INORGANIC SYNTHESIS AND INDUSTRIAL
Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 7, pp. 1148−1151.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © O.M. Polishchuk, A.A. Fakeev, N.V. Potapova, A.G. Vendilo, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 7,
Study of Magnesium Nitrate Behavior in Sodium Nitrate
Solutions at 25°С
O. M. Polishchuk, A. A. Fakeev, N. V. Potapova, and A. G. Vendilo
State Research Institute of Chemical Reagents and Especially Pure Chemical Substances, Moscow, Russia
Received December 24, 2010
Abstract—Solubility in the system KNO
O at 25°С was studied by the isothermal method.
Crystallization of potassium nitrate from aqueous solutions was studied. Coefﬁ cients of the removal of magnesium
nitrate admixture were calculated.
Potassium nitrate of reactive and special-purity grade
is rather widely applied in modern ﬁ elds of science and
industry (optics, ﬁ ber optics, etc.). Therewith heavy
demands are imposed on the contents of a great number
of admixtures (iron, copper, manganese, chrome, nickel,
cobalt, and magnesium). So, in pure-grade, analytically-
pure grade, chemically-pure grade products (GOST 4217)
the content of a magnesium admixture is normalized at
a level less than (1–2) × 10
; Sigma Ultra (USA),
less than 5 × 10
; Trace Select (“Fluka,” Switzerland),
less than 1 × 10
, and Suprapur (“Merck,” Germany),
less than 1 × 10
Magnesium is an accompanying element in the main
potassium minerals (carnallite, kainite, and schoenite)
and is present genetically in a feed stock used for the
potassium nitrate production .
An eutonic solution of the composition 9.1 wt %
and 39.1 wt % Mg(NO
was obtained at 20 ±
0.5°С [3, 4], however full data on studying the system
О were not published.
Potassium nitrate KNO
and magnesium nitrate
О are readily soluble in water at 25°С:
27.39 , 27.52 , 27.65 , and 41.94 [3, 7], 42.89
, 43.00 wt % [3, 8], respectively. Potassium nitrate
crystallizes in the rhombic system with the Pnma space
group  and Mg(NO
О, in the monoclinic system
with the Р2
/с space group , hence the absence of
their interaction in aqueous solutions can be assumed.
In this work the behavior of magnesium nitrate was
studied in a wide range of concentrations in potassium
nitrate solutions at 25°С.
To solve problems centered around magnesium nitrate
behavior when producing potassium nitrate of reactive
grade and ultra-pure grade, data on the solubility in the
О at 25° in a wide range of
concentrations of the components are necessary.
The study at magnesium nitrate macroconcentrations
was carried out by the solubility method . Ultra-pure
grade 7–5 KNO
(technical speciﬁ cation 6-09-354) and
analytically-pure grade Mg(NO
О (GOST 11088)
were used as initial substances, which were preliminarily
recrystallized from solutions in distilled water and dried
up. According to the chemical analysis and IR spectra,
the compounds corresponded to potassium nitrate [11, 12]
and magnesium nitrate hexahydrate [12, 13].
Potassium contents in samples of liquid phases and
“solid residue” were determined by the gravimetric meth-
od  and magnesium contents, by the chelatometry
method . The potassium and magnesium contents at
their joint presence were found by analyzing two aliquot
solutions. To determine potassium, 0.6% aqueous solu-
tion of sodium tetraphenylborate was added in the ﬁ rst
aliquot with stirring, after 30 min the dropped precipitate