Reaction kinetics of ZrF4 chloridation at elevated temperatures

Abstract

Zirconium metal is used in the alloy cladding of nuclear fuel rods. Necsa produces ZrF4 by reacting ammonium bifluoride with desilicated plasmadissociated zircon. The ZrF4 then undergoes a sublimation separation step to reduce the Hf content to below 100 ppm Hf. The ZrF4 is converted into ZrCl4 via its reaction with magnesium chloride. The ZrCl4 is then used in a plasma process to produce Zr metal for use in the nuclear industry. The aim of the research reported here is to obtain a first-order estimate of the reaction kinetics for the chloridation reaction. This was done using the data obtained from a dynamic thermogravimetric analysis experiment and minimising the error between experimentally determined degrees of conversion and predictions of a stepwise kinetic model predictions. The reaction was found to take place only above the sublimation point of ZrCl4. At a low enough heating rate it can be assumed the loss in mass is due to sublimation of ZrCl4, the moment it is formed and the rate of mass loss is equal to the reaction rate.