Chemical state of Fe3+ in a Fe3+-type cation exchange resin for the removal and recovery of phosphate ions and the adsorption mechanism of phosphate ion to the resin

Onchanok Juntarasakul, Kotaro Yonezu, Daisuke Kawamoto, Hironori Ohashi, Yasuhiro Kobayashi, Takeharu Sugiyama, Koichiro Watanabe, Takushi Yokoyama

Research output: Contribution to journalArticlepeer-review

Abstract

To apply the Fe3+-type cation exchange resin, Fe3+-type UBK 10, which is an effective adsorbent of selenite ions, for the removal and recovery of phosphate ions (PO43−), the adsorption mechanism of PO43− to the Fe3+-type UBK 10 resin was investigated. To elucidate the aforementioned mechanism, the chemical state of Fe3+ in the Fe3+-type UBK 10 resin and the adsorption mode of PO43− into the adsorbent were examined via 57Fe Mössbauer spectroscopy and Fe and P K-edge X-ray absorption spectroscopy. The optimum pH for the adsorption of PO43− was found to be approximately 6 and the adsorbed PO43− was rapidly desorbed using 6 mol dm-3 hydrochloric acid (HCl) through the conversion of Fe3+ to FeCl4-, which is practical for the removal and recovery of PO43−. The Fe K-edge X-ray absorption near-edge structure (XANES) spectra showed, through the appearance of three isobestic points, that Fe3+ in the Fe3+-type UBK 10 resin exists as the following four species in equilibrium, depending on the pH: two monomeric hydrolytic species of ferric ions, (-S)2FeOH and (-S)Fe(OH)2, a μ-oxo dimer with corner sharing structure, (-S)2Fe-O-Fe(S-)2, and a dihydroxo dimer with edge sharing structure, (-S)2Fe-(OH)2-Fe(S-)2 (S: SO3 group in UBK 10). It should be emphasized that a PO43− can combine with a (-S)2Fe-(OH)2-Fe(S-)2 site at pH of 6, which is an optimum pH for adsorption of PO43−, forming a bidentate-binuclear configuration, (-S)2Fe-(OH)2(OPO2O)-Fe(S-)2, through the formation of Fe-O-P bonds.

Original languageEnglish
Article number125314
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume605
DOIs
Publication statusPublished - Nov 20 2020

All Science Journal Classification (ASJC) codes

  • Surfaces and Interfaces
  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

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