Influence of magnetic field on the seeded precipitation of gibbsite from sodium aluminate solution

Sodium aluminate solutions were exposed to an electromagnetic field (0 < H < 250 kA/m) for a short time. The electrical conductivity and the structure of the exposed aluminate solutions were then measured as a function of magnetic field intensity. Furthermore, the influence of magnetic field on the gibbsite precipitation from sodium aluminate solution was also investigated. It is found that the electrical conductivity of the sodium aluminate solution with low caustic molar ratio of Na2O to Al2O3 varies with the intensity of the applied magnetic field and reaches a maximum in the presence of a magnetic field ranging from 50 to 70 kA/m. In addition, the electrical conductivity of sodium aluminate solution does not return to the initial value after shutting off the magnetic field, and the memory of magnetic treatment extends beyond two days. IR spectra of sodium aluminate solutions suggest that magnetic field treatment modifies the structure of the aluminate solution. Moreover, the gibbsite precipitation from sodium aluminate solution would be promoted when the aluminate solution was magnetically treated with a magnetic field of 52 kA/m. SEM and PSD results of the gibbsite products show that the precipitates are made up of globular particles in uniform size. It is concluded that the precipitation of gibbsite from sodium aluminate solution could be promoted by adjusting the structure and the physicochemical properties of aluminate solution by introducing a suitable magnetic field.