GB987224A - A process for the extraction of gallium - Google Patents

Abstract

Gallium is recovered from an aqueous alkali metal solution poor in gallium by treating the solution countercurrently with a liquid amalgam of a metal more electropositive than gallium, one of the two solutions being divided into droplets to increase the contact area between the two solutions. At periodic intervals the amalgam containing the gallium and a portion of the metal more electropositive than gallium is separated from the reaction mixture and the gallium recovered by distilling off the mercury, or by treating the amalgam with an acid, with water or with dilute NaOH. Gallium may then be separated from the extraction liquors by electrolytic methods. Temperatures from room temperature to 100 DEG C. may be used for the recovery step; the preferred alkali metal more electropositive than gallium is sodium and the amalgam preferably contains 0.2 to 0.3% by weight of sodium. In one method the amalgam is divided into droplets (by causing it to pass down through a perforated plate at the top of a column) which fall through an aqueous solution containing sodium gallate which flows upwardly through the column which is preferably packed, for example with Raschig rings. The amalgam which is preferably periodically replenished with sodium, and the aqueous solution are recycled until the amalgam has absorbed enough gallium to allow economic recovery. According to another embodiment, the vertical cylindrical column is provided with a series of horizontal perforated plates each of which occupies the entire cross-section of the column and each of which is pierced by a vertical overflow tube. The alkaline solution containing the sodium gallate flows upwardly through the column and is divided into fine droplets by the perforations in the plates and the amalgam is introduced on to the uppermost plate. By adjusting the flow rate of the aqueous solution the amalgam is prevented from passing through the perforations in the plates but instead passes through the overflow on to the next plate. After sufficient gallium has been absorbed by the amalgam, the latter is withdrawn from the foot of the column, the gallium recovered and the amalgam regenerated. The invention is applicable to the extraction of gallium from a sodium aluminate solution containing sodium gallate (the solution being obtained by bauxite extraction with NaOH).ALSO:Gallium is recovered from an aqueous alkali metal solution poor in gallium by treating the solution countercurrently with a liquid amalgam of a metal more electropositive than gallium, one of the two solutions being divided into droplets to increase the contact area between the two solutions. At periodic intervals the amalgam containing the gallium and a portion of the metal more electropositive than gallium is separated from the reaction mixture and the gallium recovered by distilling off the mercury, or by treating the amalgam with an acid, with water or with dilute NaOH. Gallium may then be separated from the extraction liquors by electrolytic methods. Temperatures from room temperature to 100 DEG C. may be used for the recovery step; the preferred alkali metal more electropositive than gallium is sodium and the amalgam preferably contains 0.2-0.3 by weight of sodium. In one method the amalgam is divided into droplets (by causing it to pass down through a perforated plate at the top of a column) which fall through an aqueous solution containing sodium gallate which flows upwardly through the column which is preferably packed, for example with Raschig rings. The amalgam which is preferably replenished with sodium, and the aqueous solution are recycled until the amalgam has absorbed enough gallium to allow economic recovery. According to another embodiment, the vertical cylindrical column is provided with a series of horizontal perforated plates each of which occupies the entire cross-section of the column and each of which is pierced by a vertical overflow tube. The alkaline solution containing the sodium gallate flows upwardly through the column and is divided into fine droplets by the perforations in the plates and the amalgam is introduced on to the uppermost plate. By adjusting the flow rate of the aqueous solution the amalgam is prevented from passing through the perforations in the plates but instead passes through the overflow tube on to the next plate. The invention is applicable to the extraction of gallium from a sodium aluminate solution containing sodium gallate (the solution being obtained by bauxite extraction with NaOH).