Aluminum chlorohydrate II: Physicochemical properties

Determination of the chloride content of aluminum chlorohydrate by a chloride-selective electrode indicated that γcl− 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 on 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)127+ 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 polycation. 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)127+ since the spherical nature and high uneven charge of the complex make stacking difficult.