A rapid method for the determination of growth rate kinetic constants: Application to the precipitation of aluminum trihydroxide

The growth rate kinetics of crystallization of aluminum trihydroxide from caustic aluminate solutions of aluminum-air batteries are studied in a laboratory batch isothermal precipitator. A method using high seed charges varying from 200 to 800 kg of AI(OH)(3) per m(3) of aluminate solutions is developed for the rapid determination of kinetic constants of the crystal growth rate expression. Thus, it is shown that growth rate increases with the square of the supersaturation, and the temperature effect on the growth rate follows an Arrhenius relation with an activation energy term of E/R = 8164 K. It is also shown that the growth rate of aluminum trihydroxide is very sensitive to impurities in the aluminum electrodes and to additives in the electrolytic solution. This method can be extended to other precipitation reactions characterized by very low crystal growth rates.