The synthesis of the potassium magnesium phosphates was studied by the oxidative decomposition method using EDTA-metal chelate. As a result, three potassium magnesium phosphates were successfully synthesized. These compounds are KMg
7 (PO
4)
5·12H
2O (described as KM7P5H12), K
9Mg
10 (PO
4)
9 (OH)
2·8H
2O (K9M10P9H8) and KMg
4 (PO
4)
3·7H
2O (KM4P3H7).
These potassium magnesium phosphates were prepared under several conditions as follows : concentrations of K
+ ion, Mg
2+ ion, phosphate ion and H
2O
2, and initial pH. KM7P5H12 were prepared under the conditions of the Mg
2+ /P (P : phosphoric oxyacid) molar ratio (described as R value) = 1.0 and low concentration of K
+ ion and H
2O
2. K9M10P9H8 was prepared under the conditions of R value = 0.1 and the high pH reagion. KM4P3H7 was prepared under the conditions of R value = 0.2 and low concentration of H
2O
2.
Three potassium magnesium phosphates did not change by aging them in KCl solution at 98°C, but KM7P5H12 and KM4P3H7 changed to K9M10P9H8 by aging them in K
2HPO
4 solution at 98°C. The relationship of phases equilibilium between three potassium magnesium phosphates was revealed.
View full abstract