Secondary nucleation and growth kinetics of aluminum hydroxide crystallization from potassium aluminate solution

Abstract

Aluminate hydroxide crystallization is a significant process in the recovery of aluminum from aluminum-containing ore with an alkaline method. In this work, two kinetics models for secondary nucleation and growth of aluminum hydroxide crystallization from potassium aluminate solution were developed theoretically. The numerical model based on the population balance equation in conjunction with the supersaturation measured by inductively coupled plasma optical emission spectrometry (ICP-OES) was applied to estimate the kinetic parameters of the crystallization. On the other hand, the kinetics were also evaluated by a semi-empirical power model based on the supersaturation of solution and the chord length distribution (CLD) generated by the focused beam reflectance measurement (FBRM). The activation energies for secondary nucleation and growth in the numerical model were estimated as 55.0 kJ mol−1 and 80.0 kJ mol−1, compared to values of 53.3 kJ mol−1 and 131 kJ mol−1 obtained by the FBRM-based semi-empirical power model. The kinetics of secondary nucleation and growth in both models showed around 4.5 and 2 order of dependence on Al(OH)3 (relative) supersaturation, respectively. Furthermore, the comparisons of results of two methods were discussed.