Chemistry: electrical and wave energy – Processes and products
Patent
1981-01-23
1983-01-11
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
204105R, C25C 124
Patent
active
043681085
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
The present invention relates to processes for producing rare and scattered elements and, more specifically, to processes for electrolytic recovery of gallium or gallium and vanadium from alkaline liquors resulting from alumina production.
DESCRIPTION OF THE PRIOR ART
Direct production of gallium from ores is not commercially implemented. Gallium is produced from products of processing bauxites to alumina which contain substantially the following components, percent by mass: alumina 50-60, iron oxides 15-25; silica 2-5; calcium oxide 1-3.
In addition to these components a number of rare elements are present in bauxites, including 1-2 kg/ton of vanadium pentoxide and 0.02-0.07 kg/ton of gallium.
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 an amount of about 75 percent by mass in the form of sodium gallate. Upon decomposition of aluminate solutions the predominant amount of gallium remains in the solution, due to the formation of more durable, complex compounds compared to aluminium, (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. During circulation these liquors become enriched in gallium.
Under stationary process conditions the gallium concentration in liquors becomes constant and varies within the range of from 0.15 to 0.50 g/l. The concentration value depends on the content of gallium in bauxite, bauxite composition and process technology employed in alumina production.
In a similar manner processing of vanadium is performed in the above-described Bayer's method.
Therefore, for a commercial production of gallium and vanadium from bauxites as the starting materials, use can be made of aluminate liquors.
A process known in the art is for the direct recovery of gallium from alkaline liquors resulting from alumina production on a mercury cathode (Swiss Pat. No. 333,264; 1958; FRG Pat. No. 1,051,827; 1959).
In accordance with this process, the mother aluminate liquor resulting from the Bayer's process is subjected to electrolysis on a liquid mercury cathode and nickel anode. The electrolysis is conducted under the following conditions: anodic current density, 1,000-1,200 A/m.sup.2, cathodic current density, 35 to 45 A/m.sup.2, duration of electrolysis 24 hours. Under these conditions gallium is reduced on the cathode and diffuses into the bulk of mercury. To facilitate the processes of diffusion and renewal of the cathode surface, an intensive agitation of the liquor and mercury is effected. The electrolysis is stopped when 0.5-1.0% by mass of gallium amalgam is obtained, since solubility of gallium in mercury at the temperature of 50.degree. C. is 1.5% by mass. Gallium amalgam is decomposed by means of a solution of caustic soda at the boiling temperature of the resulting solution in the presence of metallic iron. After carrying out several above-mentioned operations of the amalgam decomposition, the content of gallium in the resulting gallate solution is as high as 30 to 80 g/l. From this solution gallium is recovered in an electrolyzer with a steel
ickel/or liquid gallium cathode.
This process, however, features a low rate of the process of gallium recovery, the use of sophisticated process equipment and large amounts of mercury employed in circulation (up to 3,000 kg in the case of a flat-bottom electrolyzer). Furthermore, mercury is an excellent collector for a number of metals, therefore, the thus-produced gallium is generally strongly contaminated with iron, nickel, lead, copper and molybdenum.
It should also be noted that mercury employed in this prior art process has a high toxicity, while the rate of consumption of mercury in the process is 2 kg per one kg of gallium. Despite severe measures for ensuring safety of operation with mercury, the operating personnel is from tim
REFERENCES:
patent: 3966568 (1976-06-01), Crossley et al.
patent: 4061551 (1977-12-01), Ivanova et al.
Davydov Ivan V.
Diev Valery N.
Eremeev Arnold F.
Fomin Eduard S.
Grigorieva Anastasia D.
Adams Bruce L.
Andrews R. L.
Burns Robert E.
Lobato Emmanuel J.
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