Fluorination of zircon using ammonium bifluoride to produce ZrF4

In this work, the thermal and microstructural analysis of the reaction pathways of natural zircon with ammonium bifluoride (NH4HF2) under N-2 gas were investigated from room temperature to 850 degrees C using thermogravimetry (TGA), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD). The results indicate that the fluorination of zircon to form (NH4)(3)ZrF7 and (NH4)(2)SiF6 initiates with the melting of NH4HF2. With the increment of temperature, the departure of H2O/NH3 and NH4HF2 occurs below 175 degrees C. Subsequently, (NH4)(3)ZrF7 releases NH4F to form (NH4)(2)ZrF6 at 246.5 degrees C and (NH4)(2)SiF6 sublimes mainly at 280 degrees C. Finally, (NH4)(3)ZrF6 releases all NH4F at 330 degrees C to form ZrF4, which sublimes at similar to 700 degrees C. Based on the above results, a pilot test in kilogram scale was performed and high purity ZrF4 could be produced under the optimal conditions.