ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 11, pp. 1757!1760. + Pleiades Publishing, Inc., 2006.
Original Russian Text + V.V. Guzeev, A.N. D’yachenko, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp. 1777!1780.
AND INDUSTRIAL INORGANIC CHEMISTRY
Autoclave Breakdown of Zircon with Ammonium Fluorides
V. V. Guzeev and A. N. D’yachenko
Tomsk Polytechnic University, Tomsk, Russia
Received March 30, 2006; in final form, June 2006
Abstract-Autoclave breakdown of zircon with ammonium fluorides was studied.
Zircon is one of the main mineral sources of zir-
conium materials, but the technology of its breakdown
and processing is still labor-consuming, and much
efforts are made to improve it.
The classical industrial methods of breaking down
zirconium concentrates are sintering with fluosilicates
and chlorination. Numerous studies summarized in 
were devoted to zircon fluorination; however, it did
not gain industrial application. The fluoride technol-
ogy allows the scheme of the zirconium product proc-
essing to be reduced considerably, but high cost and
corrosive behavior of HF and F
, and also SiF
ation restrain industrial application of these reagents.
In this study we examined the autoclave breakdown
of zircon with ammonium fluorides.
Unlike fluorine and hydrogen fluoride, ammonium
fluorides are very convenient to use, as these are solid
crystalline substances under normal conditions. Am-
monium fluorides can be obtained from metal fluor-
ides by the action of ammonia water, which is the
basis for conversion and recycling of ammonium
Ammonium fluoride is known to react slowly with
zircon [2, 3]. At temperatures below 240oC, the reac-
tion rate is negligible and the degree of breakdown is
unsatisfactory for the industrial use, whereas at higher
temperatures ammonium fluoride evaporates with
Here we report new data on the zircon breakdown
with ammonium fluoride and hydrofluoride.
The essence of the method consists in the reaction
of zircon with ammonium fluoride or hydrofluoride
under isochoric conditions (in an autoclave), after
which the reaction products are separated by sublima-
tion to give zirconium tetrafluoride and dioxide. The
advantage of ammonium fluorides over other fluori-
nating agents consists in their convenient physico-
chemical properties allowing their regeneration and
The experiments were carried out with zircon sam-
ples from Tugan deposit of Tomsk oblast.
The reactions of zircon with ammonium fluoride
and hydrofluoride were studied under isochoric condi-
tions in a 100 cm
stainless steel autoclave. A weighed
portion of zircon with a grain size of 0.074 mm was
placed in the autoclave together with a weighed por-
tion of ammonium fluoride taken in a 20% excess in
relation to the stoichiometric amount calculated for
F = (NH
The autoclave was heated to 150, 200, 250, 300,
350, and 400oC and kept at these temperatures for 0.5,
1, 2, and 4 h.
After opening the autoclave, its content was trans-
ferred into a crucible and calcined for 30 min at
400oC to remove by sublimation unchanged NH
and formed (NH
. The residue in the crucible
was a mixture of unchanged ZrSiO
which 5 ml of concentrated sulfuric acid was added,
and the mixture was kept until H
peared. Zirconium in the form of ZrOSO
was leached with water from the formed cake, con-
verted to zirconium dioxide, and weighed to deter-
mine the degree of conversion.
The same procedure was used to study the reaction
of ammonium hydrofluoride with zircon
F. HF = 2(NH