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

A determination of Fe-phases and adsorption–desorption mechanisms

Journal article (2023)

Authors

C. Belloni Wetsus, European Centre of Excellence for Sustainable Water Technology, RST/Fundamental Aspects of Materials and Energy - AS
L. Korving Wetsus, European Centre of Excellence for Sustainable Water Technology
G. J. Witkamp King Abdullah University of Science and Technology
E.H. Brück RST/Fundamental Aspects of Materials and Energy - AS
P. de Jager Aquacare Europe, 'sHertogenbosch
A.I. Dugulan RST/Fundamental Aspects of Materials and Energy - AS , RID/TS/Instrumenten groep
Research Group
RST/Fundamental Aspects of Materials and Energy (AS) (TU Delft)
Copyright: © 2023 C. Belloni, L. Korving, G. J. Witkamp, E.H. Brück, P. de Jager, A.I. Dugulan
DOI: https://doi.org/10.1016/j.cej.2023.145287
Resource recovery Water treatment Phosphate adsorption Adsorbent regeneration Hybrid anion exchange adsorbents Iron oxide doping
More Info
expand_more

Published Date

2023

Language

English

Faculty

Applied Sciences

Department

RST/Radiation, Science and Technology

Research Group

RST/Fundamental Aspects of Materials and Energy

Abstract

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.