WO1993022478A1 - Electrolytic method of obtaining gallium metal - Google Patents

Electrolytic method of obtaining gallium metal Download PDF

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Publication number
WO1993022478A1
WO1993022478A1 PCT/US1992/003717 US9203717W WO9322478A1 WO 1993022478 A1 WO1993022478 A1 WO 1993022478A1 US 9203717 W US9203717 W US 9203717W WO 9322478 A1 WO9322478 A1 WO 9322478A1
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Prior art keywords
gallium
alloy
zinc
solution
alkaline solution
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PCT/US1992/003717
Other languages
French (fr)
Inventor
Sergei Pavlovich Yatsenko
Valeriy Nikolaevich Diev
Gregory Mihailovich Rubinshtein
Vladimir Vladimirovich Shafray
Vladimir Josifovich Ovsyannikov
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Usr, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Usr, Inc. filed Critical Usr, Inc.
Priority to PCT/US1992/003717 priority Critical patent/WO1993022478A1/en
Priority to AU19203/92A priority patent/AU1920392A/en
Publication of WO1993022478A1 publication Critical patent/WO1993022478A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B58/00—Obtaining gallium or indium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/12—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic alkaline solutions
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
    • C25C1/24—Alloys obtained by cathodic reduction of all their ions
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates to an improved method of obtaining gallium from sodium aluminate liquors used in alumina production wherein an alloy of gallium is first obtained using an electrolytic method and then the alloy of gallium is dissolved in an alkaline solution and further electrolyzed to produce a gallium-enriched solution. The gallium is then extracted from the gallium-enriched solution using a cementation process wherein the gallium- enriched solution is contacted with a cementating agent.
  • the alloy of gallium of the present invention is a zinc-gallium alloy and the cementating agent is aluminum.
  • Gallium is typically produced from gallium-containing alkaline-aluminate solutions produced during the Bayer process for recovering alumina from bauxites. Processing of bauxites by Bayer's method comprises leaching of aluminum oxides contained in the core by means of a solution of caustic soda. At the same time, gallium passes into the resulting aluminate solution in the form of sodium gallate. Upon decomposition of aluminate solutions, a predominant portion of the gallium remains in solution due to the formation of more durable, complex compounds as compared to aluminum in the so-called mother aluminate liquor.
  • the mother aluminate liquor after separation of aluminum hydroxide, is evaporated to a return aluminate liquor and recycled to leach a new portion of bauxite. As a result of recirculation these liquors become enriched in gallium.
  • the mother and recycle liquors obtained in the Bayer process are combined to form sodium aluminate liquors which serve as feedstock in gallium production.
  • the gallium produced from sodium aluminate liquors can be • used for producing gallium of high purity and for producing fusible alloys.
  • U.S. Patent No. 4,368,108 discloses an electrolytic method of extracting gallium from sodium aluminate liquors used in alumina production wherein the gallium is produced on a solid cathode in the form of an alloy, for example, as a gallium-zinc alloy.
  • This method is especially effective whenever the initial solutions contain a sufficient quantity of sulfur as sulfides.
  • zinc form an alloy with gallium, which promotes depolarization at the cathode, but the zinc promotes formation of insoluble sedimentary products that effectively remove other impurities from the sodium aluminate liquors.
  • the disadvantage of this method is that the prior art methods for extracting gallium from the electrolytically-produced zinc-gallium alloy are complicated.
  • the present invention is directed to overcoming these difficulties and to obtaining purer gallium as compared with prior art methods.
  • the subject invention for obtaining gallium from sodium aluminate liquors used in alumina production effectively takes advantage of a combination of methods.
  • One method is that of electrolytically extracting the gallium as an alloy of gallium from the sodium aluminate liquors used in alumina production.
  • Another method is that, of dissolving an alloy of gallium in an alkaline solution and electrolyzing the more electropositive metal from the dissolved alloy of gallium to produce a gallium-enriched solution.
  • Still another method is that of carrying out a cementation process on an alkaline solution of an alloy of gallium using aluminum as the cementating agent.
  • An advantage of the present method is that it can be used without a preliminary purification step to remove impurities such as vanadium, chromium, iron, sulfur compounds, etc. from the sodium aluminate liquors used in alumina production.
  • Another advantage of the present invention is that it can be used without employing the toxic substances such as mercury that are employed in the prior art methods.
  • Another advantage of the present method is that it can be used with a reduced consumption of valuable materials such as aluminum.
  • Another advantage of the present method is that it provides a simplified method of removing gallium from the alloy of gallium electrolytically produced from the sodium aluminate liquors.
  • gallium produced by the present method is of a high technical grade.
  • the subject invention provides a method for extracting gallium from sodium aluminate liquors, comprising the steps of:
  • An alloy of gallium is produced in the present process by using the same or a similar electrolytic recovery method as disclosed in U.S. Patent No. 4,368,108, which is herein incorporated by reference.
  • the present method includes improvements over the previously patented process wherein a 10-15% decrease in energy consumption is realized. These improvements include providing circulation of the solution and increasing the electrolyzer capacity due to the use of a buffer volume, wherein 25-30% of the total volume of the solution is outside the electrolyzer.
  • an alkaline aluminate liquor used in alumina production is electrolyzed to form an alloy of gallium.
  • a metal which forms an alloy with gallium is added to the alkaline sodium aluminate liquors in a ratio of about 1 to about 10 parts by weight of the added metal relative to gallium.
  • the metal may be, for example, zinc, lead or tin and may be added either as the metal itself, as the oxide of the metal or as an inorganic salt soluble in the aluminate liquors.
  • zinc is the metal that is added to the alkaline sodium aluminate liquors.
  • the added metal is deposited on the cathode together with gallium to form an alloy of gallium.
  • a mud rich in, for example, vanadium is also produced during electrolysis.
  • the resulting electrolytic deposit of the gallium alloy is removed from the cathode by dissolving in an alkaline solution and filtering to remove the vanadium-rich mud.
  • the alkaline solution is produced by adding any suitable alkali or caustic soda that can be added to an aqueous solution to produce a strongly alkaline solution.
  • the alkali or caustic soda is sodium hydroxide.
  • the alkaline solution thus obtained is further electrolyzed to produce a gallium-enriched solution.
  • cementation is the term used to describe processes wherein a metal is precipitated from a solution of its salts by another more electropositive metal. Since cementation reactions have been widely used in the minerals industry for the recovery of metals, Proc. Aust. Min. Met., 236, pages 25-34 (December, 1970), one skilled in the art might employ any number of variations of the cementation process and still remain within the scope of the subject invention, as herein described in more detail.
  • the gallium-enriched solution is brought into contact with an alloy including liquid gallium (the cementating base) and a metal more electropositive than gallium (the cementating agent) .
  • an alloy including liquid gallium (the cementating base) and a metal more electropositive than gallium (the cementating agent) .
  • Aluminum is an example of a preferred metal that is more electropositive than gallium.
  • the gallium-aluminum alloy is in a liquid state under the cementation conditions.
  • the aluminum is the driving force of the cementation process, and thus, is the cementating agent
  • the aluminum diffuses into the solution, and in so doing, produces electrons which reduce the gallium in the solution to metal.
  • the reduced gallium metal produced in this manner diffuses into the cementation base.
  • the cementation process of the present invention may be effectively carried out by vigorously mixing the gallium- enriched solution and the liquid gallium of the cementating base to remove diffusion limitations, by isolating the liquid gallium of the cementating base from the metallic frame of the device and by keeping the aluminum concentration constant.
  • the second metal in the gallium-enriched solution preferably zinc, is also removed by cementation from the solution together with the gallium.
  • the second metal forms an alloy with gallium.
  • the gallium alloy is recovered together with a slag product that is also prod ⁇ ced during the cementation step.
  • the gallium alloy obtained during cementation typically contains aluminum as an impurity.
  • the admixture of aluminum may be removed by washing with water. During washing the aluminum penetrates into the slag in the form of aluminum hydroxide and is separated from the liquid alloy during filtering.
  • the aluminum-containing zinc-gallium alloy obtained during the cementation process of the present invention preferably contains about 4-10 wt.% zinc. More preferably the aluminum-containing zinc-gallium alloy contains about 5-7 wt.% zinc.
  • the preferred range of zinc is determined by the requirements of the acid treatment and by the function served by zinc in removing impurities.
  • the zinc forms compounds with the impurities in the system, for example, with copper and lead. These compounds are partially removed during filtration and partially with the zinc which is removed from the gallium metal by acid treatment.
  • the content of the zinc in the zinc- gallium alloy is less than about 4 wt.% zinc, the purification of gallium from the copper and lead impurities is not as effective, and if the zinc content is greater than about 10 wt.%, further purification of the gallium from the copper and lead does not occur.
  • the time required during the acid treatment to remove the zinc from the zinc-alloy increases sharply if the zinc content is more than 10 wt.%.
  • the acid treatment of the zinc-gallium alloy obtained in the cementation process is preferably carried out in the temperature range from about 60 to about 90°C.
  • the . hydrochloric acid used in the acid treatment is prepared by means of diluting hydrochloric acid with a density of 1.19 g/cm 3 with water, wherein the acid-to-water ratio is preferably in the range from about 1:1 to about 1:2. If the hydrochloric acid used to treat the zinc-gallium alloy is diluted with an acid-to-water ratio that is greater than about 1:1, the gallium loss increases, and if the acid-to-water ratio is less than about 1:2 acid- to-water, the zinc removal decreases. Similarly, at temperatures below about 60°C during the acid treatment, the zinc removal also decreases, and at temperatures above about 90°C, the gallium loss increases.
  • the potential is controlled until the standard potential of gallium, as compared to a silver chloride electrode, is reached. Removal of the zinc continues until the zinc concentration is less than about 10 ⁇ 3 - 10 "4 wt. %.
  • the zinc concentration in the zinc-gallium solution must be not less than about 1 g/1.
  • the wt.% of zinc in the zinc-gallium alloy increases and the length of the acid treatment process increases significantly.
  • Effective separation of the gallium from the zinc-gallium alloys may also be achieved using the technique of membrane extraction.
  • impregnated liquid membranes are used. Gravitational stability of these liquid membranes is achieved by means of impregnating a thin hydrophobic matrix of TeflonTM (available from du Pont de Nemours, Wilmington, DE) with liquid. Flat roll- type membranes and hollow fibers (tubes) of small cross section have also been used.
  • the solutions contained 10 to 85 g/1 of Na 2 0. Positive results have been obtained using an extraction agent such as KelexTM-100 (available from Pechiney-Ugine-Kuhlman, Paris, France) dissolved in n-dodecane, CH 3 (CH 2 ) ⁇ 0 CH 3 . Extraction of gallium for 30 minutes from a solution with a gallium concentration of 0.1 g/1 was 80% and with a gallium concentration of 2 g/1, 90%.
  • reaction conditions are illustrative of the reaction steps that comprise this invention:
  • Step 1 Electrolysis of a sodium aluminate liquor.
  • a gallium-zinc alloy was electrolytically precipitated on a solid cathode from a sodium aluminate liquor used in the Bayer process for producing alumina. This electrolysis was carried out at a temperature of 32-34°C using an alkaline aluminate solution of the Bayer process, containing in g/1:
  • Zinc was introduced into the hot (90°C) solution in the form of zinc oxide.
  • the volume of the solution was 2.0 m 3 and the quantity of the zinc oxide 3.3 kg.
  • the electrolysis was carried out in a box-type electrolyzer with water-cooled cathodes and flat anodes.
  • the cathode * material was an acid-resistant steel, the anode material was nickel and the frame was carbon steel.
  • the current was 12 kA and the voltage 4.2 - 4.5 v.
  • the volume of the alkaline solution in the electrolyzer was 1.5 m 3 and the volume in the buffer was 0.5 m 3 .
  • the rate of the solution circulation was 1.5 m 3 /h.
  • the gallium-zinc alloy was electrolytically precipitated on the cathode.
  • the alloy contained 0.34 kg Ga, 2.5 Kg Zn andv 0.05 Kg of vanadium oxides.
  • Step 2 Dissolution and electrolysis of the zinc-gallium alloy in an alkaline solution.
  • Step 3 Cementation of the alkaline solution.
  • the production cementator used for this example had a working capacity of 2.5 m 3 and was equipped with a propeller mixer and heating coils to maintain the required temperature.
  • the mixer rotation rate was 105 rotations/min. and the distance between the mixer and the bottom of the cementator was 290 mm.
  • the temperature during cementation was maintained at 60 +/- 1°C.
  • the quantity of the alloy of aluminum and gallium used was 40 Kg.
  • the cementation process was carried out for 16 hours on the alkaline solutions obtained from step 2(c). The process was complete when the gallium concentration in the solution was reduced to 0.12 g/1.
  • the aluminum- containing zinc-gallium alloy was washed with water in a hydraulic filter press to remove aluminum from the alloy.
  • the cementation process produced 75.47 Kg of zinc-gallium alloy containing 7.24 wt.% Zn and 0.9 Kg of slag product containing 0.44 Kg gallium and 0.35 Kg zinc.
  • the zinc- gallium alloy was filtered at a temperature of 36°C through a ShottTM Filter Number 2 and was then treated at 70°C with a solution of hydrochloric acid having a density of 1.19 g/cm 3 and diluted in a 1:1 ratio with water.
  • the alloy treatment with acid was carried out under the control of potential in order to remove the zinc from the zinc-gallium alloy.
  • the initial value of the zinc- gallium alloy potential was 0.97 v. relative to a silver- chloride electrode and the final value of the metal gallium potential after removal of the zinc was 0.7 v. relative to a silver-chloride electrode.
  • the acid treatment of a portion of the zinc-gallium alloy having a weight of 25 Kg lasted 5 hours and resulted in a gallium loss of 0.3%. After acid treatment, the gallium was washed twice with distilled water to produce metal gallium having the following impurities: copper 2 x 10 "4 wt.% lead zinc iron

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Abstract

A method is disclosed for extracting gallium from a sodium aluminate liquor used in alumina production wherein an initial alloy or gallium is electrolytically obtained from the liquor. The gallium is extracted from the alloy of gallium by dissolving the alloy in an alkaline solution, further electrolyzing the alkaline solution to produce a gallium-enriched solution, carrying out a cementation process on the gallium-enriched solution to produce a second alloy of gallium and separating the gallium from the second alloy of gallium to produce purified gallium. Preferably the initial alloy of gallium is a zinc-gallium alloy and the cementating agent used in the cementation process is aluminum.

Description

ELECTROLYTIC METHOD OF OBTAINING GALLIUM METAL
FIELD OF THE INVENTION
This invention relates to an improved method of obtaining gallium from sodium aluminate liquors used in alumina production wherein an alloy of gallium is first obtained using an electrolytic method and then the alloy of gallium is dissolved in an alkaline solution and further electrolyzed to produce a gallium-enriched solution. The gallium is then extracted from the gallium-enriched solution using a cementation process wherein the gallium- enriched solution is contacted with a cementating agent. Preferably the alloy of gallium of the present invention is a zinc-gallium alloy and the cementating agent is aluminum.
BACKGROUND OF THE INVENTION
Gallium is typically produced from gallium-containing alkaline-aluminate solutions produced during the Bayer process for recovering alumina from bauxites. Processing of bauxites by Bayer's method comprises leaching of aluminum oxides contained in the core by means of a solution of caustic soda. At the same time, gallium passes into the resulting aluminate solution in the form of sodium gallate. Upon decomposition of aluminate solutions, a predominant portion of the gallium remains in solution due to the formation of more durable, complex compounds as compared to aluminum in the so-called mother aluminate liquor. The mother aluminate liquor, after separation of aluminum hydroxide, is evaporated to a return aluminate liquor and recycled to leach a new portion of bauxite. As a result of recirculation these liquors become enriched in gallium. The mother and recycle liquors obtained in the Bayer process are combined to form sodium aluminate liquors which serve as feedstock in gallium production.
The gallium produced from sodium aluminate liquors can be •used for producing gallium of high purity and for producing fusible alloys.
It is known in the art to extract gallium from the sodium aluminate liquors produced in the Bayer process by electrolysis in mercury cathode cells. However, use of mercury cathodes has disadvantages that include mercury toxicity and related environmental problems.
U.S. Patent No. 4,368,108 discloses an electrolytic method of extracting gallium from sodium aluminate liquors used in alumina production wherein the gallium is produced on a solid cathode in the form of an alloy, for example, as a gallium-zinc alloy. This method is especially effective whenever the initial solutions contain a sufficient quantity of sulfur as sulfides. In this case, not only does zinc form an alloy with gallium, which promotes depolarization at the cathode, but the zinc promotes formation of insoluble sedimentary products that effectively remove other impurities from the sodium aluminate liquors. The disadvantage of this method is that the prior art methods for extracting gallium from the electrolytically-produced zinc-gallium alloy are complicated.
It is also known in the art to remove gallium from the sodium aluminate liquors produced in the Bayer process by a direct cementation method. However, use of a direct cementation method with the sodium aluminate liquors has the disadvantage of requiring careful purification of the initial solutions to remove harmful impurities such as vanadium, sulfur compounds, sulfides and organic substances.
ADVANTAGES AND SUMMARY OF THE INVENTION
The present invention is directed to overcoming these difficulties and to obtaining purer gallium as compared with prior art methods. The subject invention for obtaining gallium from sodium aluminate liquors used in alumina production effectively takes advantage of a combination of methods. One method is that of electrolytically extracting the gallium as an alloy of gallium from the sodium aluminate liquors used in alumina production. Another method is that, of dissolving an alloy of gallium in an alkaline solution and electrolyzing the more electropositive metal from the dissolved alloy of gallium to produce a gallium-enriched solution. Still another method is that of carrying out a cementation process on an alkaline solution of an alloy of gallium using aluminum as the cementating agent.
Combining these methods with the other steps disclosed herein provides advantages over the prior art methods to extract gallium from the sodium aluminate liquors used in alumina production.
An advantage of the present method is that it can be used without a preliminary purification step to remove impurities such as vanadium, chromium, iron, sulfur compounds, etc. from the sodium aluminate liquors used in alumina production.
Another advantage of the present invention is that it can be used without employing the toxic substances such as mercury that are employed in the prior art methods.
Another advantage of the present method is that it can be used with a reduced consumption of valuable materials such as aluminum.
Another advantage of the present method is that it provides a simplified method of removing gallium from the alloy of gallium electrolytically produced from the sodium aluminate liquors.
Still another advantage is that gallium produced by the present method is of a high technical grade.
The subject invention provides a method for extracting gallium from sodium aluminate liquors, comprising the steps of:
producing an initial alloy of gallium electrolytically from a sodium aluminate liquor;
dissolving the initial alloy of gallium in an alkaline solution;
filtering the alkaline solution;
electrolyzing the filtered alkaline solution to produce a gallium-enriched solution;
cementating the gallium-enriched solution to obtain a second alloy of gallium; and
separating gallium from the second alloy of gallium. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Further objects and advantages of the subject invention will be apparent to those skilled in the art from the following detailed description of the disclosed process for extracting gallium from the sodium aluminate liquors used in alumina production.
An alloy of gallium is produced in the present process by using the same or a similar electrolytic recovery method as disclosed in U.S. Patent No. 4,368,108, which is herein incorporated by reference. The present method includes improvements over the previously patented process wherein a 10-15% decrease in energy consumption is realized. These improvements include providing circulation of the solution and increasing the electrolyzer capacity due to the use of a buffer volume, wherein 25-30% of the total volume of the solution is outside the electrolyzer.
Using this method, an alkaline aluminate liquor used in alumina production is electrolyzed to form an alloy of gallium. Prior to electrolysis, a metal which forms an alloy with gallium is added to the alkaline sodium aluminate liquors in a ratio of about 1 to about 10 parts by weight of the added metal relative to gallium. The metal may be, for example, zinc, lead or tin and may be added either as the metal itself, as the oxide of the metal or as an inorganic salt soluble in the aluminate liquors. Preferably zinc is the metal that is added to the alkaline sodium aluminate liquors. During electrolysis the added metal is deposited on the cathode together with gallium to form an alloy of gallium. A mud rich in, for example, vanadium, is also produced during electrolysis.
After electrolysis, the resulting electrolytic deposit of the gallium alloy is removed from the cathode by dissolving in an alkaline solution and filtering to remove the vanadium-rich mud. The alkaline solution is produced by adding any suitable alkali or caustic soda that can be added to an aqueous solution to produce a strongly alkaline solution. Preferably the alkali or caustic soda is sodium hydroxide. The alkaline solution thus obtained is further electrolyzed to produce a gallium-enriched solution.
The gallium contained in the gallium-enriched solution is then recovered by using a cementation process. Cementation is the term used to describe processes wherein a metal is precipitated from a solution of its salts by another more electropositive metal. Since cementation reactions have been widely used in the minerals industry for the recovery of metals, Proc. Aust. Min. Met., 236, pages 25-34 (December, 1970), one skilled in the art might employ any number of variations of the cementation process and still remain within the scope of the subject invention, as herein described in more detail.
During the process of cementation according to the present invention, the gallium-enriched solution is brought into contact with an alloy including liquid gallium (the cementating base) and a metal more electropositive than gallium (the cementating agent) . Aluminum is an example of a preferred metal that is more electropositive than gallium. The gallium-aluminum alloy is in a liquid state under the cementation conditions.
Since the aluminum is the driving force of the cementation process, and thus, is the cementating agent, when the gallium-enriched solution is brought into contact with the aluminum in the gallium-aluminum alloy, the aluminum diffuses into the solution, and in so doing, produces electrons which reduce the gallium in the solution to metal. The reduced gallium metal produced in this manner diffuses into the cementation base.
The cementation process of the present invention may be effectively carried out by vigorously mixing the gallium- enriched solution and the liquid gallium of the cementating base to remove diffusion limitations, by isolating the liquid gallium of the cementating base from the metallic frame of the device and by keeping the aluminum concentration constant.
The second metal in the gallium-enriched solution, preferably zinc, is also removed by cementation from the solution together with the gallium. The second metal forms an alloy with gallium. After cementation, the gallium alloy is recovered together with a slag product that is also prodμced during the cementation step. The gallium alloy obtained during cementation typically contains aluminum as an impurity. The admixture of aluminum may be removed by washing with water. During washing the aluminum penetrates into the slag in the form of aluminum hydroxide and is separated from the liquid alloy during filtering.
The aluminum-containing zinc-gallium alloy obtained during the cementation process of the present invention preferably contains about 4-10 wt.% zinc. More preferably the aluminum-containing zinc-gallium alloy contains about 5-7 wt.% zinc. The preferred range of zinc is determined by the requirements of the acid treatment and by the function served by zinc in removing impurities. The zinc forms compounds with the impurities in the system, for example, with copper and lead. These compounds are partially removed during filtration and partially with the zinc which is removed from the gallium metal by acid treatment. If the content of the zinc in the zinc- gallium alloy is less than about 4 wt.% zinc, the purification of gallium from the copper and lead impurities is not as effective, and if the zinc content is greater than about 10 wt.%, further purification of the gallium from the copper and lead does not occur. The time required during the acid treatment to remove the zinc from the zinc-alloy increases sharply if the zinc content is more than 10 wt.%.
The acid treatment of the zinc-gallium alloy obtained in the cementation process is preferably carried out in the temperature range from about 60 to about 90°C. The . hydrochloric acid used in the acid treatment is prepared by means of diluting hydrochloric acid with a density of 1.19 g/cm3 with water, wherein the acid-to-water ratio is preferably in the range from about 1:1 to about 1:2. If the hydrochloric acid used to treat the zinc-gallium alloy is diluted with an acid-to-water ratio that is greater than about 1:1, the gallium loss increases, and if the acid-to-water ratio is less than about 1:2 acid- to-water, the zinc removal decreases. Similarly, at temperatures below about 60°C during the acid treatment, the zinc removal also decreases, and at temperatures above about 90°C, the gallium loss increases.
During acid treatment the potential is controlled until the standard potential of gallium, as compared to a silver chloride electrode, is reached. Removal of the zinc continues until the zinc concentration is less than about 10~3 - 10"4 wt. %.
In order to obtain a zinc-gallium alloy o ^about 4 wt.% zinc or more during the cementation process, the zinc concentration in the zinc-gallium solution must be not less than about 1 g/1. At zinc concentrations greater than about 10 g/1, the wt.% of zinc in the zinc-gallium alloy increases and the length of the acid treatment process increases significantly.
Effective separation of the gallium from the zinc-gallium alloys may also be achieved using the technique of membrane extraction. For this purpose impregnated liquid membranes are used. Gravitational stability of these liquid membranes is achieved by means of impregnating a thin hydrophobic matrix of Teflon™ (available from du Pont de Nemours, Wilmington, DE) with liquid. Flat roll- type membranes and hollow fibers (tubes) of small cross section have also been used. The solutions contained 10 to 85 g/1 of Na20. Positive results have been obtained using an extraction agent such as Kelex™-100 (available from Pechiney-Ugine-Kuhlman, Paris, France) dissolved in n-dodecane, CH3(CH2)ι0CH3. Extraction of gallium for 30 minutes from a solution with a gallium concentration of 0.1 g/1 was 80% and with a gallium concentration of 2 g/1, 90%.
This invention will now be described in detail with respect to the specific preferred embodiments thereof, it being understood that the steps of the following example are intended to be illustrative only and that the invention is not intended to be limited to the materials, conditions, process parameters and the like recited herein.
EXAMPLE OF THE INVENTION
The following reaction conditions are illustrative of the reaction steps that comprise this invention:
Step 1. Electrolysis of a sodium aluminate liquor.
A gallium-zinc alloy was electrolytically precipitated on a solid cathode from a sodium aluminate liquor used in the Bayer process for producing alumina. This electrolysis was carried out at a temperature of 32-34°C using an alkaline aluminate solution of the Bayer process, containing in g/1:
Na20 - 247, A1203 - 84, Ga - 0.32, Zn - 1.3.
Zinc was introduced into the hot (90°C) solution in the form of zinc oxide. The volume of the solution was 2.0 m3 and the quantity of the zinc oxide 3.3 kg. The electrolysis was carried out in a box-type electrolyzer with water-cooled cathodes and flat anodes. The cathode* material was an acid-resistant steel, the anode material was nickel and the frame was carbon steel. The current was 12 kA and the voltage 4.2 - 4.5 v. The volume of the alkaline solution in the electrolyzer was 1.5 m3 and the volume in the buffer was 0.5 m3. The rate of the solution circulation was 1.5 m3/h. The gallium-zinc alloy was electrolytically precipitated on the cathode. The alloy contained 0.34 kg Ga, 2.5 Kg Zn andv 0.05 Kg of vanadium oxides.
Step 2. Dissolution and electrolysis of the zinc-gallium alloy in an alkaline solution.
(a) The zinc-gallium alloy electrolytically precipitated on the cathode was dissolved in an alkaline solution of 224 Kg of sodium hydroxide dissolved in 1.9 m3 of water. The alkaline solution thus obtained was separated from the vanadium-rich mud by filtering. The total alkaline solution volume was 2.0 m3 and had the following content in g/1:
- Na20 - 160, Ga - 9.5, Zn - 2.9, Cu - l x 10"3.
(b) A slag product recovered from an earlier cementation operation was dissolved in an alkaline solution that contained 130 Kg of sodium hydroxide dissolved in 0.44 m3 of water. The total solution volume was 0.5 m3 and had the following content in g/1:
Na20 - 185, Ga - 23.5, Zn - 0.14, Cu - 4 X 10"
(c) The filtered hot (70-80°C) alkaline solutions of (a) and (b) were periodically subject to electrolysis with a cathode current of 100-150 amperes/m2 to remove excess zinc, which accumulated in the solution while conducting dissolution operations of the zinc-gallium alloy. This electrolysis process is carried out in every 10-12 operations of dissolution. The residual zinc content in the solution is' 1-2 g/1. The residual levels of zinc remaining in solution after this electrolysis step assist in removal of harmful impurities, such as copper, lead, etc., during the cementation process.
Step 3. Cementation of the alkaline solution.
The production cementator used for this example had a working capacity of 2.5 m3 and was equipped with a propeller mixer and heating coils to maintain the required temperature. The mixer rotation rate was 105 rotations/min. and the distance between the mixer and the bottom of the cementator was 290 mm. The temperature during cementation was maintained at 60 +/- 1°C. The quantity of the alloy of aluminum and gallium used was 40 Kg. Granulated aluminum, containing 3 x 10"3 % copper, was used as the cementating agent, and the steady- state quantity of the aluminum portion present in the alloy of aluminum and gallium was 0.4 Kg.
The cementation process was carried out for 16 hours on the alkaline solutions obtained from step 2(c). The process was complete when the gallium concentration in the solution was reduced to 0.12 g/1. The aluminum- containing zinc-gallium alloy was washed with water in a hydraulic filter press to remove aluminum from the alloy. The cementation process produced 75.47 Kg of zinc-gallium alloy containing 7.24 wt.% Zn and 0.9 Kg of slag product containing 0.44 Kg gallium and 0.35 Kg zinc. The zinc- gallium alloy was filtered at a temperature of 36°C through a Shott™ Filter Number 2 and was then treated at 70°C with a solution of hydrochloric acid having a density of 1.19 g/cm3 and diluted in a 1:1 ratio with water.
The alloy treatment with acid was carried out under the control of potential in order to remove the zinc from the zinc-gallium alloy. The initial value of the zinc- gallium alloy potential was 0.97 v. relative to a silver- chloride electrode and the final value of the metal gallium potential after removal of the zinc was 0.7 v. relative to a silver-chloride electrode. The acid treatment of a portion of the zinc-gallium alloy having a weight of 25 Kg lasted 5 hours and resulted in a gallium loss of 0.3%. After acid treatment, the gallium was washed twice with distilled water to produce metal gallium having the following impurities: copper 2 x 10"4 wt.% lead zinc iron
Figure imgf000014_0001

Claims

We claim:
1. A method of extracting gallium from sodium aluminate liquors, comprising the steps of:
producing an initial alloy of gallium electrolytically from a sodium aluminate liquor;
dissolving the initial alloy of gallium in an alkaline solution;
filtering the alkaline solution;
electrolyzing the filtered alkaline solution to produce a gallium-enriched solution;
cementating the gallium-enriched solution to obtain a second alloy of gallium; and
separating gallium from the second alloy of gallium.
2. The method according to claim 1 wherein the initial alloy of gallium comprises a zinc-gallium alloy.
3. The method according to claim 2 wherein the zinc- gallium alloy contains 4-10 wt % zinc.
4. The method according to claim 1 wherein the gallium is separated from the second alloy of gallium by using an acid treatment.
5. The method according to claim 4 wherein the acid comprises hydrochloric acid.
6. The method according to claim 5 wherein the hydrochloric acid has a density of about 1.19 g/1 and is diluted with water in an acid-to-water ratio from about 1:1 to about 1:2.
7. The method according to claim 4 wherein the acid treatment is carried out in the range from about 60 °C to about 90 °C.
8. The method according to claim 2 wherein the concentration of zinc in the alkaline solution is not less than about 1 g/1 and-not more than about 10 g/1.
9. The method according to claim 1 wherein precipitation of the second alloy of gallium is carried out at a temperature of about 60 °C.
PCT/US1992/003717 1992-05-04 1992-05-04 Electrolytic method of obtaining gallium metal WO1993022478A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4029499A (en) * 1974-07-10 1977-06-14 Johnson Matthey & Co., Limited Recovery of gallium
US4368108A (en) * 1981-01-23 1983-01-11 Rubinshtein Georgy M Process for electrolytic recovery of gallium or gallium and vanadium from alkaline liquors resulting from alumina production

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4029499A (en) * 1974-07-10 1977-06-14 Johnson Matthey & Co., Limited Recovery of gallium
US4368108A (en) * 1981-01-23 1983-01-11 Rubinshtein Georgy M Process for electrolytic recovery of gallium or gallium and vanadium from alkaline liquors resulting from alumina production

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