Compared with crystallization of aluminium trihydroxide without treatment of ultrasound, the time of precipitation was reduced from 30 h to 15 h when the precipitation ratio was 45% under 20 kHz and 33 kHz ultrasound irradiation. The enhancement effects of two frequencies are not the same. Irradiation with 33 kHz ultrasound could shorten the induction time, increase the secondary nucleation and enhance the agglomeration. Use of 20 kHz ultrasound, however, led to prolong induction time, increase agglomeration and enhance the growth of aluminium trihydroxide. As a result, the average diameter of aluminium trihydroxide product was increased 3.7 μm. But the autoprecipitation of sodium aluminate solution was not enhanced under ultrasound irradiation.

Key words: ULTRASONIC, ALUMINIUM HYDROXIDE, CRYSTALLIZE, NUCLEATION, AGGLOMERATION, CRYSTAL GROWTH