| The study of unseeded precipitation of supersaturated caustic solution is necessary for the investigation of the Al(OH)3 crystallization mechanisms.Due to the limitation of experimental methods, determination of the critical stable nucleus size,interfacial tension,the order of nucleation remains elusive.Classical homogeneous nucleation theory is employed to describe the kinetics of the Al(OH)3 nucleation related with induction period,which is detected by traditional solution methods such as turbidity,conductivity,concentration and so on.Homogeneous nucleation of Al(OH)3 crystals from synthetic, optically clear caustic aluminate solution has been investigated with the application of a novel online conductivity analyzer and conductometric detection cell.Unseeded,isothermal,batch crystallization experiments were performed at 323K,328K,333K and solution ratio of Na/Al=1.33 with Na2Ok concentration in the range of 50～110 g/L.The homogeneous nucleation induction period was detected.The nucleation kinetics showed a seventh-order dependence upon Al2O3 relative supersaturation and a strong temperature effect.Activation energy of 50.2 kJ/mol and interfacial energy of 35 mJ/m2,the critical nucleus size of 1.5～2.0μm,agreed well with literature.The Gibbs free energy change of critical nuleus was also observed.The research suggests that the mechanism nucleation is homogeneous and chemical reaction controlled.It is pertinent to note that this self-made conductivity analyzer and conductometric detection cell are highly sensitive for detecting the formation of crystals,and are well suited for determining the induction period of Al(OH)3 crystallization with high efficiency when compared with traditional solution methods. |
PDF Full Text Request