Phosphate sorption by natural hematites |
| |
Authors: | J TORRENT U SCHWERTMANN V BARRÓN |
| |
Institution: | Departamento de Ciencias y Recursos Agricolas y Forestales, Universidad de Córdoha, Apdo. 3048, 14080 Córdoha, Spain;Lehrstuhl für Bodenkunde, Technische Universität München, 85350 Freising-Weihenstephan, Germany |
| |
Abstract: | Iron (hydr)oxides are active phosphate sorbents in soils and sediments, but no information exists on phosphate (P) sorption by natural hematites. In this study, we characterized the chemical, mineralogical and P-sorption properties of 14 hematite-rich natural materials of different origins. Phosphate sorption was described by a modified Freundlich equation including a time term. Phosphate sorbed at 1d at an equilibrium concentration of 1 mg P dm?3 ranged widely (0.2–1.7 μmol m?2). After 1 d, hematites showed a marked slow sorption. At 75 d, and an equilibrium concentration of 6mg P dm?3, the total amount of P sorbed ranged between 0.8 and 4.1 μmol mp?2. Phosphate-sorption capacity was influenced by the morphology of the coherently scattering domains: the shorter the domains in the crystallographic c relative to the a direction, the lower the P-sorption capacity. This has been observed by other authors in synthetic hematites and agrees with the idea that the prismatic faces, which have singly co-ordinated Fe-OH groups, are more active in P-sorption than other faces. The average P sorption capacity of hematites was similar to that of natural goethites (2.6 μmol P m?2) but, in contrast to these, variability among samples was high. In comparison with goethites, hematites show slower sorption and lower affinity for phosphate. |
| |
Keywords: | |
|
|