Influence of dissolved organic carbon on the efficiency of P sequestration by a lanthanum modified clay.
A laboratory scale experiment was set up to test the effect of dissolved organic carbon (DOC) as well as ageing of the La-P complex formed during phosphorus (P) sequestration by a La modified clay (Phoslock(®)). Short term (7 days) P adsorption studies revealed a significant negative effect of added DOC on the P sequestration of Phoslock(®), whereas a long-term P adsorption experiment revealed that the negative effect of added DOC was reduced with time. The reduced P binding efficiency is kinetic, as evident from solid-state (31)P magic-angle spinning (MAS) NMR spectroscopy, who showed that the P binding did not change in the presence of DOC. (31)P MAS NMR also reveals that up to 26% of the sequestered phosphate is as loosely bound redox-sensitive P species on the surface of rhabdophane (LaPO4 · nH2O, n ≤ 3). The ratio between the loosely bound P and lanthanum phosphate did not change with time, however both NMR and La LIII-extended x-ray absorption fine structure (EXAFS) spectroscopy shows a transformation of lanthanum phosphate from the initially formed rhabdophane towards the more stable monazite (LaPO4). Furthermore, the effect of natural DOC on the P binding capacity was tested using water and pore water from 16 Danish lakes. Whilst DOC has an immediate negative impact on P binding in the lake water, with time this effect is reduced.
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
Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark.
Ulla Gro
UG
Nielsen
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 Biology, University of Southern Denmark, 5230 Odense M, Denmark. Electronic address: reitzel@biology.sdu.dk.
Kasper
K
Reitzel
D000327:Adsorption; D002244:Carbon / Q000737:chemistry; D060106:Lakes / Q000737:chemistry*; D007811:Lanthanum / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry
D010758:Phosphorus; D007811:Lanthanum; D002244:Carbon
(31)P NMR; Dissolved organic carbon (DOC); EXAFS; Lake restoration; Lanthanum; P sequestration