|
|
| Occurrence and Production of Gallium |
 Occurrence
|
| Gallium does not exist in free form in nature, nor do any high-gallium minerals exist to serve as a primary source of extraction of the element or its compounds. Gallium is found and extracted as a trace component in bauxite, coal, diaspore, germanite, and sphalerite. The United States Geological Survey (USGC) estimates gallium reserves based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some flue dusts from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight. |
| Most gallium is extracted from the crude aluminium hydroxide solution of the Bayer process for producing alumina and aluminum. A mercury cell electrolysis and hydrolysis of the amalgam with sodium hydroxide (NaOH) leads to sodium gallate. Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available. |