Regeneration Process of Ammonia-Absorbed Zirconium Phosphate to Zirconium Phosphate

Zirconium phosphate [Zr(HPO4)(2)center dot H2O] absorbs 2 mol(NH3)/mol[Zr(HPO4) (2)center dot H2O] with a low equilibrium plateau ammonia concentration of around 1 ppm in water. In this study, in order to investigate the regeneration process of ammonia-absorbed zirconium phosphate [Zr(NH4PO4)(2)center dot H2O], Zr(NH4PO4)(2)center dot H2O was heat-treated above 353 K under an inert gas. Then, the structures of the heat-treated samples were evaluated using powder X-ray diffraction and thermogravimetry-mass spectrometry measurements. Zr(NH4PO4)(2)center dot H2O started to desorb ammonia and the crystal water at 353 K. Then, Zr(NH4PO4)(2)center dot H2O was changed to the anhydrous monoammoniate [Zr(NH4PO4)(HPO4)] at 473 K and formed anhydrous zirconium phosphate [Zr(HPO4)(2)] at 673 K. The anhydrous zirconium phosphate and the anhydrous monoammoniate reabsorbed ammonia in ammonia water. Those initial absorption rates were small compared with Zr(HPO4)(2)center dot H2O. The slow kinetics of the anhydrous zirconium phosphate corresponded to the small interlayer distances. The ammonia concentration composition isotherms indicated that the anhydrous zirconium phosphate and anhydrous monoammoniate have a low ammonia equilibrium plateau concentration of around 1 ppm in ammonia water. Zr(NH4PO4)(2)center dot H2O is formed from Zr(NH4PO4)(HPO4) by the reabsorption of ammonia and water after 1-10 cycles. We found that zirconium phosphate is an ammonia remover which can be used repeatedly at 473 K.