INORGANIC SYNTHESIS AND INDUSTRIAL
Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 3, pp. 345−350.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.S. Rimkevich, A.A. Pushkin, Yu.N. Malovitskii, I.V. Girenko, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 3,
Study of Fluoride Treatment
of Silica-Containing Raw Material
V. S. Rimkevich, A. A. Pushkin, Yu. N. Malovitskii, and I. V. Girenko
Institute of Geology and Nature Management, Far Eastern Branch, Russian Academy of Sciences,
Blagoveshchensk, Amur oblast, Russia
Received June 3, 2010
Abstract—An effect of ammonium hydroﬂ uoride treatment of silica-containing raw material was examined.
We described thermodynamics and kinetics of caking raw materials and their crushed materials, ammonium
hexaﬂ uorosilicate sublimation, and amorphous silica formation. Constants of rate and activation energy of the
chemical reactions were calculated.
Nowadays known types of silica-containing raw mate-
rial are applied to produce ammonium hexaﬂ uorosilicate
and amorphous silica which are widely used in various
branches of manufactures: chemical, paint-and-lacquer,
medicine, and cosmetics, and have a great demand in the
domestic and foreign markets.
The most common silica-containing raw materials
are quartz sands, which contain small amounts of
contaminants. Developed well-known methods of pro-
duction of ammonium hexaﬂ uorosilicate and amorphous
silica associated with the use of complex multi-step
processes require application of expensive reagents,
speciﬁ c source raw materials and equipment [1–3].
A goal of the study is to examine ﬂ uorination of the
silica-containing raw materials and develop environ-
mentally safe method of extraction of chemically pure
ammonium hexaﬂ uorosilicate and amorphous silica from
accessible and cheap raw materials: quartz sands.
Objects under study were quartz molding sands of
the following composition, wt %: SiO
O 0.09, K
O 0.97, other
losses during calcination (o.l.c.) 0.40 (Chalgan deposit
of feldspar kaolin-containing sands, Amur region). In
experiments we used main fraction +0.01–0.04 cm of the
quartz molding sand and its material crushed to size less
than –0.001 cm. Quartz is a main rock-forming compo-
nent present in form of β-SiO
trigonal that is stable at
normal temperature and pressure.
For processing quartz sands we used ammonium
hydrogen diﬂ uoride (NH
), pure for analysis. Under
normal conditions NH
is a stable crystalline solid of
orthorhombic structure that is environmentally safe com-
paring with ﬂ uorine, hydrogen ﬂ uoride, and hydroﬂ uoric
acid and becomes effective ﬂ uorinating agent when heat-
ing. Fluorination reactions are typical of NH
hydrogen diﬂ uoride is the more vigorous ﬂ uorinating
agent than ﬂ uorine gas . Melting point of ammonium
hydrogen diﬂ uoride is 126.8, and decomposition tem-
perature, 238°С, solubility in water, 370 g cm
The experiments were carried out in an electric
furnace of special design, where in a gradient-free
working area was a nickel or nickel-lined steel reactor.
Initial components, taken in speciﬁ ed proportions, were
thoroughly mixed and placed in Teﬂ on, glassy carbon or
platinum containers: cups, or pots, which were put into
the working area of the electric furnace and kept at 100–
500°C for 0.25–4.5 h. The value of weighted portions was
5–40 g. For trapping and collecting the volatile products
we used dual-zone condenser, the absorption of gaseous
ammonia occurred in a vessel with water. Synthesis of
the amorphous silica was carried out in the hydrolysis
apparatus, the regeneration of ammonium hydrogen
diﬂ uoride, in a laboratory evaporator–crystallizer.