Structure of Commonly Used Aluminum Sources

The synthesis of zeolites is usually conducted in slightly basic media via the condensation of silicate and aluminate. Therefore, studies on the structure and state of commonly used aluminum sources in solution are essential for studies on the synthesis of zeolites. 

Studies[20] on the polymerization state of aluminate in solution have been conducted for a long time and it has been found that the pH of the solution directly affects this state in solution. In basic solution, the main form of aluminate is AI(OH)4. When the 

The bond angle of the formed A102 is 132°. In sufficiently acidic solutions, the aluminum exists as hydrated Al3+ ion. From pH 

the aluminous cation changes by progressive hydrolysis according to the formula [Al1304(0H)24+ y.(H20)12 ](7 +, where y 0. These complex cations may co-exist with simpler species such as Al(OH)2+ and Al(OH)2+, as it is estimated that unit values of concentration ratio of certain pairs of ions occur at the following pH values  

One may summarize the various observations as follows. In strongly acid solutions, A1(H20)63+ is dominant. From pH = 6 upwards, Al3+ becomes wholly insignificant, polymeric ions are no longer important, and Al(OH)4 or A102 are dominant. The important Al(OH)4 is tetrahedral in structure and so should favor tectosilicate formation with silicates condensed into a 3-D framework. 

---