AU2017369155B2 - Wet metallurgy method for nickel oxide ore - Google Patents

Abstract

The present invention improves the nickel recovery rate in a dezincing step for removing zinc contained in a nickel oxide ore in wet metallurgy that uses high pressure acid leaching of the ore. A wet metallurgy method comprising: a leaching step S1 for acid leaching of nickel oxide ore under high pressure to obtain a leachate; a neutralization step S3 for removing a neutralization precipitate generated by adding a neutralizing agent to said leachate and obtaining a post-neutralization solution; a dezincing step S4 for removing zinc precipitate generated by blowing hydrogen sulfide gas into said post-neutralization solution to obtain a post-dezincing solution; and a nickel recovery step S5 for adding a sulfiding agent to said post-dezincing solution and recovering the nickel as a sulfide. When the hydrogen sulfide gas is blown in, said post-neutralization solution is successively passed through multiple reaction tanks that are connected in series while the volume of hydrogen sulfide gas blown into the second reaction tank from the top and subsequent reaction tanks is adjusted to 50% to 90% of the total volume of hydrogen sulfide gas blown into all of the reaction tanks.

Description

HYDROMETALLURGICAL METHOD FOR NICKEL OXIDE ORE

Technical Field

[0001]

The present invention relates to a hydrometallurgical

method in which nickel oxide ore is subjected to high

pressure 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

2800C 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

[00061

Patent Literature 1: JP 2010-37626 A

Summary of Invention

[00071

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, the present

invention seeks 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.

[00091

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.

[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 Si 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 2800C 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.

[00211

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 2 S-ZnS+H 2 SO 4

Examples

[00241

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 2600C 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 670C, 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.

[0028]

[Table 1]

Blowing Particle Blowing Particle Samples diameter of Samplesratioo) diameter of Zn sulfide (m) Zn sulfide ( m) 1 5.1 8.1 24 60.1 11.4 2 7.6 8.4 25 63.8 18.1 3 11.0 9.1 26 66.4 14.1 4 11.6 6.9 27 66.5 10.7 5 12.9 9.1 28 66.7 17.8 6 13.2 7.2 29 67.3 10.6 7 13.9 7.9 30 67.9 12.5 8 23.7 8.1 31 68.4 15.6 9 23.8 9.9 32 68.6 11.5 10 23.8 7.7 33 69.0 13.6 11 24.1 7.7 34 80.1 14.3 12 24.1 9.3 35 81.0 19.0 13 28.5 6.6 36 81.6 11.0 14 28.6 6.4 37 82.0 10.1 15 28.6 8.3 38 82.2 16.7 16 30.8 7.7 39 83.4 22.6 17 30.8 6.9 40 84.1 16.8 18 48.1 7.7 41 84.5 28.1 19 48.3 7.0 42 84.6 15.0 20 48.8 6.9 43 84.8 30.1 21 49.0 8.2 44 84.9 18.7 22 51.5 7.9 45 86.2 22.0 23 53.5 9.8 46 86.3 16.7

[0029]

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 pm 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 pm. 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.

[00301

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.

[0031]

[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

[00321

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 pm 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 pm or more, the effect

of improving filterability can be obtained in addition to

the effect of increasing the recovery rate of nickel.

[0033]

Throughout this specification and the claims which follow,

unless the context requires otherwise, the word "comprise",

and variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated integer or

step or group of integers or steps but not the exclusion of

any other integer or step or group of integers or steps.

[0034]

The reference in this specification to any prior

publication (or information derived from it), or to any

matter which is known, is not, and should not be taken as,

an acknowledgement or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims (2)

1. A hydrometallurgical method for nickel oxide ore,

comprising: 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.

2. The hydrometallurgical method for nickel oxide ore

according to claim 1, wherein in the dezincification step, the sulfurizing reaction is performed in a pH range of 2.5 or higher but 3.5 or lower.