Regeneration Process of Ammonia-Absorbed Zirconium Phosphate to Zirconium Phosphate

[Image: see text] Zirconium phosphate [Zr(HPO(4))(2)·H(2)O] absorbs 2 mol(NH(3))/mol[Zr(HPO(4))(2)·H(2)O] 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(NH(4)PO(4))(2)·H(2)O], Zr(NH(4)PO(4))(2)·H(2)O 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(NH(4)PO(4))(2)·H(2)O started to desorb ammonia and the crystal water at 353 K. Then, Zr(NH(4)PO(4))(2)·H(2)O was changed to the anhydrous monoammoniate [Zr(NH(4)PO(4))(HPO(4))] at 473 K and formed anhydrous zirconium phosphate [Zr(HPO(4))(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(HPO(4))(2)·H(2)O. 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(NH(4)PO(4))(2)·H(2)O is formed from Zr(NH(4)PO(4))(HPO(4)) 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.