Kinetics of acid neutralization by aluminum hydroxide gel.

The rate of acid neutralization by an aluminum hydroxide gel prepared by the reaction of aluminum chloride solution and strong ammonia solution was studied. The decrease in acid-consuming capacity during aging as measured by the USP test is due to a decrease in the rate of reaction rather than to a decrease in equilibrium reactivity. The reactivity profile has three phases, which are shown to be related to the structure of the gel. The rate of loss of reactivity is directly related to the extent of washing.