Features of the Behavior of Calcium and Magnesium Phosphate Sorbents in Water and Electrolyte Solutions

The hydrolytic stability of calcium and magnesium phosphates in aqueous solutions was studied in a wide pH range and in the presence of NaCl and CaCl2 electrolytes: calcium hydrogen phosphate and tricalcium phosphate are stable at pH 4.5‒10.0, and hydroxyapatite, at pH 3.0‒12.0. An increase in the ratio of the solution volume to the weight of phosphates from 250 to 500 mL/g leads to an increase in the degree of hydrolysis by a factor of 1.4–1.9. In the presence of 0.01 M NaCl and 0.001 M CaCl2, all samples exhibit high hydrolytic stability, and an increase in concentration to 1.0 M NaCl and 0.01 M CaCl2 results in deprotonization of hydrophosphate ions and the transformation of magnesium phosphates to calcium phosphates.