Intensification of precipitation of gibbsite from seeded caustic sodium aluminate liquor by seed activation and addition of crown ether

New methods were explored to intensify the precipitation of gibbsite from seeded caustic sodium aluminate liquor: gibbsite crystal seed was activated by boiling in distilled water and 15-crown-5-ether was used as additive in this investigation. Both methods promoted precipitation under selected conditions. The stability of pure sodium aluminate solution decreases in the presence of a high concentration of 15-crown-5-ether, this effect was examined using 27Al NMR. Particle size analyses showed that the product became finer when either intensifying method was introduced. The intensifying mechanism was proposed as follows: desorption of organic contaminants and adsorption of additive molecules primarily take place on the surface of large seed particles where active sites are denser, thus precipitation is promoted; available supersaturation for the small seed particle decreases as the large seeds grow rapidly thereby decreasing agglomeration giving a finer product. Scanning Electronic Microscope (SEM) images of samples support this mechanism.