Characterization of phosphate sequestration by a lanthanum modified bentonite clay: a solid-state NMR, EXAFS, and PXRD study.
Phosphate (Pi) sequestration by a lanthanum (La) exchanged clay mineral (La-Bentonite), which is extensively used in chemical lake restoration, was investigated on the molecular level using a combination of (31)P and (139)La solid state NMR spectroscopy (SSNMR), extended X-ray absorption spectroscopy (EXAFS), powder X-ray diffraction (PXRD) and sorption studies. (31)P SSNMR show that all Pi was immobilized as rhabdophane (LaPO4·n H2O, n ≤ 3), which was further supported by (139)La SSNMR and EXAFS. However, PXRD results were ambiguous with respect to rhabdophane and monazite (LaPO4). Adsorption studies showed that at dissolved organic carbon (DOC) concentration above ca. 250 μM the binding capacity was only 50% of the theoretical value or even less. No other La or Pi phases were detected by SSNMR and EXAFS indicating the effect of DOC is kinetic. Moreover, (31)P SSNMR showed that rhabdophane formed upon Pi sequestration is in close proximity to the clay matrix.
†Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark.|‡Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
Line
L
Dithmer
§Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Andrew S
AS
Lipton
‡Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
Kasper
K
Reitzel
∥Department of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, Niels Bohrs Allé 1, 5230 Odense M, Denmark.
Terence E
TE
Warner
⊥Department of Chemistry and Biotechnology, Uppsala BioCenter, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
Daniel
D
Lundberg
†Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark.
Ulla Gro
UG
Nielsen
D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry*; D000077215:Clay; D052918:Environmental Restoration and Remediation; D005068:Eutrophication; D060106:Lakes / Q000737:chemistry; D007811:Lanthanum / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010710:Phosphates / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D010710:Phosphates; D001546:Bentonite; D007811:Lanthanum; D000077215:Clay