13. Describe production of high purity germanium compounds

Production of germanium dioxide

Germanium dioxide is the main starting material for the production of germanium. The dioxide is prepared by hydrolytic decomposition of purified germanium tetrachloride:

The water used for the hydrolysis must be very pure in order to prevent contamination of GeO₂ with impurities. The water is purified by passing first through a column with activated carbon (which removes the colloidal and organic contaminants) and then, successively, through columns packed with cation and anion exchange resins which remove the cations and anions. The specific resistance of the purified water is 5*10⁶ ohm per cm³.

The hydrolysis of germanium chloride must be carried out in reactors which are not attacked by the germanium dioxide. In this respect quartz is superior to "Pyrex" glass. The hydrolysis may also be carried out in reactors made of plastic materials such as polyethylene. Germanium tetrachloride is poured (at a predetermined rate) into water, which is taken in an amount such that the resultant HCl concentration after hydrolysis is 5 N. The hydrolysis is rapid at first but then slows down. Several hours mixing is required in order to complete the reaction.

The hydrated germanium dioxide is separated by filtration, washed with purified water and alcohol, and dried at 150 to 200°. Complete dehydration of GeO₂ takes place at that temperature. The drying is carried out in quartz trays placed in electric muffle furnaces.

Precautions used to obtain high-purity germanium dioxide

We have mentioned the need for using corrosion – resistant materials in the purification and hydrolysis of germanium tetrachloride and using high-purity water. In addition, clean rooms and a dust-free atmosphere are of great importance. The air fed to the rooms must be passed through filters. It is recommended that the walls be covered with Dutch tile and the equipment be painted with synthetic paints containing no inorganic pigments.

14. Describe modern technological scheme of processing of vanadium

Concentration: The ore is passed through three-stage crushing, milled with a conventional rodmill- ballmill combination produce a product 80% passing 53 microns and passed through a three-stage low intensity magnetic separation circuit to produce a concentrate product;

Salt Roasting: The concentrate is roasted with sodium carbonate and sodium sulphate in a rotary kiln at temperatures of up to 1,150 ̊C to form water soluble vanadates. Solids exiting the rotary kiln are discharged directly into a rotary cooler that cools the solids to 350 ̊C;

Leach milling and purification: The cooled calcine is fed to a wet ball mill, which grinds the agglomerated material for improved leaching and also acts as the first stage of leaching. The slurry from the mill is pumped to thickeners where desilication and concentration of the vanadium-bearing leach liquor takes place. Thickened tailings are conveyed to the tailings disposal facility.

Ammonium metavanadate precipitation: Ammonium sulphate (AMSUL) is added to the vanadium-bearing leach liquor which allows for the precipitation of vanadium in the form of ammonium metavanadate (AMV);

De-ammoniation and fusion: The AMV filter cake is dried in a diesel-fired flash dryer and calcined in a diesel-fired AMV calciner to produce V2O5. The calcined V₂O₅ powder is charged into a fusion furnace to form molten V₂O₅;

Flaking: The molten V₂O₅ is continuously tapped and flows onto water-cooled flaking wheels forming a thin layer of V₂O₅, which solidifies and is then scraped off as the final product of V₂O₅ flakes; The V₂O₅ product can be sold directly into the vanadium market or can be processed further into a 80% FeV (Ferrovanadium) product through a simple process using an aluminothermic reactor. Vanadium plant designs for production of either ~10,350 ktpa V₂O₅ flakes (under the 1 Mtpa ROM scenario) or ~5,470 ktpa of V₂O₅ flakes (528 ktpa ROM scenario) were analysed and costed.