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Russian Journal of Applied Chemistry, Vol. 75, No. 2, 2002, pp. 203!208. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 2, 2002,
Original Russian Text Copyright C 2002 by Kitikova, Shashkova, D’yachenko.
AND ION-EXCHANGE PROCESSES
Effect of Thermal Treatment on Sorption Activity
of Calcium and Magnesium Phosphates
N. V. Kitikova, I. L. Shashkova, and A. G. D’yachenko
Institute of General and Inorganic Chemistry, National Belarussian Academy of Sciences, Minsk, Belarus
Received April 11, 2000; in final form, March 2001
Abstract-The effect of thermal treatment in the range 203800oC on the activity of hydrated calcium and
magnesium phosphates in recovery of heavy metal ions from aqueous solutions was studied. The composi-
tion and sorption properties of materials obtained in all stages of thermal treatment of hydrophosphates and
phosphates are considered. The manner in which the sorption activity of phosphates changes upon thermal
treatment is interpreted.
Hydrated calcium and magnesium phosphates, pre-
cipitated from solutions of chlorides or nitrates of
these metals with a solution of ammonium phos-
phate, are known as materials demonstrating high
efficiency in recovery of ions of heavy and nonferrous
(n = 2, 3) from aqueous solutions. In the
case of a basic salt (calcium hydroxo apatite), the
recovery of multicharged metal ions is due to the
occurrence of ion-exchange processes , with ca-
pacity 133 mg-equiv g
. In the case of calcium and
magnesium phosphates and hydrophosphates, the ab-
sorption of double- and triple-charged metal ions is
a result of the occurrence of a chemical reaction be-
tween solid phosphates and M
ions , with the
absorption of metal ions in these processes being as
high as 25 mg-equiv g
. Compounds with such a ca-
pacity for absorption of ions of heavy and nonferrous
metals are of indubitable practical interest.
Practical use of sorption-active materials assumes
that data on their thermal stability must be available.
Thermal treatment is a necessary operation in obtain-
ing a granulated form of a sorbent and a widely
adopted way of sorbent modification to unify or im-
prove their properties.
Published data on the effect of temperature on the
chemical activity of calcium and magnesium phos-
phates are lacking .
The present communication reports the results ob-
tained in studying the effect of thermal treatment in
the range 203800oC on the sorption properties of
calcium and magnesium phosphates and hydrophos-
phates precipitated from aqueous solutions.
O; hydrophosphates CaHPO
O, and also a 1 : 1 mixture of CaHPO
O were studied. The salts Mg
O, and MgHPO
crystalline, and Ca
O was an amor-
The compounds studied were synthesized as fol-
lows. Crystal hydrates of the hydrophosphates and
phosphates were precipitated from aqueous solutions
of calcium or magnesium nitrates and ammonium
phosphate at pH 5 and 10, respectively . A sorp-
tion-active mixture of calcium and magnesium hydro-
phosphates was synthesized as described in , with
natural dolomite used as raw material. A weighed
portion of dolomite was placed in a 10% phospho-
ric acid solution (M
= 1 : 6) and kept for
a week with periodic stirring. Then the solution was
decanted and the obtained precipitate of calcium and
magnesium hydrophosphates was washed with water
and dried in air.
The specific surface area of the synthesized com-
pounds was determined from the low-temperature ad-
sorption of nitrogen.
The thermal treatment of the phosphates was done
stepwise in the temperature range 203800oCina
muffle furnace. After 4 h of treatment at 200oCa
specimen was cooled and sampled for determining its
sorption activity, ground, and again placed in the
furnace at higher temperature of 300oC, etc.