Antraptseva, N. M.

Bila, G. N.

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Synthesis and chemical nature of the products of Со(ІІ) and Mg  phosphates coprecipitation

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 32 
Synthesis and chemical nature of the products of Со(ІІ) and Mg 
 phosphates coprecipitation 
N. M. Antraptseva1, G. N. Bila2 
1 National University of Life and Environmental Sciences of Ukraine, Kiev, Ukraine, 
 2 National University of Food Technologies, Kiev, Ukraine,  
e-mail: Billa2003@mail.ru 
The work carried out in terms of diversification of hydrated phosphates that contain two dif-
ferent cations in their composition the contents of which can be purposely changed. Thereby 
their physico-chemical and exploitation properties could be changed in the wide limits. 
The aim of this work was to determine the composition and chemical nature of the products 
of cobalt(II) and magnesium phosphate coprecipitation. 
The joint precipitation of Co2+ and Mg2+ cations was carried out under conditions that pro-
vide the formation of the secondary hydrated phosphates. Specific conditions of precipitation 
were chosen for separate series of experiments depending on the composition of the solid phase 
from the main process parameters. pH of the reaction solutions was changed using aqueous solu-
tions of Na2HPO4, Na3PO4 or their mixture Na2HPO4 : Na3PO4 = 2 : 1 and Na2HPO4 : Na3PO4 = 
1:1 as precipitator. Correlation in the initial solutions n = Р/∑Со2+, Mg2+ was maintained equal 
to 0.67 that was stoichiometric and it was necessary for the formation of secondary phosphates 
of divalent metals. Correlation of cations K = CO
2+/Mg2+ was varied within the range from 25.0 
to 1.5. Concentration of the solutions was changed in the range of 0.05–0.25 mol/l, the deposi-
tion temperature was maintained in the range of 50–75 oC. 
The results of complex analyzes of the solid phase showed that at the values K = 
Co2+/Mg2+=25.0–1.6 octahydrate secondary phosphates were formed. They contained both Co2+ 
and Mg2+ cations. The ratio of cations could be changed within wide limits by the variation of 
composition of the initial reagents (Table). The general formula of precipitated phosphates was 
Со3–хMgx(PO4)2 · 8H2O. The synthesized phosphates presented themselves solid solution of sub-
stitution. The region of homogeneity at the use of Na2HPO4 : Na3PO4 = 1 : 1 as a precipitator was 
maximal and could be varied in the limits 0 < х  1.00. The saturated solid solution what formed 
under these conditions which had the composition of Со2.0Mg1.0(PO4)2·8H2O. 
Table – The dependence of Сo3-хMgx(PO4)2·8H2O (0 < x  1.00) phosphates composition on 
the ratio K = Co/Mg in the initial solutions (precipitator was Na2HPO4 : Na3PO4 = 1 : 1) 
Correlation  
K = Со/Mg, mol 
The composition of the solid phase 
Chemical, wt. % Phase 
Со Mg P H2O 
25.0 41.77 0.54 13.62 15.86 Со2,9Mg0,1(PО4)2·8H2O 
9.0 40.15 1.35 13.50 15.92 Со2.75Mg0.25(PO4)2·8H2O 
4.0 37.48 2.74 14.22 16.23 Со2.51Mg0.49(PO4)2·8H2O 
2.5 34.70 4.13 14.31 16.63 Со2.27Mg0.73(PO4)2·8H2O 
1.6 31.36 5.83 14.87 17.26 Со2.0Mg1.0(PO4)2·8H2O 
1.5 28.49 8.36 15.79 17.02 
The mechanical mixture of two phases: 
Со2.0Mg(PO4)2 · 8H2O + MgHPO4 · 
3H2O 
If an aqueous Na2HPO solution was used as a precipitator the range of homogeneity of Со3–
хMgx(PO4)2 · 8H2O solid solution was 0 < х  0.54 or at Na2HPO4 : Na3PO4  = 2 : 1 it was varied 
in the limits of 0 < х  0.70. Trying to obtain octahydrate Co(II)–Mg phosphate with magnesium 
content larger than 5.83 wt. % (K = Со2+/Mg2+ < 1.6) the precipitation of mechanical mixture of 
two crystalline phases occurred. 


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Synthesis and chemical nature of the products of Со(ІІ) and Mg phosphates coprecipitation

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