A dynamic light scattering investigation of nucleation and growth in supersaturated alkaline sodium aluminate solutions (synthetic Bayer liquors)

Abstract

Dynamic light scattering was used to characterise gibbsite particle nucleation and growth in supersaturated alkaline sodium aluminate solutions. The supersaturation and temperature conditions investigated include those experienced in the crystallisation step of Bayer processing. Nuclei growth rates, which are constant for a period of several hours, are dependent on the square of supersaturation and on temperature through an Arrhenius relationship. The activation energy for nuclei growth has been determined to be 51±5 kJ mol −1. Comparisons are drawn between nuclei growth behaviour in the nanometer size range and the growth of micrometer sized gibbsite crystals under equivalent conditions. Similarities and differences are discussed with respect to the rate determining steps and growth mechanisms during gibbsite crystallisation. For nuclei less than 200 nm the growth mechanism is dominated by agglomeration or Ostwald ripening, whereas for larger nuclei, single particle growth is the dominant mechanism.