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Sorption fixed-bed column experiments were performed using a titanium phosphate ion-exchanger composed of −H2PO4 units [TiO(OH)(H2PO4)·H2O]. Model mine water containing five divalent metal ions (Cu...

The structures of hydrated phosphoric acid and phosphate ions (H2PO4–, HPO42–, and PO43–) in aqueous solution have been determined by P K-edge EXAFS and large angle X-ray scattering (LAXS). The P–O bond distance in all phosphate species studied is close to 1.53 A. The P–(O)···Oaq distances have been refined to ca. 3.6 A from the LAXS data giving a P–O···Oaq bond angle close to tetrahedral, suggesting that each oxygen or OH group of phosphoric acid and dihydrogen phosphate, on average, hydrogen bind three water molecules. The (P−)O(−H)···Oaq and (P−)O···(H−)Oaq hydrogen bonds in hydrated phosphoric acid and the H2PO4– ion are shorter than the hydrogen bonds in neat water. This supports previous infrared spectroscopic studies claiming that the hydrogen bonds in hydrated phosphoric acid and phosphate ions are stronger than the hydrogen bonds in neat water. Phosphoric acid and phosphate ions can therefore be regarded as structure making solutes. This is the first study applying transmission mode X-ray absorpt...

A titanium phosphate sorbent with linked active units (LTP) is synthesized. XRD, 31P MAS NMR, and TGA techniques are used to disclose the relation between the ion-exchange units of −HPO4 (crystalline α-TiP) and of −H2PO4 (amorphous TiP1) type. The reported kinetics data of TiP1 sorbent in batch mode have been reprocessed according to the nonlinear approach in order to explore further the sorption mechanism. It was found that the data could be well described by the pseudo-second-order model in the case of Ni2+ ions. Consequently, fixed-bed column sorption experiments of Ni2+ ions on LTP were designed, and the effects of both the amount of nickel(II) ions in the feed solution and the flow rates on the sorption equilibrium were studied. The ion-exchange capacity is estimated to be 1.6 meq·g–1 during the first four cycles before decreasing to 1.2 meq·g–1 for cycles five and six. The experimental data were simulated following the Thomas model, and desorption experiments with HCl were performed. Observations sh...

Amorphous titanium phosphate ion-exchangers are often of a “mixed type”, i.e., they contain a mixture of –HPO4 and –H2PO4 active groups. Their synthesis requires careful handling to obtain the same ...

This work focuses on the synthesis of titanium phosphate (TiP1) ion-exchanger containing solely H2PO4-groups. Based on the elemental analyses, TG, 31P MAS NMR, XRD and Raman data, the formula TiO(OH)(H2PO4)·H2O is assigned to TiP1. The synthesis requires a mild heating at 70–80 °C for a short period of time, followed by filtration and HCl-washing of the TiP1 powder. The layered nature and low crystallinity of this sorbent is confirmed by powder XRD technique. The existence of micro and mesopores in the material is established using BET method. The Na+ capacity of TiP1 is determined to be 6.3 meq g−1 which is the highest value reported for H2PO4-based sorbents. The presence of H2PO4 groups is expected to considerably increase both the pH-working range of the TiP1 sorbent and its exchange capacity towards divalent metal ions. All data for TiP1 are compared to the data for amorphous TiP containing mostly HPO4 groups.