Synthesis of high purity zirconium tetrafluoride for nuclear applications
Monnahela, Oduetse Sydney
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The RSA has a great abundance of the potentially valuable zircon (Zr(Hf)SiO4) mineral, which is mostly exported in unexploited form, leading to huge losses in potential revenue. The purpose of this project was to attempt to purify Zr of Hf as well as 3d metals for nuclear applications. The fluoride route was used to exploit the difference in sublimation temperatures as a selective separation method for ZrF4 from HfF4, or vice versa, depending on the volatility of these species. The fluorination of ZrO2, HfO2 and plasma dissociated zircon (PDZ) samples and the identification of viable conditions for separation of ZrF4 and HfF4 in an anhydrous hydrogen fluoride and fluorine atmosphere were primarily investigated. The fluorination of these species was performed to understand the chemical behaviour of the tetrafluoride species prior to separation and whether this behaviour could not be manipulated to effect separation. Thermogravimetric analyses indicated that the formation of ZrF4 is possibly via the oxyfluoride. X-ray powder diffraction was used to confirm the results. The theoretical equilibrium composition calculations for separation of ZrF4 and HfF4 were simulated. The separation was further studied by theoretically calculating the separation coefficients of ZrF4 and the metal fluoride impurities.