Germanium Production
Germanium Production
By-products of nonferrous metals, products of coke process and coal ash are used as raw feedstock for obtaining germanium. After concentration by flotation or magnetic methods germanium concentrate is processed by pyrometallurgical methods at 800-1800°C, in reducing atmosphere (CO, H2) and in the presence of S, or H2SO4, or alkali-earth metals sulphates. Germanium completely or partially passes into gaseous phase as GeO, GeO2, GeS, GeS2, Ge, which then are trapped with other volatile components and dust.
Germanium-containing dust which appears after nonferrous metals processing is subject of leaching by H2SO4 solution. Germanium concentrate is separated from solutions, usually by as well as Co-Zn codeposition with other elements, for instance, Fe as Fe(OH)3 at pH 4.8-5.4. Separated germanium is dried, roasted and treated by concentrated chlorohydric acid, distilling out the yielded GeCl4. Germanium may be isolated also by ion exchange processes with chlorohydric acid as an eluent. The solution is then distilled yielding GeCl4; or hydrolyzes by alkali liquor until GeO2.
After that GeCl4 is rectified in quartz columns, or by hydrochloric acid extraction, by thermal diffusion, by directional crystallization etc. After that GeCl4 is hydrolyzed by pure water at 20-30°C the obtained GeO2 flushed up by water and dried by spirits, ultra-high frequency currents, after which germanium is reduced by hydrogen at 600-700°C. Powder germanium is fused at 1000-1050°C and refined by zone melting, and directional crystallization. Crystals are grown by Czochralski or Stepanov crystal growth method. In this process germanium is doped in 10-3 - 10-4% by special impurities such as Sb, Ga, As, Si etc. varying semiconductor properties. The purity pf produced germanium is determined through Hall's EMF or via neutron activation analysis.