[Species distribution and coagulation behavior of covalent bonded aluminum-silicon hybrid flocculants]

Covalent bonded aluminum-silicon hybrid flocculants were synthesized by employing tetraethylorthosilicate (TEOS) and two silane coupling agents [diethoxydimethylsilane (DEDMS), gamma-aminopropylmethyldiethoxysilane (APDES)] as silicon sources, respectively. The distribution of Al species was investigated by 27Al NMR method and the coagulation behavior was evaluated by treating synthetic water containing humic acid. The results of 27Al NMR show that silicon source, Si/Al molar ratio and basicity (B) exhibit effect on the Al species distribution. In the products with APDES as silicon source, the highest content of Al13 was obtained and its amount increases with the rise of Si/Al molar ratio. The effect of B value on the Al species is similar for the three sets of flocculants. The content of monomeric species decreases with the rise of B value. At Si/Al = 0.4, there are no Al13 observed throughout the B value range in the products with TEOS as silicon source. Al13 starts to appear at a higher B value of 1.5 for the products with DEDMS as silicon source and a lower B value of 0.5 for that with APDES as silicon source, respectively. The coagulation results show that, in acidic conditions, the best dosage range of the flocculants with APDES as silicon source is the widest of the three, resulting in the best coagulation efficiency. In alkaline conditions, the coagulation efficiency of the products with TEOS as silicon source is slightly better than the other two.