Sequestration of orthophosphate by Ca2Al-NO3 layered double hydroxide – Insight into reactivity and mechanism

Belayneh Bekele, Laura Lundehøj, Nicholai Daugaard Jensen, Ulla Gro Nielsen, Claude Forano*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


This study reports the mechanism of reactivity of phosphate anions (HPO4 2−) with Ca2Al-NO3 LDH. Sequestration of PO4 by Ca2Al-NO3 was quantified by fitting the adsorption isotherm with a Langmuir model. Adsorption capacity (65.2 mgP·g−1 of LDH) is greater than the theoretical anion exchange capacity indicating further mechanism of sequestration. Partial dissolution of CaAl-NO3 results in precipitation of multiple Ca-PO4 phases. Combined characterizations by XRD, 27Al and 31P NMR, FTIR/Raman and SEM highlight the competitive precipitation of hydroxyapatite and brushite within the LDH structure. Multiple environment of PO4 anions offer promising perspective for CaAl-NO3/PO4 as slow release fertilizer.

Original languageEnglish
JournalApplied Clay Science
Pages (from-to)49-57
Publication statusPublished - 1. Aug 2019


  • Adsorption
  • Brushite
  • CaAl-NO hydrocalumite
  • Hydroxyapatite
  • Layered double hydroxides
  • Orthophosphate

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