ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 2, pp. 181!184. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + V.A. Matveev, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 2, pp. 183!186.
AND INDUSTRIAL INORGANIC CHEMISTRY
Hydrolysis of Aluminum Sulfates in
the Presence of Ammonium Sulfite
V. A. Matveev
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Scientific Center,
Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received September 4, 2006
Abstract-Hydrolysis of aluminum sulfate and potash alum in the presence of an ammonium sulfite additive
in the temperature range T
3200oC was studied. A possible reaction mechanism was suggested. The com-
position and structure of the precipitates formed were determined and certain differences in their morphology
were noted. Recommendations for practical implementation of the method of hydrolytic recovery of aluminum
from solutions of its sulfate salts were given.
Hydrolysis of aluminum sulfates is the most wide-
spread method for recovery of aluminum(III) from
solutions in sulfuric acid processing of aluminum-con-
taining raw materials into alumina . It has been
found that aluminum sulfates can be arranged in order
of increasing susceptibility to hydrolysis as follows:
aluminum sulfate < ammonium alum < sodium alum <
potash alum .
The effect of additions of ammonium, sodium, and
potassium sulfates on the hydrolysis of aluminum
sulfate has been studied [7, 8]. It was shown that
the cations can be arranged in order of increasing
effect on the degree of hydrolysis as follows: H
. It was noted that the ionic radii in-
crease in the same order, which suggests that the sol-
ubility of basic aluminum salts decreases as the ionic
radius of cations becomes larger.
The effect of temperature has been studied in de-
tail. It was found that a noticeable precipitation of
the basic aluminum sulfate is observed only at T >
200oC. For example, according to , the degree
of hydrolysis of potash alum KAl(SO
, which is
the most susceptible to hydrolysis, does not exceed
84% at 240oC. The process is hindered by accumula-
tion of sulfuric acid in solution.
High-temperature hydrolysis involves a large pow-
er expenditure and requires an intricate equipment
(autoclaves working under a pressure P > 30 atm).
This is one of the principal reasons why the hydrolytic
recovery of basic aluminum salts from sulfate solu-
tions has not been implemented in practice so far.
Therefore, it is a topical task to develop procedures
that would increase the degree of aluminum(III) ex-
traction into a precipitate of a basic salt, with a si-
multaneous pronounced decrease in the hydrolysis
In this study, the hydrolysis of aluminum sulfate
(AS) and potash alum (PA) in the presence of am-
monium sulfite was examined.
Ammonium sulfite was obtained by bubbling sul-
fur dioxide through a concentrated solution of am-
monium hydrate. As the solution was saturated, am-
monium sulfite monohydrate (NH
cipitated, which was confirmed by chemical, X-ray
phase, and IR spectroscopic analyses. According to
, ammonium sulfite obtained by various methods
contains up to 93 9.4% ammonium sulfate. Therefore,
it was taken that the content of the main substance in
the resulting salt is 95 wt %. The solution containing
10 wt % ammonium sulfite had pH
For the experiments, we prepared AS and PA (an-
alytical grade) solutions containing 80 g l
which is characteristic of solutions obtained by pro-
cessing aluminosilicate raw materials. The expendi-
ture of ammonium sulfite varied from 0.5 to 2 mol per
mole of Al
. The experimental temperature range
was from T
to 200oC (the boiling points of AS
and PA solutions were 103 and 105oC, respectively).
The duration of the process at the boiling points of
the solutions was 4 h. Hydrolysis at 125, 150, 175, and