ammonia produced by slow heating of concentrated
) of an ammonia hydrate solution .
Melting of the alum (mp ≥ 92.5°C) leads to its balling
and to an incomplete reaction. To prevent melting,
the temperature was maintained in the range 50–80°C.
The neutralization process was monitored as fol-
lows: a sample of the ammoniation product was sus-
pended in water and the pH of the suspension was
measured. After a pH ≥ 7 was reached, the neutraliza-
tion process was considered to be complete. The am-
moniation product was treated with warm water for 5–
10 min and the precipitated amorphous AH was sepa-
rated by filtration from the solution containing ammo-
nium and potassium sulfates. The AH precipitate was
subjected to aging in an ammonia hydrate solution un-
der various conditions. The treatment was carried out
in hermetically sealed vessels to prevent loss of NH
After the process was complete, the precipitate was
filtered off and washed with water to complete disap-
pearance of the SO
ion from the washing water, as
indicated by the absence of turbidization upon addition
of a drop of a barium chloride solution. The precipitate
was dried at 105°C to constant weight and examined
by various physicochemical analytical techniques. The
table shows how the phase composition of the samples
[according to the results of an X-ray phase analysis
(XPA)] and their specific surface area, determined by
the BET method from low-temperature adsorption of
nitrogen, depend on the aging conditions.
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 8, pp. 1332–1336. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.A. Matveev, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 8, pp. 1253–1257.
Specific Features of Phase Transformations
of Amorphous Aluminum Hydroxide Produced
by Ammoniation of Potassium Alum
V. A. Matveev
Institute of Chemistry and Technology of Rare Elements and Mineral Resources, Kola Scientific Center,
Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received December 10, 2007
Abstract—A novel method for neutralization of aluminum salts was suggested for the example of treatment of
crystalline potassium alum with gaseous ammonia. An assumption was made that the structure of the forming
primary particles is specific. The process of formation of a pseudoboehmite structure was studied in relation to
the aging conditions of the aluminum hydroxide precipitate.
AND INDUSTRIAL INORGANIC CHEMISTRY
Amorphous aluminum hydroxide (AH) can be
obtained by precipitation from an aluminum salt solu-
tion treated with an alkaline reagent, e.g., an ammonia
hydrate solution. There is no common opinion about
the phase composition of AH and factors affecting the
formation and stability of various forms of AH [1–5].
The reason is that the decisive influence on the chemi-
cal and phase composition, morphology, and specific
surface area of particles of the AH being formed is
exerted by a set of its synthesis conditions: pH value
and temperature of neutralization and aging, prelimi-
nary keeping of aluminum salt solutions, order and
duration of solution mixing, agitation intensity, etc.
This communication reports results obtained in a study
of the phase transformations that occur in amorphous
AH produced from potassium alum (PA) in the course
of aging of the precipitate and its thermal treatment.
PA was chosen as a source for obtaining AH be-
cause it can be rather easily isolated in a sufficiently
pure form in sulfuric acid treatment of the widely
available nepheline-containing raw materials . In
the study, potassium alum isolated from the a sulfuric
acid extract from a nepheline concentrate was used. It
had the following composition (wt %): Al
O 9.9, Fe
0.006. The specificity of obtaining
amorphous AH consisted in that the salt was neutral-
ized by direct treatment of crystalline PA with gaseous