CLIAMS:We claim :

1. A process for recovering metallic gallium from Bayer liquor generated in the Bayer process, comprising the steps of absorbing gallium in the Bayer liquor in a chelating resin by passing the Bayer liquor through the chelating resin and recycling the spent liquor to the Bayer process, acid stripping the absorbed gallium from the chelating resin and recovering the gallium from the acid solution, wherein the chelating resin has a specific surface area >500 m2/g and is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant, wherein absorbtion of the gallium in the coated chelating resin is carried out at 40-60°C, and wherein the absorbed gallium is stripped from the coated chelating resin with a mineral acid solution in a two stage acid stripping, the acid solution having a high acid concentration in the first stage acid stripping and a low acid concentration in the second stage acid stripping.

2. The process as claimed in claim 1, wherein the gallium is recovered from the acid solution by evaporating out the acid solution by heating and concentrating the gallium in the acid solution, precipitating out iron impurities in the gallium concentrate by adjusting the pH of the gallium concentrate at pH 7 to 8 with sodium hydroxide followed by removal of the precipitate comprising iron impurities by filtration, precipitating out Ga(OH)3 in the filtrate by adjusting the pH of the filtrate at pH 12 to 13 with HCl followed by removal of the precipitate comprising Ga(OH)3 by centrifuging, forming a sodium gallate solution by dissolving the Ga(OH)3 precipitate in sodium hydroxide and electrolysing the sodium gallate solution to obtain metallic gallium.

3. The process as claimed in claim 1, wherein the chelating resin is selected from the group consisting of polystyrene divinyl benzene, polystyrene copolymer and cross linked polymer.

4. The process as claimed in claim 1, wherein the extractant is 7-(5,5,7,7-tetramethyl-oct-1-en-3-yl)-8-hydroxy-quinoline.

5. The process as claimed in claim 1, wherein the two stage acid stripping is carried out with a mineral acid selected from the group consisting of HCl, H2SO4 and HNO3 with a high acid concentration of 3 to 9M in the first stage and with a low acid concentration of 0.25 to 3M in the second stage.

6. The process as claimed in claim 3, wherein the acid solution is evaporated out to 1/8th to 1/9th its volume.

7. The process as claimed in claim 1, wherein the Bayer liquor consists of caustic concentration of 200 to 280 g/L (as Na2CO3) with aluminium to caustic ratio of 0.3 to 0.4 and 100 to 250 ppm gallium.

8. The process as claimed in claim 1, wherein the gallium is absorbed in the coated chelating resin at 50-55°C.

9. The process as claimed in claims 3, wherein the sodium gallate solution is electrolysed with stainless steel cathode and Ni anode at a voltage of 3 to 4.5.V.

10. The process as claimed in claim 1, wherein the gallium is absorbed in the chelating resin to the order of 21 mg Ga/g of the extractant.

11. The process as claimed in claim 1, wherein the chelating resin is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant by boiling the resin with water, soaking the resin with acetone, air drying the resin, soaking the dried resin in the substituted 7-alkenyl-8-hydroxy quinolone extractant, washing the resin with acetone and air drying the resin.
,TagSPECI:FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2014
COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION

Process for recovering metallic gallium from Bayer liquor

APPLICANTS

Hindalco Industries Limited, 3rd Floor, Century Bhavan, Dr Annie Besant Road, Worli, Mumbai 400030, Maharashtra, an Indian Company

PREAMBLE TO THE DESCRIPTION

The following specification particularly describes this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a process for recovering metallic gallium from Bayer liquor.

BACKGROUND OF THE INVENTION
Gallium is a metal of considerable commercial importance because of its economic value due to its extensive use in the fast growing electronics industry. Gallium bearing aluminium ores is a major source of gallium. Gallium is also present in zinc ores, fly ash and Bayer liquor. Bayer liquor (Bayer process liquor or Bayer solution) is an aqueous solution of sodium aluminate generated in the Bayer process for producing alumina from bauxite. On account of the large use of gallium in electronics industry, Bayer liquor is a major source for gallium recovery. Several processes are known for recovering gallium from Bayer liquor or aqueous solution containing gallium.

In one process, Bayer solution is electrolysed using mercury as an anode and gallium in the solution is converted to an amalgam which is hydrolysed with caustic alkali. The aqueous alkali gallate solution is further electrolyzed to recover gallium. In another process, alumina in the Bayer solution is precipitated to increase the proportion of gallium to alumina and carbon dioxide is blown into the solution to coprecipitate alumina and gallium. The coprecipitate is dissolved in caustic alkali and the aqueous alkali gallate solution is electrolyzed to recover gallium. In another process, liquid-liquid extraction of an aqueous sodium aluminate solution is carried out with an extraction solvent consisting of an organic solvent and a water-insoluble substituted hydroxyquinoline. [Japanese Patent Unexamined Publication (Kokai) Nos 32411/76, 52289/78 and 99726/79].

In another process, an aqueous solution containing gallium and other impurity metals obtained from Bayer process is contacted with a chelate resin having a higher selective absorptivity for gallium than for the impurity metals until gallium is adsorbed on the chelate resin. The aqueous solution is contacted with the chelate resin at a rate of at least 20 parts by volume/hr per part by volume of the chelate resin and at a temperature not exceeding 80°C. Gallium is recovered from the chelate resin by conventional method, for example, by converting it into sodium gallate and then electrolyzing it (Indian Patent No 168916).

In another process, gallium in an aqueous solution of heavily alkaline sodium aluminate is absorbed on a stationary phase constituted by a microporous absorbent resin impregnated with 7-(alkyl or alkenyl)-8-hydroxy quinoline such as 7-(5,5,7,7,-tetramethyl-oct-1-en-3-yl)-8-hydroxy-quinoline. The microporous absorbent resin is a hydrophobic non-porous resin having a polystyrene skeleton, and having, when dry, a specific surface area, measured by the BET method, of at least equal to 450 m2g-1 of resin, a pore volume of at least 1500 mm3g-1 of resin, a mean pore diameter of between 80A° and 500 A° with at least 80% of the volume constituted by pores having a diameter of from 40 A° to 5,000 A° and a rate of expansion of swelling in an aqueous medium not exceeding 20%. The resin is impregnated with the 7-(-alkyl or alkenyl)-8-hydroxy quinoline as an alcohol solution thereof in a proportion of 230 to 700 grammes per liter, preferably 250 to 350 gm / litre of the dry resin. The gallium is recovered in a known manner by acid elution of the alcohol impregnated resin (Indian Patent No 168836).

In another process Bayer process liquor is subjected to a two stage solvent extraction in which the first stage comprises contacting the Bayer process liquor with an organic phase comprising 10-15 vol% neodecanoic acid (versatic-10) and 63-77 vol% kerosene at 1.0:1.0 aqueous to organic phase ratio at room temperature. The organic and aqueous phases are separated and the organic phase is scrubbed with 5.0-6.5 M HCl at 1.0:1.5 organic to aqueous phase ratio and subjected to stripping with 1.0-2.0M HCl solution at 1.0:1.0 organic to aqueous phase ratio. Concentrated HCl is added to the strip liquor to raise the required acid concentrate to 4M. Aliphatic carboxylic acid (1-0-5.0g/100ml) is added to the stripped solution.

The second stage solvent extraction comprises contacting the stripped solution with an organic phase having a composition of 10-20 vol% tricaprylmethyl-ammonium chloride (aliquant 336), 5-15% iso-decanol and rest kerosene at 1.0:0.25 aqueous to organic phase ratio at room temperature, for about 2 minutes followed by separation of organic phase. The organic phase is scrubbed with 5.0-6.5M HCl at 1.0 : 1.0 organic to aqueous phase ratio and stripped with 3.5-4.3M NaOH solution at 1.0 : 0.25 organic to aqueous phase ratio. The solution is filtered to remove iron hydroxide and electrolysed using copper as cathode and stainless steel as anode in a voltage range from 1.80 to – 2.2V to recover gallium.

The process is characterized by the use of an organic phase comprising 10-15 vol% alkylated 8-hydroxy quinoline (kelex 100), 10-15 vol % iso-decanol, 3-7 vol% neodecanoic acid (versatic-10) and 63-77 vol% kerosene for the first stage extraction and the use of aliphatic carboxylic acid in the second stage extraction (Indian Patent No 242319).

In another process, the Bayer liquor is brought into contact with a chelating agent composed of a water insoluble substituted quinolinol and then an inverse capturing solution composed of an acidic aqueous solution containing a substituted quinolinol is brought into contact with the chelating agent containing gallium to extract gallium into the inverse capturing solution. The gallium metal from the inverse capturing solution is recovered by electrolysis to concentrate gallium and recover the acid. The concentrated gallium solution is adjusted to a given pH and precipitate of iron hydroxide is separated and removed to obtain an iron-free gallium solution. The iron-free gallium solution is neutralized to form a gallium hydroxide slurry and the slurry is subjected to ultrafiltration to give a concentrated slurry of gallium hydroxide. The concentrated slurry of gallium hydroxide is dissolved in an alkaline solution to form an alkaline electrolytic solution of gallium and the alkaline electrolytic solution of gallium is electrolysed using stainless steel cathode and nickel anode to recover gallium metal (W005/106080).

Some of the problems of the prior art in general are environmental hazards with the use of mercury in electrolysis, expensive nature of liquid-liquid extraction, large number of process steps , use of alcohol, low recovery or yield and instability of chelate resin in the process stream. Inspite of the various known processes for recovering gallium from Bayer liquor, there is thus still scope and need for technologies and technical advancements to recover metallic gallium from Bayer liquor with high yield and high purity in a simple, economical and environmental friendly manner.

DESCRIPTION OF THE INVENTION
According to the invention there is provided a process for recovering metallic gallium from Bayer liquor generated in the Bayer process, comprising the steps of absorbing gallium in the Bayer liquor in a chelating resin by passing the Bayer liquor through the chelating resin and recycling the spent liquor to the Bayer process, acid stripping the absorbed gallium from the chelating resin and recovering the gallium from the acid solution, wherein the chelating resin has a specific surface area >500 m2/g and is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant, wherein absorbtion of the gallium in the coated chelating resin is carried out at 40-60°C and wherein the absorbed gallium is stripped from the coated chelating resin with a mineral acid solution in a two stage acid stripping, the acid solution having a high acid concentration in the first stage acid stripping and a low acid concentration in the second stage acid stripping .

According to an embodiment of the invention, the gallium is recovered from the acid solution by evaporating out the acid solution by heating and concentrating the gallium in the acid solution, precipitating out iron impurities in the gallium concentrate by adjusting the pH of the gallium concentrate at pH 7 to 8 with sodium hydroxide followed by removal of the precipitate comprising iron impurities by filtration, precipitating out Ga(OH)3 in the filtrate by adjusting the pH of the filtrate at pH 12 to 13 with HCl followed by removal of the precipitate comprising Ga(OH)3 by centrifuging, forming a sodium gallate solution by dissolving the Ga(OH)3 precipitate in sodium hydroxide and electrolysing the sodium gallate solution to obtain metallic gallium.

Preferably the chelating resin is selected from the group consisting of polystyrene divinyl benzene, polystyrene copolymer and cross linked polymer. Preferably the extractant is 7-(5,5,7,7-tetramethyl-oct-1-en-3-yl)-8-hydroxy-quinoline. Preferably the two stage acid stripping is carried out with a mineral acid selected from the group consisting of HCl, H2SO4 and HNO3 with a high acid concentration of 3 to 9M in the first stage and with a low acid concentration of 0.25 to 3M in the second stage. Preferably the acid solution is evaporated out to 1/8th to 1/9th its volume. Preferably the Bayer liquor consists of caustic concentration of 200 to 280 g/L (as Na2CO3) with aluminium to caustic ratio of 0.3 to 0.4 and 100 to 250 ppm gallium. Preferably the gallium is absorbed in the coated chelating resin at 50-55°C. Preferably the sodium gallate solution is electrolysed with stainless steel cathode and Ni anode at a voltage of 3 to 4.5.V.

According to the invention the gallium is absorbed in the chelating resin to the order of 21 mg Ga/g of the extractant.

According to an embodiment of the invention, the chelating resin is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant by boiling the resin with water, soaking the resin with acetone, air drying the resin, soaking the dried resin in the substituted 7-alkenyl-8-hydroxy quinolone extractant, washing the resin with acetone and air drying the resin.

According to the process of the invention, chelating resin coated with substituted 7-alkenyl-8-hydroxy quinolone extractant is used to absorb gallium in the Bayer liquor, which is very stable in the process stream. Therefore, gallium in the Bayer liquor is effectively absorbed in the resin and it has been possible to increase the recovery of gallium. It has been found that the coated resin is reusable atleast 60 times without any deterioration of performance. The coated resin is thus durable and reusable. The invention eliminates impregnation of the resin with alcohol solution. It employs two stage acid stripping of the gallium from the resin to effectively recover the absorbed gallium from the coated resin and also to minimize impurities in the acidic Ga solution and to ensure high yield and purity of gallium. The process of the invention is thus very simple, efficient and economical. Besides, coating of the chelating resin with the extractant is a very simple procedure and can be carried out easily and conveniently. The process of the invention is simple, efficient and economical because of this also.

The following experimental examples are illustrative of the invention but not limitative of the scope thereof:

Example 1

Chelating resin (17 g) available as XAD1180N and manufactured by Dow Chemicals Company and having specific surface area ~600 m2/g was boiled with water (200 mL) for 30 minutes and filtered to remove water. Filtered out resin was soaked with acetone (15 mL) for 5 minutes, acetone was filtered off by applying vacuum and the resin was air dried at room temperature for 15 minutes. Dry resin (4 g) was soaked in 7-(5,5,7,7)-tetramethyl-oct-1-en-3-yl-8-hydroxyl quinoline extractant (15 g) for 36 hours, washed with acetone and was air dried at room temperature for 15 minutes.

Hydroxy quinoline coated dry resin was taken in a glass column packed with glass wool at the bottom thereof and fitted with a cock valve at the bottom thereof. Glass column was also packed with glass wool at the top thereof and fitted with a beaker at the top thereof. Glass column was wound with a heating tape over it. Cock valve at the bottom was closed and water was introduced into the glass column through the beaker at the top and resin was allowed to be soaked in the water for 10 minutes. Cock valve was opened to drain off the water and closed again. 25 BV of Bayer liquor comprising caustic concentration of 230 g/L (as Na2CO3) with aluminium to caustic ratio of 0.380 and 188 ppm gallium was added into the glass column through the beaker at the top thereof and the glass column was heated.
When the temperature in the glass column rose to 50 °C as measured by thermometer, the cock valve at the bottom was opened to allow the liquor to flow out. Flow rate of the liquor was controlled by adjusting the cock valve at 2.5 BV/h. Gallium in the effluent was found to be 143 ppm. Ggallium absorption was found to be 22.1 mg Ga/g of the extractant.

Gallium absorbed in the resin was stripped with 1.25 BV of 5M HCl at a flow rate of 0.62 BV/h and then with 1.25 BV of 1.5M HCl at a flow rate of 0.62 BV/h. Acid solution was evaporated to 1/8th its original volume by heating. Gallium concentration increased to 7.5 times as analysed by ICP-AES. 60 mL of caustic lye was added to bring the concentrate pH to 7 and to precipitate out iron which was removed by filtration. 2.5 mL of 1:1 HCl was added to the filtrate to bring the pH to 12 and precipitate out Ga(OH)3. Ga(OH)3 precipitate was removed by centrifuging, washed with water and dissolved in slight excess of caustic lye to form a solution of sodium gallate. Gallium content in the sodium gallate solution was 7.0 g/L.

Sodium gallate solution was electrolysed using stainless steel cathode and Ni anode at a voltage of 4V. Gallium recovery at the cathode was ~99% and gallium purity was > 99%. Gallium absorption and acid stripping procedure was repeated 62 times and average gallium absorption was found to be 21 mg Ga/g of the extractant as analysed by ICP-AES.

The coated resin was reused 60 times without any deterioration of performance.

Example 2

Chelating resin (17 g) available as XAD1180N and manufactured by Dow Chemicals Company and having specific surface area ~650 m2/g was boiled with water (200 mL) for 30 minutes and filtered to remove water. Filtered out resin was soaked with acetone (15 mL) for 5 minutes, acetone was filtered off by applying vacuum and the resin was air dried at room temperature for 15 minutes. Dry resin (4 g) was soaked in 7-(5,5,7,7)-tetramethyl-oct-1-en-3-yl-8-hydroxyl quinoline (15 g) for 36 hours, washed with acetone and was air dried at room temperature for 15 minutes.

Hydroxy quinoline coated dry resin was taken in a glass column packed with glass wool at the bottom thereof and fitted with a cock valve at the bottom thereof. Glass column also was packed with glass wool at the top theeof and fitted with a beaker at the top thereof. Glass column was wound with a heating tape over it. Cock valve at the bottom was closed and water was introduced into the glass column through the beaker at the top and the resin was allowed to be soaked in water for 10 minutes. Cock valve at the bottom was opened to drain off the water and closed again. 25 BV of Bayer liquor comprising caustic concentration of 235 g/L (as Na2CO3) with aluminium to caustic ratio of 0.395 and 207 ppm gallium was added into the glass column through the beaker at the top thereof and the glass column was heated.

When the temperature in the glass column rose to 50 °C as measured by thermometer, the cock valve at the bottom was opened to allow the liquor to flow out. Flow rate of the liquor was controlled by adjusting the cock valve at 2.5 BV/h. Gallium in the effluent was found to be 167 ppm. Gallium absorption was found to be 20.5 mg Ga/g of the extractant.

Gallium absorbed in the resin was stripped with 1.25 BV of 5M HCl at a flow rate of 0.62 BV/h and then with 1.25 BV of 1.5M HCl at a flow rate of 0.62 BV/h. Acid solution was evaporated to 1/8th its original volume by heating. Gallium concentration increased to 7.5 times as analysed by ICP-AES. 60 mL of Caustic lye was added to bring the concentrate pH to 7 and to precipitate out iron which was removed by filtration. 2.5 mL of 1:1 HCl was added to the filtrate to bring the pH to 12 and precipitate out Ga(OH)3. Ga(OH)3 precipitate was removed by centrifuging, washed with water and dissolved in slight excess of caustic lye to form a solution of sodium gallate. Gallium content in the sodium gallate solution was 7.0 g/L.

Sodium gallate solution was electrolysed using stainless steel cathode and Ni anode at a voltage of 4V. Gallium recovery at the cathode was ~99% and gallium purity was > 99%. Gallium absorption and acid stripping procedure was repeated 62 times and average gallium absorption was found to be 21 mg Ga/g of the extractant as analysed by ICP-AES.

The coated resin was reused 60 times without any deterioration of performance.

We claim :

1. A process for recovering metallic gallium from Bayer liquor generated in the Bayer process, comprising the steps of absorbing gallium in the Bayer liquor in a chelating resin by passing the Bayer liquor through the chelating resin and recycling the spent liquor to the Bayer process, acid stripping the absorbed gallium from the chelating resin and recovering the gallium from the acid solution, wherein the chelating resin has a specific surface area >500 m2/g and is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant, wherein absorbtion of the gallium in the coated chelating resin is carried out at 40-60°C, and wherein the absorbed gallium is stripped from the coated chelating resin with a mineral acid solution in a two stage acid stripping, the acid solution having a high acid concentration in the first stage acid stripping and a low acid concentration in the second stage acid stripping.

2. The process as claimed in claim 1, wherein the gallium is recovered from the acid solution by evaporating out the acid solution by heating and concentrating the gallium in the acid solution, precipitating out iron impurities in the gallium concentrate by adjusting the pH of the gallium concentrate at pH 7 to 8 with sodium hydroxide followed by removal of the precipitate comprising iron impurities by filtration, precipitating out Ga(OH)3 in the filtrate by adjusting the pH of the filtrate at pH 12 to 13 with HCl followed by removal of the precipitate comprising Ga(OH)3 by centrifuging, forming a sodium gallate solution by dissolving the Ga(OH)3 precipitate in sodium hydroxide and electrolysing the sodium gallate solution to obtain metallic gallium.

3. The process as claimed in claim 1, wherein the chelating resin is selected from the group consisting of polystyrene divinyl benzene, polystyrene copolymer and cross linked polymer.

4. The process as claimed in claim 1, wherein the extractant is 7-(5,5,7,7-tetramethyl-oct-1-en-3-yl)-8-hydroxy-quinoline.

5. The process as claimed in claim 1, wherein the two stage acid stripping is carried out with a mineral acid selected from the group consisting of HCl, H2SO4 and HNO3 with a high acid concentration of 3 to 9M in the first stage and with a low acid concentration of 0.25 to 3M in the second stage.

6. The process as claimed in claim 3, wherein the acid solution is evaporated out to 1/8th to 1/9th its volume.

7. The process as claimed in claim 1, wherein the Bayer liquor consists of caustic concentration of 200 to 280 g/L (as Na2CO3) with aluminium to caustic ratio of 0.3 to 0.4 and 100 to 250 ppm gallium.

8. The process as claimed in claim 1, wherein the gallium is absorbed in the coated chelating resin at 50-55°C.

9. The process as claimed in claims 3, wherein the sodium gallate solution is electrolysed with stainless steel cathode and Ni anode at a voltage of 3 to 4.5.V.

10. The process as claimed in claim 1, wherein the gallium is absorbed in the chelating resin to the order of 21 mg Ga/g of the extractant.

11. The process as claimed in claim 1, wherein the chelating resin is coated with a substituted 7-alkenyl-8-hydroxy quinolone extractant by boiling the resin with water, soaking the resin with acetone, air drying the resin, soaking the dried resin in the substituted 7-alkenyl-8-hydroxy quinolone extractant, washing the resin with acetone and air drying the resin.
Dated this 23rd day of September 2014

(Jose M A)
of Khaitan & Co
Agent for the Applicants
Reg No IN/PA-44