Sodium Aluminate Solution Seed Agglomeration Process,

Seeded precipitation of sodium aluminate solution is an important process for alumina production. Agglomeration is the critical process for the controlling of the the particle size and strength of alumina. Because of the complication of sodium aluminate solution, it's essential to investigate the influences of difference process conditions on agglomeration further during the seeded precipitation of sodium aluminate solution, although structure of sodium aluminate solution, the mechanism of precipitation and precipitation kinetics have been studied by many researchers.The industrial seeds are used in our experiments. The effects of the crystallization temperature, seed mass, stirring rate, caustic concentration of liquor, molecular ratio on agglomeration were investigated. The mechanism of agglomeration was proposed. Conclusions were made as follows:1. The period of agglomeration was determined as about 6.5~9h by the curves of the crystal size distribution of aluminium hydroxide samples in the experiments. The products of aluminum hydroxide were detected to be gibbsite.2. Higher temperature is beneficial to agglomeration when the industrial seeds were used. In the later process of agglomeration, the decomposition rate of the solution would decline, the particles of+45μm in the product would increase, the degree of agglomeration would increase at high temperatures.3. The caustic concentration of the sodium aluminate solution has a great effect on agglomeration. The decomposition ratio of the solution would decrease, the particles size would decrease, the degree of agglomeration would decrease with high caustic concentration.4. The influence of α_K of the solution was similar to the caustic concentration.5. Higher seed masses will increase the decomposition ratio of the solution. The ratio of seed masses of 0.25 was advantageous to enlarge the particle size and increase the degree of agglomeration.6. The seed couldn't suspense at low stirring rate. The degree ofagglomeration will decrease, on the contrary, as the crystal sizes of aluminium hydroxide would be smashed at higher stirring rates.7. By the study of agglomeration kinetics and mechanism, it was found that the agglomeration rate constant of equal size particles was larger than that of inequable size particles. The particles with smaller size difference have larger agglomeration rate constant.8. The particles with larger size in the seeds, in fact, was involved in agglomeration, and during the process, they became larger by agglomerating with the smaller particles.