Aluminum chlorohydrate II: Physicochemical properties.

Determination of the chloride content of aluminum chlorohydrate by a chloride-selective indicated that gamma Cl leads to 1. IR analysis demonstrated that chloride was exchanged readily by nitrate and that the IR bands of the anion were not perturbed significantly. Thus, chloride is believed to act as a counterion. A high positive charge is predicted based o the critical coagulation concentration of aluminum chlorohydrate and the stability of aluminum chlorohydrate to attack by protons, as demonstrated by pH-stat titration Potentiometric titration with sodium hydroxide showed adsorption of hydroxyl anions initially, but a higher pH than expected was observed at the end-point. This behavior is consistent with the Al13O4(OH)24(H2O)7+12 complex, which would adsorb hydroxyl anions initially and in which the central tetrahedral aluminum is shielded from the added hydroxyl anions. The reaction rate with ferron (8-hydroxy-7-iodo-5-quinolinesulfonic acid) suggests that the major species in aluminum chlorohydrate is a large aluminum poly-cation. A platey morphology for lyophilized, air-dried, and spray-dried aluminum chlorohydrate was observed by scanning electron microscopy. The platey appearance is consistent with the structure of Al13O4(OH)24(H2O)7+12 since the spherical nature and high uneven charge of the complex make stacking difficult.