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

Dynamic light scattering was used to characterise gibbsite particle nucleat ion and growth in supersaturated alkaline sodium aluminate solutions. The s upersaturation and temperature conditions investigated include those experi enced in the crystallisation step of Bayer processing. Nuclei growth rates, which are constant for a period of several hours, are dependent on the squ are 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 u nder equivalent conditions. Similarities and differences are discussed with . respect to the rate determining steps and growth mechanisms during gibbsi te crystallisation. For nuclei less than 200 nm the growth mechanism is dom inated by agglomeration or Ostwald ripening, whereas for larger nuclei, sin gle particle growth is the dominant mechanism. (C) 1999 Elsevier Science B. V. All rights reserved.