Title of Invention

' A PROCESS FOR EXTRACTION OF GALLIUM FROM BAUXITE ORES"

Abstract

The present inventions relates to a process for extraction of gallium from aluminium-containing ores. More particularly this invention is concerned with recovery of Gallium in the course of extraction of aluminium from its ores, bauxite in particular. A process for extraction of gallium from aluminium-containing ores, which process comprises in combination treating bauxite ore with caustic alkali under pressure in a autoclave to convert aluminium oxide and gallium oxide to sodium aluminate and sodium gallate, respectively. Then extracting gallium present in solution with 5 -15% of a quinoline derivative and 5-12% of a straight chain higher alcohol in a hydrocarbon solvent to prevent formation of third phase. The mixture was stirred for a period varying between 20 and 60 minute for achieving complete extraction in a hydrocarbon solvent and stripping back the co-extracted aluminium in 4-8 molar hydrochloric acid and gallium in 1-3 molar hydrochloric acid. Then precipitating gallium as gallium hydroxide by raising the pH 3-4 of the gallium-containing medium centrifuging and drying precipitated gallium hydroxide and reducing the precipitated and dried hydroxide in a stream of reducing gas, hydrogen or carbon monoxide at a temperature varying between 800° to 1200° C to produce metallic gallium.

Full Text

The present inventions relates to a process for extraction of gallium from aluminium containing ores. More particularly this invention is concerned with recovery of Gallium in the course of extraction of aluminium from its ores, bauxite in particular. It is well known that pure aluminium liberated in the cathode, alumina remaining in the fused state for conduction of electric current. In the course of processing of bauxite for recovery of alumina by Bayer's Process aluminium leaches out as sodium aluminate and gallium as solid gallate. Surprising enough heretofore no attempt has been made to recover this valuable metal commercially in any aluminium plant, from which this valuable metal can be profitably recovered. In recent times gallium has acquired significant commercial importance due to the potential of much faster computer chips made of gallium-arsenide in place of silicon. Gallium-arsenide also finds increasing applications in electronics, semi-conductors, solid ceils and in analogue microwave devices. The effluent liquors from the Bayer's process of treating bauxite serves as one of the major source of gallium. Which normally builds up in gallium concentrations from 100-300 ppm depending upon the gallium content of the bauxite ore used as the starting material. As mentioned above, gallium is not commercially extracted in India but a process was developed for recovering gallium from Bayer's solutions by electrolytic reductions in Hg-cathode. This process was tried by Central Electro-Chemical Research Institute, Karaikudi, Tamilnadu. Unfortunately, this process failed to receive clearance from the Ministry of Environment, Govt. of India, due to handling of mercury in the process which is undoubtedly a hazardous materials. The solvent extractions process using a substituted alkyl quinoline and decanol has been published by National Metallurgical Laboratory, Jamshedpur, for extraction of gallium from Bayer's solutions. This process also suffers from a few drawbacks most serious of which is that the leaching has to be carried out for at least four (4) hours and the percentage of recovery of metallic gallium is not satisfactory. Further, reduction process from gallium hydroxide to metallic gallium has not been investigated. The object of the present inventions is to provide a process for extraction of gallium from the process liquor in course of extraction of aluminium by purification of bauxite. A further object of this invention is to provide a single extractive process using a chip yet inert hydrocarbon solvent widely available in India. A still further object of the present invention is to evolve a process for the recovery of gallium at a considerably fast rate, thereby reducing the contact time and saving wastage of solvent, mainly due to evaporation loss. Yet another object of this invention is to provide an extractive process of recovery of gallium wherein the quantum of recovery is near total (95%). The foregoing objective are achieved by the process for extraction of gallium from aluminium - containing ores, which process comprises in combination :- i) treating aluminium-containing ore with caustic alkali under 25-40 Kg./cm2 according to Bayer's process to convert aluminium oxide and gallium oxide to sodium aluminate and sodium galate, respectievely, 3 ii) extracting gallium present in Bayer's solution with 5-15% of a quinoline derivative and 5-12% of a straight chain hydroxylated compound in a hydrocarbon solvent, iii) stirring the mixture for a period varying between 20-60 minutes for achieving almost quantitative extraction, iv) stripping back the co-extracted aluminium in 4-8 molar hydrochloric acid and gallium in 1-3 molar hydrochloric acid, v) precipitating gallium as gallium hydroxide by raising the pH 3-4 of the gallium-containing medium obtained in step (iv), vi) centrifuging and drying the precipitated gallium hydroxide and vii) reducing the precipitated and dried hydroxide in a stream of reducing gas, hydrogen or insitu generation of carbon monoxide with dextrose, a monosaccharide, at a temperature varying between 800 C - 1200 C to produce metallic gallium. It was observed from investigations that 5-substituted alkyl quinoline are not effective in the extraction of gallium from Bayer's solution. Substitution in the 7-position greatly improves the extraction process. Use of modifier helps to prevent the formation of the third phase. It will be seen from above that extraction of gallium from Bayer's solution may be effected satisfactorily by the use of a 7-suvstituted alkyl quinoline in common hydrocarbon solvent and using a saturated alcohol of medium range molecular weight. Between C6 - C12 as a modifier, and a common hydrocarbon solvent like kerosene was used as a diluent. By following this technique of high separation factor was achieved with aluminium. It has been surprisingly been found that the extraction is almost quantitative if stirring is continued for 20-60 minutes and preferably for one hour. The co-extracted aluminium may be stripped back in a higher concentration of inorganic acid say around 4-8 molar strength, preferably between 5 and 7, gallium may be stripped back in 1-3 molar hydrochloric acid. The gallium thus stripped is precipitated by raising pH 3-4 under close control as gallium hydroxide, which is then centrifuged and dried. Metallic gallium may be obtained by thermal reduction with a reducing agent like gaseous hydrogen or insitu generation of carbon-monoxide with dextrose, a monosaccharide. It should borne in mind that under ambient conditions gallium is a liquid metal which finds applications in low temperature thermometry as well. It has also been observed that efficient extraction of gallium depends to a large extent on the pH of the medium. An optimum working range of pH was found to be between 10 - 12. Quantitative extraction has been achieved in alkaline medium rendering a possible resulting gallate to solvent extraction directly from Bayer's solution. Such a procedure not only reduces operative steps but also cuts down the cost of production. Quinoline derivative preferably bearing a alkyl substituent at 7-position is capable of forming a co-ordinated complex with the metal, with a hydroxyl group containing long chain organic solvent (C8 - C12) as modifier, quantitatively extract gallium from alkaline medium at less than or about 1 hour of stirring with better loading capacity and such a procedure has been evolved for the first time by the Applicant. Use of a cheap diluent or solvent like kerosene also brings down the production cost quite preferably with an added 4 advantage of less evaporation loss and fire hazards. 7-substituted alkyl quinoline derivative is commercially available under the Trade Name "Lix-26". The invention will now be further illustrated with a few examples, the data of which are given in a tabular form herein below from which it may be noted that the percentage of gallium is near complete. (95%). The extractive process evolved for the first time by the Applicant has resulted in recovery of extremely valuable metal with high international demand which heretofore was going to waste. The eco-friendly processes developed by the Applicant will not only help recovery of a valuable by-product but also will substantially reduces cost of production of aluminium. Since the cost of gallium is ten times more than gold in the international market. The process additionally utilizes a very little energy for its operation. It is to be noted the invention described above is by way of illustration and the invention is not to be restricted to the data given as it includes within its ambit the obvious modification and equivalents as would be apparent to a person skilled in the art. Having described invention and illustrated the same by way of Examples, it would be more particularly defined by means of the Claims appeared herein below :- 5 CLAIM :- 1. A process for extraction of gallium from aluminium-containing ores, which process comprises in combination - i) treating bauxite ore with caustic alkali under 25 - 40 Kg/cm2 pressure in a autoclave to convert aluminium oxide and gallium oxide to sodium aluminate and sodium gallate, respectively, ii) extracting gallium present in solution with 5 - 15% of a quinoline derivative and 5 - 12% of a straight chain higher alcohol in a hydrocarbon solvent to prevent formation of third phase, iii) stirring the mixture for a period varying between 20 and 60 minute for achieving in a hydrocarbon solvent, iv) stripping back the co-extracted aluminium in 4-8 molar hydrochloric acid and gallium in 1-3 molar hydrochloric acid, v) precipitating gallium as gallium hydroxide by raising the pH 3-4 of the gallium-containing medium obtain in step (iv) vi) centrifuging and drying precipitated gallium hydroxide and ' vii) reducing the precipitated and dried hydroxide in a stream of reducing gas, hydrogen or carbon monoxide at a temperature varying between 800oC to 1200 oC to produce metallic gallium as herein described. 2. A process as claimed in Claim 1, wherein the hydrocarbon solvent in kerosene and the quinoline derivative is 7-substituted alkyl quinoline. 3. A process as claimed in Claim 1, wherein the straight chain hydroxylated compound is decanol. 4. A process as claimed in Claim 3, wherein, decanol is used as modifier. 5. A process as claimed in Claims 1 to 4, wherein co-extracted aluminium is stripped back 4-8 molar hydrochloric acid and gallium in 1-3 molar hydrochloric acid. 6. A process as claimed in Claim 1, wherein extraction of gallium from the ore as gallate is done at a pH range between 10 and 12. 7. A process for extraction of gallium from aluminium-containing ores, substantially as herein before described and illustrated with reference to the appended examples. The present inventions relates to a process for extraction of gallium from aluminium-containing ores. More particularly this invention is concerned with recovery of Gallium in the course of extraction of aluminium from its ores, bauxite in particular. A process for extraction of gallium from aluminium-containing ores, which process comprises in combination treating bauxite ore with caustic alkali under pressure in a autoclave to convert aluminium oxide and gallium oxide to sodium aluminate and sodium gallate, respectively. Then extracting gallium present in solution with 5 -15% of a quinoline derivative and 5-12% of a straight chain higher alcohol in a hydrocarbon solvent to prevent formation of third phase. The mixture was stirred for a period varying between 20 and 60 minute for achieving complete extraction in a hydrocarbon solvent and stripping back the co-extracted aluminium in 4-8 molar hydrochloric acid and gallium in 1-3 molar hydrochloric acid. Then precipitating gallium as gallium hydroxide by raising the pH 3-4 of the gallium-containing medium centrifuging and drying precipitated gallium hydroxide and reducing the precipitated and dried hydroxide in a stream of reducing gas, hydrogen or carbon monoxide at a temperature varying between 800° to 1200° C to produce metallic gallium.

Documents:

00235-cal-2000-abstract.pdf

00235-cal-2000-claims.pdf

00235-cal-2000-correspondence.pdf

00235-cal-2000-description(complete).pdf

00235-cal-2000-form-1.pdf

00235-cal-2000-form-13.pdf

00235-cal-2000-form-18.pdf

00235-cal-2000-form-2.pdf

00235-cal-2000-form-3.pdf

00235-cal-2000-letters patent.pdf

00235-cal-2000-p.a.pdf

00235-cal-2000-reply f.e.r.pdf