Production
About 118 tonnes of germanium was produced in 2011 worldwide, mostly in China (80 t), Russia (5 t) and United States (3 t). Germanium is recovered as a by-product from sphalerite zinc ores where it is concentrated in amounts of up to 0.3%, especially from sediment-hosted, massive Zn–Pb–Cu(–Ba) deposits and carbonate-hosted Zn–Pb deposits. Figures for worldwide Ge reserves are not available, but in the US it is estimated at 450 tonnes. In 2007 35% of the demand was met by recycled germanium.
While it is produced mainly from sphalerite, it is also found in silver, lead, and copper ores. Another source of germanium is fly ash of coal power plants which use coal from certain coal deposits with a large concentration of germanium. Russia and China used this as a source for germanium. Russia's deposits are located in the far east of the country on Sakhalin Island. The coal mines northeast of Vladivostok have also been used as a germanium source. The deposits in China are mainly located in the lignite mines near Lincang, Yunnan; coal mines near Xilinhaote, Inner Mongolia are also used.
| Year | Cost ($/kg) |
|---|---|
| 1999 | 1,400 |
| 2000 | 1,250 |
| 2001 | 890 |
| 2002 | 620 |
| 2003 | 380 |
| 2004 | 600 |
| 2005 | 660 |
| 2006 | 880 |
| 2007 | 1,240 |
| 2008 | 1,490 |
| 2009 | 950 |
The ore concentrates are mostly sulfidic; they are converted to the oxides by heating under air, in a process known as roasting:
- GeS2 + 3 O2 → GeO2 + 2 SO2
Part of the germanium ends up in the dust produced during this process, while the rest is converted to germanates which are leached together with the zinc from the cinder by sulfuric acid. After neutralization only the zinc stays in solution and the precipitate contains the germanium and other metals. After reducing the amount of zinc in the precipitate by the Waelz process, the residing Waelz oxide is leached a second time. The dioxide is obtained as precipitate and converted with chlorine gas or hydrochloric acid to germanium tetrachloride, which has a low boiling point and can be distilled off:
- GeO2 + 4 HCl → GeCl4 + 2 H2O
- GeO2 + 2 Cl2 → GeCl4 + O2
Germanium tetrachloride is either hydrolyzed to the oxide (GeO2) or purified by fractional distillation and then hydrolyzed. The highly pure GeO2 is now suitable for the production of germanium glass. The pure germanium oxide is reduced by the reaction with hydrogen to obtain germanium suitable for the infrared optics or semiconductor industry:
- GeO2 + 2 H2 → Ge + 2 H2O
The germanium for steel production and other industrial processes is normally reduced using carbon:
- GeO2 + C → Ge + CO2
Read more about this topic: Germanium
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