热活化过程中高岭石中铝的结构变化及酸溶特性

STRUCTURAL TRANSFORMATION AND ACID DISSOCIATION BEHAVIORS OF ALUMINIUM FROM KAOLINITE UNDER THERMAL ACTIVATION

采用热重–差示扫描﹑27Al魔角旋转核磁共振﹑X射线衍射、Fourier红外光谱等方法研究了热处理过程中高岭石中铝的结构变化及其在酸中的溶解行为。研究表明:温度低于450℃时,高岭石铝氧八面体层中铝的结构基本不变,为AlⅥ;450～550℃发生脱羟基反应,高岭石结构水被脱除;550～991℃为非晶态的偏高岭石,铝的配位结构为AlⅣ,AlⅤ,AlⅥ;高于991℃时,逐渐生成γ-Al2O3和莫来石,铝变为AlⅥ和AlⅣ配位结构。溶出实验表明:经热活化后,AlⅣ,AlⅤ,AlⅥ在酸中溶解性能各不相同,偏高岭石中AlV在酸中的溶解性能最好,而莫来石和γ-Al2O3中的AlⅣ和AlⅥ很难在酸中溶解。

The structural transformation and acid dissociation behaviors of aluminum from kaolinite under thermal activation were systematically Studied by thermogravimetric-differential scanning calorimetry, aluminum-27 magic angle spinning nuclear magnetic resonance, X-ray diffraction, and Fourier transform infrared spectroscopy. The results show that A1-O octahedra sheets retain the Al^Ⅵstructure at 450℃, and hydroxyl groups are removed at temperatures from 450 ℃ to 550℃. From 550℃ to 991℃, the coordinates of aluminum are Al^, Al^Ⅴ and Al^Ⅵ in metakaolin, and metakaolin segregates into γ-Al2O3 and crystallizes into mullite at above 991℃, at which temperature, the aluminum＇s structure changes to Al^Ⅵ and Al^Ⅳ The acid dissociation properties of Al^Ⅳ, Al^Ⅴ and Al^Ⅵ are different： Al^Ⅴ from metakaolin is soluble, while Al^Ⅵ and Al^Ⅳ from T-Al2O3 and mullite are difficult to dissolve in acid.