FeOOH and (Fe,Zn)OOH hybrid anion exchange adsorbents for phosphate recovery

FeOOH and (Fe,Zn)OOH hybrid anion exchange adsorbents for phosphate recovery: A determination of Fe-phases and adsorption–desorption mechanisms

Belloni, C. (TU Delft RST/Fundamental Aspects of Materials and Energy; Wetsus, Centre for Sustainable Water Technology)
Korving, L. (Wetsus, Centre for Sustainable Water Technology)
Witkamp, G. J. (King Abdullah University of Science and Technology)
Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)
de Jager, P. (Aquacare Europe, 'sHertogenbosch)
Dugulan, A.I. (TU Delft RST/Fundamental Aspects of Materials and Energy; TU Delft RID/TS/Instrumenten groep)

2023

Hybrid anion exchange adsorbents (HAIX) seem promising to prevent eutrophication and recover phosphate (P). HAIX consist of an anion exchange resin (AIX) backbone, promoting anion physisorption (outer-sphere complex), impregnated with iron (hydr)oxide nanoparticles (NPs), for selective P chemisorption (inner-sphere complex). In this work, for the first time, as far as we know, Zn-doped iron (hydr)oxide NPs were embedded in AIX, and the performances compared with conventional HAIX, both commercial and synthesized. Zn-doped HAIX displayed improved P adsorption performances. Mössbauer spectroscopy (MS) revealed the goethite nature of the NPs, against the “amorphous hydrous ferric oxide” claimed in literature. The P adsorption comparisons, made in synthetic solution and real wastewater, underlined the crucial role of the NPs for selective P adsorption, while improving the understanding on the competition between physisorption and chemisorption. In pure P synthetic solutions, especially at high P concentrations, physisorption can “hide” chemisorption. This depends also on the anion form of the AIX, due to their higher affinity for multivalent anions, which affects HAIX adsorption selectivity and P desorption. In fact, a mild alkaline regeneration over three adsorption–desorption cycles revealed a complex interaction between the regenerant OH⁻ and the adsorbed P. OH⁻ molecules are consumed to transform phosphate speciation, causing (stronger) P re-adsorption and preventing desorption. Finally, Mössbauer spectroscopy revealed NPs agglomeration/growth after the three cycles plus final regeneration at pH 14. This study provides further understanding on the P adsorption–desorption mechanism in HAIX, drawing attention on the choice of experimental conditions for reliable performance assessment, and questioning HAIX consistent P removal and efficient P recovery in the long-term.

Adsorbent regeneration
Hybrid anion exchange adsorbents
Iron oxide doping
Phosphate adsorption
Resource recovery
Water treatment

http://resolver.tudelft.nl/uuid:fa4ac02c-48f5-445c-adf3-0382b4478bd2

https://doi.org/10.1016/j.cej.2023.145287

1385-8947

Chemical Engineering Journal, 473

Institutional Repository

journal article

© 2023 C. Belloni, L. Korving, G. J. Witkamp, E.H. Brück, P. de Jager, A.I. Dugulan