Phosphate sorption by three potential filter materials as assessed by isothermal titration calorimetry.
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 (2-1 mm and 1-0.5 mm), 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.
University of Copenhagen, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark. Electronic address: chj177@ku.dk.
Gry
G
Lyngsie
Oklahoma State University, Department of Plant and Soil Sciences, 368 Agricultural Hall, Stillwater, OK 74078-6028, USA.
Chad J
CJ
Penn
University of Copenhagen, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
Hans C B
HC
Hansen
University of Copenhagen, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
Ole K
OK
Borggaard
D000327:Adsorption; D000383:Agriculture; D002119:Calcium Carbonate; D002130:Calcium Phosphates / Q000737:chemistry; D002151:Calorimetry / Q000379:methods*; D005068:Eutrophication; D005296:Ferrous Compounds / Q000737:chemistry; D005374:Filtration / Q000295:instrumentation* / Q000379:methods; D006863:Hydrogen-Ion Concentration; D010087:Oxides; D010710:Phosphates / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry
D002130:Calcium Phosphates; D005296:Ferrous Compounds; D010087:Oxides; D010710:Phosphates; D010758:Phosphorus; C020243:calcium phosphate; C034236:ferrous oxide; D002119:Calcium Carbonate
CFH-12; Calcium phosphates; Fe-oxides; Filtralite-P; Limestone; P sorbing reactions