Technical Field
[0001] The present invention relates to a hydrometallurgical method in which nickel oxide
ore is subjected to highpressure acid leaching, and more particularly relates to a
hydrometallurgical method capable of increasing a nickel recovery rate.
Background Art
[0002] As one of hydrometallurgical method methods of nickel oxide ore, a high pressure
acid leach (HPAL) process using sulfuric acid is known. This process is different
from a conventional pyrometallurgical process generally used as a smelting method
for nickel oxide ore in that nickel oxide ore is processed under wet conditions throughout
the process without performing an oxide ore reduction step and drying step at high
temperature, and is therefore advantageous in terms of energy and cost. Further, the
HPAL process allows to obtain a nickel- and cobalt-containing sulfide (hereinafter
also referred to as a nickel/cobalt mixed sulfide) which is concentrated to a nickel
grade of about 50 to 60% by mass, and therefore high purity nickel can easily be obtained
by refining.
[0003] When nickel oxide ore as a raw material is subjected to high pressure acid leaching
to recover nickel as a product, the nickel oxide ore is generally often processed
through the following steps (a) to (d):
- (a) a leaching and solid-liquid separation step in which water is added to crushed
nickel oxide ore to obtain a slurry, sulfuric acid is then added to the slurry, the
mixture is placed in a reaction container such as an autoclave and maintained at a
temperature of about 240 to 280°C under high pressure to leach valuables such as nickel
and cobalt contained in the nickel oxide ore, and the slurry is taken out of the reaction
container after leaching and subjected to solid-liquid separation in a sedimentation
tank to separate a leachate containing nickel and cobalt from a leach residue;
- (b) a neutralization step in which the leachate is adjusted to a predetermined pH
by adding a neutralizer to precipitate an impurity such as iron to obtain a neutralized
slurry, a coagulant is added to the neutralized slurry containing a neutralized precipitate
of the impurity to separate the neutralized precipitate by solid-liquid separation
so as to obtain a post-neutralization solution containing nickel and cobalt;
- (c) a dezincification step in which a sulfurizing agent is added to the post-neutralization
solution while the amount of the sulfurizing agent added is controlled to be in an
appropriate range to remove only zinc and copper as sulfides without sulfurizing nickel
and cobalt contained as valuables in the post-neutralization solution, the thus obtained
sulfide precipitate (also referred to as zinc precipitate) is separated by solid-liquid
separation to obtain a post-dezincification solution; and
- (d) a nickel recovery step in which a sulfurizing agent is added to the post-dezincification
solution to generate a nickel/cobalt mixed sulfide, and the mixed sulfide is separated
and recovered.
[0004] For example, Patent Literature 1 discloses a hydrometallurgical method based on the
above-described high pressure acid leaching, which includes a leaching step in which
nickel oxide ore is subjected to leaching using sulfuric acid and then to solid-liquid
separation to obtain a leachate; a neutralization step in which a neutralizer is added
to the leachate to generate a neutralized precipitate containing an impurity, and
the neutralized precipitate is removed to obtain a post-neutralization solution; a
dezincification step in which hydrogen sulfide gas is added to the post-neutralization
solution to generate zinc sulfide, and the zinc sulfide is removed to obtain a mother
liquor for nickel recovery; and a nickel recovery step in which hydrogen sulfide gas
is added to the mother liquor to recover nickel and cobalt as a mixed sulfide.
[0005] In the method disclosed in Patent Literature 1, a leach residue is appropriately
added to the leachate and the pH of the post-neutralization solution is adjusted to
3.0 to 3.5 in the neutralization step, and further a sulfurization reaction is performed
in the dezincification step in a state where suspended solids including the neutralized
precipitate and the leach residue remain in the post-neutralization solution so that
the turbidity of the post-neutralization solution is 100 to 400 NTU (Nephelometric
Turbidity Unit). The thus obtained slurry containing a sulfide precipitate is subjected
to solid-liquid separation in a filtration step in the dezincification step to obtain
the sulfide precipitate and a final solution containing nickel and cobalt.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0007] In the above-described HPAL process using nickel oxide ore as a raw material, conditions
for generating a sulfide precipitate of zinc in the dezincification step approximate
to conditions for generating a sulfide precipitate of nickel, and therefore there
is often a case where nickel loss occurs due to coprecipitation of zinc and nickel
in the zinc precipitate. The recovery rate of nickel has a great impact on the economic
efficiency of the process, and therefore it is desirable to reduce nickel loss as
much as possible.
[0008] In light of the above circumstances, it is an object of the present invention to
provide a hydrometallurgical method for nickel oxide ore based on high pressure acid
leaching which is capable of increasing the recovery rate of nickel by reducing the
amount of nickel coprecipitated with impurities such as zinc and copper when zinc
contained in the nickel oxide ore is removed.
Solution to Problem
[0009] In order to achieve the above object, the present inventors have found that the recovery
rate of nickel can be increased by providing two or more reaction tanks connected
in series for the dezincification reaction, and by adjusting the distribution ratio
of hydrogen sulfide gas blown into the reaction tanks when a dezincification reaction
(sulfurization reaction) is performed by sulfurization by adding a sulfurizing agent
to a post-neutralization solution obtained by neutralizing a leachate obtained by
subjecting nickel oxide ore to high pressure acid leaching. This finding has led to
the completion of the present invention.
[0010] More specifically, the present invention is directed to a hydrometallurgical method
for nickel oxide ore, including: a leaching step in which nickel oxide ore is subjected
to acid leaching under high pressure, and a leach residue is then removed to obtain
a leachate; a neutralization step in which a neutralizer is added to the leachate
to generate a neutralized precipitate, and the neutralized precipitate is removed
to obtain a post-neutralization solution; a dezincification step in which hydrogen
sulfide gas is blown into the post-neutralization solution to generate a zinc precipitate,
and the zinc precipitate is removed to obtain a post-dezincification solution; and
a nickel recovery step in which a sulfurizing agent is added to the post-dezincification
solution to recover nickel as a sulfide, wherein in the dezincification step, the
hydrogen sulfide gas is blown into two or more reaction tanks connected in series
to allow the post-neutralization solution to flow therethrough in order in such a
manner that an amount of the hydrogen sulfide gas blown into the second and following
reaction tanks from top is adjusted to 50% or more but 90% or less of a total amount
of the hydrogen sulfide gas blown into all the reaction tanks.
Advantageous Effects of Invention
[0011] According to the present invention, it is possible to reduce the amount of nickel
coprecipitated with impurities such as zinc and copper when zinc contained in nickel
oxide ore is removed, thereby increasing the recovery rate of nickel.
Brief Description of Drawings
[0012]
FIG. 1 is a process flow chart showing a hydrometallurgical method for nickel oxide
ore according to an embodiment of the present invention.
FIG. 2 is a graph obtained by plotting a relationship between the particle diameter
of each of samples of zinc sulfide obtained in Examples and the blowing ratio of hydrogen
sulfide gas during generation of the zinc sulfide.
FIG. 3 is a graph obtained by plotting a relationship between the Ni grade of each
of samples of zinc sulfide obtained in Examples and the blowing ratio of hydrogen
sulfide gas during generation of the zinc sulfide.
FIG. 4 is a graph obtained by plotting a relationship between the Ni grade and the
particle diameter of each of samples of zinc sulfide obtained in Examples.
Description of Embodiments
[0013] Hereinbelow, a hydrometallurgical method for nickel oxide ore according to an embodiment
of the present invention will be described. As shown in FIG. 1, the hydrometallurgical
method starts from a leaching step S1 in which nickel oxide ore as a raw material
is crushed into small pieces by a crushing means such as a crusher, and water is added
thereto to obtain a slurry. Then, sulfuric acid is added to the slurry, and the mixture
is placed in a pressure vessel such as an autoclave and subjected to sulfuric acid
leaching under high temperature and pressure at, for example, 240 to 280°C to leach
nickel and cobalt as valuables.
[0014] Then, in a solid-liquid separation step S2, a slurry obtained by the above-described
sulfuric acid leaching is subjected to multistep washing, and then a leach residue
is removed from the slurry by solid-liquid separation to obtain a leachate containing
nickel, cobalt, and impurity elements. Then, in a neutralization step S3, an alkali
such as calcium hydroxide or calcium carbonate is added as a neutralizer to the leachate
to adjust the pH of the leachate to precipitate the impurity elements as a neutralized
precipitate. Then, a flocculant (coagulant) is added to a slurry containing the neutralized
precipitate, and the slurry is subjected to solid-liquid separation to remove the
neutralized precipitate to obtain a post-neutralization solution containing nickel
and cobalt. It is to be noted that if necessary, the neutralized precipitate obtained
in the neutralization step S3 may be returned to the solid-liquid separation step
S2. As shown by a dotted line in FIG. 1, at least part of the leach residue obtained
in the solid-liquid separation step S2 may be added to the leachate in the neutralization
step S3.
[0015] Then, in a dezincification step S4, hydrogen sulfide gas is blown as a sulfurizing
agent into the post-neutralization solution to generate a zinc-containing sulfide
precipitate (zinc sulfide), and a slurry containing the sulfide precipitate is subjected
to solid-liquid separation to remove the zinc sulfide to obtain a post-dezincification
solution. Finally, in a nickel recovery step S5, a sulfurizing agent such as hydrogen
sulfide gas is added to the post-dezincification solution to generate a nickel/cobalt
mixed sulfide containing nickel and cobalt, and a slurry containing the nickel/cobalt
mixed sulfide is subjected to sold-liquid separation to recover the nickel/cobalt
mixed sulfide and to obtain a post-sulfurization solution (barren solution). As shown
in FIG. 1, if necessary, the barren solution may be returned to the solid-liquid separation
step S2.
[0016] In the embodiment of the hydrometallurgical method according to the present invention,
zinc is selectively precipitated and settled as a sulfide in the dezincification step
S4 so as to be separated from nickel and cobalt. At this time, two or more reaction
tanks for blowing hydrogen sulfide gas into the post-neutralization solution are provided
to perform a sulfurization reaction, and are connected in series so that the post-neutralization
solution obtained in the neutralization step flows therethrough in order. Further,
the ratio of the amount of hydrogen sulfide gas blown into the second and following
reaction tanks from the top out of the reaction tanks connected in series to the amount
of hydrogen sulfide gas blown into all the reaction tanks (hereinafter also referred
to as "blowing ratio") is adjusted to be in an appropriate range. This makes it possible
to reduce the amount of nickel coprecipitated with impurities such as zinc and copper,
thereby increasing the recovery rate of nickel.
[0017] More specifically, in the dezincification step S4, when n-number of reaction tanks
for performing a dezincification reaction are provided in the order of a No. 1 reaction
tank, a No. 2 reaction tank, a No. 3 reaction tank, ... and a No. n reaction tank
from the top so that the post-neutralization solution flows therethrough in this order,
the ratio of the amount of hydrogen sulfide gas blown into (n-1)-number of reaction
tanks including the No. 2 and following reaction tanks to the amount of hydrogen sulfide
gas blown into all the reaction tanks from the No. 1 reaction tank to the No. n reaction
tank (i.e., blowing ratio) is adjusted to 50% to 90%. This makes it possible to reduce
the amount of nickel coprecipitated with impurities such as zinc and copper.
[0018] Further, when the blowing ratio is set to such a high value, particles of the sulfide
precipitate can grow to have a large particle size. As a result, solid-liquid separability
in the dezincification step can also be improved. In the dezincification step, fine
particles of the sulfide precipitate are likely to be formed. Therefore, when a slurry
containing such fine particles is subjected to solid-liquid separation using a filtration
device such as a filter press, a filter cloth is quickly clogged so that the volume
of a liquid that can pass through the filter cloth reduces. In order to recover the
filter cloth, the filter cloth needs to be frequently backwashed or replaced, which
may reduce production efficiency. However, when the blowing ratio is set to such a
high value as described above, particles of the sulfide precipitate have a large diameter
so that filterability improves.
[0019] As described above, in order to improve not only the recovery rate of nickel but
also solid-liquid separability, the blowing ratio is preferably adjusted to 60% to
90%, more preferably 60% to 85%. This makes it possible to increase the particle diameter
of particles of zinc sulfide (also referred to as "zinc sulfide precipitate") to be
finally generated which allows to prevent the clogging of a filter cloth of a subsequent
filtration device, such as a filter press. As a result, the ability of the filtration
device to allow a liquid to pass through it improves, which makes it possible to improve
productivity. The reason why such an increase in blowing ratio allows particles of
the zinc sulfide precipitate to grow to have a large particle diameter is because
when the blowing ratio increases, the number of fine particles of sulfides of impurities
including zinc which are generated in an early stage of a sulfurization reaction in
the No. 1 reaction tank decreases, and particles of the sulfides grow using these
small number of fine particles as nuclei (also referred to as "seeds") in the No.
2 and following reaction tanks.
[0020] When the blowing ratio is less than 60%, the ratio of hydrogen sulfide gas blown
into the No. 1 reaction tank is relatively high. In this case, fine particles of zinc
sulfide as nuclei are excessively generated in the No.1 reaction tank, and particles
of sulfides grow using these large number of fine particles as nuclei in the No. 2
and following reaction tanks, which makes it difficult to obtain particles of zinc
sulfide having a large particle diameter. On the other hand, when the blowing ratio
exceeds 90%, generation of fine particles of zinc sulfide as nuclei is suppressed
in the No. 1 reaction tank, which leads to a shortage of seeds. In this case, there
is a fear that particle grow is insufficient in the No. 2 and following reaction tanks.
That is, when more than 10% but less than 40% of hydrogen sulfide gas supplied to
all the reaction tanks is blown into the No. 1 reaction tank, seeds can be stably
generated. More specifically, the blowing ratio may be appropriately adjusted so that
the particles grow to the extent that a filter cloth is not easily clogged in subsequent
filtration treatment.
[0021] It is to be noted that when three or more reaction tanks are provided in series,
the last reaction tank may serve as a buffer tank into which a large amount of hydrogen
sulfide gas is not blown. When the last reaction tank serves as a buffer tank, a reaction
time can be secured by the buffer tank even when the short pass of a processed liquid
occurs in the reaction tanks located upstream from the last reaction tank, which prevents
a reduction in total reaction efficiency. However, the number of reaction tanks for
dezincification reaction is preferably 3 or less. This is because when there are a
large number of reaction tanks in which substantially no sulfurization reaction occurs,
problems occur such as waste of equipment costs and energy costs and redissolution
of the zinc sulfide precipitate due to the oxidation of the slurry staying in the
excess reaction tanks by air contained in the slurry. Further, zinc sulfide particles
separately prepared or zinc sulfide particles recovered by solid-liquid separation
may be supplied to the No. 1 reaction tank as seeds, which makes it possible to generate
coarser zinc sulfide particles.
[0022] In the dezincification step S4, a dezincification reaction is preferably performed
at a pH of 2.5 or higher but 3.5 or lower. If the pH is lower than 2.5, zinc is insufficiently
separated due to redissolution of zinc sulfide that has once been generated. On the
other hand, if the pH exceeds 3.5, elements, such as iron and nickel, that should
not be removed may also be precipitated, which increases a precipitate load on a filter
cloth or a filtration device used in subsequent filtration treatment. Particularly,
in the case of iron, a large amount of fine precipitate is generated, which promotes
the clogging of a filter cloth. Therefore, in order to achieve a sufficient flow rate
of the filter cloth, the filter cloth needs to be frequently backwashed, which may
reduce production efficiency.
[0023] It is to be noted that in the dezincification reaction, an acid is generated after
the reaction as shown in the following formula 1. Therefore, the dezincification reaction
is preferably performed while the pH is maintained at 2.7 or higher but 3.0 or lower
so that the pH falls within the above range even when an acid is generated.
[Formula 1] ZnSO
4+H
2S→ZnS+H
2SO
4
Examples
[0024] Nickel oxide ore was subjected to hydrometallurgical leaching at high temperature
and pressure in accordance with a process flow chart shown in FIG. 1 to recover nickel
in the form of a sulfide. More specifically, nickel oxide ore including laterite ore,
saprolite ore, and limonite ore and sulfuric acid were placed in an autoclave as a
pressure vessel and heated to a temperature of 240 to 260°C by a steam heater to perform
leaching under high pressure, and then the obtained leach slurry was subjected to
solid-liquid separation to remove a leach residue to obtain a leachate. Calcium hydroxide
was added as a neutralizer to the leachate to adjust the pH of the leachate to 3.0
to 3.5 to generate a neutralized precipitate. Then, an anionic flocculant was added
to remove the neutralized precipitate by solid-liquid separation to obtain a post-neutralization
solution.
[0025] Then, three reaction tanks (No. 1 reaction tank, No. 2 reaction tank, No. 3 reaction
tank) were prepared which were connected in series and each of which had an almost
cylindrical shape having a diameter of 7.7 m and a height of 12 m (capacity: 460 m
3). The post-neutralization solution was continuously supplied to the first No. 1 reaction
tank at a flow rate of 1200 to 1450 m
3/hr so as to flow through the No. 1 reaction tank, the No. 2 reaction tank, and the
No. 3 reaction tank in this order. Further, hydrogen sulfide gas was blown into each
of these three reaction tanks to sulfurize zinc contained in the post-neutralization
solution to generate zinc sulfide. At this time, the ratio of the amount of hydrogen
sulfide gas blown into the No. 2 reaction tank and the No. 3 reaction tank to the
amount of hydrogen sulfide gas blown into all the three reaction tanks, that is, the
blowing ratio was changed little by little from 5.1% to 86.3%.
[0026] Then, a post-sulfurization solution taken out of the last No. 3 reaction tank was
supplied to a Buchner funnel, in which a filter cloth was placed on a perforated plate
having a plurality of pores and a diameter of 60 cm, and subjected to solid-liquid
separation by vacuum suction on the filtrate side. In this way, zinc sulfide (zinc
sulfide precipitate) samples 1 to 46 generated at different blowing ratios were obtained.
It is to be noted that blowing of hydrogen sulfide gas into the No. 2 reaction tank
and the No. 3 reaction tank was performed in such a manner that most of the hydrogen
sulfide gas was blown into the No. 2 reaction tank, that is, the No. 3 reaction tank
was used to react zinc sulfide particles grown in the No. 2 reaction tank with remaining
dissolved hydrogen sulfide gas to finally grow the zinc sulfide particles. More specifically,
the amount of hydrogen sulfide gas blown into the No. 3 reaction tank was appropriately
increased or decreased without changing the blowing ratio on the basis of the particle
diameter of sampled grown zinc sulfide particles.
[0027] The following Table 1 shows the blowing ratio during generation of each of the zinc
sulfide samples 1 to 46 and the particle dimeter of each of the zinc sulfide samples
1 to 46 generated at the shown blowing ratio. FIG. 2 shows a graph obtained by plotting
a relationship between the blowing ratio and the particle dimeter of zinc sulfide.
The particle diameter of zinc sulfide was measured by observing the sample collected
during steady operation with a microscope and by using a Microtrac. It is to be noted
that the pH and temperature of the slurry in the reaction tanks during generation
of the zinc sulfide samples 1 to 46 were maintained at 2.7 to 2.9 and 60 to 67°C,
respectively. The composition of the post-neutralization solution was as follows:
nickel concentration 3.5 to 4.0 g/L, iron concentration 0.7 to 1.4 g/L, and zinc concentration
60 to 140 mg/L. The zinc concentration of the post-dezincification solution was reduced
to about 5 to 12 mg/L.
[Table 1]
Samples |
Blowing ratio (%) |
Particle diameter of Zn sulfide (µm) |
1 |
5.1 |
8.1 |
2 |
7.6 |
8.4 |
3 |
11.0 |
9.1 |
4 |
11.6 |
6.9 |
5 |
12.9 |
9.1 |
6 |
13.2 |
7.2 |
7 |
13.9 |
7.9 |
8 |
23.7 |
8.1 |
9 |
23.8 |
9.9 |
10 |
23.8 |
7.7 |
11 |
24.1 |
7.7 |
12 |
24.1 |
9.3 |
13 |
28.5 |
6.6 |
14 |
28.6 |
6.4 |
15 |
28.6 |
8.3 |
16 |
30.8 |
7.7 |
17 |
30.8 |
6.9 |
18 |
48.1 |
7.7 |
19 |
48.3 |
7.0 |
20 |
48.8 |
6.9 |
21 |
49.0 |
8.2 |
22 |
51.5 |
7.9 |
23 |
53.5 |
9.8 |
24 |
60.1 |
11.4 |
25 |
63.8 |
18.1 |
26 |
66.4 |
14.1 |
27 |
66.5 |
10.7 |
28 |
66.7 |
17.8 |
29 |
67.3 |
10.6 |
30 |
67.9 |
12.5 |
31 |
68.4 |
15.6 |
32 |
68.6 |
11.5 |
33 |
69.0 |
13.6 |
34 |
80.1 |
14.3 |
35 |
81.0 |
19.0 |
36 |
81.6 |
11.0 |
37 |
82.0 |
10.1 |
38 |
82.2 |
16.7 |
39 |
83.4 |
22.6 |
40 |
84.1 |
16.8 |
41 |
84.5 |
28.1 |
42 |
84.6 |
15.0 |
43 |
84.8 |
30.1 |
44 |
84.9 |
18.7 |
45 |
86.2 |
22.0 |
46 |
86.3 |
16.7 |
[0028] As can be seen from the results shown in Table 1 and FIG. 2, particles of the zinc
sulfide samples 24 to 46 obtained by adjusting the ratio of hydrogen sulfide gas blown
into the No. 2 and following reaction tanks to 60% or higher but 90% or lower were
coarse and had a particle diameter of about 10 µm or more. These zinc sulfide samples
24 to 46 were prepared by continuously performing smelting over several days (at least
24 hours) per sample at different blowing ratios, but a filtration device to which
the slurry taken out of the No. 3 reaction tank was supplied was not clogged. On the
other hand, particles of all the zinc sulfide samples 1 to 23 prepared at a blowing
ratio of less than 60% were fine and had a particle diameter of less than 10 µm. Each
of these zinc sulfide samples 1 to 23 were prepared by continuously performing smelting
at different blowing ratios, and as a result, a filtration device was clogged before
the elapse of 24 hours.
[0029] Then, 37 zinc sulfide samples were randomly selected from the zinc sulfide samples
1 to 46, and their nickel grades were measured by ICP. The nickel grade of the zinc
sulfide and the blowing ratio are shown in the following Table 2. FIG. 3 is a graph
obtained by plotting a relationship between the nickel grade and the blowing ratio.
Further, FIG. 4 is a graph obtained by plotting a relationship between the particle
diameter and the nickel grade of the zinc sulfide.
[Table 2]
Samples |
Blowing ratio (%) |
Ni grade of Zn sulfide (%) |
1 |
5.1 |
1.7 |
2 |
7.6 |
1.2 |
5 |
12.9 |
1.7 |
6 |
13.2 |
1.7 |
7 |
13.9 |
1.0 |
8 |
23.7 |
1.2 |
9 |
23.8 |
1.2 |
10 |
23.8 |
1.1 |
11 |
24.1 |
1.3 |
16 |
30.8 |
1.7 |
17 |
30.8 |
1.2 |
18 |
48.1 |
1.0 |
19 |
48.3 |
1.3 |
20 |
48.8 |
1.3 |
21 |
49.0 |
1.4 |
22 |
51.5 |
0.6 |
23 |
53.5 |
0.7 |
24 |
60.1 |
0.7 |
25 |
63.8 |
0.5 |
26 |
66.4 |
0.6 |
27 |
66.5 |
0.8 |
29 |
67.3 |
0.6 |
30 |
67.9 |
0.5 |
31 |
68.4 |
0.6 |
32 |
68.6 |
0.4 |
33 |
69.0 |
0.5 |
34 |
80.1 |
0.4 |
35 |
81.0 |
0.8 |
36 |
81.6 |
0.4 |
37 |
82.0 |
0.7 |
39 |
83.4 |
0.4 |
41 |
84.5 |
0.6 |
42 |
84.6 |
0.4 |
43 |
84.8 |
0.6 |
44 |
84.9 |
0.5 |
45 |
86.2 |
0.7 |
46 |
86.3 |
0.8 |
[0030] As can be seen from Table 2 and FIG. 3, the nickel grade of the zinc sulfide can
be reduced to 1% or less by setting the blowing ratio to 50% or more. Further, as
can be seen from FIG. 4, the nickel grade of the zinc sulfide can be reduced to 1%
or less by allowing particles of the zinc sulfide to have a particle dimeter of about
10 µm or more, that is, by setting the blowing ratio of hydrogen sulfide gas to about
60% or more as can be seen from Table 1 and FIG. 2. As described above, when the particle
diameter of the zinc sulfide is 10 µm or more, the effect of improving filterability
can be obtained in addition to the effect of increasing the recovery rate of nickel.