Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE IMVENTION
METHOD FOR RECOVERING GALIIUM
BACKGROUND OF THE INVENTION
FIELD OF TEIE INVENTION
The present invention relates to a method for
recovering gallium. More particularly, it relates to a
method for advantageously recovering gallium from a
strongly basic aqueous solution such as an aqueous sodium
aluminate solution formed by a Bayer process.
DESCRIPTION OF THE PRIOR ART
. It is known that gallium is contained in bauxite in
an amount of from 0.002 to 0.01%. In the process for the
production of alumina by a Bayer process, an alkali is
recycled for repeated use, and a substantial amount of
gallium is con-tained in the aqueous sodium aluminate
solution formed in this process. An amalgamation method
has been known as a method for recovering gallium from
the aqueous sodium aluminate solution formed by this
Bayer process. In recent years, a liquid-liquid
extraction method has been developed as a superior method
which will take the place of the amalgamation method.
According ~o this method, gallium is extracted from the
aqueous sodiu}n aluminate solution containing gallium by
means of an extracting agent prepared by dissolving a
water-insoluble substituted quinolinol such as 7-(1-
vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol in an
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organic solvent, ~nd then the extracting agent containing
gallium is reverse]y extracted with an aqueous acid
solution to recover gallium (Japanese Unexamined Patent
Publication No. 32~11/1976). This method is practically
useful as an industrial method, but it has a drawback
that the substituted quinolinol in the extracting agent
is susceptible to degradation. As a method for
overcoming this drawback, there has been proposed a
method wherein a quinolinol substituted by an alkyl group
instead of the alkenyl group is used (Japanese Unexamined
Patent Publication No. 52289/1978), or a me-thod wherein
the operation is conducted in an inert atmosphere
(Japanese Unexamined Patent Publication No. 40212/1979).
SUMMARY OF THE INVENTION
The present inventors have conducted a research to
develop a method for recovering gallium in an
industrially more advantageous manner than these liquid-
liquid extraction methods, and as a result, have found
that when the water-insoluble substituted quinolinol used
in these liquid-liquid extraction methods is supported on
a porous polymer, such a porous polymer exhibits
excellent adsorptivity for gallium. Further, it has been
unexpectedly found that the substituted quinolinol fixed
in this porous polymer does not undergo degradation very
much even if repeatedly used for the recovery of gallium
from the aqueous sodium aluminate solution. The presént
invention has been accomplished on the basis oE this
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discovery, and presents a ~otally new rnethod which may be
called an impregnated resin method.
Namely, the present invention provides a method for
recovering yallium from an aqueous solution containing
gallium, which comprises contacting the aqueous solution
containing galliurn to a porous polymer having a
water-insoluble substituted quinolinol retained therein,
to let the polymer adsorb gallium, and then eluting
gallium from the polymer.
DETAILED DESCRIPTION OF THE INVENTION
Now, the present invention will be described in
detail with refexence to the preferred embodiments.
The present invention i5 concerned with a method for
separating gallium in an aqueous solution by the
adsorption with a solid adsorbing agent. The present
invention is particularly useful for the recovery of
gallium from a strongly basic aqueous solution, usually a
strongly basic aqueous solution having a p~ of at least
10. ~ typical representative of such a strongly basic
aqueous sclution containing gallium is an aqueous sodium
aluminate solution formed by a Bayer process. As is well
known, in the Bayer process, bauxite is treated with an
aqueous sodium hydroxide solution to form an aqueous
sodium aluminate solution. This aqueous sodium aluminate
solution is then subjected to hydrolysis, whereby a part
thereof is converted to aluminum hydroxide and sodium
hydroxide. The formed aluminum hydroxide is separated,
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and the remaining aqueous sodium aluMinate sollltion
containing sodium hydroxide i6 adjusted ~or its
concentra-tion and used ayain for the treatment of
bauxite. The aqueous sodium aluminate solution after the
separation of aluminum hydroxide is cornposed, for
instance, of from 150 to 200 g/liter of Na2O~ from 70 to
lO0 g/liter of A12O3 and about 200 mg/li-ter of gallium.
The present invention can be advantageously applied for
the recovery of gallium from such an aqueous sodium
lO aluminate solution.
In the present invention, various types of
conventional polymers may be used as the porous polymer
useful as the carrier for the substituted ~uinolinol. It
is usual to employ a porous polymer having a pore volume
15 of from 0.1 to 2 ml/g, preferably from 0.3 to 1.2 ml/g as
measured by mercury injection method, and an internal
surface area of at least 10 m /g, preferably from 50 to
800 m2/g as measured by BET method. Such porous polymers
may be produced by various methods. However, they are
~ usually prepared by the copolymerization of a monovinyl
compound with a polyvinyl compound, or polyvinyl
compounds with one another, or by the homopolymerization
of a polyvinyl compound. ~s such vinyl compounds, there
may be mentioned hydrocarbons such as styrene,
methylstyrene, vinylnaphthalene, butadiene or piperylene;
styrene derivatlves such as chlorostyrene, nitrostyrene
or aminostyrene; acrylonitrile derivatives such as~-
,
- s
acrylonitrile, methacrylonitrile or ~-acetoxy-
acrylonitrile; acr~lic acid, methac~ylic acid and esters
thereof; divinyl benzene, divinyl toLuene, divinyl
xylene, divinyl naphthalene, divinyl ethylbenzene,
5 divinyl sulfone, divinyl ketone, divinyl furan, divinyl
pyridine, diallyl phthalate, diallyl succinate, ethylene
glycol dimethacrylate, diallyl amine, and N,N'-ethylene
bisacrylamide. As a method for producing porous polymers
from these vinyl compounds, it is usual to employ a
conventional precipitation solvent method or a linear
polymer co-existence method. In the precipitation
solvent method, the monomer is dissolved in a solvent
which is capable of dissolving the monomer, but incapable
of dissolving the homopolymer, and then subjected to
suspension polymerization in the presence of a suitable
polymerization initiator, to obtain a spherical polymer
having a diameter of from 0.1 to l mm. In the linear
polymer co-existence method, the monomer and the linear
polymer such as polystyrene are dissolved in a suitable
solvent, and likewise subjected to suspension
polymerization, and the linear polymer is extracted and
removed from the formed polymer with a suitable solvent.
The porous polymer to be used in the present
invention preferably has a polarity to some extent.
Accordingly, preferred is a porous polymer composed
essentially of acrylonitrile or its derivative; acrylic
acid, methacrylic acid or an ester thereo~; divinyl-
sulfone, divinyl ketone, divinyl furan, diallyl
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phthalate, diallyl succinate, or ethylene glycol
dimethacrylate. Particularly preferred is a porous
polymer composed essentially of an ester such as an
acrylate, a me-thacrylate, diallyl phthalate, diallyl
succinate, or ethylene glycol diacrylate or
dimethacrylate. As a commercial product of such an
ester-type porous polymer, there may be mentioned HP-2MG
from Mitsubishi Chemical Industries, Ltd., or XAD-7 or
~AD-8 from Rohm and Haas Co.
In the present invention, a water-insoluble
substituted quinolinol is supported on the above-
mentioned porous polymer, and used for the separation o~
gallium. Like in the case of the liquid-liquid
extraction, in the present invention, gallium is believed
lS to form a complex with the substituted quinolinol, which
is then adsorbed on the porous polymer. Accordingly, as
the water-insoluble substituted quinolinol, those
represented by the following general formula may be
employed as in the case of the conventional liquid-liquid
extraction method.
R R
R ~
OH
wherein R is a hydrocarbon group or a hydrogen atom.
It is preferred to employ a 7-substituted-8-
quinolinol having a substituted or unsubstituted
hydrocarbon group at the 7-position. As the hydrocarbon
group, those haviny a carbon number of from 5 to 20,
~ ~3~ 3'
particularly from 8 to 20, are preferred. E'or instance,
there may be mentioned a 1,~,~,5-te~ramethylheptyl group,
a 1,4,~,6,6-pentamethyl-1-heptenyl group or a l-vinyl-
3,3,5,5-tetramethylhexyl group.
In order to support the above-men-tioned substituted
quinolinol on the porous polymer, the substituted
quinolinol is dissolved in a suitable solvent, and the
porous polymer is immersed and impregnated therein.
As mentioned above, the adsorptivity of the porous
10 polymer for gallium is dependent on the subst~tuted
~uninolinol supported or retained in -the polymer.
Therefore, the greater the amount of the quinolinol
retained in the porous polymer, the better.
;; A great amount of the substituted quinolinol may be
-~ 15 retained by a method wherein the porous polymer is put in
a solution of the substituted quinolinol, and then the
solvent is removed by evaporation. According to this
method, it i5 possible to retain from 0.1 to 0.6 g of the
substituted quinolinol per 1 g of the polymer when the~
20 polymer is a porous polymer having a pore volume of from
0.3 to 1.2 ml/g~
The above method represents a typical method for
retaining the substituted quinolinol in the porous
~` polymer according to the present invention. However, in
25 the present invention, the manner of retaining the
quinolinol is not restricted to such a typical method,
but generally covers such a manner tha-t the substituted
quinolinol is held in the porous polymer by a physical or
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chemical affinity other than reactions, and is not
substantially eluted ~rom the polymer by the operation of
the adsorption or elution of gallium, or any other
operation according to the present invention, and at
least no substantial elution of the substituted
quinolinol is observed by the washing with water.
According to the present invention, by means of the
porous polymer having the substituted quinolinoL retained
therein, thus prepared, gallium is adsorbed from the
aqueous solution containing gallium. The adsorption
operation may be carried out in a agitation tank system.
However, it is advantageous to conduct the adsorption in
a column system.
The higher the operation temperature, the greater the
adsorption speed. Therefore, the adsorption operation is
usually conducted at a temperature of from 40 to 80 C.
Gallium adsorbed on the porous polymer is then eluted
- with an acidic eluting solution to recover gallium. As
the eluting solution, sulfuric acid, nitric acid,
hydrochloric acid or the like is usually employed.
Sulfuric acid or nitric acid is employed at a
concentration of at least 0.5 mol/liter, preferably at
least 1 mol/liter. In the case of hydrochloric acid, if
the concentration exceeds about 5 mol/liter, gallium is
likely to form a chlorocomplex ion ([GaCl4] ), which will
then bond, by ion exchange, to the nitrogen atom of the
substituted quinolinol turned into a pyridinium ion by
the presence of hydrochloric acid, whereby gallium is
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hardly eluted. Therefore, the concentration oE
hydrochloric acid should be at most 5 mol/liter.
Usually, the concentration of hydrochloric acid is
selected within a range of ~rom 0.1 to 5 mol/liter,
particularly from 0.5 to 4 mol/liter.
In the case where the recovery of gallium in the
sodium aluminate formed by a Bayer process is conducted
according to the method of the present inventi.on,
aluminum as well as gallium is adsorbed on the porous
10 polymer, and in the above-mentioned eluting method,
gallium and aluminum are eluted simultaneously. To avoid
the simultaneous elution~ firstly the porous polymer is
` treated with from 0.01 to 0.1 mol/liter of sul~uric acid
or nitric acid to elute aluminum, and then treated with
15 at least 0.5 mol/liter of sulfuric acid or nitric acid to
: elute gallium. In the case where hydrochloric acid is
used as the elut.ing agent, firstly the porous polymer is
, treated with hydrochloric acid having a concentration
exceeding S mol/liter to elute aluminum, and then treated
20 with hydrochloric acid having a concentration of from 0.1
to 5 mol/liter to elute gallium. Of these two-step
elution methods, the former is a method in which the
difference in the stability o the respective complexes
of aluminum and gallium is utilized by controlling the
25 acid concentration, whereas the latter is a method
wherein the chlorocomplex ion-forming ability of gallium
is utilized. By either method, aluminum and gallium-can
be substantially completely separated and recovered from
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the porous polymer. Further, in the method wherein the
chlorocomplex ion-forminy ability is utilized, it is also
possible to use a highly concentrated aqueous alkaline
solution instead of hydrochloric acid having a
5 concentration of from 0.1 to 5 mol/liter, whereby gallium
is eluted by ion exchange.
According to the present invention, the recovery of
gallium from the gallium-containing aqueous solution is
conducted as described above, and accordingly, the
operation is simple and the loss of the water-insoluble
substituted quinolinol into the aqueous phase is small as
compared with the conventional liquid-liquid extraction
method. Further, the present invention has a feature
that the degradation of the substituted quinolinol is
remarkably reduced. The reason for this is not clearly
understood. However, this is believed somehow related to
the fact that substituted quinolinol is fixed in the
porous polymer.
Now, the present invention will be described in
further detail with reference to Examples. However, it
should be understood that the present invention is by no
means restricted to these specific Examples.
E~AMPLE l
A solution obtained by dissolving 2.25 g of Kelex lO0
[effective component: 7~ vinyl-3,3,5,5-tetramethyl-
a 1`~ e~k
hexyl)-8-quinolinol]~of Messrs. AshLand Chemical Co. in
lO ml of acetone, was added to 15 g of Amberlite XAD-7 ~a
polymer of ethylene glycol dimethacrylate, particlé size:
~J~ S
- 11 ~6/ oe fr~c/~ ~ ~ f
0.5 mm) i.e. a synthetic adsorbe]. manufactured by~Rohm
and ~aas Co. Then, whlLe stirriny the mixture, acetone
was evaporated over a period of 2 hours. Then, the dried
product was washed with a 3N aqueous sodium hydroYide
solution and 6N hydrochloric acid, and then washed with
water, and the water around XAD-7 was removed. 5 g of
such XAD-7 having the substituted quinolinol retained
therein, was packed in a column having inner diameter o~
18 mm ~the packing height: about 30 mm). After 3N sodium
hydroxide was passed through the column, 10 ml of an
aqueous sodium aluminate solution of 50C prepared in the
after-mentioned manner was passed therethrough at a flow
rate of 1 ml/min.
Preparation of the aqueous sodium aluminate solution
To a 3N aqueous sodium hydroxide solution, aluminum
hydroxide and metal galliurn were dissolved to have
the respective concentrations of Al = 0.2 mol/liter
and Ga = 2.46 x 10 3 mol/liter, to obtain an aqueous
sodium aluminate solution containing gallium.
Then, a 3N aqueous sodium hydroxide solution and
water were successively passed through the column for
washing, and then gallium was eluted b-y passing 20 ml of
lN hydrochloric acid at a :Elow rate of 1 ml/min.
The gallium and aluminum concentrations in the
aqueous sodium aluminate solution after the column
treatment and in the eluting solution, were
quantitatively analyzed by atomic-absorption spectro-
photometry, whereby the adsorption rate of gallium was
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100~, and the elution rate was 97.5%, ~7hereas the
adsorp-tion rate of aluminum was 15-~, and the elution rate
was 97%.
By using the above-mentioned column and aqueous
sodium aluminate solution, the adsorption-elution
operation was repeated 9 times under the same conditions,
whereby no substatial change was obser~ed each time in
the adsorption rates and elution rates of gallium and
aluminum. Further, no elution of Kelex retained in the
polymer was visually observed during these operations,
and further no change in the outer appearance of the
polymer was observed between the initial and final
stages, and no color change was observed.
EXAMPLE 2
The adsorption-elution operation was conducted in the
same manner as in Example 1 except that 4N sulfuric acid
was used instead of hydrochloric acid in Example 1,
whereby the adsorption rate of gallium was 100% and the
elution rate was 99%, whereas the adsorption rate of
aluminum was 14% and the elution rate was 98%.
COMPARATIVE EXAMPLE 1
100 ml of a kerosine solution containing 8~ of Relex
100 and 100 ml of the same aqueous sodium alumlnate
solution as used in Example 1, were mixed and stirred at
` 25 50C for 2 hours, and then the mixture was permitted to
` separate in-to an organic layer and an aqueous layer.
To the organic layer, 100 ml-of lN hydrochloric- acid
was mixed, and the mixture was stirred at 50C for 2
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hours, and then perrnitted to separate into an organic
layer and an aqueous layer. The gal:Liurn concentration in
this aqueous layer was quantitatLvely analyzed, whereby
the extraction rate of gallium wa.s 80%.
By using the same extracting agent, the above-
mentioned extraction-reverse extraction was repeated,
whereby the organic layer was gradually colored red ~rom
the fifth operation.
EXAMPLE 3
The substituted quinolinol was retained in the same
manner as in Example 1 except that HP-2MG (divinyl
benzene-type polymer) i.e. a synthetic adsorber
manufactured by Mitsubishi Chemical Industries, Ltd. was
used instead of XAD-7 in Example 1. HP-2MG having the
substituted quinolinol retained therein, thus prepared,
was packed in a column having an inner diameter of 9 mm
to have a packing height of about 150 mm.
By using thls column, the adsorption-elution
operation was repeated 5 times in the same manner as in
Example 1 except that the aluminum hydroxide and metal
gallium concentrations in the aqueous sodium aluminate
solution containing gallium were adjusted to be Al = 1.4
mol/liter and Ga - 2.4 x 10 3 mol/liter.
To examine -the effects of the repetition, the gallium
concentration in the aqueous sodium aluminate solution
and the gallium and aluminum concentrations in the
eluting solution after the column treatment in the third
operation and thereafter, were quantitatively analyzed by
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atomic-absorption spectrophotometry, whereby the
adsorption rate of gallium was at least 90~ in every
operation, and other results were as shown below.
OperationRecover~ rate (~)*
cycle Ga Al
3 94,6 0~21
4 96.3 0.24
97.1 0.24
* The recovery rate is a rate relative to
the gallium or aluminum in the aqueous
sodium aluminate solution containing
gallium.
No elution of Kelex retained in the polymer was
; visually observed during the above operations, and no
substantial change in the outer appearance of the polymer
was observed between the initial and final stages of the
operations.
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