
aqueous
ammonia solution. In general, a suitable iron-complexing agent is capable of
solubilizing
and/or complexing a substantial portion of the iron present in the source
material. By
"substantial portion " is meant at least about 10%, 15%, 20%, 25%, 30%, 35%,
40%, 45%,
50%, 55%, 60%, 65%, 70%, 75%. 80%, 85%, 90 %, 95%, 98%, 99% or about 100% of
the iron alloyed with nickel in the nickel-containing source material, or any
value between
about 10% to about 100% of the iron alloyed with nickel in the nickel-
containing source
material.
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[0051] Exemplary iron-complexing agents include, without limitation citric
acid,
glycolic acid, lactic acid, malic acid, tartaric acid, or other a-hydroxy
carboxylic acid-
based agents or siderophores dihydroxyphenylalanine (DOPA); 1-amino-w-
(hydroxyamino)alkanes, w-N-hydroxy amino acids, etc., or salts thereof. It is
understood
that the concentration of the iron-complexing agent may be varied by a person
of skill in
the art, depending on a number of factors, including the amount of iron
alloyed with nickel
in the nickel-containing source material, or the amount of solubilizable iron
in the nickel-
containing source material. Accordingly, the amount of the iron-complexing
agent may be
adjusted as necessary up to its solubility limit, as known in the art or
determined by
standard assays.
[0052] The iron-complexing agent may be added as a salt or in the acidic form
(e.g.,
citric acid); for citrate, a suitable form may be as an ammonium salt, e.g.
the dibasic,
(NH4)2C607H6, or tribasic, (NH4)3C607H5 form, or may be as a sodium salt. The
solubility
of exemplary citrate salts are set forth in Table 1.
Table 1.
Molar
Salt CAS Water solubility Ref MW solubility
sodium citrate
tribasic g/L at Sigma-
dihydrate [6132-04-3] 29.4 20 C Aldrich 294.1 0.1
ammonium g/L at Sigma-
citrate dibasic [3012-65-5] 226 20 C Aldrich 226.19 1.0
potassium
citrate g/L at Sigma-
monobasic [866-83-1] 115 20 C Aldrich 230.2 0.5
potassium
citrate tribasic g/L at Sigma-
monohydrate [6100-05-6] 324 20 C Aldrich 324.42 1.0
sodium citrate
dibasic g/L at Sigma-
sesquihydrate [6132-05-4] 263 20 C Aldrich 263.1 1.0
sodium citrate [18996-35- g/L at Sigma-
monobasic 5] 53.5 20 C Aldrich 214.11 0.2
ammonium g/L at
citrate tribasic [3458-72-8] N/A 20 C
g/L at
citric acid [77-92-9] 590 20 C 192.12 3.1
citric acid g/L at
monohydrate [5949-29-1] 651 20 C 210.14 3.1
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[0053] In alternative embodiments, citrate may be present in a concentration
of about
mM to about 3 M or greater, or any value therebetween such as about 50 mM, 75
mM,
100 mM, 200 mM, 500 mM, 750 mM etc.
[0054] A suitable sulfur-containing reductant may be any agent capable of
facilitating or accelerating leaching of nickel, for example, by accelerating
corrosion of the
nickel-containing source material and may include, without limitation,
inorganic sulfur
compounds such as thiosulfate, dithionite, bisulfide, sulfide, or elemental
sulfur, or may
include organic sulfur compounds such as thiols. It is understood that the
concentration of
the sulfur-containing reductant may be varied by a person of skill in the art.
Accordingly,
the amount of the sulfur-containing reductant may be adjusted as necessary up
to its
solubility limit, as known in the art or determined by standard assays.
[0055] The suitable sulfur-containing reductant, if used, may be added as a
salt. For
example, thiosulfate, if used, may also be added as an ammonium salt, e.g.
ammonium
thiosulfate, (NH4)2S203, or as a sodium salt. In alternative embodiments, the
thiosulfate
may be present at a concentration of at least 0.1 mM (0.01 g/L S2032-). In
alternative
embodiments, the thiosulfate may be present at a concentration of about 0.1 mM
to about
100 mM or any value therebetween, such as about 2mM to about 50 mM. In
alternative
embodiments, the thiosulfate may be present up to its solubility limit.
[0056] In alternative embodiments, non-ionic organic compounds, for example,
thiourea, thioacetamide, or thiols, may be used as suitable sulfur-containing
reductants.
[0057] In one exemplary embodiment, where nickel is present as awaruite and
citrate
and thiosulfate are used as the iron-complexing agent and sulfur-containing
reductant,
respectively, the leaching process may proceed as follows:
Ni3Fe + 9/402 + 2(NH4)3cit + 3NH3 + 3(NH4)2SO4 -> 3[Ni(NH3)4]SO4 +
(NH4)3[Fe(cit)2] + 9/2H2O
[0058] The nickel is dissolved as an ammine complex, and the iron as a citrate
complex. Thiosulfate does not appear in the above equation because it has a
non-
stoichiometric role. Without being bound to a particular theory, thiosulfate
may interact
with the surface of the alloy mineral, and may either break down the oxide
passive layer,
forming a non-protective sulfur passive layer, or convert the mineral surface
from an alloy
to a sulfide phase, which is amenable to leaching in an alkaline ammonium
citrate
medium.
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[0059] The nickel-containing source material may be subjected to leaching by
contacting the nickel-containing source material with an aqueous ammonia
solution that
includes an iron-complexing agent under suitable conditions, thus extracting a
sufficient
quantity of the nickel from the nickel-containing source material. A sulfur-
containing
reductant may be optionally used.
[0060] It is to be understood that the pressure, pH, temperature, time, etc.
may have
an effect on the amounts and concentrations of iron-complexing agent and
sulfur-
containing reductant required to achieve solubilization and/or complexation of
a
substantial portion of the iron and extraction of a sufficient quantity of the
nickel from the
nickel-containing source material - such conditions may be termed "suitable
conditions"
and may be determined by the skilled person based on the knowledge in the art
and the
teachings herein. In addition, the nickel-containing source material may
determine the
conditions used in processes according to the invention. By "sufficient
quantity" of the
nickel is meant at least at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%,
45%,
50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90 %, 95%, 98%, 99% or about 100% of
nickel present in the nickel-containing source material, or any value between
about 5% to
about 100% of nickel present in the nickel-containing source material, as
determined by
assays described herein or known in the art. In alternative embodiments, a
"sufficient
quantity" of the nickel is meant at least at least about 5%, 10%, 15%, 20%,
25%, 30%,
35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90 %, 95%, 98%, 99% or
about 100% of the nickel alloyed with iron in the nickel-containing source
material, or any
value between about 5% to about 100% of the nickel alloyed with iron in the
nickel-
containing source material, as determined by assays described herein or known
in the art.
[0061] The leaching may be carried out at a temperature range of about 20 C to
about
90 C, or any value therebetween, for example, about 25 C, 30 C, 35 C, 40 C, 45
C, 50 C,
55 C, 60 C, 65 C, 70 C, 75 C, 80 C, or about 85 C. In some embodiments, the
leaching
temperature may be as high as possible to achieve efficient leaching of a
sufficient
quantity of nickel present in the nickel-containing source material, as
determined by
assays described herein or known in the art, at atmospheric pressure. In
alternative
embodiments, the leaching temperature may be as high as possible to achieve
efficient
leaching of a sufficient quantity of nickel alloyed with iron in the nickel-
containing source
material, as determined by assays described herein or known in the art, at
atmospheric
pressure. In alternative embodiments, the leaching temperature may be at least
about
50 C. In alternative embodiments, the leaching temperature may be no greater
than about
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80 C. In alternative embodiments, the temperature may not exceed the boiling
point of
the leaching solution (e.g., 100 C at sea level in a non-pressurized vessel)
although it is to
be understood that the presence of salts, changes in pressure, etc. may alter
the boiling
point.
[0062] The leaching may be carried out for a period of time sufficient to
release a
sufficient quantity of nickel present in the nickel-containing source
material, or release a
sufficient quantity of nickel alloyed with iron in the nickel-containing
source material, as
determined by assays described herein or known in the art, into solution. In
alternative
embodiments, the leaching may be carried out for about 24 hours, 48 hours, 72
hours, or
longer. In alternative embodiments, the leaching may be carried out for a
period of weeks
or months, for example, in heap leaching processes.
[0063] The leaching may be carried out at a suitable pH, for example a weakly
alkaline pH. In alternative embodiments, the pH may range from about 7.0 to
about 9.0 or
any value therebetween, such as about 7.25, 7.5, 7.75, 8.0, 8.25, 8.5, or
about 8.75. It is
understood that the suitable pH would depend on the temperature, and may be
varied as
appropriate by a person of skill in the art. In alternative embodiments, the
pH may be
maintained at levels suitable for containment of the ammonia, to minimize loss
of the
ammonia.
[0064] In alternative embodiments, a suitable source of air or oxygen may be
streamed into the leaching tank.
[0065] The leaching may be carried out at atmospheric pressure. In alternative
embodiments, pressures higher than atmospheric pressure may be used and the
leaching
process may be carried out in a pressurized vessel.
[0066] The leaching may be carried out using conventional procedures known in
the
art. In general, the leaching may be carried out while agitating the leach
solution, for
example, in a stirred tank. In alternative embodiments, the leaching may be
carried out on
heaps.
[0067] The leaching may be carried out without substantial pre-treatment of
the
nickel-iron source material. For example, in the case of a nickel-containing
ore, the
leaching may be carried out without subjecting the ore to elevated
temperatures i.e.,
roasting. In some embodiments, the nickel-containing ore may be milled prior
to leaching.
In alternative embodiments, the nickel-containing ore may be in the form of a
concentrate.
In alternative embodiments, gravity and/or magnetic separations may be carried
out on the
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source material, and the residue leached according to the processes according
to the
invention.
[0068] Recovery of nickel from the leach solution can be by any of the
conventional
means such as solvent extraction and electrowinning, precipitation as a salt,
reduction with
hydrogen to the metallic form, etc. In alternative embodiments, the nickel
need not be
separately recovered from the solubilized iron or other components of the
leachate such as
copper or cobalt, which may be present in the leachate in significant amounts.
In
alternative embodiments, the leachate may be precipitated for example for
processing at a
remote site. In alternative embodiments, direct electrowinning from the
ammonia-citrate-
(thiosulfate) solution to form a ferronickel product may be desirable.
[0069] The present invention will be further illustrated in the following
examples.
[0070] EXAMPLES
[0071] Example I Josephinite tank test at 50 C)
[0072] In this example, a milled josephinite sample (nickel present primarily
as an
iron alloy) was leached in a stirred-tank at 50 C. The following salts were
added to 1.3 kg
of deionized water: 148.7 g of (NH4)2SO4, 20.9 g of Na2SO4, 33.1 g of
Na3cit.2H2O
(where cit = C6H5073-) and 0.5 g of Na2S2O3. The pH was adjusted to -8.6 with
43 mL of
2 M NaOH solution, and a further 157 g of water was added to bring the total
to 1.5 kg.
The solution was transferred to a jacketed vessel fitted with an oxygen
sparger, a pH probe
and a temperature probe and was thermally equilibrated to 50 C. Agitation was
achieved
by an impeller operating at 1200 rpm. Oxygen was bubbled at a constant rate of
30 mL
min 1. The pH was adjusted to 8.00 with further addition of NaOH solution (105
mL).
Finely milled josephinite (1.49 g) grading 61.3% Ni was added. Solution
samples were
taken at various intervals, filtered, and analyzed for nickel and iron by XRF.
The pH was
readjusted to 8.00 after sampling, as required. Nickel extraction was complete
after 23
hours (Figure 2). The final concentrations of nickel and iron were 662 and 171
ppm,
respectively.
[0073] The effects of citrate and thiosulfate concentration were established
at 50 C
(Figures 3 and 4). The citrate concentration affected the final nickel
extraction, whereas
the thiosulfate concentration strongly influenced the rate of leaching, and
high
concentrations were detrimental to the leaching rate.
[0074] Exam lp a II (Josephinite tank test at 25 C)
[0075] In this example, a milled josephinite sample (nickel present as an iron
alloy)
was leached in a stirred-tank at 25 C. The following salts were added to 1.3
kg of
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deionised water: 128.8 g of (NH4)2SO4, 42.6 g of Na2SO4, 33.9 g of (NH4)2Hcit
(where
Hcit = C6H6072-) and 11.9 g of Na2S2O3. The pH was adjusted to -8.6 with 123
mL of 2 M
NaOH solution, and a further 178 g of water was added to bring the total to
1.5 kg. The
solution was transferred to a jacketed vessel fitted with an oxygen sparger, a
pH probe and
a temperature probe and was thermally equilibrated to 25 C. Agitation was
achieved by an
impeller operating at 1200 rpm. Oxygen was bubbled at a constant rate of 30 mL
min- 1.
The pH was adjusted to 8.50 with further addition of NaOH solution (18 mL).
Finely
milled josephinite (1.48 g) grading 61.3% Ni was added. Solution samples were
taken at
various intervals, filtered, and analysed for nickel and iron by XRF. The pH
was
readjusted to 8.50 after sampling, as required. Nickel extraction reached 66%
after 24
hours (Figure 5). The final concentrations of nickel and iron were 414 and 131
ppm,
respectively.
[0076] The effects of varying the citrate and thiosulfate concentration on the
leaching
reaction were also determined at 25 C. Higher concentrations of both, compared
to 50 C,
were required for satisfactory leaching to occur (see Figure 6 and Table 2).
Table 2: Summary of nickel extraction (%) from josephinite at 25 C
Citrate (mM)
50 100 300 750
S2032" 2 - - 53.3 49.2
(mM) 10 39.6 - - -
50 53.5 66.6 - -
[0077] Example III (FP001 /Quebec sample tank test at 50 C)
[0078] In this example, a milled serpentinite ore sample (FP001, Quebec
sample),
containing nickel only in awaruite and silicate minerals, was leached in a
stirred-tank at
50 C. The elemental composition and mineralogy of Sample FP001, as determined
by
ICP-MS, were as follows:
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Table 3
FPOOI composition (ICP-MS)*
Al 1096 ppm Pb 11 ppm
Ba 3 ppm Mg 262057 ppm
Ca 533 ppm Mn 704 ppm
Cr 489 ppm Ni 3142 ppm
Co 88 ppm Sc 3 ppm
Cu 12 ppm v 2 ppm
Fe 27659 ppm Zn 59 ppm
La 63 ppm
* analysed for but not detected:
Sb, As, Bi, Cd, Hg, Mo, P, K, Ag, Na, Sr, TI,
Ti, W, Zr
Table 4
FP001 Mineralogy
Ni-Fe Alloy 0.39
Ni-Sulphide 0.00
Serpentine 62.26
Olivine 30.89
Clinopyroxene 0.01
Orthopyroxene 0.10
Amphibole 1.03
Talc 0.49
Quartz 0.10
Feldspars 0.01
Epidote 0.00
Chlorite 0.46
Micas/Clays 0.05
Other Silicates 0.00
Fe-Oxides 0.94
Chromite 1.67
Sulphides 0.01
Other Oxides 0.01
Carbonate 0.00
Mg-Oxide/Hydroxide 1.58
Other 0.00
Total 100.00
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[0079] The following salts were added to 1.3 kg of deionised water: 148.7 g of
(NH4)2SO4, 31.5 g of Na2SO4, 22.1 g of Na3cit (where cit = C614507 3-) and 0.5
g of
Na2S2O3. The pH was adjusted to -8.6 with 40 mL of 2 M NaOH solution, and a
further
135 g of water was added to bring the total to 1.5 kg. The solution was
transferred to a
jacketed vessel fitted with an oxygen sparger, a pH probe and a temperature
probe and was
thermally equilibrated to 50 C. Agitation was achieved by an impeller
operating at 1200
rpm. Oxygen was bubbled at a constant rate of 30 mL min 1. The pH was adjusted
to 8.00
with further addition of NaOH solution (26 mL). Finely milled serpentinite ore
(95.3 g)
grading 0.31% total Ni was added. Solution samples were taken at various
intervals,
filtered, and analysed for nickel and iron by XRF. The pH was readjusted to
8.00 after
sampling, as required. Nickel extraction reached 71% after 48 hours (Figure 7)
based on
nickel concentration in solution. The final concentrations of nickel and iron
were 142 and
170 ppm, respectively. Based on ICP-MS measurements of the head and tail
grade, the
nickel extraction was 78.9% (Table 5).
Table 5
Elemental comptta lilon of serpent dte-nwaralte ore before and after loathing
(ppm;
excluding oxygen, sulbr and silicon)
Element Head Tail
Na - 853
Mg 256700 253721
Al 1103 1268
Ca 535 195
V 2 -
Se 3 4
Cr 509 994
Mn 709 552
Fe 27288 29861
Co 89 30
NI 3099 708
Cu 12 24
Zn 59 81
As 9
Zr - 48
Ag - 3
Sb - 9
Ba 3 5
La 63
Bi 12 8
Mass (g) 95.3 87.8
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[0080] Example IV (FP226 standard condition tank test 50 C)
[0081] Sample FP226 - tank leaching
[0082] Hand specimen-sized pieces from Northern British Columbia, Canada,
referred to as Sample FP226, were crushed in a series of jaw and gyratory
crushers to fine
gravel size and then milled for 60 s in -100 g batches in a ring mill. This
process resulted
in a pale grey powder. The elemental composition of Sample FP226, as
determined by
ICP-MS, was as follows:
Table 6
FP226 composition (ICP-MS)*
Cu 531 ppm La 28 ppm
Pb 37 ppm Sr 1 ppm
Zn 160 ppm Sc 8 ppm
Co 94 ppm Al 2700 ppm
Ni 2275 ppm Ca 5900 ppm
Ba 29 ppm Fe 55200 ppm
Cr 1726 ppm Mg 283100 ppm
V 21 ppm Na 100 ppm
Mn 799 ppm
* analysed for but not detected:
Ag, As, Sb, Hg, Mo, TI, Bi, Cd, W, Zr (ppm); Ti, K, P (%)
[0083] A leaching test starting at the standard conditions (pH 8.00, 50 C, 1.5
M
[NH3]t tai, 50 mM citrate, 2.0 mM S2032-; pulp density 86 g L-1) was conducted
on this
sample. After 47 hours had elapsed, the nickel extraction (based on 0.228%
total Ni from
ICP-MS analysis) was 37%, and appeared to have peaked (Figure 8).
[0084] Example V (Aggressive tank test Sample FP226)
[0085] More aggressive conditions were used in a subsequent test (Figures 9
and 10).
Specifically, the ammonia concentration was doubled to 3.0 M, the citrate
concentration
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was increased 10-fold to 500 mM, and the temperature was raised to 60 C. The
thiosulfate concentration was held constant at 2.0 mM. Rather than preparing
the leaching
solution from ammonium sulfate, sodium citrate and sodium hydroxide, citric
acid and
aqueous ammonia were used. The citric acid (144.1 g) was dissolved in -1 L of
water,
and the ammonia (300 mL) was added. The total volume of the solution was then
brought
up to 1500 mL, without any adjustment of pH (which was 9.9). Note that this
procedure
differs from that used previously, in which -1500 g of water (less the sodium
hydroxide
solution) was added to the solid components. The two methods therefore
resulted in
different final volumes. A higher than normal pulp density (160 g L:1) was
used to ensure
a higher nickel concentration in solution, in order to obtain more reliable
XRF data.
[0086] During the test, no attempt was made to maintain the pH at a fixed
value. At
60 C, the starting pH was 8.92, and it decreased during the test at a
decreasing rate. The
initial leaching rate exceeded that of the FPO0I test, although the final
extraction was
lower (based on total nickel). A major difference between this sample and
Example III
(FP001/Quebec) is the iron content - 2.7% in Example III and 5.5% in this
example
(another difference could be the awaruite particle size). Rates of Ni and Fe
leaching were
indistinguishable (Figure 11).
[0087] Example VI (Aggressive no citrate tank test, Sample FP226)
[0088] A further test was run at similar conditions to Example V, in the
absence of
citrate. The solution was prepared by diluting aqueous ammonia with water and
titrating
to pH 10 using diluted sulfuric acid. The solution therefore contained sulfate
instead of
citrate. When the temperature was raised to 60 C, the solution pH prior to
adding the
solid was 8.58 rather than 8.92, which may be due to the lack of citrate in
the solution
changing the temperature dependence of the solution pH. The nickel extraction
curve is
shown in Figure 12. The maximum nickel extraction (41 %) was obtained after 24
hours,
which may indicate a non-awaruite source of nickel. The iron concentration
during the
test remained essentially zero, as would be expected in the absence of
citrate. The lack of
iron dissolution also led to only a small decrease in pH (from 8.58 to 8.48)
during the test,
as iron hydrolysis was minimal.
[0089] After the success of the `aggressive' conditions, a more systematic
investigation was initiated, starting with testing the effect of higher pH,
keeping all other
parameters at the standard conditions. Surprisingly, in this Sample, the
nickel extraction
at pH 9.00 (Figure 13) was worse than at the standard conditions (pH 8.00).
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[0090] Comparison of the nickel extraction based on analysis of the solids
after
leaching and the solution measurements carried out during leaching indicated
that the
extraction was lower based on the solid.
[0091] The four tests run on sample FP226 are compared below in Figure 14, and
the
conditions are summarised in Table 7. The aggressive conditions resulted in
the best
nickel extraction. The other two tests (aggressive without citrate and
standard conditions)
reached the approximately the same point (-40% by solution and -34% by solid),
although the extraction from the aggressive (no citrate) test was slightly
more rapid.
Table 7: Conditions used in FP226 tests
Aggressive High
Condition Standard Aggressive
(no citrate) pH
pH 8.00 8.9 8.6 9.00
(initially) (initially)
T ( C) 50 60 60 50
[NH3]totati (M) 1.5 3.0 3.0 1.5
Citrate (mM) 50 500 0 50-100
S2032 (mM) 2.0 2.0 2.0 2.0
Ni (solution 38.3 62.1 42.8 31.4
ova)
Ni (solid %) 35.4 41.5 33.4
[0092] Example VII (Sample FP226, Various conditions)
[0093] A series of small scale tests were carried out in 250 mL conical flasks
on
Sample FP226, varying pH (7-10), temperature (50-80 C) and milling time (1-5
min) as
well as thiosulfate (2-50 mM), citrate (50-250 mM) and ammonia (1.5-3.0 M)
concentration. Pulp density and shaking speed were held constant. Each test
was titrated
at ambient temperature to the desired pH, and was not adjusted again. The
tests were run
for 24 hours, at which point the solution was filtered and nickel and iron
measured by
XRF. The details of each test and the results are given in Table 8. Oxygen
limitation was
not a problem, since the amount of oxygen in the flask was many times more
than required
to leach awaruite and any magnetite. Furthermore, gas-liquid mixing was
adequate, since
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the initial amount of dissolved oxygen was insufficient to leach the amount of
nickel and
iron found in solution.
Table 8: Conditions and results of the flask tests (based on total Ni and Fe
from ICP-MS
of milled FP226)
[NH31T T 5203 - Citrate Milling Ni Fe
(M) PH ( C) (mM) (mM) (min) (%) (%)
1.5 9 50 50 50 1 27.6 1.93
1.5 9 50 25 50 1 28.1 1.93
Thiosulfate 1.5 9 50 10 50 1 26.9 1.96
1.5 9 50 5 50 1 28.7 1.98
1.5 9 50 2 50 1 27.3 1.96
1.5 9 50 5 50 1 21.6 1.86
1.5 9 50 5 100 1 23.1 2.36
Citrate 1.5 9 50 5 150 1 24.0 2.58
1.5 9 50 5 200 1 24.4 2.69
1.5 9 50 5 250 1 25.5 2.70
2.0 9 50 5 50 1 23.7 2.02
2.5 9 50 5 50 1 23.1 2.02
3.0 9 50 5 50 1 25.3 1.92
~T 1.0 9 50 5 250 1 24.9 2.93
[ ~H3]T
1.5 9 50 5 250 1 25.2 2.82
2.0 9 50 5 250 1 25.1 2.80
2.5 9 50 5 250 1 25.0 2.74
3.0 9 50 5 250 1 25.2 2.58
1.5 7 50 5 50 1 28.4 2.53
pH 1.5 8 50 5 50 1 26.4 2.45
1.5 10 50 5 50 1 23.5 0.38
Temperature 1.5 9 60 5 50 1 25.1 2.12
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1.5 9 60 5 100 1 26.0 2.83
1.5 9 60 5 250 1 27.9 3.32
1.5 9 70 5 50 1 37.9 2.70
1.5 9 70 5 100 1 40.6 3.37
1.5 9 70 5 250 1 41.0 4.05
1.5 9 80 5 50 1 33.9 2.44
1.5 9 80 5 250 1 39.5 3.96
1.5 9 50 5 50 2 26.2 1.89
1.5 9 50 5 250 2 32.7 3.34
Milling
1.5 9 50 5 50 5 32.9 1.51
1.5 9 50 5 250 5 33.0 3.65
[0094] Figures 15a-d show the effects of thiosulfate, citrate, ammonia, pH and
temperature on nickel extraction from Sample FP226. Thiosulfate and ammonia
had little
influence on this sample, whereas the extraction increased slightly as citrate
increases, and
increasing pH inhibits nickel extraction. The biggest effect by far appeared
to be
temperature. Note that the data marked as 80 C were actually closer to 75 C,
since the
incubating shaker was not able to maintain 80 C. The `standard condition'
stirred-tank
test (2 mM S2032-, 50 mM citrate, 1.5 M [NH3]c ,a1, pH 9, 50 C) leached 35.4%
(based on
solids), and another test at 70 C (with 100 mM citrate and 5 mM thiosulfate)
leached
38.9% (solution XRF); the equivalent shake-flask tests leached 27.3% and
40.6%.
[0095] The effects on iron extraction are shown in Figures 16a-d. Thiosulfate
had
little effect on iron extraction, whereas increasing total ammonia slightly
decreased iron
extraction. Increasing citrate concentration and temperature both resulted in
greater iron
solubility. Increasing pH dramatically decreased iron solubility. Since the
majority of the
iron is not derived from awaruite (typical molar ratio of iron to nickel in
solution is about
two, compared to one third in awaruite), the lack of dependence on thiosulfate
and
ammonia was expected. Without being bound to any particular theory, much of
the
dissolved iron may be from dissolution of magnetite. Any change to the
conditions that
increases the stability of Fe(OH)3 relative to citrate complexes of Fe(III),
such as a pH
increase, decreases the dissolved iron concentration. Hence, an increase in
the
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concentration of citrate increases iron solubility, as citrate complexes
become more stable.
The effects of temperature may affect the pKa of ammonia, citrate and Fe(III);
the net
effect is increased iron solubility.
[0096] The effect of particle size was investigated using milling time as a
surrogate
for the actual particle size distribution (Figures 17 and 18). For both 50 and
250 mM
citrate, five minutes of milling in a ring mill resulted in the best nickel
extraction. Longer
milling time decreased iron extraction for 50 mM citrate, whereas it was
increased for 250
mM citrate. Without being bound to any particular theory, this could be due to
adsorption
of citrate on particle surfaces, and 50 mM citrate was no longer adequate to
hold iron in
solution when presented with a greater surface area. With sufficient citrate,
as
demonstrated by the 250 mM citrate conditions, iron extraction increased with
increasing
milling time (i.e. smaller particle size).
[0097] The `aggressive' conditions used in the stirred-tank test (60 C, 3.0 M
[NH3]t tai, 0.5 M citrate, 2.0 mM S2032-, pH initially -10 at room
temperature), were
carried out in an equivalent shake-flask test and several variations on those
conditions
were also carried out (Table 9). Additionally, a `blank' test was also carried
out at
otherwise `aggressive' conditions, lacking thiosulfate and citrate. These
tests were run for
24 hours and analysed as above, with the `blank' and `aggressive' tests
providing a
minimum and maximum extraction range for the shake-flask tests. The blank
achieved
just 12.3% nickel extraction, whereas the `aggressive' conditions leached
40.1% nickel,
along with 4.03% iron. Iron extraction in the `blank' test was just 0.12%, as
expected in
the absence of citrate.
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Table 9: Conditions and results of flask tests varying the `aggressive'
conditions
(based on total Ni and Fe from ICP-MS of milled FP226)
[NH3] T T 5203 2- Citrate Milling Ni Fe
(M) PH ( C) (mM) (mM) (min) (%) (%)
Blank 3.0 9 60 0 0 1 12.3 0.12
Aggressive 3.0 10 60 2 500 1 40.1 4.03
1.5 10 60 2 500 1 29.8 3.04
1.5 10 60 2 250 1 30.0 2.76
1.5 10 60 2 100 1 28.1 1.84
Variations 3.0 10 60 2 100 1 34.1 1.74
3.0 10 60 50 500 1 42.0 3.84
3.0 9 60 2 500 1 35.1 4.25
3.0 10 60 0 500 1 30.8 4.07
[0098] In Figure 19, the effects of thiosulfate and citrate (at 3.0 M
[NH3]total) on
nickel and iron extraction are plotted together. These figures show that in
the absence of
both thiosulfate and citrate (circle), very little nickel and no iron was
leached. Increasing
citrate resulted in both more nickel and more iron being extracted, whereas
increasing
thiosulfate had a minor effect. Substantial nickel leaching occured at high
citrate, even in
the absence of thiosulfate. Iron leaching remained independent of thiosulfate
at the
`aggressive' conditions, as was the case at the `standard' conditions.
[0099] The effects of citrate and ammonia (at constant thiosulfate) on nickel
and iron
extraction are plotted in Figure 20. At the `standard' total ammonia
concentration (1.5 M),
varying citrate had a negligible effect on nickel leaching. At high ammonia
(3.0 M
[NH31t wi), there was an increase in nickel extraction with an increase in
citrate
concentration. Increasing citrate resulted in greater extraction of iron, with
a more
dramatic effect at the higher ammonia concentration. Increasing the ammonia
concentration, at 500 mM citrate, increased the iron extraction, whereas at
100 mM citrate,
the iron extraction was unaffected by an increase in [NH3]t tai from 1.5 to
3.0 M.
[00100] Additional iron-complexing agents, such as tartaric acid, oxalic acid,
glycolic
acid, lactic acid and malic acid, were compared at 100 mM complexant, 2 mM
thiosulfate,
1.5 M [NH3]t tal, pH 9 (initially), 50 C and 150 g/L pulp density. Figure 21
and Table 10
compare the effect of different complexants on nickel and iron extraction.
Without being
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bound to any theory, the relatively poor performance of oxalate for nickel
leaching may be
because of poor solubility of oxalate complexes, thereby probably blocking the
surface of
the awaruite grains. Malic acid achieved almost as effective nickel extraction
as citrate
and tartrate, while dissolving significantly less iron.
Table 10: Nickel and iron extraction using different iron-complexing agents
Complexing Ni Fe
agent (%) (%)
citrate* 23.7 2.17
tartrate 22.3 1.57
oxalate 13.6 0.15
glycolate 19.7 0.17
lactate 18.7 0.19
malate 21.3 0.62
* 100 mM citrate, 2.5 mM thiosulfate, 1.5 M NH3, pH 9, 50 C
[00101] Example VIII Sample FP226 tank test at 70 C)
[00102] Based on the results of the shake-flask tests, which showed that
temperature
had a strong effect on the final nickel extraction, a tank test was carried
out at 70 C (with
1.5 M [NH3]t tai, 150 g/L pulp density and pH 9 initially), with slightly
higher thiosulfate
(5 mM) and citrate (100 mM). The nickel leaching curve (Figure 22) shows that
the
extraction reached 28% after 6 hours and 39% after 48 hours. Iron extraction
followed a
similar trajectory (Figure 23). In this test, the pH was titrated to 9 at
ambient temperature
and then not adjusted again - at the beginning of the test it was 7.35 (due to
the
temperature increase to 70 C), and decreased during the test to -7 (Figure
24). The pH
drop corresponded closely with the increase in nickel and iron concentration.
[00103] Example IX - Brazilian nickel sulfide ore
[00104] A Brazilian nickel sulfide ore composed of ultramafic material,
containing
nickel in sulfide and silicate minerals, was used. The elemental composition
is shown in
Table 11.
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Table 11
Brazilian sulfide ore composition
(ICP-MS)*
Sc 29 ppm Ba 96 ppm
V 151 ppm La 8 ppm
Cr 858 ppm Pb 40 ppm
1467
Mn ppm Na 6400 ppm
114700
Co 146 ppm Mg ppm
3898 40000
Ni ppm Al ppm
1425
Cu ppm P 500 ppm
Zn 180 ppm K 2200 ppm
43800
Sr 133 ppm Ca ppm
Zr 15.5 ppm Ti 2800 ppm
115800
Mo 10 ppm Fe ppm
Ag 0.7 ppm
*Analysed for but not detected:
As, Cd, Sb, W, Hg, TI, Bi (ppm)
[00105] XRD analysis of Brazilian nickel-copper sulfide ore (pyrrhotite
contains
nickel as an impurity, -I%), was as shown in Table 12:
Table 12
Mineral Ideal Formula %
Quartz Si02 1.8
Clinochlore (Mg1Fe2~)5A1(Si3A1)Olo(OH)8 2.9
Muscovite KAI2A1Si3O10(OH)2 6.8
Talc Mg3Si4Olo(OH)2 3.7
Actinolite Ca2(Mg,Fe2+)5Si8022(OH)2 22.6
Cummingtonite Mg7Si8O22(OH)2 5.6
Plagioclase NaAlSi3O8 - CaAl2Si2O8 12.8
Calcite CaCO3 1.4
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Enstatite Mg2Si206 34.2
Chalcopyrite CuFeS2 0.9
Pyrrhotite Fei_,S 5.2
Vermiculite (Mg,Fe2+,Al)3(Si,Al) 1.9
4010(OH)24H20
Total 100.0
[00106] The mineralogy was therefore about 92.3% silicate (shaded areas in
Table
12), about 1.4 % Calcite (CaC03), about 0.9% Chalcopyrite (CuFeS2), and about
5.2%
Pyrrhotite (Fel_,S) (total about 99.8%).
[00107] The gravel sized ultramafic material, containing nickel in sulfide and
silicate
minerals, was milled for 30 s in a ring mill, and then leached in a stirred-
tank at 50 C. The
following salts were added to 1.3 kg of deionised water: 148.7 g of (NH4)2SO4
and 53.3 g
of Na2SO4. The pH was adjusted to -8.9 with 90 mL of 2 M NaOH solution, and a
further
135 g of water was added to bring the total to 1.5 kg. The solution was
transferred to a
jacketed vessel fitted with an oxygen sparger, a pH probe and a temperature
probe and was
thermally equilibrated to 50 C. Agitation was achieved by an impeller
operating at 1200
rpm. Oxygen was bubbled at a constant rate of 30 mL min-'. The pH was adjusted
to 8.00
with further addition of NaOH solution (8 mL). Finely milled ore (50.0 g)
grading 0.39%
total Ni was added. Solution samples were taken at various intervals,
filtered, and analysed
for nickel by AAS. The pH was readjusted to 8.00 after sampling, as required.
Nickel
extraction reached 65% after 54 hours (Figure 25) based on nickel
concentration in
solution. The final concentration of nickel was 85 ppm.
[00108] A subsequent test was carried out on the same material with 50 mM of
citrate
in solution. The following salts were added to 1.2 kg of deionised water:
148.7 g of
(NH4)2SO4, 32.0 g of Na2SO4 and 22.1 g of Na3cit.2H20 (where cit = C61-15073).
The pH
was adjusted to -8.6 with 34 mL of 2 M NaOH solution, and a further 266 g of
water was
added to bring the total to 1.5 kg. The solution was transferred to a jacketed
vessel fitted
with an oxygen sparger, a pH probe and a temperature probe and was thermally
equilibrated to 50 C. Agitation was achieved by an impeller operating at 1200
rpm.
Oxygen was bubbled at a constant rate of 30 mL min-'. The pH was 8.06
initially and was
not adjusted down to 8.00. Finely milled ore (50.0 g) grading 0.39% total Ni
was added.
Solution samples were taken at various intervals, filtered, and analysed for
nickel and iron
CA 02761731 2011-11-10
WO 2010/135819 PCT/CA2010/000782
26
by XRF. The pH was readjusted to 8.00 after sampling, as required. Nickel
extraction
reached 70% after 69 hours (Figure 25) based on nickel concentration in
solution. The
final concentrations of nickel and iron were 91 and 522 ppm, respectively.
[00109] A further test was carried out on the same material with 100 mM of
citrate in
solution. The following salts were added to 1.2 kg of deionised water: 148.7 g
of
(NH4)2SO4, 10.7 g of Na2SO4 and 44.1 g Na3cit.2H20. The pH was adjusted to
8.91 with
87 mL of 2 M NaOH solution, and a further 214 g of water was added to bring
the total to
1.5 kg. The solution was transferred to a jacketed vessel fitted with an
oxygen sparger, a
pH probe and a temperature probe and was thermally equilibrated to 50 C.
Agitation was
achieved by an impeller operating at 1200 rpm. Oxygen was bubbled at a
constant rate of
30 mL min-. The pH was adjusted to 8.00 with a further 7 mL of NaOH. Finely
milled
ore (50.0 g) grading 0.39% total nickel was added. Solution samples were taken
at various
intervals, filtered, and analysed for nickel by AAS. The pH was readjusted to
8.00 after
sampling, as required. Nickel extraction reached 81% after 48 hours (Figure
25) based on
nickel concentration in solution. The final concentration of nickel in
solution was 105
ppm.
[00110] This example showed that the addition of citrate increased both the
rate of
nickel extraction and the final nickel recovery in a nickel sulfide containing
source
material (Figure 25).
[001111 All citations are hereby incorporated by reference.
[00112] The present invention has been described with regard to one or more
embodiments. However, it will be apparent to persons skilled in the art that a
number of
variations and modifications can be made without departing from the scope of
the
invention as defined in the claims.
