Tuning the stability and phosphate sorption of novel MnII/IVFeII/III layered double hydroxides

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Layered double hydroxides (LDHs) have been intensively studied for phosphate (Pi) removal but suffer from poor stability and low sorption affinity under ambient conditions. In this paper, well crystallized MnIIFeIIFeIII-Cl, MnIIFeIII-CO3 and novel MnIVFeIII-CO3 LDHs were synthesized. The LDHs show fast Pi sorption with 90 % uptake within 20 min, and high Pi sorption capacity of 11 mg P/g at low solution Pi concenrations of 0.1 mg P/L, corresponding to a very high Pi sorption affinity (Kd 1.1 × 105 L/kg). Fast MnII dissolution from the MnIIFeIIFeIII-Cl LDHs and formation of MnFe2O4 at pH 7 were observed in aqueous suspensions of non-oxidized material where up to 70% of total Mn was released within 2 h. However, when interlayer Cl- was exchanged with CO32−, much lower Mn dissolution (5.4%) was observed. Furthermore, after oxidation of MnII to MnIV, the obtained MnIVFeIII-CO3 LDH maintained the layered structure of LDH and the particles were surrounded by birnessite nanorods. The MnIVFeIII-CO3 LDH showed excellent stability but lower Pi sorption capacity. However, a high sorption affinity was maintained which is attributed to more positively charged Fe-centered sorption sites. XPS and ATR-FTIR data together with DFT calculations demonstrated that Pi was mainly sorbed via the formation of mononuclear mono- and bidentate Pi surface complexes on planar LDH particle surfaces.

Original languageEnglish
Article number132177
JournalChemical Engineering Journal
Number of pages11
Publication statusPublished - 2022

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Publisher Copyright:
© 2021 The Author(s)

    Research areas

  • DFT, Mn-Fe LDH, Mn oxidation, Phosphate surface complexation, Solubility

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