1070-4272/02/7505-0712$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 5, 2002, pp. 712!714. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 5,
2002, pp. 730!733.
Original Russian Text Copyright + 2002 by Mitrofanova.
AND INDUSTRIAL INORGANIC CHEMISTRY
Complexation of Calcium Ions with Dicarboxylic Acids
in Aqueous Solutions
G. V. Mitrofanova
Mining Institute, Kola Scientific Center, Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received July 11, 2001; in final form, December 2001
Abstract-Complexation of calcium ion with malonic, succinic, glutaric, and adipic acids at 25oC and ionic
strength I = 0.3 (KCl) was studied by pH-potentiometric titration.
Monocarboxylic acids obtained from vegetable raw
material are the traditional collecting agents in apatite
flotation from apatite3nepheline ores. However, per-
manent increase in the cost of these reagents and their
short supply make urgent the search for new collect-
ing agents obtained from inexpensive raw materials. It
is known that introduction of a second functional
group into a collecting agent molecule changes its
flotation properties. Among the bifunctional com-
pounds capable to be collectors, dicarboxylic acids
are of interest as the basis of new synthetic reagents
capable to substitute collectors of vegetable origin
in apatite flotation .
In dressing of apatite-containing ores under condi-
tions of circulating water supply, the liquid phase of
the flotation pulp contains substantial amounts of cal-
cium (up to 30 mg l
), which decreases the activity
of reagents and increases their consumption. There-
fore, it is important to study complexation of dicar-
boxylic acids with calcium ions.
The reference data on stability constants of calcium
complexes with these acids  either are incon-
sistent (i.e., for succinic acid) or refer to formation
of only one complex. The known stability constants of
calcium complexes with malonic, succinic, glutaric,
and adipic acids, recalculated by Davies equation to
zero ionic strength, are listed in Table 1.
In this work, complexation of calcium ion with
malonic, succinic, glutaric, and adipic acids was
studied, and the stability constants of the compounds
formed were determined.
Complexation was studied by pH-potentiometric
titration at 25oC and ionic strength of 0.3 (KCl). Pre-
liminarily we determined under the same conditions
the protonation constants of the corresponding acid
, required to calculate the complexation
The pH of solutions was measured with glass and
Ag/AgCl electrodes on an I120.1 ionometer with an
error of 0.01 pH unit.
Preliminary studies with 5010
L = 1 : 1  showed the absence of calci-
um complexes in the solution [the formation function
calculated from the experimental
data was negative]. Therefore, we took more concen-
trated solutions of acids (0.1030.15 M) and added
calcium nitrate (0.1 M, I = 0.3). The concentration
L was 1:5 and 1:3.
The dicarboxylic acids were recrystallized three
times from ethanol and dried at reduced pressure.
The acid concentration in the solution was set gravi-
metrically and refined by pH-potentiometric titration.
Chemically pure grade calcium nitrate and potassium
chloride were used. The calcium concentration was
determined by complexometric titration. The KOH
Table 1. Stability constants of calcium complexes with
Acid ³ logb
Mal ³ 2.50, 2.16, ³ 
³ 2.75, (1.25)* ³ 
Suc ³ 2.00 ³ 
³ 2.40, 1.90 ³ 
³ 2.10 (0.99) ³ 
Gl ³ 1.76 ³ 
Ad ³ 2.19 ³ 
* In parentheses is logb