Phosphorus (P) removal from freshwater bodies to ultra-low concentrations is fundamental to prevent eutrophication, while its recovery is necessary to close the P usage cycle. Iron oxide-based adsorbents seem promising candidates, being abundant, cheap, and easy to synthesize compounds, with good affinity for P. Affinity is the key parameter when targeting ultra-low concentrations. Also, adsorbent regeneration and re-use is fundamental for the economic viability, hence the adsorbent stability is important. Goethite, (α-FeOOH), is one of the most stable iron (Fe3+) (hydr)oxide species, with higher affinity, but lower adsorption capacity (per kg) compared to other species. Doping could change goethite surface properties, to boost the adsorption capacity, while preserving the high stability and affinity for P. In this work, pure goethite was compared to goethite doped (5%at.) with different elements of different preferential oxidation states: Zn2+, Mn3+, and Zr4+. Doping was successfully achieved for all elements, albeit Zr showed a lower Fe substitution than targeted. Zn doping increased the goethite point of zero charge and adsorption capacity (per mass and per surface area), preserving the high affinity, while Mn- and Zr- doping displayed a decrease in all the parameters. These could be explained with surface protonation as a charge compensation mechanism in Zn2+-for-Fe3+ substitution. The regeneration test showed improved P recovery for Zr- and Zn-doped goethite. All samples remained stable throughout the whole process. This work provides promising insights on doping as a strategy to manipulate iron oxides surface properties and for developing a highly performing and long-lasting goethite-based adsorbent.
Bibliographical noteKAUST Repository Item: Exported on 2023-07-19
Acknowledgements: This work was performed in the cooperation framework of Wetsus, European Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân and the Northern Netherlands Provinces. This research received funding from the Netherlands Organization for Scientific Research (NWO) in the framework of the Innovation Fund for Chemistry, and from the Ministry of Economic Affairs and Climate Policy in the framework of the TKI/PPS-Toeslagregeling. The authors thank the participants of the research theme “Phosphate recovery” for the interest, fruitful discussions, and financial support. A special thanks goes to Pim de Jager and Raimonda Buliauskaitė (Aquacare) for the frequent knowledge exchange and interest in the research, Harm van der Kooi for the technical support, Michel Steenvoorden and Maxim Ariens for the support with Mössbauer spectroscopy related matters, Kees Goubitz (TU Delft) for the support on XRD, Wiel Evers (TU Delft) for the TEM measurements, Jouk Jansen (TU Delft) for the support with SAED analysis, Renata van der Weijden (WUR) for the fruitful discussions, Prashanth Suresh Kumar (Plaksha University) and Terica Sinclair for the support and guidance, Amandine Dronne, Varad Kapur, Maddalena Tigli for the work done together.
ASJC Scopus subject areas
- Waste Management and Disposal
- Process Chemistry and Technology
- Chemical Engineering (miscellaneous)