Abstract:

The aluminium hydroxide was firstly produced by the seeded precipitation process from the sodium aluminate solution with a higher Nk value（mass concentration of sodium oxide in sodium aluminate solution,g/L） for the crystal seed. After filtration and washing,the aluminium hydroxide serosity with the medium grain diameters D₅₀ of about 1.0 μm was grinded and obtained by wet ball-milling in water.The serosity subsequently was added and dispersed into a sodium aluminate solution at a temperature of 35~42 ℃ for 50~70 min,at a final crystal seed ratio of below 0.3%（the ratio of alumina contents between crystal seed and solution）.Then the new serosity was added into a sodium aluminate solution with a lower N_k value and a temperature of 58~70 ℃,after a retention time of about 35 h the sodium aluminate solution was filtered,the filter cake was washed and dried.The aluminium hydroxide powder with a particle size of about 2.0 μm was obtained.Characterization of XRD and SEM indicated that the product was gibbsite with pseudo-hexagonal or tetragonal block shape.And several important conditions of influencing the particle size were also discussed.The process solved effectively the accumulatiton problem of impurities in the aluminium hydroxide production process and had the lower production cost.

Key words: super-fine aluminum hydroxide, sodium aluminate solution, seeded precipitation, crystal seed ratio, crystal seed