At NFC, Hafnium free high purity Zirconium is produced limiting critical impurities like Hf, N2 and C which makes it suitable for nuclear and other specialized applications.
The raw material for producing Zirconium metal is Zircon sand. Zircon is Zirconium Silicate containing 67% Zirconium in association with about 2% Hafnium. The removal of Hafnium is an important step in the nuclear metallurgy of Zirconium as Hafnium is an absorber of Neutrons. The permissible limit for Hafnium is very less in Zirconium. The first step of removal of Silica involves the treatment of zircon with Caustic Soda. The resulting frit is washed with water to remove water soluble Sodium Silicate. Then Zirconium and Hafnium are brought into solution with Nitric Acid. The separation of Zirconium from Hafnium and other impurities is achieved by solvent extraction using Tributyl Phosphate in Kerosene as the solvent, where Zirconium is preferentially extracted into the organic phase leaving Hafnium and other impurities in aqueous phase. The Zirconium-laden organic is then stripped to recover pure Zirconium in aqueous solution. Zirconium Hydroxide is precipitated from the pure solution using Ammonia and the Hydroxide is filtered, washed, dried and calcined in a rotary kiln to obtain pure Zirconium Oxide. The oxide is hammer milled to fine powder.
Hafnium free Zirconium Oxide are converted to Zirconium Tetrachloride (ZrCl4) intermediate through chlorination operation in static bed reactors.
Zirconium Tetrachloride is reduced to Zirconium through Kroll’s magnesiothermic reduction operation with MgCl2 as byproduct.
The reduced mass of Zirconium after mechanical separation of MgCl2 is subjected to Pyro-Vacuum Distillation operation for removal of entrapped Mg and MgCl2 to get pure Zirconium.
The distilled mass is subjected to a series of size reduction operations for further use.