Preparation of sodium aluminate from the leach liquor of diasporic bauxite in concentrated NaOH solution

Abstract

A new process to produce monosodium aluminate hydrates (MAH) by fast crystallization from the leach liquor of a diasporic bauxite in concentrated NaOH solution is presented. The crystallization of MAH was carried out easily compared to the precipitation of gibbsite and the effect of agitation, initial concentration of sodium aluminate, seed amount and the presence of red mud were systematically studied in a batch crystallizer. The apparent kinetics of crystallization followed a second order rate law with an apparent activation energy for MAH crystallization of 38.0 kJ/mol which implies a surface-diffusion controlled mechanism. X-Ray diffraction and scanning electron microscopy identified the structure of MAH as Na 2O·Al 2O 3·2.5H 2O with a flake crystal morphology. The molar ratio α of Na 2O to Al 2O 3 in the MAH products was < 1.2 after a simple wash by dilute sodium aluminate.