ALUMINOSILICATE ORES PROCESSED BY A FLUORIDE METHOD
A. N. D’yachenko,
A. A. Andreev,
A. S. Buinovskii,
and R. I. Kraidenko
Translated from Novye Ogneupory, No. 5, pp.8–11,May,2006.
Original article submitted November 9, 2005.
An innovative method for preparation of mullite-based refractories from aluminosilicate topaz ores is pro
posed in which the mineral ore is treated with ammonium fluoride; the excess silicon dioxide is removed in the
form of gaseous ammonium hexafluorosilicate. The desiliconized mixture is sintered to obtain a lightweight
mullite refractory with a fibrous structure.
Mullite composed of 72% Al
and 28% SiO
ever-increasing application in high-temperature technologies;
mullite-based ceramics display low heat conductivity and
high strength and are in widespread use as heat-insulating
and refractory materials. For all its superior thermophysical
properties and large natural mineral reserves, mullite produc-
tion in Russia is still in the early stage of development. The
demands of the domestic mullite market are at present
mainly satisfied by the supply of ready-made mullite refrac-
tories purchased from foreign manufacturers [1, 2].
In Russia, a few manufacturers are concerned with the
production of mullite-based refractory materials. Mullite ma
terials are available from Ogneupory Joint-Stock Co. (Tula
Region) and Semiluki Refractory Plant Joint-Stock Co.
(Semiluki, Voronezh Region); however, they contain less
than 62% Al
and their refractoriness is much inferior to
that of pure mullite materials. The best raw materials for pro
duction of mullite are quartz-topaz ores. In Siberia, the
world’s largest deposits of quartz-topaz ores have been dis
covered with an overall topaz content of 200 million tons.
The domestic market demand for topaz is about 300 thou
sand tons. The precursor concentrate obtained by ore flota
tion contains some 40% aluminum oxide, 45% silicon dioxi
de, and 10% hydroxyl fluoride compounds. To extract mulli
te, part of the silicon dioxide and fluorine should be removed.
The processing of quartz-topaz ore includes two major
stages: (i) flotation beneficiation in the topaz component and
(ii) desiliconization and sintering of the desiliconized con
centrate to a mullite condition. A schematic of the process
and the averaged composition of initial, intermediate, and fi-
nal products are shown in Fig. 1.
Desiliconization and sintering (mullitization) of the
desiliconized semi-finished product are critical and power-
consuming stages of the quartz-topaz-to-mullite conversion.
For removing the excess SiO
, aluminum fluoride was used;
this interacts with SiO
and converts it to ammonium hexa-
fluorosilicate . An advantage of ammonium fluoride as a
desiliconizing agent is that it can be completely recovered
. The cycle of fluoroammonium desiliconization is shown
Refractories and Industrial Ceramics Vol. 47, No. 3, 2006
1083-4877/06/4703-0146 © 2006 Springer Science+Business Media, Inc.
Tomsk Polytechnical University, Tomsk, Russia.
Al O 5 – 25%
F ,OH 1–5%
Al O 40%
Al O 72%
Fig. 1. A schematic diagram of the quartz-topaz ore processing.
SiO +6NHF=(NH ) SiF +4NH +2HO
(NH ) SiF + NH OH = SiO + 6NH F + 2H O
42 6 4 2 4 2