Aluminum hydroxide crystallization from aluminate solution using carbon dioxide gas: Effect of temperature and time

The influence of temperature and carbonation duration time on the phase, morphology, particle size and purity of aluminum hydroxide produced by carbonation of aluminate solution obtained from sintered nepheline syenite leaching have been studied. Carbonation experiments were carried out at different conditions such as temperature range of 60-90 °C and cooling to room temperature during 8 h, constant temperature of 80 °C during 8 h, time range of 2-10 h and 80 °C. The products were analyzed by XRD, LDS, FESEM and XRF methods. Results show that bayerite was the major phase of aluminum hydroxide for all products; however, amount of gibbsite was formed with bayerite at constant temperature of 80 °C. The particle size distribution of the products was bimodal. The mean particle size of the all bayerite precipitates increased from 8.3 µm at 60 °C to 12.9 µm at 90 °C. The particle size of product decreased slightly from 12.6 to 11.9 µm during constant temperature process. Increasing the carbonation duration time tended to increase the size of the particles and the larger particle size was seen for 4 and 8 h. Morphologies of products were consisted of coarse ovoid-shaped and small spherical particles at all temperatures and times. The product at constant temperature included pseudo-hexagonal prism and ovoid-shaped morphology. By increasing the temperature and time of carbonation from 60 to 80 °C and 2-10 h, the amount of Al2O3 in the products increased whereas decreased at 90 °C because of the presence of other elements in the product. The amount of Al2O3 in product at constant temperature decreased whereas a higher amount of silica was existed in the product. According to results, at 80 °C and during 8 h, a single phase product with good particle size and purity can be produced.