| An important step in the production of aluminate from bauxite by the Bayer process is the crystallization of alumina trihydrate from caustic aluminate solution, which takes up most of the residence time. Because of the low precipitation rate and lower precipitation yield than theroretical precipitation ratios, study on promoting Gibbsite particles precipitating from caustic aluminate solutions is always hotspot in aluminum industry. In this paper, precipitation of A1(OH)3 from supersaturated sodium aluminate solution processed by ultrasound was investigated, and the mechanism of ultrasound action was explored by the experiment of unseeded precipitation crystal growth , Raman spectrum.The precipitation of A1(OH)3 from supersaturated sodium aluminate solution processed by ultrasound is researched in the difference frenquency and temperature condition.The results indicate that the nucleation,agglomeration of large grain and precipitation rate are promoted by ultrasound, but the A1(OH)3 structure is not changed whether ultrasound or not. The experiment of unseeded precipitation show that the induction time is shorten, the nucleation and crystal growth are promoted by ultrasound. According to the particle size distribution information on sodium aluminate seeded precipitation,the rate expression of each basic process ,which is secondary nucleation, agglomeration or crystal growth on seeded precipitation ,is obtained. Differential reactor is adopted to study the radial growth of crystal. The results appear that the line growth rate of A1(OH)3 obey the rule of A L-McCake whether ultrasound or not.The Raman spectrum analysis show that ultrasound changed the equilibrium of aluminate anion ,thereby affecting the structure of sodium aluminate. Combined with the effect of seeded precipitation and unseeded precipitation with ultrasound ,it can be concluded that the formation of growth unit [A16(OH)|8(H2O)6] was promoted by ultrasound,then the precipitation rate was improved. |
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