Effect of seed density

Literature has revealed limited kinetic data on secondary nucleation of alumina trihydrate in the precipitator of the Bayer Process for alumina production. A batch agitated, isothermal, three litre crystallizer was used in the study. A Coulter-Counter was utilized as the particle sizing equipment. The effects of seed density, supersaturation and temperature on secondary nucleation were investigated. Maximum nucleation rates were found to occur at about 70 C and for any crystallization temperature, the nucleation rate passed through a maximum. The correlated equation for the effective secondary nucleation rate of alumina trihydrate is... 

Effect of Seed Density. Figure 3 shows the results obtained for batch nucleation runs at 70 C for various seed densities. The seeds used were taken directly from alumina trihydrate bags supplied by Alcoa of Australia Ltd. 

Table I. Effect of Seed Density on Total Number of Nuclei...

Figure 3(a). Effect of seed density on nucleation at 70 C. Number of crystals 1.2 im) vs crystallization time. 

Saini, S. and T. M. Wick 2003. Concentric cylinder bioreactor for production of tissue engineered cartilage Effect of seeding density and hydrodynamic loading on construct development. Biotechnol Prog 19(2) 510-21. 

Effect of Seed Size. The effect of seed size on the nucleation rate was investigated by using screened seeds of sizes in the range of 53 - 63,63 - 75 and 75 - 90 im. Hie se density and temperature used in tiiis study were 200 g/l and 70 C respectively. The results are illustrated in Figures 4(a) and 4(b). 

Figure 4(a). Effect of seed size on nucleation at 70°C, 200 g/1 seed density. Desupersaturation curve. 

Fig. 8 Effect of seed crystals on stability of population density...

Methyl methacrylate-butyl acrylate copolymer latex particles were synthesised by both seeded and unseeded semicontinuous emulsion copolymerisation. Particle size and surface charge densities were characterised by TEM and potentiometric and conductimetric titrations. An investigation of the effect of surface density on zeta-potential is described. 18 refs. 

In all such laboratory studies, plant conditions and compositions should be employed as far as possible. Agglomeration rates tend to increase with the level of supersaturation, suspension density and particle size (each of which will, of course, be related but the effects may exhibit maxima). Thus, agglomeration may often be reduced by operation at low levels of supersaturation e.g. by controlled operation of a batch crystallization or precipitation, and the prudent use of seeding. Agglomeration is generally more predominant in precipitation in which supersaturation levels are often very high rather than in crystallization in which the supersaturation levels are comparatively low. 

Effect of Temperature. To study the effect of temperature, the nucleation runs were conducted by keeping all the other variables constant i.e. seed density = 200 g/l, impeller speed at 350 rpm and solution concentration adjusted such that the initial absolute supersaturation (AG C ) r 0.9 at the temperatures studied. The results are shown in Figures 5(a) and 5(b). 

Figure 5(b). Effect of temperature on nucleation for seed density of 200 g/1. Nucleation rate vs supersaturation. 

Fig. 3.8. Effect of amount of seeds added and their size on time required to reach a bulk density of 300 g/1 during dry granulation of carbon black in a laboratory drum [17,36]. (Carbon black pellets used as seeds (L/S)o is the initial volume ratio of fines to seeds.)...

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