Ultrasound On The Bayer Seed Process

Based on the deep research on gibbsite precipitation process and the practical and theoretical combination of chemical reaction improvement under ultrasound, aluminate sodium solution is disposed under ultrasound to enhance precipitation rate and shorten precipitation time. Results show that it is a good method and has broad application foreground because it has obvious effect and the flow of disposing is simple.The main results are as follows:1.Orthometric experiments are made with the factors of the concentration of sodium aluminate liquor, the method of treatment, temperature, ultrasonic power and the sonication time using ultrasonic cleaner. The order of the factors which affect the precipitation ratio and the optimum condition for the improvement of aluminium hydroxide precipitation under ultrasonic cleaner has been got. Compared with the crystallization of aluminium hydroxide without the treatment of ultrasound, the precipitation ratio is increased by 9% when the reaction took place for 6 h. At the same time the time of precipitation is reduced from 30 h to 15 h when the precipitation ratio is 45%.2.An equipment with ultrasonic horn, which has three frequencies and adjustable power, has been designed based on the development of sonochemistry and industry flow of Bayer Process.3.Used the equipment with ultrasonic horn, combining and applying the theory of cavitation, the effect of ultrasonic frequency, power and sonication time on the precipitation is found that the precipitation speed can be improved and the precipitation time can be shortened when the power is up to the threshold value.4.Combined the structure theory of aluminate sodium liquor, the effect of concentration of aluminate sodium, the molecule ratio of Na2OIAl2O3 and temperature of reaction on precipitation is indicated that the decomposition of A120(OH)62 and the transformation of Al(OH)4?to transition structure under ultrasound are effected by the variety of liquor quality.5.The precipitation process under ultrasound has been studied. It is found that induction time and secondary nucleation are changed, but the autoprecipitation of aluminate sodium liquor is not enhanced under ultrasound. Agglomeration and growth of aluminium hydroxide under ultrasound are increased though the enhancements under three frequencies are not the3sarne.6. The growth rate equation without ultrasound is concluded as fOllow:P = --M = l0' x ..p(--ty) x (A -- A. )'of RTThe growh rate equation under ultrasound is the same as that of withoutultrasound, with exception of activation energy reduced and thefrequency factor changed.7. Wan spectra of l08, l40g/l aluminate sodium are compared with andwithout ultrasound. The peak near 540cm-', which is the representation ofAl,O(OH).'-, is disappeared and the peak near 625cm-l,which is therepresentation of Al(OH).-', is reduced. It is deduced that Al,O(OH),'- isdecomposed entirely and Al(OH).-' is changed to the transition smictUretreated by ultrasound.