U.S. patent application number 16/071920 was filed with the patent office on 2019-01-24 for method for recovering scandium.
The applicant listed for this patent is SUMITOMO METAL MINING CO., LTD.. Invention is credited to Tatsuya Higaki, Hiroshi Kobayashi, Shin-ya Matsumoto, Hidemasa Nagai.
Application Number | 20190024213 16/071920 |
Document ID | / |
Family ID | 59398183 |
Filed Date | 2019-01-24 |
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United States Patent
Application |
20190024213 |
Kind Code |
A1 |
Higaki; Tatsuya ; et
al. |
January 24, 2019 |
METHOD FOR RECOVERING SCANDIUM
Abstract
The method for recovering scandium pertaining to the present
invention has: a first neutralization step for passing a solution
containing scandium over an ion exchange resin, adding a
neutralizing agent to the eluent eluted from the ion exchange resin
and performing a neutralization treatment, and obtaining a primary
neutralized sediment and a primary neutralized filtrate by
solid-liquid separation; a second neutralization step for further
adding a neutralizing agent to the primary neutralized filtrate and
performing a neutralization treatment, and obtaining a secondary
neutralized sediment and a secondary neutralized filtrate by
solid-liquid separation; a hydroxide dissolution step for adding
acid to the secondary neutralized sediment and obtaining a
hydroxide solution; a solvent extraction step for subjecting the
hydroxide solution to solvent extraction; and a scandium recovery
step for recovering scandium oxide from a raffinate separated in
the solvent extraction step.
Inventors: |
Higaki; Tatsuya;
(Niihama-shi, JP) ; Matsumoto; Shin-ya;
(Niihama-shi, JP) ; Nagai; Hidemasa; (Niihama-shi,
JP) ; Kobayashi; Hiroshi; (Niihama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO METAL MINING CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
59398183 |
Appl. No.: |
16/071920 |
Filed: |
January 11, 2017 |
PCT Filed: |
January 11, 2017 |
PCT NO: |
PCT/JP2017/000601 |
371 Date: |
July 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 3/42 20130101; C22B
3/24 20130101; C22B 3/44 20130101; C22B 59/00 20130101; Y02P 10/20
20151101; C22B 3/0005 20130101; C22B 3/08 20130101; Y02P 10/234
20151101 |
International
Class: |
C22B 59/00 20060101
C22B059/00; C22B 3/08 20060101 C22B003/08; C22B 3/24 20060101
C22B003/24; C22B 3/42 20060101 C22B003/42; C22B 3/44 20060101
C22B003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2016 |
JP |
2016-011739 |
Claims
1. A method of recovering scandium, comprising: a first
neutralization step of allowing a solution containing scandium to
pass through an ion exchange resin, adding a neutralizing agent to
an eluate eluted from the ion exchange resin, performing a
neutralization treatment, and obtaining a primary neutralized
precipitate and a primary neutralized filtrate by solid-liquid
separation; a second neutralization step of further adding a
neutralizing agent to the primary neutralized filtrate, performing
a neutralization treatment, and obtaining a secondary neutralized
precipitate and a secondary neutralized filtrate by solid-liquid
separation; a hydroxide dissolution step of adding an acid to the
secondary neutralized precipitate to obtain a hydroxide solution; a
solvent extraction step of subjecting the hydroxide solution to
solvent extraction; and a scandium recovery step of recovering
scandium oxide from a raffinate liquid separated in the solvent
extraction step, wherein the secondary neutralized precipitate is
dissolved using sulfuric acid as the acid so that pH of a hydroxide
solution to be obtained is maintained in the range of 0.8 to 1.5 in
the hydroxide dissolution step.
2. The method of recovering scandium according to claim 1, wherein
pH of the eluate is adjusted to the range of 3.5 to 4.5 in the
first neutralization step.
3. The method of recovering scandium according to claim 1, wherein
pH of the primary neutralized filtrate is adjusted to the range of
5.5 to 6.5 in the second neutralization step.
4. (canceled)
5. The method of recovering scandium according to claim 1, wherein
the solution containing scandium to pass through the ion exchange
resin is a barren liquor to be obtained by hydrometallurgy of
nickel oxide ore, the hydrometallurgy including: a leaching step of
leaching the nickel oxide ore with sulfuric acid under high
temperature and high pressure to obtain a leachate; a
neutralization step of adding a neutralizing agent to the leachate
to obtain a neutralized precipitate containing impurities and a
post-neutralization liquid; and a sulfuration step of adding a
sulfurizing agent to the post-neutralization liquid to obtain
nickel sulfide and a barren liquor.
6. The method of recovering scandium according to claim 2, wherein
the solution containing scandium to pass through the ion exchange
resin is a barren liquor to be obtained by hydrometallurgy of
nickel oxide ore, the hydrometallurgy including: a leaching step of
leaching the nickel oxide ore with sulfuric acid under high
temperature and high pressure to obtain a leachate; a
neutralization step of adding a neutralizing agent to the leachate
to obtain a neutralized precipitate containing impurities and a
post-neutralization liquid; and a sulfuration step of adding a
sulfurizing agent to the post-neutralization liquid to obtain
nickel sulfide and a barren liquor.
7. The method of recovering scandium according to claim 3, wherein
the solution containing scandium to pass through the ion exchange
resin is a barren liquor to be obtained by hydrometallurgy of
nickel oxide ore, the hydrometallurgy including: a leaching step of
leaching the nickel oxide ore with sulfuric acid under high
temperature and high pressure to obtain a leachate; a
neutralization step of adding a neutralizing agent to the leachate
to obtain a neutralized precipitate containing impurities and a
post-neutralization liquid; and a sulfuration step of adding a
sulfurizing agent to the post-neutralization liquid to obtain
nickel sulfide and a barren liquor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for recovering
scandium, and more particularly, it relates to a method for
recovering scandium by which scandium contained in nickel oxide ore
is easily and efficiently recovered.
BACKGROUND ART
[0002] Scandium is extremely valuable as an additive for
high-strength alloys and an electrode material for fuel cells.
However, scandium has not yet been used widely due to the small
production quantity and high cost thereof.
[0003] Incidentally, a trace amount of scandium is contained in
nickel oxide ore such as laterite ore and limonite ore. However,
nickel oxide ore has not been industrially utilized as a nickel raw
material for a long time since it contains nickel at a low grade.
Hence, it has been rarely studied to industrially recover scandium
from nickel oxide ore.
[0004] Nonetheless, in recent years, the HPAL process has been
emerging as a practical method, in which nickel oxide ore is
introduced into a pressure vessel along with sulfuric acid, and
heated at a high temperature of 240.degree. C. to 260.degree. C. to
allow solid-liquid separation into a nickel-containing leachate and
a leach residue. In the HPAL process, a neutralizing agent is added
to the leachate obtained to separate impurities, and then a
sulfurizing agent is added to the resulting leachate from which
impurities are separated out, allowing recovery of nickel as nickel
sulfide. Subsequently, this nickel sulfide may be subjected to a
known nickel refinement process to obtain electrolytic nickel and
nickel salt compounds.
[0005] In the HPAL processes as described above, scandium contained
in nickel oxide ore will be contained in a leachate along with
nickel (see Patent Document 1). Subsequently, when a neutralizing
agent is added to a leachate obtained from the HPAL process to
separate impurities, and a sulfurizing agent is then added, nickel
is recovered as nickel sulfide while scandium remains in the acidic
solution after addition of the sulfurizing agent. In this way,
nickel can effectively be separated from scandium by using the HPAL
process.
[0006] A method of separating scandium by using a chelating resin
has also been documented (see Patent Document 2). Specifically,
according to the method disclosed in Patent Document 2,
nickel-containing oxide ore is first treated at high temperature
and high pressure under an oxidizing atmosphere to selectively
extract nickel and scandium into an acidic aqueous solution.
Subsequently, the pH of the resulting acidic solution is adjusted
to the range of 2 to 4, and nickel is then selectively precipitated
and recovered as a sulfide by means of a sulfurizing agent. Next,
scandium is adsorbed to a chelating resin by bringing the solution
obtained after nickel recovery into contact with the chelating
resin, the chelating resin is washed with a dilute acid, and then
scandium is eluted from the chelating resin by bringing the
chelating resin after washing into contact with a strong acid.
[0007] Further, as a method of recovering scandium from the
aforementioned acidic solution, the method of recovering scandium
by means of solvent extraction has also been proposed (see Patent
Documents 3 and 4). Specifically, according to the method disclosed
in Patent Document 3, an organic solvent is first added to an
aqueous-phase scandium-containing solution to extract a scandium
component into the organic solvent, the organic solvent comprising
2-ethylhexyl sulfonic acid-mono-2-ethylhexyl diluted with kerosene,
and the aqueous-phase scandium-containing solution containing one
or more of at least iron, aluminum, calcium, yttrium, manganese,
chromium, and magnesium in addition to scandium. Then, in order to
separate yttrium, iron, manganese, chromium, magnesium, aluminum,
and calcium extracted into the organic solvent along with scandium,
an aqueous solution of hydrochloric acid is added, and scrubbing is
performed to remove these elements. Then, an aqueous solution of
NaOH is added to the organic solvent to transform scandium
remaining in the organic solvent into a slurry containing
Sc(OH).sub.3, and the slurry is filtered to obtain Sc(OH).sub.3,
which is then dissolved in hydrochloric acid to obtain an aqueous
solution of scandium chloride. Then, oxalic acid is added to the
aqueous solution of scandium chloride thus obtained to obtain a
precipitate of scandium oxalate, and this precipitate is filtered
to separate iron, manganese, chromium, magnesium, aluminum, and
calcium into the filtrate and then calcined to obtain high purity
scandium oxide.
[0008] Moreover, Patent Document 4 describes a method of
selectively separating and recovering scandium from a
scandium-containing supply liquid, the method comprising: bringing
the scandium-containing supply liquid into contact with an
extracting agent at a certain ratio in a batch process.
[0009] As the grade of scandium recovered by these methods, it is
known that a purity of about 95% to 98% in terms of scandium oxide
is obtained. However, a higher purity, for example, a grade of
about 99.9% is required in order to exert favorable properties in
applications such as electrolytes of fuel cells of which the demand
has increased in recent years although it is a sufficient grade for
applications such as addition to alloys.
[0010] However, various impurity elements such as manganese and
magnesium are contained in the nickel oxide ore described above in
addition to iron and aluminum although the kinds and amounts
thereof vary depending on the region from which the nickel oxide
ore is mined.
[0011] The impurity elements have acceptable upper limits of grade
and each element is required to be separated and removed to a
content equal to or less than the acceptable limit in the case of
using scandium in applications such as electrolytes of fuel
cells.
[0012] However, some impurity elements exhibit behavior similarly
to that of scandium in the chelating resins and the organic
solvents disclosed in Patent Document 2 and Patent Document 3, and
it is thus difficult to effectively separate and recover scandium.
In addition, impurities such as iron and aluminum are contained in
the leachate of nickel oxide ore at much higher concentrations than
scandium, and a method suitable for industrial recovery of high
purity scandium from nickel oxide ore has not been found out since
the recovery of scandium is also affected by these large amounts of
impurities.
[0013] As described above, it has been difficult to efficiently
recover high purity scandium by effectively separating a large
variety of impurities such as iron and aluminum contained in large
amounts even when it is attempted to recover scandium from nickel
oxide ore. [0014] Patent Document 1: Japanese Unexamined Patent
Application, Publication No. H03-173725 [0015] Patent Document 2:
Japanese Unexamined Patent Application, Publication No. H09-194211
[0016] Patent Document 3: Japanese Unexamined Patent Application,
Publication No. H09-291320 [0017] Patent Document 4: PCT
International Publication No. WO2014/110216
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0018] The present invention has been proposed in view of the
circumstances as described above, and an object thereof is to
provide a method for recovering scandium by which high purity
scandium can be easily and efficiently recovered from nickel oxide
ore.
Means for Solving the Problems
[0019] The inventors of the present invention have conducted
intensive investigations to solve the problems described above. As
a result, it has been found out that it is possible to easily and
efficiently recover high purity scandium from nickel oxide ore by
subjecting a solution obtained through a two-stage neutralization
treatment of an eluate obtained by allowing an acidic solution
containing scandium to pass through an ion exchange resin to
solvent extraction, and the present invention has been thus
completed. That is, the present invention provides the
following.
[0020] (1) A first embodiment of the present invention provides a
method for recovering scandium, including: a first neutralization
step of allowing a solution containing scandium to pass through an
ion exchange resin, adding a neutralizing agent to an eluate eluted
from the ion exchange resin, performing a neutralization treatment,
and obtaining a primary neutralized precipitate and a primary
neutralized filtrate by solid-liquid separation; a second
neutralization step of further adding a neutralizing agent to the
primary neutralized filtrate, performing a neutralization
treatment, and obtaining a secondary neutralized precipitate and a
secondary neutralized filtrate by solid-liquid separation; a
hydroxide dissolution step of adding an acid to the secondary
neutralized precipitate to obtain a hydroxide solution; a solvent
extraction step of subjecting the hydroxide solution to solvent
extraction; and a scandium recovery step of recovering scandium
oxide from a raffinate liquid separated in the solvent extraction
step.
[0021] (2) A second embodiment of the present invention provides
the method for recovering scandium according to the first
embodiment, in which pH of the eluate is adjusted to the range of
3.5 to 4.5 in the first neutralization step.
[0022] (3) A third embodiment of the present invention provides the
method for recovering scandium according to the first or second
embodiment, in which pH of the primary neutralized filtrate is
adjusted to the range of 5.5 to 6.5 in the second neutralization
step.
[0023] (4) A fourth embodiment of the present invention provides
the method for recovering scandium according to any one of the
first to third embodiments, in which the secondary neutralized
precipitate is dissolved using sulfuric acid as the acid so that pH
of a hydroxide solution to be obtained is maintained in the range
of 0.8 to 1.5 in the hydroxide dissolution step.
[0024] (5) A fifth embodiment of the present invention provides the
method for recovering scandium according to any one of the first to
fourth embodiments, in which the solution containing scandium to
pass through the ion exchange resin is a barren liquor to be
obtained by hydrometallurgy of nickel oxide ore, the
hydrometallurgy including: a leaching step of leaching the nickel
oxide ore with sulfuric acid under high temperature and high
pressure to obtain a leachate; a neutralization step of adding a
neutralizing agent to the leachate to obtain a neutralized
precipitate containing impurities and a post-neutralization liquid;
and a sulfuration step of adding a sulfurizing agent to the
post-neutralization liquid to obtain nickel sulfide and a barren
liquor.
Effects of the Invention
[0025] According to the present invention, high purity scandium can
simply and efficiently be recovered from nickel oxide ore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 shows a flow diagram for illustrating the method of
recovering scandium.
[0027] FIG. 2 shows a flow diagram for illustrating an example of
the entire process flow in which the method of recovering scandium
is used.
[0028] FIG. 3 is a flow diagram for describing the flow of a
neutralization step.
[0029] FIG. 4 is a graphical representation showing the pH of a
solution and the ratio (precipitation rate) of each element
precipitated from the solution when a neutralizing agent is added
to a scandium eluate.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0030] Below, specific embodiments of the present invention
(hereinafter referred to as the "present embodiments") will be
described in detail with reference to the drawings. It should be
noted that the present invention is not limited to the following
embodiments, but can be implemented with appropriate modifications
made without departing from the spirit of the present invention.
Note that the phrase "X to Y" (X and Y may be any numerical values)
as used herein means "X or more and Y or less".
<<1. Method of Recovering Scandium>>
[0031] FIG. 1 is a flow diagram showing an example of the method of
recovering scandium according to the present embodiment. The above
method of recovering scandium comprises: separating scandium from
impurities in a scandium-containing acidic solution obtained by
leaching nickel oxide ore with an acid such as sulfuric acid,
thereby simply and effectively recovering high purity scandium.
[0032] In this method for recovering scandium, an eluate (scandium
eluate) obtained by allowing an acidic solution containing scandium
to pass through an ion exchange resin to adsorb the scandium to the
ion exchange resin and then bringing an acid solution into contact
with the ion exchange resin is subjected to a two-stage
neutralization treatment to separate impurities and to concentrate
scandium. Then, the scandium-concentrated acidic solution is
further subjected to solvent extraction using an extractant such as
an amine-based extractant to extract impurities contained in the
acidic solution into the extractant and thus to separate the
impurities from scandium which is to remain in the acidic solution
(raffinate liquid) after the extraction.
[0033] Scandium contained in the raffinate liquid by this solvent
extraction is transformed into a solid shape that is suitably
applied as a product, for example, by a method in which a
precipitate of a hydroxide is obtained by adding an alkali to the
raffinate liquid and performing a neutralization treatment or
scandium is recovered as a precipitate of an oxalate by an
oxalate-formation treatment using oxalic acid while the residual
impurities are separated, whereby scandium is recovered as crystals
of high purity scandium hydroxide or scandium oxalate.
[0034] Note that the crystals of scandium hydroxide and scandium
oxalate thus obtained are transformed into the form of scandium
oxide by calcination according to a known method and the like. The
scandium oxide thus generated can be used as a material for an
electrolyte of a fuel cell and also it can be used in an
application in which scandium metal is obtained by a method such as
molten salt electrolysis and then added to aluminum to form an
alloy.
[0035] As described above, in the method for recovering scandium
according to the present embodiment, scandium is further
concentrated by subjecting the solution (eluate) in which scandium
is concentrated through the ion exchange treatment to a two-stage
neutralization treatment and then a solvent extraction treatment
using a solvent extractant such as an amine-based extractant is
performed when separating and recovering scandium. According to
such a method, it is possible to more effectively separate
impurities and to efficiently recover high purity scandium through
a stable operation even from a raw material, which contains a large
amount of impurities, such as nickel oxide ore.
[0036] More specifically, as shown in the flow diagram of FIG. 1,
the method for recovering scandium according to the present
embodiment includes a nickel oxide ore hydrometallurgy treatment
step S1 of leaching nickel oxide ore with an acid such as sulfuric
acid to obtain an acidic solution containing scandium, a scandium
elution step S2 of removing impurities from the acidic solution to
obtain a scandium eluate in which scandium is concentrated, a
neutralization step S3 of adding a neutralizing agent to the
scandium eluate and performing a neutralization treatment to obtain
a solution (an extraction starting liquid) containing scandium at a
high concentration, a solvent extraction step S4 of subjecting the
extraction starting liquid obtained to solvent extraction using an
amine-based extractant and the like to extract impurities into the
extractant and thus to separate the impurities from scandium which
is to remain in the acidic solution after the extraction, and a
scandium recovery step S5 of recovering scandium from the raffinate
liquid.
<<2. Respective Steps in Method for Recovering
Scandium>>
<2-1. Step of Hydrometallurgy Treatment of Nickel Oxide
Ore>
[0037] For the scandium-containing acidic solution from which
scandium is to be recovered, an acidic solution obtained by
treating nickel oxide ore with sulfuric acid can be used.
[0038] Specifically, for the acidic solution to be subjected to
solvent extraction, a barren liquor can be used which is obtained
through the hydrometallurgy treatment step S1 of nickel oxide ore,
the hydrometallurgy treatment step S1 comprising: a leaching step
S11 of leaching nickel oxide ore with an acid such as sulfuric acid
under high temperature and high pressure to obtain a leachate; a
neutralization step S12 of adding a neutralizing agent to the
leachate to obtain a neutralized precipitate containing impurities
and a post-neutralization liquid; and a sulfuration step S13 of
adding a sulfurizing agent to the post-neutralization liquid to
obtain nickel sulfide and a barren liquor. Below, the process flow
of the hydrometallurgy treatment step S1 of nickel oxide ore will
be described.
(1) Leaching Step
[0039] The leaching step S11 comprises adding sulfuric acid to a
slurry of nickel oxide ore, for example, in a high temperature
pressurized vessel (an autoclave) and the like, and stirred at a
temperature of 240.degree. C. to 260.degree. C. to form a leach
slurry comprising a leachate and a leach residue. Note that a
treatment in the leaching step S11 can be performed according to
the publicly known HPAL process, which is described, for example,
in Patent Document 1.
[0040] Here, examples of nickel oxide ore include so-called
laterite ore such as limonite ore and saprolite ore. The content of
nickel in laterite ore is usually 0.8 wt % to 2.5 wt %, and
contained as a hydroxide or a silica magnesia (magnesium silicate)
mineral. Further, these types of nickel oxide ore contain
scandium.
[0041] In the leaching step S11, solid-liquid separation is
performed to obtain a leachate containing nickel, cobalt, scandium,
and the like; and a leach residue as a hematite while washing the
resulting leach slurry comprising the leachate and the leach
residue. In the above solid-liquid separation treatment, for
example, the leach slurry is mixed with a washing liquid, and then
solid-liquid separation is performed in a solid-liquid separation
apparatus such as a thickener using an aggregating agent supplied
from an apparatus for supplying an aggregating agent and the like.
Specifically, the leach slurry is first diluted with the washing
liquid, and then the leach residue in the slurry is condensed as a
precipitate in the thickener. Note that in the above solid-liquid
separation treatment, solid-liquid separation is preferably
performed while washing the leach slurry by a multi-stage washing
process using multistaged solid-liquid separation cells such as
thickners.
(2) Neutralization Step
[0042] The neutralization step S12 comprises adding a neutralizing
agent to the leachate obtained from the aforementioned leaching
step S11 to adjust pH, thereby obtaining a neutralized precipitate
containing impurity elements and a post-neutralization liquid.
After the neutralization treatment in the above neutralization step
S12, valuable metals such as nickel, cobalt, and scandium will be
contained in the post-neutralization liquid while most impurities
including iron and aluminum will be included in the neutralized
precipitate.
[0043] For the neutralizing agent, publicly known substances may be
used, including, for example, calcium carbonate, slaked lime,
sodium hydroxide, and the like.
[0044] In the neutralization treatment of the neutralization step
S12, the pH is preferably adjusted to the range of 1 to 4,
preferably to the range of 1.5 to 2.5 while preventing oxidation of
the leachate separated. When the pH is less than 1, neutralization
may be insufficient, and the neutralized precipitate and the
post-neutralization liquid may not be separated. On the other hand,
when the pH is more than 4, not only impurities including aluminum
but also valuable metals such as scandium and nickel may be
contained in the neutralized precipitate.
(3) Sulfuration Step
[0045] The sulfuration step S13 comprises adding a sulfurizing
agent to the post-neutralization liquid obtained from the
aforementioned neutralization step S12 to obtain nickel sulfide and
a barren liquor. Nickel, cobalt, zinc, and the like are transformed
into sulfides, and scandium and the like is contained in the barren
liquor after the sulfuration treatment in the above sulfuration
step S13.
[0046] Specifically, in the sulfuration step S13, a sulfurizing
agent such as gaseous hydrogen sulfide, sodium sulfide and
hydrogenated sodium sulfide is added to the resulting
post-neutralization liquid to form sulfides (a mixture of nickel
and cobalt sulfides) comprising nickel and cobalt with less
impurity components; and a barren liquor having a low and
stabilized level of nickel and containing scandium and the
like.
[0047] In the sulfuration treatment of the sulfuration step S13,
sedimentation and separation treatment of a slurry of the mixture
of nickel and cobalt sulfides is performed using a sedimentation
apparatus such as a thickener to separate and recover the mixture
of nickel and cobalt sulfides from the bottom of the thickener.
Meanwhile, the barren liquor as an aqueous solution component is
overflown for recovery.
[0048] In the method of recovering scandium according to the
present embodiment, the barren liquor obtained through each step of
the hydrometallurgy treatment step S1 of nickel oxide ore can be
used as an acidic solution containing scandium and other
impurities, the acidic solution being a target for the process for
recovering scandium.
<2-2. Scandium (Sc) Elution Step>
[0049] As described above, the barren liquor as a
scandium-containing acidic solution obtained by leaching nickel
oxide ore with sulfuric acid may be used as a target solution for
the process for recovering scandium. However, for example, the
barren liquor as a scandium-containing acidic solution contains, in
addition to scandium, aluminum, chromium and various other
impurities remaining in the solution without being sulfurized after
the aforementioned sulfuration treatment in the sulfuration step
S13. In view of the above, a scandium eluate (scandium-containing
solution) is preferably generated by preliminarily removing
impurities contained in the acidic solution to concentrate scandium
(Sc) in the scandium elution step S2 before the acidic solution is
subjected to solvent extraction.
[0050] In the scandium elution step S2, impurities such as aluminum
contained in the acidic solution may be separated and removed by a
method of ion exchange treatment, for example, using a chelating
resin to obtain a scandium-containing solution with scandium
concentrated.
[0051] FIG. 2 represents a flow diagram showing an example of the
method of removing impurities contained in the acidic solution to
concentrate and elute scandium, comprising a step (an ion exchange
step) of performing an ion exchange reaction using a chelating
resin. In this step, the barren liquor obtained from the
sulfuration step S13 in the hydrometallurgy treatment step S1 of
nickel oxide ore is brought into contact with a chelating resin to
allow scandium in the barren liquor to be adsorbed by the chelating
resin, and then a scandium (Sc) eluate is obtained. Note that the
ion exchange step as an example of the scandium elution step S2 is
referred to the "ion exchange step S2".
[0052] Specifically, examples of the ion exchange step S2 include a
step comprising: an adsorption step S21 of bringing the barren
liquor into contact with a chelating resin to allow scandium to be
adsorbed by the chelating resin; an aluminum removing step S22 of
allowing 0.1 N or less of sulfuric acid to make contact with the
chelating resin which has adsorbed scandium to remove aluminum
adsorbed by the chelating resin; a scandium elution step S23 of
allowing 0.3 N or more and 3 N or less of sulfuric acid to make
contact with the chelating resin to obtain a scandium eluate; and a
chromium removing step S24 of allowing 3 N or more of sulfuric acid
to make contact with the chelating resin which has been subjected
to the scandium elution step S23 to remove chromium which has been
adsorbed by the chelating resin in the adsorption step S21. Below,
an overview of each step will be described, but the ion exchange
step S2 shall not be limited to it.
[Adsorption Step]
[0053] In the adsorption step S21, the barren liquor is brought
into contact with a chelating resin to allow scandium to be
adsorbed by the chelating resin. There is no particular limitation
for the type of the chelating resin, and for example, a resin
having iminodiacetic acid as a functional group can be used.
[Aluminum Removing Step]
[0054] In the aluminum removing step S22, the chelating resin which
has adsorbed scandium in the adsorption step S21 is brought into
contact with 0.1 N or less of sulfuric acid to remove aluminum
adsorbed by the chelating resin. Note that when removing aluminum,
the pH is preferably maintained in the range of between 1 or more
and 2.5 or less, and more preferably maintained in the range of
between 1.5 or more and 2.0 or less.
[Scandium Elution Step]
[0055] In the scandium elution step S23, the chelating resin which
has been subjected to the aluminum removing step S22 is brought
into contact with 0.3 N or more and less than 3 N of sulfuric acid
to obtain a scandium eluate. When obtaining the scandium eluate,
the normality of sulfuric acid used as an eluate is preferably
maintained in the range of between 0.3 N or more and less than 3 N,
and more preferably maintained in the range of between 0.5 N or
more and less than 2 N.
[Chromium Removing Step]
[0056] In the chromium removing step S24, the chelating resin which
has been subjected to the scandium elution step S23 is brought into
contact with 3 N or more of sulfuric acid to remove chromium which
has been adsorbed by the chelating resin in the adsorption step
S21. A normality of sulfuric acid used as an eluate of less than 3
N is not preferred when removing chromium because chromium may not
be removed properly from the chelating resin.
<2-3. Neutralization Step>
[0057] As described above, in the scandium elution step S2,
scandium is separated from impurities by virtue of the selectivity
of the chelating resin, and scandium separated from impurities is
recovered as a scandium eluate. However, all impurities may not be
completely separated from scandium due to the limited capability of
a chelating resin to be used.
[0058] Accordingly, separation of scandium from impurities can be
further facilitated by subjecting the scandium eluate collected in
the scandium elution step S2 to solvent extraction using as the
scandium eluate an extraction starting liquid in the solvent
extraction step S4 described below.
[0059] However, in general, higher is the concentration of the
target component in the extraction starting liquid to be subjected
to solvent extraction, the higher is the separation performance of
unwanted impurities in the solvent extraction step S4. Further, a
less amount of a liquid will be subjected to solvent extraction
when a higher concentration of scandium is contained in the
extraction starting liquid, assuming the same amount of scandium is
to be processed. As a result, a less amount of an extractant will
be used. This can further provide various advantages such as
improved operating efficiency owing to smaller equipment for the
solvent extraction treatment.
[0060] In view of the above, in the present embodiment, in order to
increase the concentration of scandium in the scandium eluate,
i.e., in order to concentrate scandium, a neutralizing agent is
added to the scandium eluate eluted from the chelating resin in the
scandium elution step S2 (the scandium elution step S23) to adjust
pH, thereby forming a precipitate of scandium hydroxide. The
resulting precipitate of scandium hydroxide is then re-dissolved by
adding an acid to obtain a highly concentrated scandium solution
(an extraction starting liquid). As described above, the process
efficiency of solvent extraction can be improved by subjecting the
scandium eluate to the neutralization treatment before the solvent
extraction step S4 to concentrate scandium.
[0061] Moreover, un-precipitated impurities may be separated out by
subjecting a scandium-containing precipitate to solid-liquid
separation, the scandium-containing precipitate being temporarily
formed from the scandium eluate after performing the aforementioned
neutralization treatment.
[0062] Specifically, as shown in FIG. 2, this neutralization step
S3 includes a neutralization step S31 composed of two stages of
adding a neutralizing agent to the scandium eluate to adjust the pH
of the solution to a predetermined pH range and obtaining a
neutralized residue and a neutralized filtrate and a hydroxide
dissolution step S32 of dissolving the neutralized precipitate
obtained by adding an acid thereto and obtaining a re-dissolved
liquid containing scandium at a high concentration.
[Neutralization Step]
[0063] In the neutralization step S31, a neutralizing agent is
added to the scandium eluate to adjust the pH of the solution to a
predetermined range and scandium contained in the scandium eluate
is transformed into a precipitate of scandium hydroxide. In the
neutralization step S31, a neutralized precipitate composed of
scandium hydroxide and a neutralized filtrate are generated in this
way.
[0064] The neutralizing agent is not particularly limited, and for
example, sodium hydroxide and the like can be used.
[0065] Here, in the present embodiment, the pH adjustment by
neutralization using a neutralizing agent is performed in two
stages as the neutralization treatment in this neutralization step
S31. This makes it possible to more efficiently separate impurities
and to concentrate scandium. FIG. 3 is a diagram for describing the
flow of the two-stage neutralization treatment in the
neutralization step S31. As shown in the flow chart of FIG. 3, the
neutralization step S31 includes a first neutralization step of
performing the first stage of neutralization and a second
neutralization step of performing the second stage of
neutralization.
(First Neutralization Step)
[0066] Specifically, in the neutralization treatment by the
two-stage pH adjustment, the first stage of neutralization is
performed in which a neutralizing agent such as sodium hydroxide is
added to the scandium eluate to adjust the pH of the solution to a
predetermined range as the first neutralization step. By this first
stage of neutralization, most of impurities such as iron and
chromium, which are less basic than scandium, are transformed into
precipitates in the form of hydroxides and the primary neutralized
precipitate is separated from the primary neutralized filtrate by
filtration. Note that scandium is concentrated in the primary
neutralized filtrate.
[0067] In the neutralization treatment in the first neutralization
step, the pH of the solution is preferably adjusted to the range of
3.5 to 4.5 by addition of a neutralizing agent. In addition, the pH
of the solution is more preferably adjusted to about 4.0. It is
possible to more efficiently concentrate scandium in the primary
neutralized filtrate by adding a neutralizing agent to the solution
so that the pH of the solution is in this range and thus performing
neutralization.
(Second Neutralization Step)
[0068] Next, as the second neutralization step, the second stage of
neutralization is performed in which a neutralizing agent such as
sodium hydroxide is further added to the primary neutralized
filtrate obtained by the first stage of neutralization to adjust
the pH of the solution to a predetermined range. By this second
stage of neutralization, scandium hydroxide is obtained as a
secondary neutralized precipitate while nickel, which is a
component more basic than scandium, does not precipitate and thus
remains in the secondary neutralized filtrate, and the secondary
neutralized precipitate, namely, a hydroxide of scandium from which
impurities have been separated can be obtained by performing
solid-liquid separation.
[0069] In the neutralization treatment in the second neutralization
step, the pH of the primary neutralization filtrate is adjusted so
as to be in the range of preferably 5.5 to 6.5 by addition of a
neutralizing agent. In addition, the pH of the primary neutralized
filtrate is more preferably adjusted to about 6.0. It is possible
to more efficiently generate a precipitate of scandium hydroxide by
adding a neutralizing agent to the primary neutralized filtrate so
that the pH of the solution is in this range and thus performing
neutralization.
[0070] The concentration of sodium hydroxide and the like used as a
neutralizing agent in the neutralization treatment may be
appropriately selected. However, local increase in pH may occur in
a reaction vessel when a highly concentrated neutralizing agent of
more than 4 N is added. This may result in a local pH of more than
4.5. If this occurs, impurities may disadvantageously be
co-precipitated with scandium, and thus high purity scandium may
not be obtained. For this reason, a neutralizing agent is
preferably a solution diluted to 4 N or less so that neutralization
in a reaction vessel proceeds as uniformly as possible.
[0071] On the other hand, when the concentration of a neutralizing
agent such as a sodium hydroxide solution is too low, the amount of
the solution to be added increases accordingly. This is not
preferred because the amount of liquid to be handled increases,
resulting in a larger equipment size and thus increased cost. For
this reason, a neutralizing agent with a concentration of more than
1 N is preferably used.
[0072] Note that a precipitate obtained by adding an alkaline
neutralizing agent such as sodium hydroxide, like the
aforementioned primary neutralized precipitate and secondary
neutralized precipitate, usually has very poor filterability.
Therefore, a seed crystal may be added to improve filterability
when performing neutralization. A seed crystal is preferably added
in an amount of about 1 g/L or more relative to a solution before
the neutralization treatment.
[Hydroxide Dissolution Step]
[0073] In the hydroxide dissolution step S32, the neutralized
precipitate (secondary neutralized precipitate) which is recovered
through the two-stage neutralization treatment in the
neutralization step S31 described above and thus contains scandium
hydroxide as a main component is dissolved by adding an acid
thereto to obtain a hydroxide solution to be a re-dissolved liquid.
In the present embodiment, the re-dissolved liquid thus obtained is
used as an extraction starting liquid for the solvent extraction
treatment in the solvent extraction step S4 to be described
later.
[0074] There is no particular limitation the acid for dissolving
the neutralized precipitate, but sulfuric acid is preferably used.
Note that the re-dissolved liquid is a scandium sulfate solution
when sulfuric acid is used.
[0075] For example, when sulfuric acid is used, there is no
particular limitation for the concentration thereof, but a sulfuric
acid solution with a concentration of 2 N or more is preferably
used for dissolution in view of the industrially preferred rate of
reaction.
[0076] Note that it is possible to obtain an extraction starting
liquid having an arbitrary scandium concentration by adjusting the
slurry concentration at the time of dissolution using sulfuric acid
and the like. For example, the pH of the solution is maintained
preferably in the range of 0.8 to 1.5 and more preferably about 1.0
when 2 N sulfuric acid is added for dissolution, and it is possible
to efficiently perform the dissolution of scandium hydroxide and to
suppress loss of scandium recovery due to undissolution by
maintaining this pH during the dissolution. Note that with regard
to the pH range described above, there is a possibility that
dissolution of scandium hydroxide does not efficiently proceed when
the pH is more than 1.5. On the other hand, it is not preferable
that the pH is as low as less than 0.8 since a strongly acidic
solution is obtained, the amount of the neutralizing agent to be
added for the wastewater treatment of neutralizing the solution
after being subjected to the removal of scandium increases, and the
cost and labor thus mount up.
<2-4. Solvent Extraction Step>
[0077] Next, in the solvent extraction step S4, the re-dissolved
liquid (hydroxide solution) obtained through the neutralization
step S3 of subjecting the scandium eluate to a neutralization
treatment is used as an extraction starting liquid and this is
brought into contact with an extractant to obtain a raffinate
liquid containing scandium. Note that the re-dissolved liquid to be
subjected to solvent extraction is an acidic solution containing
scandium and other impurity elements as described above, and this
is referred to as the "scandium-containing solution".
[0078] There is no particular limitation for the aspect of the
solvent extraction step S4, but a solvent extraction, for example,
as shown in FIGS. 1 and 2, is preferably performed, the solvent
extraction comprising: an extraction step S41 of mixing the
scandium-containing solution with an organic solvent as an
extracting agent to allow separation of a post-extraction organic
solvent into which impurities and a trace amount of scandium are
extracted and a raffinate liquid in which scandium remains; a
scrubbing step S42 of mixing the post-extraction organic solvent
with a sulfuric acid solution to separate a trace amount of
scandium extracted into the post-extraction organic solvent into an
aqueous phase, thereby obtaining a post-washing liquid; and a
backward extraction step S43 of adding a backward extracting agent
to the post-washing organic solvent to perform backward extraction
of impurities from the post-washing organic solvent.
(1) Extraction Step
[0079] In the extraction step S41, a scandium-containing solution
and an organic solvent containing an extractant are mixed together
and impurities in the organic solvent are selectively extracted to
obtain an organic solvent containing impurities and a raffinate
liquid. In the method for recovering scandium according to the
present embodiment, a solvent extraction treatment using an
amine-based extractant is preferably performed in this extraction
step S41. It is possible to more efficiently and effectively
extract impurities and thus to separate the impurities from
scandium by performing the solvent extraction treatment using an
amine-based extractant in this way.
[0080] Here, the amine-based extractant has a low selectively for
scandium, and does not require a neutralizing agent during
extraction, and may have other characteristics. For example, the
followings can be used as the amine-based extractant: those known
under the trade names of, for example, a primary amine Primene
JM-T, a secondary amine LA-1, a tertiary amine TNOA
(Tri-n-octylamine), TIOA (Tri-i-octylamine), and the like.
[0081] When performing extraction, the amine-based extractant is
preferably used after diluted with, for example, a
hydrocarbon-based organic solvent and the like. There is no
particular limitation for the concentration of the amine-based
extractant in an organic solvent, but it is preferably about 1 vol
% or more and about 10 vol % or less, in particular more preferably
about 5 vol %, in view of phase separability during the extraction
and backward extraction described below.
[0082] Moreover, there is no particular limitation for the volume
ratio of the organic solvent and the scandium-containing solution
when performing extraction, but the molar amount of the organic
solvent is preferably 0.01 times or more and 0.1 times or less
relative to the molar amount of metal in the scandium-containing
solution.
(2) Scrubbing (Washing) Step
[0083] When a trace amount of scandium is co-existent in a solvent
into which impurities are extracted from the scandium-containing
solution in the extraction step S41 as described above, a scrubbing
(washing) treatment (the scrubbing step S42) is performed on the
organic solvent (the organic phase) to separate scandium into the
aqueous phase, thereby recovering scandium from the extractant
before performing backward extraction of the extract liquid
obtained from the extraction step S41.
[0084] Washing the organic solvent to separate a trace amount of
scandium extracted with the extractant in the scrubbing step S42 as
described above can allow scandium to separate into a washing
liquid, and thus can further improve the recovery rate of
scandium.
[0085] For a solution (a washing solution) used for scrubbing, a
sulfuric acid solution, a hydrochloric acid solution, and the like
can be used. Further, solutions to which water-soluble chlorides
and sulfates are added can also be used. Specifically, when a
sulfuric acid solution is used as a washing solution, a solution
having a concentration in the range of between 1.0 mol/L or more
and 3.0 mol/L or less is preferably used.
[0086] The number of washing stages (the number of times) may also
depend on the identities and concentrations of impurity elements,
and thus may appropriately be selected depending on the amine-based
extractant, extraction conditions, and the like to be used. For
example, when the phase ratio of the organic phase (O) to the
aqueous phase (A), O/A is 1, the number of washing stages of about
3 to 5 can allow scandium extracted into the organic solvent to be
separated below the detection limit of an analyzer.
(3) Backward Extraction Step
[0087] In the backward extraction step S43, impurities are
backward-extracted from the organic solvent used for extracting
impurities in the extraction step S41. Specifically, in the
backward extraction step S43, the backward extraction solution (the
backward extraction starting liquid) is added to and mixed with an
organic solvent containing an extractant to effect a reaction
opposite to that in the extraction treatment of the extraction step
S41. This enables backward extraction of impurities to give a
post-backward extraction liquid containing impurities.
[0088] As described above, in the extraction treatment in the
extraction step S41, preferably, impurities are selectively
extracted using an amine-based extractant as an extractant. From
this fact, it is preferable to use a solution containing a
carbonate such as sodium carbonate or potassium carbonate as the
backward extraction solution from the viewpoint of effectively
separating the impurities from the organic solvent containing an
amine-based extractant and regenerating the extractant.
[0089] For example, the concentration of a carbonate-containing
solution serving as the backward extraction solution is preferably
about 0.5 mol/L or more and 2 mol/L or less in view of avoidance of
excessive use.
[0090] Note that when scrubbing treatment is performed for the
organic solvent containing an extractant in the scrubbing step S42
as described above, a backward extraction solution may similarly be
added to the post-scrubbing extractant to perform the backward
extraction treatment.
[0091] An extractant from which impurities has been separated out
by performing the backward extraction treatment in which a solution
of a carbonate salt such as sodium carbonate is added to a
post-extraction extractant or a post-scrubbing extractant as
described above can be used again repeatedly as an extractant in
the extraction step S41.
<2-5. Scandium Recovery Step>
[0092] Next, in the scandium recovery step S5, scandium is
recovered from the raffinate liquid obtained from the extraction
step S41 in the solvent extraction step S4, or from the washing
liquid after scrubbing when scrubbing is performed in the scrubbing
step S42.
[Crystallization Step]
[0093] The crystallization step S51 is a step of crystallizing
scandium contained in the raffinate liquid and the like into a
precipitate of a scandium salt and recovering the precipitate.
[0094] The method of crystallizing and recovering scandium is not
particularly limited, and a known method can be used, but examples
thereof may include a method in which an alkali is added to the
raffinate liquid and the like, a neutralization treatment is
performed, and a precipitate of scandium hydroxide is generated and
recovered. It is also possible to use a method (oxalate-formation
treatment) in which a precipitate of an oxalate is generated using
an oxalic acid solution and recovered. According to these methods,
it is possible to more effectively separate impurities and thus to
obtain crystals of scandium, which is preferable.
[0095] Note that the crystals such as scandium hydroxide and
scandium oxalate obtained by the methods described above can be
transformed into high purity scandium oxide by subjecting the
crystals to solid-liquid separation, then washing, and a treatment
in the roasting step S52 to be described later.
[Roasting Step]
[0096] The roasting step S52 is a step of washing the precipitate
of scandium hydroxide, scandium oxalate, and the like obtained in
the crystallization step S51 with water, drying the precipitate,
and then roasting the precipitate. Scandium can be recovered as
extremely high purity scandium oxide by being subjected to this
roasting treatment.
[0097] There is no particular limitation for the roasting
conditions, but for example, heating in a tubular furnace at about
900.degree. C. for about 2 hours may be used. Note that a
continuous furnace such as a rotary kiln is preferably used for
industrial production because both drying and roasting can be
performed with the same equipment.
EXAMPLES
[0098] Below, the present invention will be described in more
detail with reference to Examples. However, the present invention
shall not in any sense be limited to these Examples.
<<Investigation on pH and Precipitation Behavior in
Neutralization Treatment>>
[0099] Pressurized acid leaching of nickel oxide ore with sulfuric
acid was performed according to the known method such as the method
described in Patent Document 1. The pH of the resulting leachate
was adjusted to remove impurities and then a sulfurizing agent was
added to the leachate to separate nickel, thereby preparing a
barren liquor. Table 1 below shows the concentrations of scandium,
aluminum, and iron in the resulting barren liquor.
[0100] Note that when a neutralizing agent was added to a solution
having the above composition to form a precipitate, thereby
obtaining a hydroxide comprising scandium and other impurity
components, the grade of scandium hydroxide was as low as about 0.1
wt %.
TABLE-US-00001 TABLE 1 Composition of barren liquor Sc Al Fe [mg/L]
14 2,800 1,000
[0101] Next, the barren liquor in Table 1 was subjected to an ion
exchange treatment by a known method using a chelating resin to
obtain a scandium eluate having the composition shown in Table 2
below.
TABLE-US-00002 TABLE 2 Scandium eluate Sc Al Fe Ni Cr [mg/L] 100 30
40 10 2
[0102] Next, the resulting scandium eluate (composition in Table 2)
was sampled, placed in a container, and a 4 N sodium hydroxide
solution was then added thereto with stirring to adjust the pH to
1.
[0103] Subsequently, it was allowed to stand after stopping
stirring. The amount of the liquid was then measured, and the
supernatant (primary neutralized filtrate) after the precipitate
(primary neutralized precipitate) was sedimented was collected.
Then, stirring was started again, and a 4 N sodium hydroxide
solution was added again to adjust the pH of the solution to 2.
Then it was allowed to stand after stopping stirring. The amount of
the liquid was then measured, and the supernatant (secondary
neutralized filtrate) was collected. Then stirring was started
again. This procedure was repeated to prepare samples of the
respective scandium eluates having a pH of the solution in the
range of 1 to 6.
[0104] Each sample prepared was analyzed by ICP for the components
such as scandium, iron, aluminum, and nickel. Note that the amount
calculated from the analytical value of each component and the
fluid volume of each sample corresponds to the amount of that
component present in the solution at each pH. The difference
between the amount of the component present in the solution and the
initial amount calculated from the analytical value and the initial
volume of the scandium eluate shown in Table 2 corresponds to the
amount of the precipitate generated by the pH adjustment
(neutralization). The ratio obtained by dividing the amount of the
precipitate by the aforementioned initial amount is defined as the
precipitation rate (%).
[0105] FIG. 4 shows each pH and the precipitation rates of the
components shown in Table 2. As shown in the graphical
representation of FIG. 4, iron is found to show increased
precipitation rates in the pH region of more than 3, and almost
completely precipitated at 4.5 to 5 or more. Moreover, aluminum is
found to show increased precipitation rates when the pH is more
than 4.5. In contrast, scandium is also found to show increased
precipitation rates when the pH is more than 4.5, but the increase
is more gradual than that of aluminum. Note that nickel starts to
precipitate when the pH is becoming more than 6.
EXAMPLES: TWO-STAGE NEUTRALIZATION TREATMENT
Example 1
(First Stage of Neutralization)
[0106] Based on the results shown in FIG. 4, the scandium eluate
having a composition shown in Table 2 was placed in a container and
a 4 N sodium hydroxide solution was added thereto with stirring so
that the pH of the solution was adjusted to 4, thereby performing
the first stage of neutralization treatment.
[0107] After this first stage of neutralization treatment,
solid-liquid separation was performed using filter paper and
Nutsche, and as a result, a primary neutralized precipitate and a
primary neutralized filtrate were obtained.
[0108] By analysis using ICP, the ratio (partitioning) of the
amount of a precipitate generated to the amount of substance
contained in the scandium eluate having the composition shown in
Table 2 was evaluated as the precipitation rate (%). Table 3 below
shows the precipitation rates by the first stage of neutralization
treatment.
TABLE-US-00003 TABLE 3 Precipitation rate of each element component
Sc Al Fe Ni Cr [%] 4 4 89 0 50
[0109] As shown in Table 3, iron and chromium as impurities in the
solution were able to be effectively precipitated as neutralized
precipitates by adding a neutralizing agent to the solution until
the pH of the solution became 4 and thus performing neutralization,
and were able to be separated from scandium which was partitioned
into the primary neutralized filtrate.
(Second Stage of Neutralization)
[0110] Next, the resulting primary neutralized filtrate was placed
in a container, and a 4 N sodium hydroxide solution was added
thereto so that the pH of the solution was adjusted to 6, thereby
performing the second stage of neutralization treatment.
[0111] After this second stage of neutralization treatment,
solid-liquid separation was performed as in the first stage of
neutralization treatment, and as a result, a secondary neutralized
precipitate and a secondary neutralized filtrate were obtained.
[0112] By analysis using ICP, the ratio (partitioning) of the
amount of a precipitate generated to the amount of substance
contained in the primary neutralized filtrate was analyzed as the
precipitation rate (%). Table 4 below shows the precipitation rates
by the second stage of neutralization treatment.
TABLE-US-00004 TABLE 4 Precipitation rate of each element component
Sc Al Fe Ni Cr [%] 88 99 99 4 94
[0113] As shown in Table 4, almost 90% of scandium mostly remained
in the filtrate without precipitating in the first stage of
neutralization was partitioned into the secondary neutralized
precipitate by the second stage of neutralization. In contrast,
nickel, which was more basic than scandium, did not precipitate
during either the first or second stage of neutralization, and
remained in the secondary neutralized filtrate, and thus was able
to be effectively separated from scandium.
[0114] Note that it seems that among the components (composition
shown in Table 2) in the scandium eluate, large amounts of iron and
chromium also precipitate in the second stage of neutralization
from the results shown in Table 4. However, most of these
components have already partitioned into the primary neutralized
precipitate in the first stage of neutralization, and have been
separated from scandium. Therefore, the amount of these components
to be partitioned into the secondary neutralized precipitate itself
is reduced.
[0115] From the above results, it has been found that with
reference to the ratios (precipitation rates) of the components
partitioned into the secondary neutralized precipitate from which
scandium has been solidified and recovered to those contained in
the scandium eluate, aluminum is significantly precipitated other
than scandium and iron, chromium, nickel, and others are
effectively separated by performing such a two-stage neutralization
treatment as shown in Table 5 below.
TABLE-US-00005 TABLE 5 Precipitation rate of each element component
Sc Al Fe Ni Cr [%] 82 99 6 4 31
<<Recovery of Scandium>>
(Hydroxide Dissolution Treatment)
[0116] Next, a 2 N sulfuric acid solution was added to the
resulting secondary neutralized precipitate, and dissolution was
performed while maintaining the pH at around 1 to obtain a
re-dissolved liquid (hydroxide solution) shown in Table 6
below.
TABLE-US-00006 TABLE 6 Re-dissolved liquid Sc Al Fe [g/L] 20 7.2
0.6
(Solvent Extraction Treatment)
[0117] Next, 50 liters of an organic solvent in which an
amine-based extractant (The Dow Chemical Company, Primene JM-T) was
adjusted to 5 vol % with a solvent (Shellsol A150, Shell Chemicals
Japan, Ltd.) was mixed with 100 liters of the re-dissolved liquid
having the composition shown in Table 6 as an extraction starting
liquid, and the mixture was stirred at room temperature for 60
minutes to effect a solvent extraction treatment. By this solvent
extraction treatment, a raffinate liquid containing scandium was
obtained. Note that no cladding was formed during extraction, and
phase separation after still standing also proceeded rapidly.
[0118] The composition of each element contained in the organic
phase extract obtained by the above extraction was analyzed. The
percentage of the value obtained by dividing the amount of each
element contained in the organic phase extract by the amount of
that element contained in the pre-extraction liquid (extraction
starting liquid) was calculated, and the results are shown in Table
7 below as the extraction rate (%).
TABLE-US-00007 TABLE 7 Extraction rates of various elements Sc Al
Fe [%] 4 -- -- (Note that "--" in Table 7 indicates that it was not
analyzed or the measured value was less than the lower measurement
limit.)
[0119] As seen from the results of extraction rates shown in Table
7, the majority of scandium contained in the pre-extraction liquid
was partitioned into the raffinate liquid through the solvent
extraction treatment. Note that other impurities were transferred
to the organic solvent and were able to be effectively separated
from scandium although not shown in Table 7.
[0120] Subsequently, 50 liters of a 1 mol/L sulfuric acid solution
was mixed with 50 liters of the organic solvent which was obtained
after the extraction treatment and contained a slight amount of
scandium (the organic phase extract) so that the phase ratio (O/A)
became 1, and the mixture was stirred for 60 minutes, and then
washed. Then, the mixture was allowed to stand for separation of
the aqueous phase. The organic phase was again mixed with 50 liters
of a fresh 1 mol/L sulfuric acid solution, and washed. The aqueous
phase was then separated in a similar manner. The washing operation
as described above was repeated 5 times in total.
[0121] By washing the organic phase extract for 5 times in this
way, scandium contained in the organic phase extract was allowed to
separate into the aqueous phase, enabling recovery of scandium. In
contrast, impurities contained in the organic phase extract were
eluted at levels of as low as 1 mg/L, showing that only scandium
extracted into the organic solvent was able to be effectively
separated into the aqueous phase, and only impurities were able to
be removed.
[0122] Subsequently, 1 mol/L sodium carbonate was mixed with the
organic phase extract after washing so as to give a phase ratio O/A
of 1/1, and stirred for 60 minutes to effect backward extraction of
impurities into the aqueous phase.
[0123] The composition of various elements contained in the
post-backward extraction liquid obtained by this backward
extraction operation was analyzed. The percentage of the value
obtained by dividing the amount of each element contained in the
post-backward extraction liquid by the amount of that element
extracted into the organic phase by the extraction treatment was
calculated, and the results are shown in Table 8 below as the
recovery rate (%).
TABLE-US-00008 TABLE 8 Recovery rates of various elements Sc Al Fe
[%] 25 -- -- (Note that "--" in Table 8 indicates that it was not
analyzed or the measured value was less than the lower measurement
limit.)
[0124] As seen from the results of recovery rates shown in Table 8,
most of iron and aluminum were able to be separated and scandium
was able to be recovered by performing the solvent extraction
treatment described above.
(Oxalate-Formation Treatment)
[0125] Next, crystals of oxalic acid dihydrate (Mitsubishi Gas
Chemical Company, Inc.) was dissolved in the resulting raffinate
liquid in an amount calculated to be twice of the amount of
scandium contained in that raffinate liquid, and stirred and mixed
for 60 minutes to generate a white crystalline precipitate of
scandium oxalate.
(Roasting Treatment)
[0126] Next, the resulting precipitate of scandium oxalate was
filtered by aspiration, and washed with pure water, and was dried
at 105.degree. C. for 8 hours. Then, the dried scandium oxalate was
placed in a tubular furnace, and maintained at 850.degree. C. to
900.degree. C. to perform roasting (calcination), thereby obtaining
scandium oxide.
[0127] The scandium oxide obtained by performing roasting was
analyzed by the emission spectroscopic analysis. Table 9 below
shows the removal rates (%) each obtained by dividing the content
of a material after roasting by the content of that material before
the oxalate-formation treatment.
TABLE-US-00009 TABLE 9 Removal rates of various elements Sc Al Fe
[%] 0 100 99.9
[0128] As seen from the results of the removal rates in Table 9,
aluminum and iron other than scandium as well as other impurities
not shown in the table were able to be removed almost completely,
and ultra high purity scandium oxide of which the purity as
scandium oxide (Sc.sub.2O.sub.3) was more than 99.9 wt % was able
to be obtained.
COMPARATIVE EXAMPLE
Comparative Example 1
[0129] The barren liquor which was used in Example 1 and had the
same composition as that shown in Table 1 above was subjected to an
ion exchange treatment by the same method as in Example 1 to obtain
a scandium eluate having the same composition as that shown in
Table 2.
(One-Stage Neutralization)
[0130] Based on the results shown in FIG. 4, a 4 N sodium hydroxide
solution was added to the scandium eluate and the scandium eluate
was neutralized so that the pH of the solution was in the range of
5 to 6 to generate a precipitate. Then, solid-liquid separation was
performed to obtain a precipitate of scandium hydroxide.
[0131] Next, 2 N sulfuric acid was added to the resulting scandium
hydroxide, and dissolution was performed while maintaining the pH
at around 1 to obtain a re-dissolved liquid having a composition
shown in Table 10 below.
TABLE-US-00010 TABLE 10 Re-dissolved liquid Sc Al Fe [g/L] 20 10
4
[0132] When the re-dissolved liquid (composition shown in Table 10)
obtained by the conventional method is compared with the
re-dissolved liquid obtained in Example 1, namely, the re-dissolved
liquid (composition shown in Table 6) obtained through the
two-stage neutralization treatment, there is a large difference in
aluminum concentration and iron concentration although the scandium
concentration is the same. That is, it has been confirmed that
aluminum and iron, which are impurities, can be effectively
separated by performing a two-stage neutralization treatment as
performed in Example 1.
* * * * *