1070-4272/01/7412-1981 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 12, 2001, pp. 1981!1984. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 12, 2001,
Original Russian Text Copyright + 2001 by Fakeev, Sukhanovskaya.
AND INDUSTRIAL INORGANIC CHEMISTRY
A Study of Calcium Nitrate Purification
A. A. Fakeev and A. I. Sukhanovskaya
State Research Institute of Chemical Reagents and Ultrapure Chemical Substances, Moscow, Russia
Received September 25, 2000; in final form, March 2001
Abstract-Two methods of calcium nitrate purification were studied: crystallization from aqueous solutions
and joint precipitation of impurities from aqueous solutions onto inorganic collectors (calcium hydroxide or
carbonate and hydrated aluminum or zirconium oxides). The efficiency of purification of calcium nitrate
solutions was studied and the purification coefficients were calculated for hydrated aluminum or zirconium
oxides as collectors.
Calcium nitrate is widely used in metallurgical,
chemical, and food industries, glass manufacture,
agriculture, etc. .
In chemical industry, calcium nitrate is a key com-
pound for preparing the most practically significant
calcium products (carbonate, hydroxide, phosphate,
chromate, oxalate, etc.) [2, 3].
In recent years, ultrapure calcium compounds (car-
bonate, phosphate, and fluoride) have found applica-
tion in fabrication of optical fibers, optical glass,
single crystals, and phosphors. This required the dev-
elopment of a method for deep purification of calcium
nitrate, which is the most accessible raw material .
The great number of publications devoted to calcium
nitrate purification stems from the necessity for
preparing pure and ultrapure calcium salts.
The efficiency of crystallization purification of cal-
cium nitrate can be estimated from data on phase equi-
libria in water3salt systems. Analysis of the solubility
diagrams in the systems Ca(NO
is Sr, Ba , Be , Ni [6, 7], Ag ,
Cu(II) , Fe(III) , Co [11, 12], or Mn(II) ,
at 25oC indicates the lack of isomorphism (i.e., the
systems are of simple eutonic type), and the apparent
possibility of separating calcium nitrate and nitrates
of the above metals. However, joint crystallization of
nonisomorphous impurities is a much more complex
process, since the quantitative characteristics of the
component distribution at low concentrations of one
of the components cannot be, as a rule, predicted
solely on the basis of solubility diagrams . It is
this fact that made necessary prolonged and rather
complex experimental studies.
Crystallization from aqueous solutions as a method
for purification of calcium nitrate was proposed in
[3, 14]. It was shown that double crystallization res-
ults in the removal of iron salts and makes the lead
concentration 15320 times lower.
The impurity distribution upon crystallization of
calcium nitrate from nitric acid solutions has not been
studied. However, by analogy with strontium and
barium nitrates, this process seems to be efficient for
calcium nitrate purification, with, however, the sol-
ubility of the compound being rather high (29.8 wt %
in 40% HNO
at 25oC ). This necessitates treat-
ment of large volumes of mother liquors and makes
the technology more complex.
A way to purify 20% calcium nitrate solutions by
precipitation of sparingly soluble metal sulfides at
pH 4.535.0, addition of H
at pH 7.6, and sub-
sequent adsorption of impurities onto glass wool has
been described . The thus obtained product con-
tains 5 0 10
35 0 10
iron ions and 1 0 10
manganese and heavy metal ions each.
Use of complexing reagents (sodium diethyldithio-
carbamate , sodium salt EDTA , lumogallion
IREA, and rubeanic acid ), with subsequent ad-
sorption of the formed complexes, excess amount of
complexing reagents, and products of their partial
decomposition onto ion-exchange resins or activated
carbon, is an efficient method for purification of cal-
cium nitrate solutions. However, the described meth-
ods involve introduction of complexing agents, which
makes necessary their thorough removal from the
purified solutions and special pretreatment of sorbents