Production of Gallium from Bayer Liquor of Alumina Refinery

Hi Friends,

In earlier post, we have already discussed the characteristics and applications of Gallium metal. In present post, we will describe various production processes for recovery of Gallium as byproduct from Bayer liquor of Alumina refinery. Crude Gallium of 97.0 to 99.9% purity is produced as byproduct from the circulating liquor of Bayer alumina plants. 


Production process:
Over a period of time, many processes have been developed for recovery of this strategic metal as listed below-

1. Carbonation process,
2. Mercury process, 
3. Cementation process,
4. Solvent extraction process and 
5. Extraction with chelating agents.

Most of the old plants in the World are operative with Mercury process but this process is not recommended now because of associated environmental problems. Here, we are describing the Carbonation process for recovery of Gallium from Bayer liquor as it is commercially viable eco-friendly process where as other processes are yet to be commercialized. The method for purification, storage and transportation have also been briefly described here in subsequent paragraphs.

Carbonation process involves treatment of aluminate liquor of Bayer process in two controlled stages. In first stage, major portion of hydrated alumina present in Bayer liquor gets precipitated but over 90% of Gallium remains in solution because of its higher solubility in NaOH than that of hydrated alumina. The Gallium rich decanted liquor is subjected to second stage carbonation resulting in precipitation of Gallium along with remaining hydrated alumina. This precipitate of mixed hydroxides contains about 0.30% to 1.0% of Gallium. The precipitate is dissolved in aqueous solution of sodium hydroxide yielding a concentrated solution of sodium aluminate and sodium gallate. Gallium concentration in this solution is sufficiently high for carrying out electrolytic deposition of Gallium. The electrolysis of this filtered alkaline solution is performed with stainless steel as cathode and pure nickel as anode. At times, liquid Gallium cathode is also used. The cells operate at 60-70 degree C with voltage at about 4 v. The concentration of Gallium hydroxide and Sodium hydroxide is kept at around 1:1 and not less than 1:6 in order to prevent separation of Gallium hydroxide. The cathodic current density is about 100 A/dm2 and current yield of 75% with Gallium concentration more than 40 gpl. The liquid Gallium accumulated at the bottom of electrolytic cell is periodically run into a cast mold. The crude Gallium thus obtained has the purity of 97.0% to 99.9%. The depleted liquor containing about 0.30 gpl Gallium is returned back to Bayer circuit of Alumina refinery.

Purification:

The crude gallium is washed in stages with hydrochloric and nitric acids followed by its filtration through porous plates like sintered glass. Here, 99.0% to 99.9% Gallium is obtained. For technological applications, minimum six-nines i.e. 99.9999%, is the required specification which is achieved by adopting fractional crystallization technique.

Storage and Transportation:

The Gallium metal is either packed in cold gelatine capsules or plastic containers and sold in lumps of 10 grams to 20 kg. During transportation, the temperature is strictly controlled below 20 degree C.

Trust, the production, purification, storage and handling of Gallium have been described to the extent possible based on which the process flow diagram can be developed for implementation of project. Please put your views / suggestions / remarks / comments, if any.

Regards.

Kunwar Rajendra