Abstract:
More than 30 percent of the global demand for zircon (ZrSiO4) is
supplied by South Africa. A significant amount of the zircon is
exported, and beneficiated products are then imported for industrial
applications locally. Beneficiating the zircon locally could have a
positive impact on the local market, since zircon is only one of many
such cases. Ammonium acid fluoride serves as an alternative
anhydrous fluorinating agent for zircon in the synthesis of several
metal fluorides1,2. It provides an effective dry fluorinating method
and is easier to handle than hydrogen fluoride or fluorine gas. Zircon
exposed to extreme plasma temperatures dissociates and becomes
more reactive. The reaction of the plasma-dissociated zircon
(ZrO2·SiO2) with the ammonium acid fluoride (NH4F·xHF, where x =
1 to 5) forms two main intermediate compounds (NH4)3ZrF7(s) and
(NH4)2SiF6(s), the latter decomposing to form volatile products at
relatively low temperatures, providing easy separation of the silicon
and zirconium compounds. The ammonium zirconate compound
decomposes to form zirconium tetrafluoride (ZrF4), which can be
further manufactured into zirconium metal, to name but one product.
Data on the kinetics of the reaction of ammonium acid fluoride with
zircon and plasma-dissociated zircon, combined with the thermodynamic
parameters of the reaction, is essential for the development
of an industrial process for the production of a precursor for the
manufacturing of zirconium metal, namely anhydrous ZrF4. Both the
reaction kinetics and reaction parameters will be included in this
study, as well as some proof that the reaction proceeds to ZrF4 on a
small batch scale. If the exact reaction parameters can be pinned
down, a wide spectrum of anhydrous metal fluorides can be
synthesized through this fluorination route.
