PHASE SYSTEMS MELAMINE-H3PO4-H2O AND MELAMINE-NH3-H3PO4-H2O AT 25-DEGREES-C

The C//3H//6N//6-H//3PO//4-H//2O and C//3H//6N//6-NH//3-H//3PO//4-H//2O phase systems were determined from 0 to 50% P//2O//5 at 25 degree C. Eleven adducts between melamine and H//3PO//4/NH//4H//2PO//4 were isolated, identified, and characterized crystallographically. Below 10% P//2O//5, the solubility of melamine in these systems was less than 0. 3%. Above 30% P//2O//5, the solubility of melamine ranged up to about 8%. The results indicate that the precipitation of melamine-phosphoric acid adducts, especially C//3H//6N//6 multiplied by (times) H//3PO//4, provides a practical process for purifying wet-process phosphoric acid.