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 f rom caustic aluminate solutions of aluminum-air batteries are studied in a laboratory batch isothermal precipitator. A method using high see d charges varying from 200 to 800 kg of AI(OH)(3) per m(3) of aluminat e solutions is developed for the rapid determination of kinetic consta nts of the crystal growth rate expression. Thus, it is shown that grow th rate increases with the square of the supersaturation, and the temp erature effect on the growth rate follows an Arrhenius relation with a n activation energy term of E/R = 8164 K. It is also shown that the gr owth 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 characte rized by very low crystal growth rates.