Abstract: Decomposition of sodium aluminate solution using methanol for production of coarse Al(OH)3 particles was studied. The effects of reaction temperature, concentration of caustic aluminate solution, caustic ratio, silica index, stirring intensity and methanol amount on the particle size and morphology of Al(OH)3 were examined. The results showed that spherical coarse particles of Al(OH)3 could be obtained under the conditions of solution composition with about 180 g/L Na2O, 1.5~1.6 molecular ratio and mass ratio of alumina to silica larger than 550, volume ratio of solution to methanol 1:1, and temperature 60 ℃. Their average particle size could reach about 80 mm. The longitudinal and radial growth speeds of Al(OH)3 growth unit were changed by addition of methanol. The radial growth speed was faster and growth unit became thinner with the more amount of methanol, for instance, with a value of about 100 nm when volume ratio of sodium aluminate solution to methanol was 1:1. Furthermore the crystal structure of Al(OH)3 particles changed from Bayerite to Gibbsite with the increase of temperature while the weight loss agreed with the theoretical value by DSC-TGA analysis.

Key words: methanol, sodium aluminate solution, aluminum hydroxide, morphology, particle size distribution

摘要： 对甲醇分解NaAl(OH)4溶液制备大颗粒Al(OH)3进行了工艺研究，考察了分解温度、分子比(Na2O/Al2O3摩尔比)、Na2O浓度、硅量指数(Al2O3/SiO2质量比)、搅拌速度和甲醇用量对产品粒度和形貌的影响. 结果表明，在NaAl(OH)4溶液的Na2O浓度为180 g/L、分子比为1.5~1.6，硅量指数550以上及甲醇与NaAl(OH)4溶液等体积的优化条件下，控制分解温度60℃，可得到平均粒径达80 mm的球形Al(OH)3. 甲醇的加入改变了Al(OH)3生长基元的径向和轴向生长速率，甲醇量越大，径向生长速率越快，生长基元越薄. 当甲醇与NaAl(OH)4溶液体积比为1:1时，Al(OH)3生长基元的厚度在100 nm左右. 随分解温度升高，Al(OH)3由Bayerite型向Gibbsite型转变，热重-差热值与理论值吻合.

关键词: 甲醇, NaAl(OH)4溶液, Al(OH)3, 形貌, 粒度分布