Precipitation of Al(OH)3 crystals from supersaturated sodium aluminate solution irradiated with ultrasonic sound

The influence of ultrasonic irradiation on precipitation of Al(OH)3 crystals from supersaturated aluminate solution has been investigated under batch condition of isothermal crystallization. The results indicated that, the precipitation rate was greatly increased by ultrasonic irradiation. Compared with general process, the time of precipitation ratio from 0% to 45% was reduced about 15 h under the irradiation of 20 kHz, and also 33 kHz. The effect of ultrasound on the precipitation process varies with ultrasound frequency. Irradiation of 33 kHz ultrasound shortens the induction period and increases the second nucleation, while 20 kHz enhance agglomeration and growth of Al(OH)3 which result in the increasing of the average diameter of final product by around 5 μm. Raman spectra and UV-absorbance analysis indicated that ultrasound is beneficial to the formation of sodium–aluminate ion pair, which will increase the decomposition rate of supersaturated aluminate solution.