INVESTIGATION OF THE UNSEEDED NUCLEATION OF GIBBSITE, AL(OH)(3), FROMSYNTHETIC BAYER LIQUORS

This paper presents the novel application of multi-angle laser light s cattering (MALLS) together with transmission electron microscopy (TEM) , powder X-ray diffraction (XRD) and In-lens field emission scanning e lectron microscopy (IFESEM) for studying the unseeded nucleation of gi bbsite from synthetic Bayer liquor (sodium aluminate). The effects of supersaturation in the absence or presence of a known inhibitor (sodiu m gluconate) were examined. In each series of experiments, both homoge neous and heterogeneous primary nucleation mechanisms were observed. F or the unpoisoned liquor used in this work the nucleation appeared to be homogeneous for supersaturation ratios greater than 2.51 +/- 0.07 a nd heterogeneous for lower values. From the induction period measureme nts, the interfacial tension at 60 degrees C was determined to be 45 /- 6 mJ m(-2), and used to predict the critical nucleus size of 1.2 +/ - 0.1 nm. This was then compared to the measured particle sizes from s amples examined by TEM (10-40 nm) and IFESEM (similar to 50 nm). A cry stallite size was determined by XRD to be 22 +/- 6 nm, The presence of sodium gluconate inhibitor extended the region over which homogeneous nucleation is dominant, but did not affect the measured value of the interfacial tension and hence the critical nucleus size. This is consi stent with the poison inhibiting processes on the solid phase and not the solution phase. (C) 1998 Published by Elsevier Science B.V. All ri ghts reserved.