Solubility of Dicalcium Phosphate Dihydrate (DCPD) and Tricalcium Phosphate (TCP) in Some Aqueous Salt Solutions.

Abstract

The solubility of DCPD and TCP in salt solutions of Na2SO4, NaCl, KCl, MgCI2, CaCl2, and a mixture of Na2SO4, MgCl2 and CaCl2 was tested in comparison with the solubility of the phosphate compounds in distilled water. Five concentrations (500, 1000, 2500, 5000 and 7500 ppm) of the salt solutions were employed. Extractable P from DCPD was found to increase when the ionic strength of the saline solutions was increased. Solution of P was higher in the monovalent salt solutions relative to the divalent salt MgCl2 and distilled water. On the other hand, extractable P from TCP decreased as the ionic strength of the NaCl and KCl was increased, but an increase in the ionic strength of the Na2SO4 and MgCl2, led to an increase in solution P. However, an increase in ionic strength of the CaCl2 solution had a depressing effect upon the solubility of both phosphate compounds. The investigations seem to suggest the following order of arrangement of the extracting solutions with respect to liberation of phosphate from the two compounds studied: For DCPD: Na2SO4 > NaCl > KCl the mixed salt solution > MgCl2 > CaCl2. For TCP: Na2SO4 > KCl > NaCl > MgCl2 > CaCl2