Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 5, pp. 711−715.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © O.M. Polishchuk, A.A. Fakeev, V.M. Retivov, A.G. Vendilo, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 5,
AND INDUSTRIAL INORGANIC CHEMISTRY
Puriﬁ cation of Potassium Nitrate Solutions by Coprecipitation
of Impurities on Hydrated Aluminum Oxide
O. M. Polishchuk, A. A. Fakeev, V. M. Retivov, and A. G. Vendilo
State Research Institute of Chemicals and Ultrapure Substances, Federal State Unitary Enterprise, Moscow, Russia
Received October 19, 2011
Abstract—Coprecipitation of 3d-element impurities from potassium nitrate solutions on hydrated aluminum oxide
was studied. The efﬁ ciency of the process was examined in relation to the weight of the collector, the solution–
collector contact time, pH of medium, concentration of microimpurities, and presence of oxidant. The parameters
for efﬁ cient puriﬁ cation of potassium nitrate solutions were determined.
Collectors having different compositions (organic
and inorganic collectors) have traditionally been used
extensively for concentration and separation of elements
in analytical chemistry and radiochemistry, as well as for
water treatment purposes [1, 2]. Due to high efﬁ ciency ex-
hibited particularly at low concentrations of elements and
suitability for simultaneous removal of many impurities,
collectors offer much promise for preparation of ultrapure
substances. In this particular case, the isomorphism and
isodimorphism phenomena complicating the crystalliza-
tion of most of salts from aqueous solutions  produce
a beneﬁ cial effect via contributing to coprecipitation of
Despite being the subject of numerous publications,
coprecipitation of impurities on collectors has only lim-
ited application for puriﬁ cation of inorganic substances
so far. This is largely due to complexity and inadequate
understanding of the processes involved [4, 5].
Here, we studied puriﬁ cation of aqueous solutions
of potassium nitrate on an inorganic collector, hydrated
aluminum oxide (HAO).
As collector for puriﬁ cation of aqueous solutions
of potassium nitrate served HAO of the composition
O, which was precipitated in the potassium ni-
trate solution being puriﬁ ed by adding calculated amounts
of 17-3 ultrapure grade aluminum nitrate Al(NO
[TU (Technical Speciﬁ cations) 6-09-3657] and of an
aqueous solution of chemically pure grade potassium
hydroxide KOH [GOST (State Standard) 24363].
The potassium nitrate solutions were prepared from
preliminarily recrystallized and dried 7–5 ultrapure
(TU 6-09-354) in a 20 wt% concentration
to comply with the process requirements (with increas-
ing concentration the viscosity of the solution tends to
increase, thereby hindering sedimentation and separation
of the collector).
In our experiments we used standard solutions con-
taining 1 mg ml
of each of iron(III), chromium(III),
manganese(II), copper(II), cobalt(II), and nickel(II)
impurity elements, prepared according to GOST 4212.
The calculated volumes of the solutions containing the
impurity elements were added to 50 ml of 20% potassium
nitrate solution at 25°C and stirred, after which a sample
for analysis was taken. Next, the calculated amounts of
aluminum nitrate were added to the resulting solution, and
10% aqueous solution of potassium hydroxide was poured
gradually with stirring to pH 7.5–8.0 (pH-410 pH-meter,
Akvilon), and the resulting mixture was stirred for 0.5 h.
The precipitated collector was ﬁ ltered off using a SPA-
0.25 ﬁ lter, after which a sample for analysis was taken
from the puriﬁ ed solution. Unless otherwise speciﬁ ed, all