Aluminum hydroxide crystallization from aluminate solution using carbon dioxide gas: effect of pH and seeding

The effect of pH and seeding were studied on phase, particle size, morphology, purity and conversion of aluminum hydroxide produced by carbonation of solution of sintered nepheline syenite alkaline leaching. Carbonation experiments were done at initial pH range of 9-11 and variable during carbonation, seed ratio range of 0.5-2 and constant temperature and time of 80 degrees C and 8 h respectively. The main phase of products at pH of 9, 10 and 11 were dawsonite, a mixture of dowsonite and imogolite and bayerite respectively. Adding seed did not change the phase of products but improved the particle size and conversion of the products. The particle size increased due to agglomeration and crystal growth mechanisms but by increasing the seed ratio crystal growth was the dominant mechanism. According to results, at 80 degrees C, initial pH 11 and variable during carbonation and seed ratio of 2, a desirable product can be produced.