Transformation of planar Mögel Al13 coagulant during the dilution and aging process

Transformation of a novel planar Mögel Al13 (Al13(OH)24(H2O)2415+, simplified as M-Al13) coagulant in the dilution and aging process was investigated with Ferron colorimetric method, electrospray ionization mass spectrometry (ESI-MS) and 27Al NMR spectroscopy. Special attention has been paid to the transformation process of M-Al13 to stereo Keggin Al13 (ɛ-AlO4Al12(OH)24(H2O)127+, simplified as K-Al13). M-Al13 was found to be an unstable aluminum species and could be decomposed into oligomers as Al1, Al2 and Al3 when dissolved in solution. These newly formed oligomers were also found to polymerize into K-Al13 by self-assembly during the dilution process. More K-Al13 species could be continuously formed at the initial aging period of the diluted solution. On the whole, the hydrolysis and aging behavior of planar M-Al13 in aqueous solution is quite different from those of the K-Al13 species, which may provide insight into the structure re-organization mechanism of polymeric Al species in solution.

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► The Mögel Al13 would decompose into oligomeric species at high concentration.
► Mögel Al13 would transform to Keggin Al13 at lower concentration.
► Transformation of Mögel Al13 to Keggin Al13 is a time dependent reaction.
► More Mögel Al13 transformed to Keggin Al13 under longer aging period.
► The concentration profile is used to interpret transformation process.