CA1042629A

CA1042629A - Recovery of gallium oxide from solutions

Info

Publication number: CA1042629A
Application number: CA216,510A
Authority: CA
Inventors: Harry C. Snyder (Jr.)
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1974-12-20
Filing date: 1974-12-20
Publication date: 1978-11-21

Abstract

ABSTRACT OF THE DISCLOSURE

Method for recovery of gallium from sodium aluminate solutions by co-precipitation of alumina and gallium oxide, followed by introducing sodium aluminate into the resultant solution to co-precipitate further alumina and gallium oxide.
The specification discloses a process in which carbon dioxide is fed into gallium-containing sodium aluminate solutions in sufficient amount to co-precipitate alumina and part of the gallium as gallium oxide and form sodium bicarbonate in the solutions, after which sodium aluminate is fed into the resultant solution, whereby further alumina and gallium oxide are co-precipitated from the solution. The respective degrees to which dissolved gallium is precipitated by gassing the solution with carbon dioxide, and by adding sodium aluminate to the gassed solution, as described above, ordinarily depends on the relative economy of those respective procedures in the recovery of gallium oxide. Normally, it is economically feasible to precipitate the major portion of the gallium by gassing the solution with carbon dioxide and forming at least 90 grams per liter of sodium bicarbonate in the solution, prior to adding sodium aluminate to recover further gallium oxide from the solution.

Description

1~42629 ~his invention relates to the recovery of gallium fr.om sodium aluminate solutions.
. ~ ., - - .

In the well known Bayer process for the recovery of alumina from aluminas;, such as bauxite, by digesting the ore in hot caustic soda solution to form a sodium aluminate solution, followed by precipitation of alumina hydrate from the solution and recycling the resultant caustic soda-con-taining "spent liquor" to digest further bauxite, gallium values in the ore are dissolved and accumulate in the solution in repeated digests until an equilibrium is reached, usually at about 0.1-0.2 grams of gallium per liter of solution.
- Also, sodium aluminate solutions containing a low concentration of dissolved gallium can be produced by digesting in hot caustic soda solution of gallium-containing anode alloy from the well known 3-layer process for the purification of aluminium.
U.S. patents 2,574,008 and 2,~82,376 disclose recovering gallium values from sodium aluminate solutions by co-~recip-itating gallium oxide and alumina by feeding carbon dioxide into the solution, after preliminarily precipitating alumina and thercby decreasing the ratio of alumina to gallium in the solution, In effecting co-~recipitation of gallium oxide and alùmina in that manner, especially when the co-precipitation is accomplished slowly from solutions containing low concen-trations of yallium, it is uneconomical to recover all of the 1~4Z6Z9 gallium from the solution, despite feeding enough carbon dioxide that the solution contains a substantial proportion of sodium bicarbonate. Such unprecipitated gallium represents an economic loss.

It is an object of this invention to provide an economical and convenient process for precipitating further gallium oxide following co-precipitation of alumina and gallium oxide from sodium aluminate solutions by introducing carbon dioxide into the solution.
In accordance with the invention, carbon dioxide is fed into gallium-containing sodium aluminate solutions in sufficient amount to co-precipitate alumina and part of the gallium as gallium oxide and form sodium bicarbQnate in the solutions, after which sodium aluminate is fed into the resultant solution, whereby further alumina and gallium oxide are co-precipitated from the solution. The respective degrees to which dissolved gallium is precipitated by gassing the solution with carbon dioxide, and by adding sodium aluminate to the gassed solution, as described above, ordinarily depends on the relative economy of those respective procedures in the recovery of gallium oxide. Normally, it is economically feasible to precipitate the major portion of the gallium by gassing the solution with carbon dioxide and forming at least 90 grams per liter of sodium bicarbonate in the solution, prior to adding sodium aluminate to recover further gallium oxide from the solution.
In carrying out the abovementioned procedure of co-precipitating alumina and gallium oxide by adding sodium aluminate to the solution, the sodium aluminate employed may be either in solid form or in solution, but preferably in the foxm of a solution. The amount of sodium aluminate added depend~ on ~uch factors as the amount of gallium oxide to be 1~426Z9 precipitated, and the proportion of the dissolved gallium present which it is desired to precipitate.
Circulating the co-~recipitated alumina and gallium oxide through the solution for an extended time by agitation of the solution and precipitate is effective in promoting precipitation of additional gallium oxide, and whether that procedure is to be used is also a factor to take into consideration in determining the amount of sodium aluminate to be added to the solution. Such agitation can be effected by well-known means for stirring slurries.
The following example illustrates the practice of the invention:
Carbon dioxide was fed into a solution containing 4.6 grams per liter of alumina, 12.7 grams per liter of total caustic and 0.169 grams per liter of dissolved gallium, such gassing ~eing continued over a period of 21 hours, by which time sufficient alumina and gallium oxide had been co-precipi-tated that the resultant solution contained only 0.091 grams per liter of dissolved gallium, and less than 0.02 grams per liter of alumina, together with 88.7 grams per liter of sodium bicarbonate. Thereafter a portion of the solution, designated Portion A, was stirred continuously for 48 hours.
Sodium aluminate solution was fed into a second portion (designated Portion B) of the solution resulting from the abovementioned gassing step, in sufficient amount to add

2.5 grams per liter of alumina to the solution, and the slurry was stirred continuously for 48 hours at the same rate as was employed in stirring Portion A. At the end of 16 hours alumina and gallium oxide had precipitated from both portions A and B, but in the case o~ Portion A the solution still contained 0.073 gram~ per liter of dissolved gallium, whereas, Porti~n B contained only 0.~04 grams per liter of dissolved gal~ium. 4

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of precipitating gallium oxide from sodium aluminate solutions containing dissolved gallium, comprising feeding into the solution sufficient carbon dioxide to co-precipitate alumina and part of the gallium oxide from the solution and produce sodium bi-carbonate in the solution, and thereafter co-precipitating further alumina and gallium oxide from the resultant solution by feeding sodium aluminate into that solution.