U.S. patent application number 15/304898 was filed with the patent office on 2017-06-22 for hydrometallurgical process for nickel oxide ore.
The applicant listed for this patent is SUMITOMO METAL MINING CO., LTD.. Invention is credited to Masaki IMAMURA, Yasumasa KAN, Go OHARA.
Application Number | 20170175227 15/304898 |
Document ID | / |
Family ID | 54323896 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170175227 |
Kind Code |
A1 |
OHARA; Go ; et al. |
June 22, 2017 |
HYDROMETALLURGICAL PROCESS FOR NICKEL OXIDE ORE
Abstract
Provided is a hydrometallurgical process for nickel oxide ore
for recovering nickel and cobalt using a high pressure acid leach
process, the process achieving simplification and durability
improvement of production facilities, achieving cost reduction and
suppression of environmental risk by the compression of the
capacity of a tailings dam for storing wastes, and being capable of
recycling and effectively utilizing the wastes as a resource. The
hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process includes
an ore processing step, a leaching step, a solid-liquid separation
step, a neutralization step, a zinc removal step, a sulfurization
step, and a final neutralization step, and further includes step
(A), or further includes step (A) and, step (B-1) and/or step (B-2)
after step (A).
Inventors: |
OHARA; Go; (Tokyo, JP)
; KAN; Yasumasa; (Tokyo, JP) ; IMAMURA;
Masaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO METAL MINING CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
54323896 |
Appl. No.: |
15/304898 |
Filed: |
March 27, 2015 |
PCT Filed: |
March 27, 2015 |
PCT NO: |
PCT/JP2015/059674 |
371 Date: |
October 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 3/08 20130101; C22B
23/0461 20130101; Y02P 10/20 20151101; Y02P 10/212 20151101; C22B
3/44 20130101; C22B 23/005 20130101; C22B 1/24 20130101; C22B
23/0415 20130101; C22B 3/22 20130101; C22B 23/043 20130101 |
International
Class: |
C22B 3/00 20060101
C22B003/00; C22B 1/24 20060101 C22B001/24; C22B 3/44 20060101
C22B003/44; C22B 3/08 20060101 C22B003/08; C22B 3/22 20060101
C22B003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2014 |
JP |
2014-086590 |
Claims
1. A hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process
comprising an ore processing step, a leaching step, a solid-liquid
separation step, a neutralization step, a zinc removal step, a
sulfurization step, and a final neutralization step, the
hydrometallurgical process further comprising, step (A): a step of
separating chromite particles from an ore slurry produced in the
ore processing step by a recovery process including specific
gravity separation, and then classifying the chromite particles to
recover a high-concentration chromite concentrate having a grade of
chromium(III) oxide of at least more than 50% by weight.
2. A hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process
comprising an ore processing step, a leaching step, a solid-liquid
separation step, a neutralization step, a zinc removal step, a
sulfurization step, and a final neutralization step, the
hydrometallurgical process further comprising: step (A): a step of
separating chromite particles from an ore slurry produced in the
ore processing step by a recovery process including specific
gravity separation, and then classifying the chromite particles to
recover a high-concentration chromite concentrate having a grade of
chromium(III) oxide of at least more than 50% by weight; followed
by at least one of: step (B-1): a neutralization step of subjecting
a leachate to neutralization with at least one of a calcium-based
neutralizing agent and a magnesium-based neutralizing agent, the
leachate being produced by subjecting the ore slurry, in which the
chromium grade has been reduced by separating the chromite
particles in step (A), sequentially to the leaching step and the
solid-liquid separation step; and step (B-2): a neutralization step
of subjecting a leach residue slurry to neutralization with a
magnesium-based neutralizing agent, the leach residue slurry being
produced by subjecting the ore slurry, in which the chromium grade
has been reduced by separating the chromite particles in step (A),
sequentially to the leaching step and the solid-liquid separation
step, to thereby recover hematite particles from the leach residue
slurry.
3. The hydrometallurgical process for nickel oxide ore of claim 2,
wherein step (A) is followed by step (B-1) and step (B-2).
4. The hydrometallurgical process for nickel oxide ore according to
claim 2, wherein the recovery process in step (A) comprises
subjecting the ore slurry to classification with a cyclone to form
a particulate iron-leaned ore slurry in which fine iron hydroxide
particles have been reduced, and then recovering chromite particles
contained in the particulate iron-leaned ore slurry from the
particulate iron-leaned ore slurry as a chromite concentrate using
specific gravity separation.
5. The hydrometallurgical process for nickel oxide ore according to
claim 4, wherein the recovery process in step (A) comprises
subjecting the ore slurry to classification with a cyclone without
diluting the slurry concentration of the ore slurry.
6. The hydrometallurgical process for nickel oxide ore according to
claim 2, wherein the recovery process in step (A) comprises
collecting a whole amount of the chromite excluding unavoidable
loss into an underflow in the classification with the cyclone.
7. The hydrometallurgical process for nickel oxide ore according to
claim 2, wherein the specific gravity separation comprises a step
of using a density separator.
8. The hydrometallurgical process for nickel oxide ore according to
claim 2, wherein the specific gravity separation comprises a step
of using a spiral concentrator.
9. The hydrometallurgical process for nickel oxide ore according to
claim 2, wherein the specific gravity separation comprises a step
of using a density separator and a step of using a spiral
concentrator.
10. The hydrometallurgical process for nickel oxide ore according
to claim 7, wherein the step of using a density separator comprises
treating a concentrated slurry with the density separator twice or
more.
11. The hydrometallurgical process for nickel oxide ore according
to claim 8, wherein the step of using a spiral concentrator
comprises treating a concentrated slurry with the spiral
concentrator twice or more.
12. The hydrometallurgical process for nickel oxide ore according
to claim 8, wherein a pulp content of the slurry fed to the spiral
concentrator is 15 to 35% by weight of solid.
13. The hydrometallurgical process for nickel oxide ore according
to claim 7, wherein an amount of Teeter water fed to the density
separator is 0.5 to 7.0 [m.sup.3h.sup.-1/m.sup.2].
14. The hydrometallurgical process for nickel oxide ore according
to claim 1, wherein the chromite concentrate separated by the
specific gravity separation is subjected to magnetic separation
which is a physical separation to remove magnetite from the
chromite concentrate as a magnetic material and recover a
non-magnetic material as a high-concentration chromite
concentrate.
15. The hydrometallurgical process for nickel oxide ore according
to claim 2, wherein step (B-2) comprises setting pH after the
neutralization at 4 to 7 and after the neutralization, performing
final neutralization with an alkali other than the magnesium-based
neutralizing agent.
16. The hydrometallurgical process for nickel oxide ore according
to claim 2, wherein step (B-2) comprises subjecting the leach
residue slurry or a neutralized residue slurry including the leach
residue slurry to classification with a cyclone to recover a
classified fine particle portion obtained by the classification as
a concentrate of hematite.
17. The hydrometallurgical process for nickel oxide ore according
to claim 2, wherein the ore processing step is a step of performing
removal of foreign matter from mined raw ore and particle size
adjustment of the ore to form an ore slurry; the leaching step is a
step of adding sulfuric acid to the ore slurry and stirring a
resulting mixture at high temperature and high pressure to form a
leach slurry composed of a leach residue and a leachate; the
solid-liquid separation step is a step of subjecting the leach
slurry to multi-stage washing to obtain a leachate containing
nickel and cobalt and a leach residue slurry; the neutralization
step is a step of adding an alkali to the leachate to form a
neutralized precipitate slurry containing trivalent iron and a
mother liquor for nickel recovery; the zinc removal step is a step
of blowing hydrogen sulfide gas into the mother liquor to form a
zinc sulfide precipitate slurry and a mother liquor for nickel and
cobalt recovery; the sulfurization step is a step of blowing
hydrogen sulfide into the mother liquor for nickel and cobalt
recovery to produce a mixed sulfide containing nickel and cobalt
and a barren liquor; and the final neutralization step is a step of
adding excess of the barren liquor to the leach residue slurry and
adjusting pH to 8 to 9 to obtain a final neutralized residue.
18. The hydrometallurgical process for nickel oxide ore according
to claim 17, wherein the particle size adjustment in the ore
processing step is performed by sieving with a particle size of 2
mm or less.
19. The hydrometallurgical process for nickel oxide ore according
to claim 18, wherein a grade of chromium(III) oxide in the chromite
concentrated is 41% by weight or more.
20. The hydrometallurgical process for nickel oxide ore according
to claim 1, wherein the ore processing step is a step of performing
removal of foreign matter from mined raw ore and particle size
adjustment of the ore to form an ore slurry; the leaching step is a
step of adding sulfuric acid to the ore slurry and stirring a
resulting mixture at high temperature and high pressure to form a
leach slurry composed of a leach residue and a leachate; the
solid-liquid separation step is a step of subjecting the leach
slurry to multi-stage washing to obtain a leachate containing
nickel and cobalt and a leach residue slurry; the neutralization
step is a step of adding an alkali to the leachate to form a
neutralized precipitate slurry containing trivalent iron and a
mother liquor for nickel recovery; the zinc removal step is a step
of blowing hydrogen sulfide gas into the mother liquor to form a
zinc sulfide precipitate slurry and a mother liquor for nickel and
cobalt recovery; the sulfurization step is a step of blowing
hydrogen sulfide into the mother liquor for nickel and cobalt
recovery to produce a mixed sulfide containing nickel and cobalt
and a barren liquor; and the final neutralization step is a step of
adding excess of the barren liquor to the leach residue slurry and
adjusting pH to 8 to 9 to obtain a final neutralized residue.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to a hydrometallurgical
process for nickel oxide ore, specifically relates to a
hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt from nickel oxide ore using a high pressure acid
leach process including an ore processing step, a leaching step, a
solid-liquid separation step, a neutralization step, a zinc removal
step, a sulfurization step, and a final neutralization step, in
which problems are solved by suppressing the wear, caused by an ore
slurry produced from the ore processing step, of facilities such as
conveyance piping and a pump for conveying the ore slurry and
improving the durability of the facilities to thereby reduce the
amount of a final neutralized residue produced from the final
neutralization step and allow the compression of the capacity of a
tailings dam for storing a leach residue, a neutralized
precipitate, and the like to be discarded to thereby reduce cost
and environmental risk; and impurity components which can be
recycled and effectively used as a resource can be separated and
recovered.
[0003] 2. Description of the Related Art
[0004] In recent years, raw material cost for metal smelting has
significantly increased with the further progress of
oligopolization of mining rights for mineral resources, such as
coal, iron, copper, nickel, cobalt, chromium, and manganese.
Therefore, also in metal smelting, technical development has been
made, as a measure for cost reduction, for using a low-grade raw
material which has not been used since it is disadvantageous in
terms of cost.
[0005] For example, since a material excellent in corrosion
resistance at high temperature and high pressure has been developed
in nickel smelting, a hydrometallurgical process based on a high
pressure acid leach process, in which nickel oxide ore is subjected
to acid leach with sulfuric acid under pressure, has attracted
attention.
[0006] The high pressure acid leach process is advantageous in
terms of energy cost since it does not have dry process steps such
as a reduction step and a drying step unlike a pyrometallurgical
process which is a conventional common smelting method for nickel
oxide ore, and the high pressure acid leach process is continuously
considered to be a promising technique as a smelting method for
low-grade nickel oxide ore.
[0007] Therefore, in order to improve the completeness as a
smelting process, various proposals have been made, focusing on a
leaching step at a high temperature under pressure, with respect to
improvement in the leaching rate of nickel and cobalt, solution
purification of a leachate, and reduction in the amount of
operation materials used, and the like.
[0008] As an example of the process for utilizing leaching at a
high temperature under pressure, there has been proposed a method
for recovering valuable metals such as nickel, cobalt, and
manganese from oxide ores containing these metals, the method
including steps (a) to (c) (refer to, for example, Japanese Patent
Laid-Open No. H06-116660) as below.
[0009] Step (a): subjecting previously slurried oxide ore to
atmospheric leach under an acidic condition with sulfuric acid
using a high pressure acid leach solution obtained in step (b) to
obtain an atmospheric leach solution and an atmospheric leach
residue;
[0010] Step (b): allowing the atmospheric leach residue obtained in
step (a) to react with sulfuric acid in an oxidizing atmosphere at
high temperature and high pressure to obtain a high pressure acid
leach solution; and
[0011] Step (c): adding a neutralizing agent to the atmospheric
leach solution obtained in step (a) to neutralize the same,
followed by adding an alkali sulfide compound thereto to recover
nickel and cobalt in the leachate as sulfides.[0006]
[0012] In the method including the above steps, the nickel leaching
rate from ores is improved by performing two-stage leaching in
which the ore slurry is subjected to atmospheric leach (step (a))
and then the atmospheric leach residue is subjected to high
pressure acid leach (step (b)), and at the same time, the load of
the neutralization step (step (c)) is reduced by neutralizing the
excess acid contained in the leachate from the high pressure acid
leach with the alkali component contained in the atmospheric leach
residue.
[0013] However, there have been problems in that the two-stage
leaching has increased the number of equipment to increase cost and
labor, and a large amount of dilute solution produced in the
washing of the leach residue has required cost.
[0014] Therefore, in order to solve these problems, a method
including steps (1) to (4) described below has been proposed (refer
to, for example, Patent Literature 2) as another process of
utilizing leaching at high temperature under pressure.
[0015] (1) Leaching step: forming a slurry of nickel oxide ore,
adding sulfuric acid to the slurry, and stirring the slurry at a
temperature of 220 to 280.degree. C. to form a leach slurry;
[0016] (2) Solid-liquid separation step: washing the leach slurry
obtained in the previous leaching step using a multi-stage
thickener to separate it into a leachate containing nickel and
cobalt and a leach residue;
[0017] (3) Neutralization step: adjusting the leachate obtained in
the solid-liquid separation step with calcium carbonate to a pH of
or less while suppressing the oxidation of the leachate to produce
a neutralized precipitate containing trivalent iron and separate
the leachate into a neutralized precipitate slurry and mother
liquor for nickel recovery; and
[0018] (4) Sulfurization step: blowing hydrogen sulfide gas into
the mother liquor for nickel recovery obtained in the
neutralization step to produce a sulfide containing nickel and
cobalt and separate the sulfide from a barren liquor.
[0019] Here, an outline of a practical plant based on the technique
disclosed in Japanese Patent Laid-Open No. 2005-350766 will be
described with reference to the drawings.
[0020] FIG. 2 is a smelting process diagram illustrating an example
of practical plants based on the hydrometallurgical process for
nickel oxide ore disclosed in Japanese Patent Laid-Open No.
2005-350766.
[0021] As shown in FIG. 2, in (1) ore processing step, nickel oxide
ore 8 first forms a mixed solution with water, and the mixed
solution is then subjected to foreign matter removal therefrom and
ore particle size adjustment to form an ore slurry 9.
[0022] Next, in (2) leaching step, the resulting ore slurry 9 is
subjected to high pressure acid leach using sulfuric acid to form a
leach slurry 10.
[0023] The resulting leach slurry 10 is subjected to (3)
solid-liquid separation step followed by multi-stage washing to be
separated into a leachate 11 containing nickel and cobalt and a
leach residue slurry 12.
[0024] The separated leachate 11 is subjected to (4) neutralization
step to be separated into a neutralized precipitate slurry 13
containing trivalent iron hydroxide and mother liquor (1) 14 for
nickel recovery (1).
[0025] The separated mother liquor (1) 14 as one product is
subjected to (5) zinc removal step of adding a sulfurizing agent to
be separated into a zinc sulfide precipitate 15 containing zinc
sulfide and mother liquor (2) 16 for nickel recovery.
[0026] The mother liquor (2) 16 as the other product is subjected
to (6) sulfurization step to be separated into a mixed sulfide 17
containing nickel and cobalt and a barren liquor 18 from which
nickel and the like are removed. The barren liquor 18 is used as
washing water for a leach residue in (3) solid-liquid separation
step.
[0027] Finally, the leach residue slurry 12 is subjected to (7)
final neutralization step together with excess barren liquor 18 to
be neutralized, and a final neutralized residue 19 is stored in a
tailings dam 20.
[0028] The features of the method disclosed in Japanese Patent
Laid-Open No. 2005-350766 include the following: the consumption of
a neutralizing agent and the amount of precipitates in the
neutralization step can be reduced by the multi-stage washing of
the leach slurry in the solid-liquid separation step; since the
true density of the leach residue can be increased, solid-liquid
separation characteristics can be improved; and the process is
simplified by performing the leaching step only by high pressure
acid leach. Thus, the method disclosed in Japanese Patent Laid-Open
No. 2005-350766 is considered to be advantageous against the method
proposed in Japanese Patent Laid-Open No. H06-116660.
[0029] Moreover, it is considered that, when the barren liquor is
used as a washing solution to be used in the solid-liquid
separation step, nickel adhering to the leach residue can be
leached and recovered utilizing remaining sulfuric acid, and
repeated use of water can be performed effectively and
efficiently.
[0030] Further, it is considered that, when the neutralized
precipitate slurry is transferred to the solid-liquid separation
step, the loss of nickel can be reduced, which is more
advantageous.
[0031] However, the practical plant using this method will have the
following problems.
[0032] A first problem is the wear of facilities, which is required
to be suppressed.
[0033] The nickel oxide ore is conveyed between the steps in the
form of a slurry. The wear of the materials of facilities is
significantly accelerated by the conveyed slurry, and especially
the frequency of maintenance of the facilities such as piping and
pumps in the leaching step is high, which greatly causes an
increase in maintenance cost and a reduction in the rate of plant
operation.
[0034] A second problem is the amount of the final neutralized
residue, which is required to be reduced.
[0035] The leach residue obtained in the solid-liquid separation
step is combined with the excess barren liquor produced from the
sulfurization step, and the resulting mixture is rendered harmless
by the neutralization of adding a limestone slurry or a slaked lime
slurry thereto.
[0036] The final neutralized residue produced from the final
neutralization step (hereinafter, may be referred to as final
neutralization step), which is stored in a tailings dam, contains
not only impurity components such as hematite and chromite in the
leach reside but also gypsum formed by the neutralization.
Therefore, the final neutralized residue cannot be recycled, and
the construction and the maintenance of the tailings dam have been
a heavy cost burden.
[0037] Therefore, a solution to the above problems has been
required for a practical plant using a hydrometallurgical process
based on a conventional high pressure acid leach process.
[0038] Further, in order to solve the above problems effectively
and economically, it is an effective means to efficiently separate
and recover impurity components contained in the ore or the leach
residue, and it has also been required to recycle and effectively
use these impurity components.
[0039] Therefore, the present applicant has proposed, in Japanese
Patent Laid-Open No. 2010-95788, a hydrometallurgical process for
nickel oxide ore including, in the hydrometallurgical steps based
on a high pressure acid leach process, a step of a physically
separating and recovering, from an ore slurry, particles containing
at least one selected from silica mineral, chromite, and
silica-magnesia mineral and a step of a physically separating and
recovering hematite particles in a leach residue slurry. However,
further improvement has been required for efficiently separating
and recovering the impurity components contained in the ore or the
leach residue.
[0040] In view of such circumstances, an object of the present
invention is to provide, in view of the problems of conventional
art, a hydrometallurgical process for nickel oxide ore for
recovering nickel and cobalt from nickel oxide ore using a high
pressure acid leach process including an ore processing step, a
leaching step, a solid-liquid separation step, a neutralization
step, a zinc removal step, a sulfurization step, and a final
neutralization step, in which the problems are solved by
suppressing the wear, caused by an ore slurry produced from the ore
processing step, of facilities such as conveyance piping and a pump
for conveying the ore slurry and improving the durability of the
facilities to thereby increase the percentage of a solid in the ore
slurry to simplify the facilities in the ore processing step, and
by reducing the amount of a final neutralized residue produced from
the final neutralization step and compressing the capacity of a
tailings dam for storing a leach residue, a neutralized
precipitate, and the like to be discarded to thereby reduce cost
and environmental risk; and impurity components such as chromite
and hematite which can be recycled and effectively used as a
resource can be separated and recovered.
SUMMARY
[0041] In order to achieve the above object, the present inventors
have made extensive and intensive studies on the solution of the
above problems in the hydrometallurgical process for recovering
nickel and cobalt from nickel oxide ore by a high pressure acid
leach process. As a result, the present inventors have found that a
method including: step (A) of separating and recovering, by a
specific method, particles containing chromite in an ore slurry
produced from an ore processing step; and, after a leaching step
and a solid-liquid separation step after step (A), at least one
step selected from steps (B) of neutralizing and recovering by a
specific method which does not produce gypsum is effective as a
solution of the above problems, and the present invention has been
completed based on this finding.
[0042] Specifically, the first aspect of the present invention is a
hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process
including an ore processing step, a leaching step, a solid-liquid
separation step, a neutralization step, a zinc removal step, a
sulfurization step, and a final neutralization step, the method
further including step (A): a step of separating chromite particles
from an ore slurry produced in the ore processing step by a
recovery process including specific gravity separation, and then
classifying the chromite particles to recover a high-concentration
chromite concentrate having the grade of chromium(III) oxide of at
least more than 50% by weight.
[0043] Specifically, the second aspect of the present invention is
a hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process
including an ore processing step, a leaching step, a solid-liquid
separation step, a neutralization step, a zinc removal step, a
sulfurization step, and a final neutralization step, the method
including step (A) and, after passing through step (A), further
including step (B-1) or step (B-2):
[0044] step (A): a step of separating chromite particles from an
ore slurry produced in the ore processing step by a recovery
process including specific gravity separation, and then classifying
the chromite particles to recover a high-concentration chromite
concentrate having the grade of chromium(III) oxide of at least
more than 50% by weight;
[0045] step (B-1): a neutralization step of subjecting a leachate
to neutralization, the leachate being produced by subjecting the
ore slurry, in which the chromium grade has been reduced by
separating the chromite particles in step (A), sequentially to the
leaching step and the solid-liquid separation step, wherein at
least one of a calcium-based neutralizing agent and a
magnesium-based neutralizing agent is used for the neutralization;
and
[0046] step (B-2): a neutralization step of subjecting a leach
residue slurry to neutralization, the leach residue slurry being
produced by subjecting the ore slurry, in which the chromium grade
has been reduced by separating the chromite particles through step
(A), sequentially to the leaching step and the solid-liquid
separation step, to thereby recover hematite particles from the
leach residue slurry, wherein a magnesium-based neutralizing agent
is used for the neutralization to recover hematite particles from
the leach residue slurry.[0023]
[0047] The third aspect of the present invention is a
hydrometallurgical process for nickel oxide ore for recovering
nickel and cobalt using a high pressure acid leach process
including an ore processing step, a leaching step, a solid-liquid
separation step, a neutralization step, a zinc removal step, a
sulfurization step, and a final neutralization step, the method
including step (A), step (B-1), and step (B-2):
[0048] step (A): a step of separating chromite particles from an
ore slurry produced in the ore processing step by a recovery
process including specific gravity separation, and then classifying
the chromite particles to recover a high-concentration chromite
concentrate having the grade of chromium(III) oxide of at least
more than 50% by weight;
[0049] step (B-1): a neutralization step of subjecting a leachate
to neutralization, the leachate being produced by subjecting the
ore slurry, in which the chromium grade has been reduced by
separating the chromite particles in step (A), sequentially to the
leaching step and the solid-liquid separation step, wherein at
least one of a calcium-based neutralizing agent and a
magnesium-based neutralizing agent is used for the neutralization;
and
[0050] step (B-2): a neutralization step of subjecting a leach
residue slurry to neutralization, the leach residue slurry being
produced by subjecting the ore slurry, in which the chromium grade
has been reduced by separating the chromite particles in step (A),
sequentially to the leaching step and the solid-liquid separation
step, to thereby recover hematite particles from the leach residue
slurry, wherein a magnesium-based neutralizing agent is used for
the neutralization to recover hematite particles from the leach
residue slurry.
[0051] The fourth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to third aspects, wherein the recovery process in step (A)
includes subjecting the ore slurry to classification with a cyclone
to form a particulate iron-leaned ore slurry in which fine iron
hydroxide particles have been reduced, and then recovering chromite
particles from the particulate iron-leaned ore slurry having
contained the chromite particles as a chromite concentrate using
specific gravity separation.
[0052] The fifth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
fourth aspect, wherein the recovery process in step (A) includes
subjecting the ore slurry to classification with a cyclone without
diluting the slurry concentration of the ore slurry.
[0053] The sixth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to fifth aspects, wherein the recovery process in step (A)
includes collecting the whole amount of the chromite excluding
unavoidable loss into the underflow in the classification with a
cyclone.
[0054] The seventh aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to sixth aspects, wherein the specific gravity separation
includes a step of using a density separator.
[0055] The eighth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to sixth aspects, wherein the specific gravity separation
includes a step of using a spiral concentrator.
[0056] The ninth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to sixth aspects, wherein the specific gravity separation
includes a step of using a density separator and a step of using a
spiral concentrator.
[0057] The tenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
seventh and ninth aspects, wherein the step of using a density
separator includes treating a concentrated slurry with the density
separator twice or more.
[0058] The eleventh aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
eighth and ninth aspects, wherein the step of using a spiral
concentrator includes treating a concentrated slurry with the
spiral concentrator twice or more.
[0059] The twelfth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
eighth, ninth, and eleventh aspects, wherein the pulp content of
the slurry fed to the spiral concentrator is 15 to 35% by weight of
solid, preferably 20 to 30% by weight of solid.
[0060] The thirteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
seventh, ninth, and tenth aspects, wherein the amount of Teeter
water fed to the density separator is 0.5 to 7.0 [m3h-1/m2].
[0061] The fourteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to thirteenth aspects, wherein the chromite concentrate
separated by specific gravity separation is subjected to magnetic
separation which is a physical separation to remove magnetite from
the chromite concentrate as a magnetic material and recover a
non-magnetic material as a high-concentration chromite
concentrate.
[0062] The fifteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
second or third aspect, wherein step (B-2) includes setting pH
after neutralization at 4 to 7 and after the neutralization,
performing final neutralization with an alkali other than the
magnesium-based neutralizing agent.
[0063] The sixteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
second or third aspect, wherein step (B-2) includes subjecting the
leach residue slurry or a neutralized residue slurry including the
leach residue slurry to classification with a cyclone to recover a
classified fine particle portion obtained by the classification as
a concentrate of hematite.
[0064] The seventeenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to sixteenth aspects, wherein the ore processing step is a
step of performing removal of foreign matter contained in the mined
raw material ore and particle size adjustment of the ore to form an
ore slurry; the leaching step is a step of adding sulfuric acid to
the ore slurry and stirring the resulting mixture at high
temperature and high pressure to form a leach slurry including a
leach residue and a leachate; the solid-liquid separation step is a
step of subjecting the leach slurry to multi-stage washing to
obtain a leachate containing nickel and cobalt and a leach residue
slurry; the neutralization step is a step of adding an alkali to
the leachate to form a neutralized precipitate slurry containing
trivalent iron and mother liquor for recovering nickel; the zinc
removal step is a step of blowing hydrogen sulfide gas into the
mother liquor to form a zinc sulfide precipitate slurry and mother
liquor for nickel and cobalt recovery; the sulfurization step is a
step of blowing hydrogen sulfide into the mother liquor for nickel
and cobalt recovery to produce a mixed sulfide containing nickel
and cobalt and a barren liquor; and the final neutralization step
is a step of adding excess barren liquor to the leach residue
slurry and adjusting pH to 8 to 9 to obtain a final neutralized
residue.
[0065] The eighteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to seventeenth aspects, wherein the particle size adjustment
of the ore in the ore processing step is performed by sieving with
a particle size of 2 mm or less.
[0066] The nineteenth aspect of the present invention is the
hydrometallurgical process for nickel oxide ore according to the
first to eighteenth aspects, wherein the grade of chromium(III) the
concentrated chromite is 41% by weight or more.
Advantageous Effect of Invention
[0067] The hydrometallurgical process for nickel oxide ore of the
present invention produces an industrially remarkable effect
because conventional problems can be solved as shown below by
adopting step (A) and step (B) in a hydrometallurgical process for
recovering nickel and cobalt from nickel oxide ore using a high
pressure acid leach process including an ore processing step, a
leaching step, a solid-liquid separation step, a neutralization
step, a zinc removal step, a sulfurization step, and a final
neutralization step.
[0068] By adopting step (A) in the present invention, particles
containing chromite in the ore slurry produced from the ore
processing step can be separated and recovered to thereby
significantly suppress the wear of facilities such as piping and a
pump during the conveyance of the ore slurry.
[0069] Further, since chromite is separated before the
hydrometallurgy, a reduction in the amount of the leach residue can
be expected, and the amount of a final neutralized residue can also
be reduced. Furthermore, if the separated chromite is concentrated,
the concentrate can also be effectively used as a resource.
[0070] By adopting step (B) in the present invention, hematite in
the leach residue produced from the solid-liquid separation step is
separated and recovered to thereby achieve a reduction in the
amount of a final neutralized residue produced from the final
neutralization step, thereby capable of compressing the capacity of
a tailings dam for storing a leach residue, a neutralized
precipitate, and the like to be discarded to thereby reduce cost
and environmental risk, and the hematite separated and recovered
can also be effectively used as an iron resource.
BRIEF DESCRIPTION OF DRAWINGS
[0071] FIG. 1 is a smelting process diagram showing an embodiment
of the hydrometallurgical process for nickel oxide ore according to
the present invention.
[0072] FIG. 2 is a smelting process diagram showing an example of a
practical plant based on a conventional hydrometallurgical process
for nickel oxide ore.
[0073] FIG. 3 is an execution flow chart in Example 1 of the
present invention.
[0074] FIG. 4 is an execution flow chart in Example 2 of the
present invention.
[0075] FIG. 5 is an execution flow chart in Comparative Example 1
of the present invention.
[0076] FIG. 6 is an execution flow chart in Comparative Example 4
of the present invention.
DETAILED DESCRIPTION
[0077] The hydrometallurgical process for nickel oxide ore of the
present invention, for recovering nickel and cobalt using a high
pressure acid leach process including an ore processing step, a
leaching step, a solid-liquid separation step, a neutralization
step, a zinc removal step, a sulfurization step, and a final
neutralization step, includes step (A), or after passing through
step (A), includes step (B-1) and/or step (B-2).
[0078] [Steps]
[0079] Step (A)
[0080] Step (A) is a step of separating chromite particles from an
ore slurry produced in the ore processing step by a recovery
process including specific gravity separation, and then classifying
the chromite particles to recover a high-concentration chromite
concentrate. [0081] Step (B)
Step (B-1)
[0082] The ore slurry, in which the Cr grade has been reduced in
step (A), is treated in the leaching step and the solid-liquid
separation step, and a leachate after the solid-liquid separation
step is neutralized in step (B-1) with a Mg-based neutralizing
agent such as Mg(OH).sub.2 and MgO and a Ca-based neutralizing
agent such as CaCO.sub.3 and Ca(OH).sub.2.
Step (B-2)
[0083] The ore slurry, in which the Cr grade has been reduced in
step (A), is treated in the leaching step and the solid-liquid
separation step, and a leach residue slurry after the solid-liquid
separation step is neutralized in step (B-2) with a Mg-based
neutralizing agent such as Mg(OH).sub.2 and MgO to recover hematite
particles.
[0084] It is important for solving problems that the production
method of the present invention includes step (A) as an essential
step.
[0085] By adopting step (A), particles containing chromite in the
ore slurry produced from the ore processing step as the previous
step are separated and recovered to thereby impart the effect of
suppressing the wear of facilities such as piping and a pump during
the conveyance of the ore slurry.
[0086] That is, the wear is suppressed by separating chromite
having extremely high hardness generally contained in nickel oxide
ore. Further, a reduction in the amount of a leach residue can be
expected by removing chromite in advance from the ore slurry before
hydrometallurgy, and, as a result, the amount of a final
neutralized residue can also be reduced.
[0087] Furthermore, if the chromite which has been separated and
recovered can be sufficiently concentrated, it can also be
effectively used as a resource.
[0088] On the other hand, by adopting step (B) including step (B-1)
and step (B-2), hematite in the leach residue produced from the
solid-liquid separation step is separated and recovered to thereby
reduce the amount of a final neutralized residue produced from the
final neutralization step, thereby capable of compressing the
capacity of a tailings dam for storing a leach residue, a
neutralized precipitate, and the like to be discarded to thereby
reduce cost and environmental risk. At the same time, the hematite
separated and recovered can also be effectively used as an iron
resource.
[0089] That is, since iron in the nickel oxide ore is hydrolyzed at
a high temperature in the leaching step, iron is contained in the
form of hematite in the final neutralized residue. However, since
the final neutralized residue contains not only chromite in the
leach residue but also gypsum formed by neutralization using a
neutralizing agent containing Ca, the iron grade is as low as 30 to
40% by weight, and it is difficult to effectively use the final
neutralized residue as it is as an ironmaking raw material or the
like.
[0090] This is because sulfur (gypsum; calcium sulfate), chromium
(chromite), and the like contained in the final neutralized residue
are components that influence the distribution of minor components
into pig iron, the quality of steel products, and the like, and it
is required to suppress the inclusion of these impurity
elements.
[0091] In contrast, since the neutralization in step (B-2) of the
present invention is performed only by using a Mg-based
neutralizing agent, MgSO4 having high solubility is produced to
suppress the fixing of sulfur to a solid and allow hematite having
a low sulfur grade to be separated and recovered.
[0092] Next, the outline of the hydrometallurgical process for
nickel oxide ore of the present invention will be described with
reference to FIG. 1.
[0093] FIG. 1 is a smelting process diagram showing an embodiment
of the hydrometallurgical process for nickel oxide ore according to
the present invention.
[0094] As shown in FIG. 1, in [1] ore processing step, nickel oxide
ore 8 first forms a mixed solution with water, and foreign matter
removal from the mixed solution and ore particle size adjustment
are then performed to form an ore slurry 9.
[0095] Subsequently, the ore slurry 9 is subjected to newly
provided step (A) to separate and recover chromite 23. An autoclave
feed slurry 22 as the other product is subjected to [2] leaching
step.
[0096] Here, valuable components such as nickel and cobalt are
leached with sulfuric acid from the autoclave feed slurry 22 using
an autoclave or the like to form a leach slurry 10.
[0097] The formed leach slurry 10 is subjected to [3] solid-liquid
separation step using a multi-stage thickener or the like to be
separated into a leachate 11 containing nickel and cobalt and a
leach residue slurry 12.
[0098] The separated leachate 11 is subjected to step (B-1) to be
separated into a residue after step (B-1) 26 containing trivalent
iron hydroxide as a main component and mother liquor (1) 14
containing nickel.
[0099] The separated mother liquor (1) 14 as one product is
subjected to [5] zinc removal step of adding a sulfurizing agent to
be separated into a zinc sulfide precipitate 15 containing zinc
sulfide and mother liquor (2) 16 for nickel recovery.
[0100] Next, the mother liquor (2) 16 as the other product is
subjected to [6] sulfurization step of adding a sulfurizing agent
to be separated into a mixed sulfide 17 containing nickel and
cobalt and a barren liquor 18.
[0101] Note that the barren liquor 18 is used as washing water for
a leach residue in [3] solid-liquid separation step. The barren
liquor 18 may also be fed to the final neutralization step.
[0102] A part of the leach residue slurry 12 is fed to step (B-2)
together with excess barren liquor 18 and subjected to
neutralization to separate and recover hematite 28.
[0103] At this time, a treatment solution after step (B-2) 27 and
the leach residue slurry 12 which has not be fed to step (B-2) are
fed to [7] final neutralization step and neutralized to a pH of
about 8 to 9.
[0104] A resulting final neutralized residue 19 is stored in a
tailings dam 20.
[0105] Hereinafter, each step will be described further in
detail.
[1] Ore Processing Step and Step (A)
[0106] The ore processing step is a step of performing foreign
matter removal and ore particle size adjustment to form an ore
slurry.
[0107] In this step, nickel oxide ore is sieved by elutriation or
the like to separate foreign matter that cannot be leached in the
leaching step, an ore that is hardly transported with a pump, and
the like.
[0108] Generally, the sieving particle size is about 2 mm, and an
ore having a particle size larger than about 2 mm is classified and
separated.
[0109] A slurry is formed of an ore passed through the sieving
treatment, and the slurry is then settled and concentrated to
prepare an autoclave feed slurry in which the solid concentration
in the slurry (hereinafter, referred to as slurry concentration)
has been adjusted. Note that the slurry concentration may be
generally suitably adjusted to about 30 to 45% by weight.
[0110] The nickel oxide ore serving as a raw material to be treated
by the hydrometallurgical process of the present invention is
mainly so-called lateritic ore, such as limonite ore and saprolite
ore.
[0111] The nickel content of the lateritic ore is normally 0.8 to
2.5% by weight, and nickel is contained as hydroxide or hydrous
silica-magnesia (magnesium silicate) mineral.
[0112] Further, the iron content is 10 to 50% by weight, and
although iron is mainly in the form of trivalent hydroxide
(goethite), divalent iron is partly contained in hydrous
silica-magnesia mineral or the like. Silicic acid components are
contained in silica mineral, such as quartz and cristobalite
(amorphous silica), and hydrous silica-magnesia mineral.
[0113] Furthermore, most of chromium components are contained in an
amount of 1 to 5% by weight as chromite mineral containing iron or
magnesium. In addition, magnesia components are contained not only
in hydrous silica-magnesia mineral but also in silica-magnesia
mineral substantially containing no nickel which is unweathered and
has high hardness.
[0114] As described above, in lateritic ore, silica mineral,
chromite mineral, and silica-magnesia mineral are so-called gangue
components which do not substantially contain nickel.
[0115] That is, the ore slurry produced from the ore processing
step contains chromite which generally gives significant influence
on the wear of facilities such as piping and a pump in the leaching
step.
[0116] Therefore, it is desirable to separate and recover chromite
in advance in the ore processing step from the ore slurry prepared
in the ore processing step.
[0117] Here, the distribution state of each component in the ore
particles constituting the ore slurry will be described.
[0118] The EPMA observation of nickel oxide ore shows that a
portion having high chromium content is present as a single phase
independent of a portion having high iron content in a relatively
high ratio, and a large number of the portion having high chromium
content has a particle size of 20 to 1000 .mu.m.
[0119] This shows that the mineral containing chromium is contained
at a higher level in particles having a size of about 20 .mu.m or
more, while the mineral containing nickel and iron is contained at
a higher level in particles having a size of about 20 .mu.m or
less.
[0120] Therefore, in order to effectively separate and recover
chromite from the ore slurry, it is important to slurry the ore
after removing coarse particles, crush nickel oxide ore in the ore
slurry so that it may have a suitable particle size, and set a
suitable classification particle size.
[0121] Note that the crushed particle size at this time, which is
determined in consideration of the original purpose for forming the
ore slurry, is preferably about 2 mm or less.
[0122] Table 1 shows an example of the ore particle size
distribution of the ore slurry obtained by crushing the ore to a
particle size of about 2 mm or less and the grade of each component
in each particle size section.
[0123] From Table 1, it can be seen that chromium, silicon,
magnesium, and the like are concentrated in the coarse particle
portions having a particle size of 75 .mu.m or more, while iron is
concentrated in the fine particle portion having a particle size of
75 .mu.m or less.
TABLE-US-00001 TABLE 1 Distribution Particle size [% by Chemical
composition [% by weight] [.mu.m] weight] Fe Cr Si Mg -2000 + 1400
0.9 36.0 2.0 14.0 6.0 +850 1.8 37.0 3.0 13.0 6.0 +355 2.7 33.0 3.0
12.0 5.0 +75 5.3 42.0 5.0 9.0 3.0 -75 89.3 47.0 3.0 6.0 2.0 Average
100.0 45.7 2.7 6.6 2.0
[0124] Next, step (A) is a step of separating and recovering
chromite in the ore slurry produced from the ore processing step.
Mineral particles of silica mineral, silica-magnesia mineral, or
the like can also be separated and removed as intermediates of the
step.
[0125] Note that step (A) may also be performed included in the ore
processing step or performed following the ore processing step.
[0126] The method of step (A) is not particularly limited, but
methods using various physical separation means to separate
chromite from the ore slurry can be applied to the method of step
(A). Among the physical separation means, in order to concentrate
chromite up to, for example, 41 to 50% by weight Cr.sub.2O.sub.3 in
which chromite is easily recycled as a resource after it is
separated and recovered, a wet-physical separation method including
specific gravity separation and classification for recovery of the
ore in the particle-size range in which chromite is concentrated
are essential from the analysis of the distribution state of each
component in the ore particles constituting the ore slurry.
[0127] That is, as shown in Table 1, the grade which can be
concentrated by classification is limited, and separation utilizing
specific-gravity difference is required in addition to
classification.
[0128] The classification particle size in the classification may
be any particle size as long as goethite containing nickel in the
fine particle portion is efficiently separated, and is preferably
selected from the range of 20 to 150 .mu.m, more preferably 45 to
75 .mu.m.
[0129] That is, the lower limit of the classification point that
can be industrially performed is about 20 and when the
classification particle size is less than 20 the concentration of
chromite in the coarse particle portion will be insufficient, and
nickel in the ore slurry used in the leaching step will be lost. On
the other hand, when the classification particle size is more than
150 .mu.m, the removal of silica mineral, chromite, and
silica-magnesia in the fine particle portion will be
insufficient.
[0130] Further, the technique in the classification is not
particularly limited, but it is desirable to select cyclone
classification which has high performance and is capable of
large-amount treatment.
[0131] Generally, it is known that the specific gravity of chromite
is higher than that of iron hydroxide such as goethite, and
chromite that is coarse and has a high specific gravity and
goethite that is fine and has a low specific gravity can be
efficiently separated with a cyclone.
[0132] The operating pressure of the cyclone is desirably 0.1 to
0.3 MPa when separation performance and treatment speed are taken
into consideration.
[0133] The shape of the cyclone is desirably adjusted so that the
pulp content of the underflow may be 50% by weight or more.
[0134] Further, the pulp content of the ore slurry to be fed to the
cyclone is, but not particularly limited to, preferably 10 to 30%
by weight, more preferably 15 to 20% by weight.
[0135] The separation with the cyclone can be performed even if the
pulp content is less than 10% by weight, but such a pulp content
requires a large amount of water and is disadvantageous for the
settling and concentration in a subsequent step. Further, if the
pulp content is higher than 30% by weight, the viscosity of the
slurry may increase to disturb the separation.
[0136] That is, when the pulp content after the ore processing step
is set to the above range of 10 to 30% by weight, additional
feeding of water is not required, and a tank for dilution is also
not required. Therefore, the above pulp content range is
preferred.
[0137] By optimizing the pulp content, the cyclone operating
pressure, and the cyclone shape as described above, the
distribution of chromite to the overflow can be mostly eliminated,
which is preferred in terms of chromite recovery.
[0138] After goethite containing nickel is separated and removed as
much as possible by the classification using a cyclone described
above, chromite is further concentrated with a specific gravity
separation apparatus.
[0139] The specific gravity separation apparatus to be used is not
particularly limited, but it is preferred to select at least one of
a shaking table, a density separator, and a spiral concentrator,
and it is more preferred to select at least one of a density
separator and a spiral concentrator, which are suitable for
large-amount treatment.
[0140] When a spiral concentrator is used, the pulp content of the
slurry fed thereto is preferably more than 15% by weight and less
than 35% by weight, more preferably more than 20% by weight and
less than 30% by weight.
[0141] When the pulp content is 15% by weight or less, the
separation performance may be deteriorated, and when the pulp
content is 35% by weight or more, the flow of particles on the
chromite concentration side (inner side) may stagnate during the
separation with a spiral concentrator to produce build-up to
prevent sufficient separation.
[0142] Further, when a spiral concentrator is used, the recovery
rate of chromite will be increased by subjecting chromite (outer
side) concentrated to 15% by weight or more and 40% by weight or
less to spiral treatment several times.
[0143] Further, when a density separator is used, the amount of
Teeter water is desirably set to 0.5 to 7.0 [m3h-1/m2].
[0144] Here, Teeter water refers to water for floating the above
ore particles in the density separator. Teeter water floats the ore
particles to form a fluidized bed to gather heavy particles in a
lower layer. Teeter water may also be referred to as fluidization
water.
[0145] When the amount of Teeter water is less than 0.5, the effect
of hindered settling will be small, and specific gravity separation
will not be efficiently performed.
[0146] On the other hand, when the amount of Teeter water is larger
than 7.0, even chromite particles may be caused to move upward to
be lost on the overflow side. In this case, the amount of chromite
in the slurry to be fed to the leaching step increases, which is
disadvantageous from the point of view of not only the recovery of
chromite but also the reduction in the Cr grade in hematite.
[0147] Further, the Cr.sub.2O.sub.3 grade is increased by treating
the slurry with a density separator several times.
[0148] Furthermore, the Cr.sub.2O.sub.3 grade in chromite can be
concentrated up to 41 to 50% by weight or more only by the specific
gravity separation, but in order to concentrate chromite to higher
concentration, it is desired to separate and remove magnetite
contained in a very small amount.
[0149] Since the specific gravity of magnetite to be removed is
extremely close to the specific gravity of chromite, magnetic
separation is utilized.
[0150] The magnetic field strength in the magnetic separation is
not particularly limited but varies depending on belt speed, belt
thickness, and apparatus, and it is preferably in the range of 200
[Oe] to 2000 [Oe].
[0151] If the magnetic field strength is less than 200 [Oe], the
magnetic field may be so weak that separation and removal of
magnetite may be insufficient. On the other hand, if the magnetic
field strength is more than 2000 [Oe], the removal of magnetite
will be no problem, but even chromite may be magnetized to prevent
magnetic separation.
[0152] Particularly desirably, a low-intensity magnetic separator
may be used.
[0153] Further, after specific gravity separation or magnetic
separation, chromite obtained by these treatments is subjected to
classification.
[0154] For example, a Non-Mag slurry obtained by low-intensity
magnetic separation can be subjected to classification with a
classifier provided with a 53 .mu.m-mesh screen and a 300
.mu.m-mesh screen to thereby increase the Cr.sub.2O.sub.3 grade
obtained by the classification.
[2] Leaching Step
[0155] The leaching step is a step of adding sulfuric acid to the
ore slurry obtained through the ore processing step and step (A)
and then stirring the resulting mixture at a temperature of 220 to
280.degree. C. to form a leach slurry including a leach residue and
a leachate. In this step, a preheater, an autoclave, and a flash
tank are used as main facilities.
[0156] In this leaching step, the leaching of nickel, cobalt and
the like as sulfates and the fixation of leached iron sulfate as
hematite are performed by the leaching reaction represented by
reaction formulas (1) to (3) and the high temperature thermal
hydrolysis reaction represented by reaction formulas (4) and
(5).
[0157] However, since the fixation of iron ions does not proceed to
completion, the liquid portion of the resulting leach slurry
usually contains divalent and trivalent iron ions in addition to
nickel, cobalt and the like.
[Formula 1]
[Leaching reaction]
MO+H.sub.2SO.sub.4.fwdarw.MSO.sub.4+H.sub.2O (1)
(wherein M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn, or the
like.)
2Fe(OH).sub.3+3H.sub.2SO.sub.4.fwdarw.Fe.sub.2(SO.sub.4).sub.3+6H.sub.2O
(2)
FeO+H.sub.2SO.sub.4.fwdarw.FeSO.sub.4+H.sub.2O (3)
[Formula 2]
[High temperature thermal hydrolysis reaction]
2FeSO.sub.4+H.sub.2SO.sub.4+1/2O.sub.2.fwdarw.Fe.sub.2(SO.sub.4).sub.3+H-
.sub.2O (4)
Fe.sub.2(SO.sub.4).sub.3+3H.sub.2O.fwdarw.Fe.sub.2O.sub.3+3H.sub.2SO.sub-
.4 (5)
[0158] The reaction temperature in the leaching step is 220 to
280.degree. C., preferably 240 to 270.degree. C.
[0159] That is, iron is fixed as hematite by performing the
reactions in this temperature range.
[0160] If the reaction temperature is lower than 220.degree. C.,
iron will remain dissolved in the reaction solution since the rate
of the high temperature thermal hydrolysis reaction is slow.
Therefore, the solution purification load for removing iron will
increase, making it very difficult to separate iron from nickel. On
the other hand, if the temperature is higher than 280.degree. C.,
the high temperature thermal hydrolysis reaction itself will be
accelerated, but it will be difficult to select a material of a
vessel used in high pressure acid leach, and the steam cost for
increasing temperature will also increase. Therefore, a temperature
of higher than 280.degree. C. is not suitable.
[0161] The amount of sulfuric acid used in the leaching step is,
but not particularly limited to, a slightly excessive amount
relative to the stoichiometric amount required for iron in the ore
to be leached and converted to hematite, for example, 300 to 400 kg
per ton of the ore. Particularly, if the amount of sulfuric acid
added per ton of the ore is more than 400 kg, the cost of sulfuric
acid and the cost of a neutralizing agent in a subsequent step will
increase. Therefore, such an amount is not preferred. Further, the
amount of sulfuric acid used in view of a leaching step product is
aimed to be 25 to 50 g/L, preferably 35 to 45 g/L, in terms of the
concentration of free sulfuric acid at the completion of
leaching.
[0162] By satisfying the above conditions, the true density of the
leach residue is increased; a high density leach residue is stably
produced; and the solid-liquid separability of the slurry is
improved. As a result, the facilities of the solid-liquid
separation step, which is the subsequent step, can be
simplified.
[0163] That is, when the slurry containing the leaching residue is
settled, if the above concentration is less than 25 g/L, the
settling concentration of solids will be incomplete, and floating
solids will remain in the supernatant. This is because the rate of
high temperature thermal hydrolysis reaction is slow; dehydration
of iron hydroxide does not proceed sufficiently; and hematite
having a low true density is formed.
[0164] On the other hand, if the above concentration is more than
50 g/L, it will be necessary to improve the durability of leaching
facilities, and the amount of a neutralizing agent required for
neutralizing the acid will be significantly increased. Therefore,
such a concentration is disadvantageous in terms of cost.
[3] Solid-Liquid Separation Step
[0165] The solid-liquid separation step is a step of subjecting the
leach slurry formed in the previous leaching step to multi-stage
washing to obtain a leachate containing nickel and cobalt and a
leach residue. Thereby, nickel and the like which adhere to the
leach residue and are discarded are recovered in the leachate
[4] Neutralization Step [Step (B-1) and Step (B-2)]
(4-1) Neutralization Step 1 [Treatment of Leachate]
[0166] Step (B-1)
[0167] Step (B-1) is a step of neutralizing the leachate 11
separated in the previous solid-liquid separation step,
specifically a step of adding a neutralizing agent (pH adjuster) to
the leachate 11 obtained in the leaching step so that it has a pH
in the range of 4 or less, preferably 3.2 to 3.8, while suppressing
the oxidation of the leachate 11, to form a residue after step
(B-1) 26 as a neutralized precipitate slurry containing trivalent
iron and mother liquor (1) 14 for nickel recovery.
[0168] By using this step, the excess acid used in the leaching
step is neutralized, and trivalent iron ions remaining in the
leachate are removed.
[0169] If pH exceeds 4 in the neutralization, the production of
nickel hydroxide will increase.
[0170] Therefore, it is preferred to use, as a neutralizer, a
Mg-based neutralizer which does not contain Ca, such as a Mg-based
alkali such as Mg(OH).sub.2, and MgO which dissolves in the
leachate and shows alkalinity.
[0171] When a neutralizing agent containing Ca, such as CaCO.sub.3,
is used, gypsum will be produced. A part of the residue after step
(B-1) 26 as the neutralized precipitate slurry produced in this
step is returned to the solid-liquid separation step and repeatedly
used. Therefore, incorporation of gypsum into the leach residue
slurry may occur, which does not give significant influence on the
hematite grade since the amount of gypsum is small. Here, a
Ca-based neutralizer may be used without problems.
[5] Zinc Removal Step
[0172] The zinc removal step is a step of blowing hydrogen sulfide
gas into the mother liquor obtained in the previous step to produce
a sulfide containing zinc to form a zinc sulfide precipitate slurry
and mother liquor for nickel and cobalt recovery, prior to the step
of separating nickel and cobalt as sulfides.
[0173] This is a step of selectively removing zinc by suppressing
the rate of sulfurization reaction by generating mild conditions in
the sulfurization reaction to suppress the co-precipitation of
nickel which co-exists at a higher concentration than zinc.
[0174] The resulting zinc sulfide precipitate slurry can be sent to
the final neutralization step (7) and treated, similar to the
neutralized precipitate slurry obtained in the neutralization
step.
[6] Sulfurization Step
[0175] The sulfurization step is a step of blowing hydrogen sulfide
into the mother liquor (2) for nickel and cobalt recovery obtained
in the zinc removal step to produce a mixed sulfide (zinc sulfide
precipitate) 17 containing nickel and cobalt and barren liquor
18.
[0176] Here, the resulting barren liquor 18 has a pH of about 1 to
and contains not only impurities such as iron, magnesium, and
manganese which are contained without being sulfurized, but also a
very small amount of nickel and cobalt as a recovery loss.
Therefore, the barren liquor 18 is used as washing water for the
leach residue in the solid-liquid separation step and as washing
water for the neutralization residue produced in the neutralization
step.
(4-2) Neutralization Step 2 [Treatment of Leach Residue Slurry]
[0177] Step (B-2)
[0178] Step (B-2) is a step of neutralizing a part of the leach
residue (leach residue slurry: represented by reference numeral 12
in FIG. 1) produced in the solid-liquid separation step with a
Mg-based neutralizing agent, such as a Mg-based alkali, such as
Mg(OH)2, and MgO to recover hematite particles.
[0179] The method for step (B-2) is not particularly limited, but a
Ca-based alkali is not used as a neutralizing agent. For example,
if CaCO.sub.3 is used as a neutralizing agent, it will react with
adhering sulfuric acid to produce gypsum. Since the gypsum has low
solubility, it is precipitated as a solid and increases the sulfur
grade in the residue. On the other hand, since MgSO.sub.4 has high
solubility, it is not easily precipitated as a solid and effective
for reducing sulfur.
[0180] Therefore, as a neutralizing agent, Mg(OH)2 which is a
Mg-based alkali is preferred, but a Mg-based neutralizing agent
such as MgO may be used.
[0181] Here, the analysis of the distribution state of each
component in the ore particles constituting the leach residue
slurry 12 will be described.
[0182] First, Table 2 shows an example of the ore particle size
distribution of the leach residue obtained by leaching the ore
slurry obtained by crushing the ore to a particle size of about 2
mm or less and the grade of each component in each particle size
section.
TABLE-US-00002 TABLE 2 Distribution Particle size [% by Chemical
composition [% by weight] [.mu.m] weight] Fe Cr Si Mg -2000 + 1400
0.0 -- -- -- -- +850 0.0 -- -- -- -- +355 0.1 28.0 2.0 24.0 0.0 +75
0.7 26.0 7.0 25.0 1.0 -75 99.1 45.0 2.0 8.0 1.0 Average 100.0 44.6
2.5 7.8 1.0
[0183] As shown in Table 2, it can be seen that iron is
concentrated in the fine particle portion having a particle size of
75 .mu.m or less, and silicon is separated from this portion. Note
that the analysis of the leach residue has been performed for a
leach residue slurry which had been washed with water to remove
adhering sulfuric acid.
[0184] From the above results, utilizing the fact that the
particles containing iron in a high content are finer particles
than particles containing chromium, silicon, and the like in high
contents, the particles containing iron in a high content can be
separated from the coarse particle portion containing chromium,
silicon, and the like in high contents and driven away out of the
system to recover hematite as a resource by screening means such as
a classification method.
[0185] The classification method is preferably a treatment with a
cyclone or the like which is capable of large-amount treatment.
[7] Final Neutralization Step
[0186] The final neutralization step is a step of adding the
treatment solution after step (B-2) 27 obtained in step (B-2), the
leach residue slurry 12 after the solid-liquid separation step
which has not been treated in step (B-2), the residue after step
(B-1) 26, and optionally a slurry formed from the zinc sulfide
precipitate 15 obtained in the zinc removal step to prepare a
mixture and further adding a limestone slurry and a slaked lime
slurry to the mixture to adjust the pH to about 8 or 9, thereby
precipitating metal ions in the solution as a neutralized
precipitate to obtain a final neutralized residue 19. Note that the
resulting final neutralized residue 19 is stored in the tailings
dam 20.
EXAMPLES
[0187] Hereinafter, the present invention will be further described
by Examples, but the present invention is not limited at all to
these Examples.
[0188] In Examples, X-ray fluorescence analysis or ICP emission
spectrometry was used for analyzing metals.
Example 1
[0189] In the production flow of the present invention in FIG. 1,
the ore slurry 9 was subjected to step (A) according to the
execution flow chart shown in FIG. 3, in which the ore slurry 9 was
subjected to classification with a hydrocyclone to separate
goethite and then subjected to specific gravity separation once
with a density separator and a spiral concentrator in combination
in this order.
[0190] The ore slurry having the composition shown in Table 3 was
classified using a hydrocyclone (manufactured by Daiki Ataka
Engineering Co., Ltd., Model MD-9) as a classifier used in step
(A).
[0191] In Example 1, the classification was performed under the
conditions of a slurry concentration of 15% by weight, a slurry
temperature of normal temperature, and an operating pressure of 0.2
MPa.
[0192] The ore slurry composition and the composition of the
underflow from the hydrocyclone (hydrocyclone U/F) are shown
together in Table 3. Note that the unit in the following tables is
% by weight.
TABLE-US-00003 TABLE 3 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Ore slurry
2.5 4.4 51.5 1.2 Hydrocyclone U/F 13.5 6.0 45.2 0.8 Unit: % by
weight
[0193] As shown in Table 3, in the coarse particle portion obtained
from the hydrocyclone (hydrocyclone U/F), the level of
Cr.sub.2O.sub.3 increased to 13.5% by weight versus 2.5% by weight
in the feed, and the level of SiO.sub.2 increased to 6.0% by weight
versus 4.4% by weight in the feed; on the other hand, the level of
Fe decreased to 45.2% by weight versus the iron grade of 51.5% by
weight in the feed.
[0194] The above results show that silica mineral and chromite are
concentrated and separated in the coarse particle portion by the
classification of the ore slurry.
[0195] Next, in order to grasp the separability of a density
separator, the hydrocyclone U/F (slurry concentration: 33% by
weight) was fed to a density separator (manufactured by Outotec,
Inc., "Tanksizer TS-Lab", tank inside diameter: 228.6 mm).
[0196] The feed rate of the slurry was set to 56 [kg/Hr], and the
slurry temperature was set to normal temperature.
[0197] The treatment was performed by setting the amount of Teeter
water at this time to 6.9 [m3h-1/m2] and the set point (set value
of a density meter) to 20.
[0198] The compositions of the feed to the density separator
(hydrocyclone U/F) and the underflow from the density separator
(density separator U/F) are shown in Table 4.
TABLE-US-00004 TABLE 4 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Hydrocyclone
U/F 13.5 6.0 45.2 0.8 Density separator U/F 16.9 1.9 35.2 0.7 Unit:
% by weight
[0199] As shown in Table 4, in the coarse particle portion obtained
from the density separator (density separator U/F), the level of
Cr.sub.2O.sub.3 increased to 16.9% by weight versus 13.5% by weight
at the classification with the hydrocyclone (hydrocyclone U/F); on
the other hand, the level of SiO.sub.2 decreased to 1.9% by weight
versus 6.0% by weight, and the level of iron decreased to 35.2% by
weight versus 45.2% by weight.
[0200] The above results show that chromite is concentrated and
separated in the coarse particle portion by the density separator
treatment.
[0201] Further, in order to grasp the separability of a spiral
concentrator, the hydrocyclone U/F (slurry concentration: 33% by
weight) was subjected to a separation test with a spiral
concentrator (manufactured by Outotec, Inc., "MC7000").
[0202] The results are shown in Table 5.
TABLE-US-00005 TABLE 5 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Hydrocyclone
U/F 13.5 6.0 45.2 0.8 Concentrate 41.1 0.5 28.3 0.2 Middling 24.4
1.5 32.5 0.4 Tailing 5.3 4.2 48.0 1.5 Unit: % by weight
[0203] As shown in Table 5, in the "Concentrate" obtained from the
spiral concentrator, the level of Cr.sub.2O.sub.3 increased to
41.1% by weight versus 13.5% by weight in the feed.
[0204] The level of Cr.sub.2O.sub.3 increased to 24.4% by weight in
the Middling. On the other hand, the level of Cr.sub.2O.sub.3 was
5.3% by weight in the Tailing.
[0205] These results show that chromite is separated also by spiral
treatment.
[0206] Then, according to the flow in FIG. 3, the density separator
U/F (1) (slurry concentration: 75% by weight) obtained from the
density separator was diluted with water to a slurry concentration
of 25% by weight, and the diluted slurry was subjected to a
separation test with a spiral concentrator (manufactured by
Outotec, Inc., "MC7000").
[0207] The results of the test are shown in Table 6.
TABLE-US-00006 TABLE 6 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Density
separator 16.9 1.9 35.2 0.7 U/F Concentrate 41.2 0.6 28.5 0.3
Middling 24.3 1.6 32.7 0.5 Tailing 5.0 4.5 48.3 1.7 Unit: % by
weight
[0208] As shown in Table 6, in the "Concentrate" obtained from the
spiral concentrator, the level of Cr.sub.2O.sub.3 increased to
41.2% by weight versus 16.9% by weight in the feed.
[0209] In the Middling, the level of Cr.sub.2O.sub.3 increased to
24.3% by weight. On the other hand, in the Tailing, the level of
Cr.sub.2O.sub.3 was 5.0% by weight.
[0210] These results show that chromite is separated by spiral
treatment.
[0211] Next, the "Concentrate" obtained from the spiral test was
diluted to a slurry concentration of 20% by weight, and the diluted
slurry was fed to a low-intensity magnetic separator (manufactured
by Outotec, Inc., "Inprosys benchtop LIMS") at a feed rate of 45.4
[kg/Hr] to obtain a magnetic material (Mag) and a non-magnetic
material (Non-Mag).
[0212] The results are shown in Table 7.
TABLE-US-00007 TABLE 7 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Feed 41.2
0.6 28.5 0.3 Mag 29.5 0.8 43.7 0.4 Non-Mag 45.3 0.6 23.1 0.2 Unit:
% by weight
[0213] As shown in Table 7, the level of Cr.sub.2O.sub.3 obtained
from the low-intensity magnetic separation (non-magnetic
material/Non-Mag) increased to 45.3% by weight versus 41.2% by
weight in the feed. On the other hand, the level of Fe decreased to
23.1% by weight from 28.5% by weight.
[0214] In contrast, from the fact that the Fe grade of
Cr.sub.2O.sub.3 (magnetic material/Mag) was as high as 43.7% by
weight, it can be seen that hematite was separated and removed by
magnetic separation, and the Cr.sub.2O.sub.3 grade of chromite
increased.
[0215] From the above results, it can be said that the ore slurry
can be concentrated to a concentration exceeding the
Cr.sub.2O.sub.3 grade of generally commercially available chromite
by sequentially treating the ore slurry with a hydrocyclone, with a
density separator twice, and with a spiral concentrator.
[0216] Further, the recovery rate of the resulting chromite was
42.5% by weight.
[0217] Note that the recovery rate was determined by the following
Formula (6).
[Expression 1]
Recovery rate [%]=weight of recovered Cr.sub.2O.sub.3/weight of
Cr.sub.2O.sub.3 in charged ore (6)
[0218] Next, the chromite obtained by the low-intensity magnetic
separation treatment was subjected to classification as shown
below.
[0219] The non-magnetic slurry obtained by the low-intensity
magnetic separation was subjected to classification with a
classifier (manufactured by DALTON Co., Ltd.: vibrating screen
702CB) provided with a 53 .mu.m-mesh screen and a 300 .mu.m-mesh
screen.
[0220] The results are shown in Table 8.
As shown in Table 8, the level of Cr.sub.2O.sub.3 obtained by the
classification increased to 51.4% by weight versus 45.3% by weight
in the feed.
[0221] On the other hand, the level of Fe increased from 23.1% by
weight to 31.2% by weight.
[0222] From the above results, it can be said that, in the smelting
method of the present invention shown in Example 1, the ore slurry
can be concentrated to a concentration exceeding the
Cr.sub.2O.sub.3 grade of generally commercially available
chromite.
[0223] The recovery rate of the chromite obtained in Example 1 was
19%. Note that the recovery rate was determined by the Formula
(6).
TABLE-US-00008 TABLE 8 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Non-Mag 45.3
0.4 23.1 0.1 After 51.4 0.4 31.2 0.1 classification Unit: % by
weight
Example 2
[0224] In the production flow of the present invention in FIG. 1,
the ore slurry was subjected to step (A) as shown in the execution
flow chart of step (A) in FIG. 4, in which the ore slurry was
subjected to specific gravity separation repeatedly twice with a
density separator and then subjected to specific gravity separation
with a spiral concentrator.
[0225] First, the ore slurry having the composition shown in Table
9 was classified using a hydrocyclone (manufactured by Daiki Ataka
Engineering Co., Ltd., Model MD-9) as a classifier used in step
(A).
[0226] In Example 2, the classification was performed under the
conditions of a slurry concentration of 15% by weight, a slurry
temperature of normal temperature, and an operating pressure of 0.2
MPa.
[0227] The ore slurry composition and the composition of the
hydrocyclone U/F are shown together in Table 9. Note that the unit
in the following tables is % by weight.
TABLE-US-00009 TABLE 9 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Ore slurry
2.5 4.4 51.5 1.2 Hydrocyclone U/F 13.5 6.0 45.2 0.8 Unit: % by
weight
[0228] As shown in Table 9, in the coarse particle portion obtained
from the hydrocyclone (hydrocyclone U/F), the level of
Cr.sub.2O.sub.3 increased to 13.5% by weight versus 2.5% by weight
in the feed, and the level of SiO.sub.2 increased to 6.0% by weight
versus 4.4% by weight in the feed; on the other hand, the level of
Fe decreased to 45.2% by weight versus the iron grade of 51.5% by
weight in the feed.
[0229] The above results show that silica mineral and chromite are
concentrated and separated in the coarse particle portion by the
classification of the ore slurry.
[0230] Next, the hydrocyclone U/F (slurry concentration: 33% by
weight) was fed to a density separator (manufactured by Outotec,
Inc., "Tanksizer TS-Lab", tank inside diameter: 228.6 mm).
[0231] The feed rate of the slurry was set to 56 [kg/Hr], and the
slurry temperature was set to normal temperature.
[0232] The treatment was performed by setting the amount of Teeter
water at this time to 6.9 [m3h-1/m2] and the set point (set value
of a density meter) to 20.
[0233] The compositions of the feed to the density separator (1)
(hydrocyclone U/F) and the underflow from the density separator (1)
(density separator U/F (1)) are shown in Table 10.
TABLE-US-00010 TABLE 10 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni
Hydrocyclone U/F 13.5 6.0 45.2 0.8 Density separator 16.9 1.9 35.2
0.7 U/F (1) Unit: % by weight
[0234] As shown in Table 10, in the coarse particle portion
obtained from the density separator (1) (density separator U/F
(1)), the level of Cr.sub.2O.sub.3 increased to 16.9% by weight
versus 13.5% by weight at the cyclone classification (HC-U/F); on
the other hand, the level of SiO.sub.2 decreased to 1.9% by weight
versus 6.0% by weight, and the level of iron decreased to 35.2% by
weight versus 45.2% by weight.
[0235] The above results show that chromite is concentrated and
separated in the coarse particle portion by the density separator
treatment.
[0236] The density separator U/F (1) (slurry concentration: 75% by
weight) was diluted with water to a slurry concentration of 40% by
weight, and the diluted slurry was subjected to the density
separator treatment again. The compositions of the feed to the
density separator (2) (density separator U/F (1) obtained by the
first density separator treatment) and the underflow from the
density separator (2) (density separator U/F (2) obtained by the
second density separator treatment) are shown in Table 11.
TABLE-US-00011 TABLE 11 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Density
separator 16.9 1.9 35.2 0.7 U/F (1) Density separator 21.1 1.3 30.6
0.4 U/F (2) Unit: % by weight
[0237] Table 11 shows that the level of Cr.sub.2O.sub.3 increased
from 16.9% by weight to 21.1% by weight. It can be verified that
the concentration of chromite proceeds by repeating the treatment
with a density separator in this way.
[0238] Next, the density separator U/F (2) (slurry concentration:
75% by weight) obtained from the density separator (2) was diluted
with water to a slurry concentration of 25% by weight, and the
diluted slurry was subjected to a spiral test with a spiral
concentrator (manufactured by Outotec, Inc., "MC7000").
[0239] The results of the test are shown in Table 12.
TABLE-US-00012 TABLE 12 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Density
separator 21.1 1.3 30.6 0.4 U/F (2) Concentrate 44.5 0.4 24.8 0.2
Middling (1) 30.3 1.1 28.4 0.3 Tailing 6.3 3.0 42.0 1.1 Unit: % by
weight
[0240] As shown in Table 12, in the "Concentrate" obtained from the
spiral concentrator, the level of Cr.sub.2O.sub.3 increased to
44.5% by weight versus 21.1% by weight in the feed. In the Middling
(1), the level of Cr.sub.2O.sub.3 increased to 30.3% by weight. On
the other hand, in the Tailing, the level of Cr.sub.2O.sub.3 was
6.3% by weight.
[0241] These results show that chromite is separated by spiral
treatment.
[0242] Next, the separation of the Middling (1) having a
Cr.sub.2O.sub.3 concentration of 30.3% by weight was subjected to
the spiral treatment again. The results are shown in Table 13.
TABLE-US-00013 TABLE 13 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Middling
(1) 30.3 1.1 28.4 0.3 Concentrate 42.5 0.4 24.7 0.2 Middling (2)
19.4 1.8 27.6 0.5 Tailing 19.5 2.2 36.1 0.7 Unit: % by weight
[0243] As shown in Table 13, in the "Concentrate", the level of
Cr.sub.2O.sub.3 increased to 42.5% by weight versus 30.3% by weight
in the feed by subjecting the Middling (1) to the spiral treatment
again. On the other hand, the level of Cr.sub.2O.sub.3 decreased to
19.4% by weight in the Middling (2) and to 19.5% by weight in the
Tailing. These Middling (2) and Tailing may optionally be subjected
to the spiral treatment again.
[0244] The "Concentrates" obtained by the two spiral tests were
mixed and diluted to a slurry concentration of 20% by weight, and
the diluted slurry was fed to a low-intensity magnetic separator
(manufactured by Outotec, Inc., "Inprosys benchtop LIMS") at a feed
rate of 45.4 [kg/Hr] to obtain a magnetic material (Mag) and a
non-magnetic material (Non-Mag). The results are shown in Table
14.
TABLE-US-00014 TABLE 14 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Feed 44.1
0.4 24.7 0.2 Mag 31.6 0.6 36.6 0.3 Non-Mag 48.5 0.4 20.0 0.1 Unit:
% by weight
[0245] As shown in Table 14, the level of Cr.sub.2O.sub.3 obtained
from the low-intensity magnetic separation (non-magnetic
material/Non-Mag) increased to 48.5% by weight versus 44.1% by
weight in the feed. On the other hand, the level of Fe decreased to
20.0% by weight from 24.7% by weight.
[0246] In contrast, since the Fe grade of Cr.sub.2O.sub.3 (magnetic
material/Mag) was as high as 36.6% by weight, it can be seen that
magnetite was separated and removed by magnetic separation, and the
Cr.sub.2O.sub.3 grade of chromite increased.
[0247] From the above results, the ore slurry can be concentrated
to a concentration exceeding the Cr.sub.2O.sub.3 grade of generally
commercially available chromite by sequentially treating the ore
slurry with a hydrocyclone, with a density separator twice, and
with a spiral concentrator.
[0248] Further, the recovery rate of the resulting chromite was 44%
by weight.
[0249] The recovery rate was determined by Formula (6) in the same
manner as in Example 1.
[0250] Next, the chromite obtained by the low-intensity magnetic
separation treatment was subjected to classification as shown
below.
[0251] The non-magnetic slurry obtained by the low-intensity
magnetic separation was subjected to classification with a
classifier (manufactured by DALTON Co., Ltd.: vibrating screen
702CB) provided with a 53 .mu.m-mesh screen and a 300 .mu.m-mesh
screen.
[0252] The results are shown in Table 15.
[0253] As shown in Table 15, the level of Cr.sub.2O.sub.3 obtained
by the classification increased to 55.0% by weight versus 48.5% by
weight in the feed. On the other hand, the level of Fe increased
from 20.0% by weight to 27.0% by weight.
[0254] From the above results, it can be said that, in the smelting
method of the present invention shown in Example 2, the ore slurry
can be concentrated to a concentration exceeding the Cr2O3 grade of
generally commercially available chromite.
[0255] The recovery rate of the chromite obtained in Example 2 was
20%. Note that the recovery rate was determined by the Formula (6)
in the same manner as in Example 1.
TABLE-US-00015 TABLE 15 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Non-Mag
48.5 0.4 20.0 0.1 After 55.0 0.4 27.0 0.1 classification Unit: % by
weight
Comparative Example 1
[0256] After the classification with a hydrocyclone according to
the execution flow in Comparative Example 1 shown in FIG. 5, the
separation was performed using a high-mesh separator by the size of
solids contained in the ore slurry, instead of the specific gravity
separation in Example 1.
[0257] The ore slurry was classified using a hydrocyclone
(manufactured by Daiki Ataka Engineering Co., Ltd., Model "MD-9")
as a classifier.
[0258] Here, the classification was performed under the conditions
of a slurry concentration of 9.8% by weight, a slurry temperature
of normal temperature, and an operating pressure of 0.22 MPa.
[0259] The hydrocyclone underflow (hydrocyclone U/F) having a
slurry concentration of 33% by weight was diluted to a slurry
concentration of 4.9% by weight, and the diluted slurry was charged
into a high-mesh separator (manufactured by Kikosha Co., Ltd.,
"KUC-612S").
[0260] The feed rate to the high-mesh separator was 0.98
[m.sup.3/hour]; the rotation speed of the bucket was 0.8 rpm; the
bucket length was 75 mm; and the bucket had holes each having a
diameter of 4 mm opened at a pitch of 6 mm, in which the rate of
hole area was 40%.
[0261] The amount of washing water was set to 6 m3/hour.
[0262] The compositions of the ore slurry and the hydrocyclone
underflow (hydrocyclone U/F) and the composition of the underflow
of the high-mesh separator (high-mesh separator U/F) are shown in
Table 16.
TABLE-US-00016 TABLE 16 Cr.sub.2O.sub.3 Ni Ore slurry 4.1 1.1
Hydrocyclone U/F 13.0 0.8 High-mesh 19.1 0.5 separator U/F Unit: %
by weight
[0263] As is obvious from Table 16, the Cr.sub.2O.sub.3 grade was
concentrated from 4.1% by weight in the ore slurry to 13.0% by
weight in the coarse particle portion of the hydrocyclone
(hydrocyclone U/F), and to 19.1% by weight in the coarse particle
portion of the high-mesh separator (high-mesh separator U/F), but
the target level of the composition of commercially available
products was not obtained.
[0264] In this step, although there was no particular problem in
the concentration with the hydrocyclone, it can be determined that
the concentration with the high-mesh separator is insufficient.
[0265] Then, the cause was investigated as follows.
[0266] Each of the underflows (hydrocyclone U/F and high-mesh
separator U/F) was sieved with a 75 .mu.m-mesh screen, and the
oversize and the undersize of the 75 .mu.m-mesh screen were
analyzed to obtain the results shown in Table 17.
TABLE-US-00017 TABLE 17 Grade [% by weight] Size Distribution Total
Total [.mu.m] [% by weight] Cr Cr.sub.2O.sub.3 Fe Ni Cr
Cr.sub.2O.sub.3 Hydrocyclone +75 43 16.7 24.4 36.0 0.5 8.9 13.0 U/F
-75 57 3.0 4.4 50.6 1.0 High-mesh +75 85 14.2 20.7 38.1 0.5 13.1
19.1 separator U/F -75 15 6.7 9.8 49.8 0.7
[0267] In Table 17, the Cr grade of the underflow of the high-mesh
separator (high-mesh separator U/F) was 14.2% by weight (20.7% by
weight in terms of Cr.sub.2O.sub.3), which was lower than 16.7% by
weight (24.4% by weight in terms of Cr.sub.2O.sub.3) of the
underflow of the hydrocyclone (hydrocyclone U/F). Thus, it was
found that the specific gravity separation was not achieved at
all.
[0268] These results reveal that the high-mesh separator worked
only for slime removal and did not work for specific gravity
separation.
[0269] Thus, it is found that the ore slurry cannot be concentrated
to chromite having a Cr2O3 grade equivalent to the level of
commercially available products unless specific gravity separation
is performed.
Example 3
[0270] The overflow of the hydrocyclone and the overflow of the
density separator in Example 1 were charged into an autoclave at a
solid weight ratio of 77:15, and thereto was added 98% sulfuric
acid. The resulting mixture was subjected to high pressure acid
leach under the following conditions to produce a leach slurry
10.
[0271] Further, the produced leach slurry was separated into a
leachate 11 and a leach residue slurry 12 by a solid-liquid
separation step.
[Leaching Conditions]
[0272] Leaching temperature: 245.degree. C.
[0273] Leaching time: 60 minutes
[0274] Final (at the completion of leaching) free sulfuric-acid
concentration: 40 [g/L]
[0275] Slurry concentration: 30% by weight
[0276] Autoclave volume: 5 L
[0277] Next, in order to know the Cr.sub.2O.sub.3 grade in the
leach residue slurry 12, Mg(OH).sub.2 slurry having a concentration
of 20% by weight as a neutralizing agent was added to the leach
residue slurry 12 to neutralize the leach residue slurry so that it
might have a pH of 2.5 at 70.degree. C.
[0278] Next, the slurry was subjected to solid-liquid separation
using 5C filter paper followed by adding the Mg(OH).sub.2 slurry
until the resulting slurry has a pH of 6, and the resulting slurry
was then further subjected to solid-liquid separation using 5 C
filter paper.
[0279] The Cr.sub.2O.sub.3 grade of the resulting final neutralized
residue was 0.9% by weight. Since MgSO.sub.4 produced has high
solubility, the residue had a sulfur grade of 0.53% by weight.
Comparative Example 2
[0280] When the ore slurry in Example 1 was treated in the same
manner as in Example 3 except that the ore slurry was charged into
an autoclave without treating the slurry with the hydrocyclone and
the density separator, the Cr.sub.2O.sub.3 grade of the resulting
final neutralized residue was 2.1% by weight.
[0281] Since MgSO4 produced has high solubility, the residue had a
sulfur grade of 0.53% by weight.
[0282] As is obvious from a comparison between Example 3 and
Comparative Example 2, chromite in the ore slurry was able to be
separated and removed to halve the Cr.sub.2O.sub.3 grade in the
residue by first classifying the ore slurry with the hydrocyclone
and then treating with the density separator which is one of the
specific gravity separation apparatuses.
Comparative Example 3
[0283] A leach residue slurry 12 was prepared in the same manner as
in Example 3; a slaked lime slurry with a concentration of 25% by
weight was added as a neutralizing agent to the entire amount of
the leach residue slurry to neutralize the slurry to a pH of 8.5 at
60.degree. C. to precipitate metal ions as a precipitate; and a
neutralization residue and a treatment solution after
neutralization were obtained by solid-liquid separation.
[0284] The neutralization residue was subjected to cyclone
classification to separate hematite 28.
[0285] A slaked lime slurry with a concentration of 25% by weight
was added to a mixed solution obtained by mixing the treatment
solution after neutralization with a remaining neutralization
residue from which hematite 28 had been separated, and the
resulting mixture was then repeatedly subjected to solid-liquid
separation with 5C filter paper to obtain a final neutralized
residue.
[0286] The resulting final neutralized residue had a
Cr.sub.2O.sub.3 grade of 0.8% by weight. Since CaSO4 produced has
low solubility, the residue had a sulfur grade of 5.72% by weight
and a Ca grade of 8.49% by weight.
Comparative Example 4
[0287] As shown in the execution flow chart of Comparative Example
in FIG. 6, the separation test was performed under the same
conditions as in Example 1 except that the ore slurry was subjected
to the specific gravity separation once in the same manner as in
Example 1 without the classification with the hydrocyclone and
finally subjected to the classification with the hydrocyclone.
[0288] Table 18 shows the results obtained by subjecting the ore,
which had not been subjected to the classification with the
hydrocyclone, to the specific gravity separation with the density
separator.
[0289] The Cr2O3 concentration of the underflow from the density
separator was not as high as that of the underflow obtained by
treating a feed which had been subjected to classification (refer
to the density separator U/F in Table 4), probably because the feed
(ore slurry) had a high viscosity.
TABLE-US-00018 TABLE 18 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Feed 2.5
4.4 51.5 1.2 Density separator 9.5 2.5 40.2 1.0 U/F Unit: % by
weight
[0290] The results of the separation of the density separator U/F
with a spiral concentrator are shown in Table 19.
[0291] As is obvious from Table 19, even when the specific gravity
separation with the spiral concentrator was performed, the Cr2O3
concentration was 25.3% by weight, which was less than 41% by
weight.
[0292] This is probably because since coarse particles and fine
particles are not separated in the density separator, the slurry
viscosity is high, and the effect of the spiral concentrator cannot
be exhibited.
TABLE-US-00019 TABLE 19 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Density
separator 9.5 2.5 40.2 1.0 U/F Concentrate 25.3 0.8 32.6 0.5
Middling 13.6 2.1 37.3 0.8 Tailing 2.8 5.9 55.2 2.6 Unit: % by
weight
[0293] Subsequently, classification with the hydrocyclone was
performed.
[0294] As shown in Table 20, the concentration of Cr2O3 was 35.3%
by weight, which did not satisfy 41% by weight or more.
TABLE-US-00020 TABLE 20 Cr.sub.2O.sub.3 SiO.sub.2 Fe Ni Concentrate
25.3 0.8 32.6 0.5 Hydrocyclone U/F 35.3 2.5 28.6 0.2 Unit: % by
weight
[0295] It was impossible to concentrate the ore slurry up to a
concentration that is higher than the Cr.sub.2O.sub.3 grade of
generally commercially available chromite. Thus, it is found that
it is important in chromite recovery to remove fine particles by
performing cyclone classification first.
[0296] As is obvious from the above results, the hydrometallurgical
process for nickel oxide ore of the present invention is suitable
as a smelting method based on high pressure acid leach utilized in
the hydrometallurgical field of nickel oxide ore.
REFERENCE SIGNS LIST
[0297] 8 Nickel oxide ore [0298] 9 Ore slurry [0299] 10 Leach
slurry [0300] 11 Leachate [0301] 12 Leach residue slurry [0302] 14
Mother liquor (1) [0303] 15 Zinc sulfide precipitate [0304] 16
Mother liquor (2) [0305] 17 Ni and Co mixed sulfide [0306] 18
Barren liquor [0307] 19 Final neutralized residue [0308] 20
Tailings dam [0309] 22 Autoclave feed slurry [0310] 23 Chromite
[0311] 26 Residue after step (B-1) [0312] 27 Treatment solution
after step (B-2) [0313] 28 Hematite
* * * * *