Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 11, pp. 1658−1661.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.M. Sizyakov, E.V. Tikhonova, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 11, pp. 1746−1750.
AND INDUSTRIAL INORGANIC CHEMISTRY
Physical and Chemical Transformations of Calcium
in Aluminate Solutions from Alumina Production
V. M. Sizyakov and E. V. Tikhonova
St. Petersburg State Mining University, St. Petersburg, Russia
Received March 26, 2012
Abstract—The data available from the literature are analyzed. The complex behavior of calcium in aluminate
solutions was studied. The scattered results obtained in studying the calcium transformations in aqueous solutions
containing aluminate ion are summarized and presented in the form of a scheme and phase diagram, which are
useful for the development of lime technologies in various industries, including alumina production. In addition,
the phase diagram outlines the most technologically important ﬁ elds of research intended for obtaining desired
products and is also suitable for forecasting processes.
Aluminate solutions from alumina production are a
complex multicomponent system. In addition to main
leaching products, they contain impurity ions, which
also pass to a solution from aluminum-containing raw
materials. Moreover, the aluminate solutions accumulate
by-products formed in recycling of industrial stream,
which change properties of the solutions and causes a
number of technological problems.
Interestingly, for more than one decade lime is used
as a ﬁ rst agent in solving many problems of alumina
production all around the world. These are recovery
of caustic alkali in “aged” solutions from its carbonate
forms (causticization), treatment of aluminate solutions
to remove red mud solid particles by ﬁ ltration (ﬁ ltering
additives), etc. Likely, lime is the most in demand reagent
of alumina production after caustic soda and is consumed
in the form of CaO powder and in hydrated form (milk of
lime). However, there are only few complex studies on
the system lime - aluminate alkaline solution.
In the study, the literature data on the lime chemistry
in aluminate alkaline solutions are analyzed. The gen-
eralized data obtained in foreign and domestic studies
are presented in a convenient form (scheme and phase
diagram) suitable to outline ways for further research and
ﬁ nd directions of lime technology practically important
for various industrial branches.
Lime (slaked or CaO powder) pass a solution to im-
mediately form calcium hydroaluminates with varied
concentration of water molecules. It has long been es-
tablished  that in the solutions of strong electrolytes
and in the presence of aluminate ions calcium hydroxide
is instable and instantly forms one or more
types of hydroaluminates with the general formula
О. According to the experiments of
, the process is limited by the diffusion of aluminate
ions to the Са(ОН)
nucleus not entered the reaction.
The inhibition effect of solid aluminate products in the
form of a tight crust was determined for a powder and a
compacted disc in .
Calcium hydroaluminates have the lamellar structure
consisting of alternation of [Ca
charge compensating anions with water molecules. The
general form of the reaction is:
O + 4OH
where L is the anion incorporated into the hydroaluminate
The type of the anion incorporated into the interlayer
space depends on the composition of the solution. For an