ENRICHMENT OF KYANITE BY CARBOTHERMAL REDUCTION
N. N. Grishin,
O. A. Belogurova,
and A. G. Ivanova
Translated from Novye Ogneupory, No. 6, pp. 11 – 20, June 2010.
Original article submitted March 26, 2010.
Thermodynamic analysis is provided for possible reactions. A carbothermal reduction scheme is developed
for kyanite in a pseudoclosed system. A dependence is given for the yield of Al
on the amount of reduction.
A product is obtained that may be used for producing mullite-corundum refractories (GOST 24704).
Keywords: kyanite, carbothermal reduction, pseudoclosed system, thermodynamic analysis.
In world practice kyanite ore is in demand as an effective
refractory and ceramic raw material . It is possible to pre-
pare high quality alumina directly from kyanite by both al-
kali and acid methods as a result of existence of amphoteric
properties for aluminum, although these technologies have a
number of disadvantages: the multistage nature, a require-
ment for expensive chemically resistant equipment, use of
corrosive reagents, a requirement for using a considerable
amount ecologically unsafe waste materials, a considerable
water requirement, etc. [2, 3]. Therefore new methods are
studied for preparing aluminum oxide from aluminosilicates
with the aim of increasing their sphere of application and ex
panding the raw material base for producing alumina. In par
ticular, in order to separate Al
that are present
together carbothermal reduction of kyanite and kaolin clays
has been studied [4, 5].
During enrichment of kyanite concentrate of the Khizo
vaarsk deposit for aluminum oxide by carbothermal reduc
tion raw material is used with the following content of basic
components, %: Al
40.94 . The technol
ogy is represented by the following main stages: charge prep
aration, containing kyanite concentrate, a reducing agent and
a loosening additions, compaction of specimens at low pres
sure (50 MPa) or preparation of pellets, high-temperature
(1700°C) treatment of specimens with exposure at the maxi
mum temperature for 1–2h;separation of specimens from
the charge; grinding them with the aim of opening concre
tions; gravitation separation of the high alumina part from
the silica and calcined alumina part in an oxidizing atmo
sphere at 700°C with preparation of the final product. The
separated product (Al
12%) may be used for
producing mullite-corundum refractory (GOST 24704 “Co-
rundum and high-alumina refractory objects”) or alumina by
a successively combined scheme .
In order to improve quality of the high-alumina product
obtained conditions for performing the process are varied.
For example, increasing the time for raising the temperature
during firing led to an increase in Al
content and to a re-
duction in SiO
content (Table 1).
A similar effect may also be obtained as a result of an
overall increase in the specimen soaking time at the tempera
ture exceeding the threshold temperature for the reduction
reaction. A nonlinear dependence has been revealed for the
results of enrichment on the amount of reducing agent added
(Fig. 1). Equations for the curves in Fig. 1 have the following
+ 1.085x + 88.94, R
= 0.91; (1)
Refractories and Industrial Ceramics Vol. 51, No. 3, 2010
1083-4877/10/5103-0146 © 2010 Springer Science+Business Media, Inc.
I. V. Tananaev Institute of Chemistry and Rare Element Technol
ogy and Mineral Resources, KNTs RAN, Apatity, Russia.
TABLE 1. Content of Main Components After Reduction Firing of
Specimens at 1700°C with a Different Time of Temperature Increase
Component content, %, with time
for increase in temperature*, h
* Soaking time 1 h.