Complete Column Trials for Water Refinement Using Titanium(IV) Phosphate Sorbents

Abstract

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 show that regeneration and reutilization of the LTP ion-exchanger are possible through at least six cycles. It is revealed that the sorption performances in column conditions could be undoubtedly predicted from the corresponding batch sorption data.

Competitive Sorption of Metal Ions on Titanium Phosphate Sorbent (TiP1) in Fixed-Bed Columns: A Closed-Mine Waters Study

“…The amounts of metal ions sorbed on TiP1 determined from the Thomas model ( q Th ) are in very good agreement with the ones calculated from the experimental data. Similar observations were reported for another TiP system, where the Thomas model was used to describe the sorption of nickel ions . The breakthrough curves of model mine water could not be fitted accurately using the Thomas approach (with the exception of copper) due to the competitive sorption phenomenon that is strongly pronounced when all metal ions are present in equal amounts and/or the sorption equilibrium is maintained.…”

“…For aluminum, the desorption volume is about 70 BV, which is higher than for the other metals. Another study has also shown that it is possible to use HCl as a desorption solution instead of HNO 3 . It is advisible to examine the possibilities of complexation between the acid and the metal to determine the most suitable desorption solution to utilize.…”

“…Similar observations were reported for another TiP system, where the Thomas model was used to describe the sorption of nickel ions. 23 The breakthrough curves of model mine water could not be fitted accurately using the Thomas approach (with the exception of copper) due to the competitive sorption phenomenon that is strongly pronounced when all metal ions are present in equal amounts and/or the sorption equilibrium is maintained. Besides, the Thomas constants' errors were assessed by the Monte Carlo method using 1000 random simulations.…”

“…Another study has also shown that it is possible to use HCl as a desorption solution instead of HNO 3 . 23 It is advisible to examine the possibilities of complexation between the acid and the metal to determine the most suitable desorption solution to utilize. A slower flow rate or a higher concentrated acidic solution could be used to bring down the desorption volume, but all shall be performed according to industrial-case specifics.…”

“…Our exploratory data on the TiP1 and the reported data for LTP (with active TiP1 part) show that the column efficiency can be affected after the sixth regeneration cycle and that it has been kept at about 70% for the single component system. 23 ■ CONCLUSIONS…”