Isolation of dissolved organic matter from aqueous solution by precipitation with FeCl3: mechanisms and significance in environmental perspectives

Ferric ions can bind strongly with dissolved organic matter (DOM), including humic acids (HA), fulvic acids (FA), and protein-like substances, whereas isolation of Fe-DOM precipitates (Fe-DOMP) and their biochemical characteristics remain unclear. In this work FeCl 3 was used to isolate DOM components from various sources, including river, lake, soil, cow dung, and standard tryptophan and tyrosine, through precipitation at pH 7.5-8.5. The Fe-DOMP contribute to total DOM by approximately 38.6- 93.8% of FA, 76.2% of HA and 25.0-30.4% of tryptophan and tyrosine, whilst fluorescence spectra allowed to monitor/discriminate the various DOM fractions in the samples. The relative intensity of the main infrared peaks such as 3406-3383 cm -1 (aromatic OH), 1689-1635 cm -1 (-COOH), 1523-1504 cm -1 (amide) and 1176-1033 cm -1 (-S=O) show either to decline or disappear in Fe-DOMP. These results suggest the occurrence of Fe bonds with various functional groups of DOM, indicating the formation of ?-d electron bonding systems of different strengths in Fe-DOMP. The novel method used for isolation of Fe-DOMP shows promising in opening a new frontier both at laboratory and industrial purposes. Furthermore, results obtained may provide a better understanding of metal- organic complexes involved in the regulation of the long-term stabilization/sequestration of DOM in soils and waters.