Phosphate sorption by three potential filter materials as assessed by isothermal titration calorimetry

Research output: Contribution to journalArticle


Phosphorus eutrophication of lakes and streams, coming from drained farmlands, is a serious problem in areas with intensive agriculture. Installation of phosphate (P) sorbing filters at drain outlets may be a solution. The aim of this study was to improve the understanding of reactions involved in P sorption by three commercial P sorbing materials, i.e. Ca/Mg oxide-based Filtralite-P, Fe oxide-based CFH-12 and Limestone in two particle sizes (2-1mm and 1-0.5mm), by means of isothermal titration calorimetry (ITC), sorption isotherms, sequential extractions and SEM-EDS. The results indicate that P retention by CFH is due to surface complexation by rapid formation of strong Fe-P bonds. In contrast, retention of P by Filtralite-P and Limestone strongly depends on pH and time and is interpreted due to formation of calcium phosphate precipitate(s). Consequently, CFH can unambiguously be recommended as P retention filter material in drain outlets, whereas the use of Filtralite-P and Limestone has certain (serious) limitations. Thus, Filtralite-P has high capacity to retain P but only at alkaline pH (pH≥10) and P retention by Limestone requires long-time contact and a high ratio between sorbent and sorbate.


  • Gry Lyngsie
  • Chad J. Penn
  • Hans C B Hansen
  • Ole K. Borggaard
External organisations
  • University of Copenhagen
  • Oklahoma State University, Stillwater
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Ocean and River Engineering
  • Environmental Management


  • Calcium phosphates, CFH-12, Fe-oxides, Filtralite-P, Limestone, P sorbing reactions
Original languageEnglish
Pages (from-to)26-33
Number of pages8
JournalJournal of Environmental Management
Publication statusPublished - 2014 Oct 1
Publication categoryResearch
Externally publishedYes