SCIENCES of SOILS, Rel. 2, 1997 -

Natural organic matter sorption on different mineral surfaces studied by DRIFT spectroscopy

Kaiser Klaus and Wolfgang Zech

Institute of Soil Science and Soil Geography, University of Bayreuth, 95440 Bayreuth, Germany


Key Words

natural organic matter, sorption, DRIFT spectroscopy


Sorption on mineral surfaces is an important process controlling natural organic matter (NOM) translocation in soils. In this study, we tried to characterize the functional units of NOM being sorbed on the surfaces of different mineral phases (goethite, hematite, ferrihydrite, gibbsite, amorphous Al(OH)3, kaolinite and illite) by diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy to gain information about the chemical structures responsible for the NOM sorption. The sorption capacity of gibbsite, illite, and kaolinite is too low to give a sufficient surface enrichment of organic material for recording DRIFT spectra of sorbed NOM. The spectra of NOM sorbed on amorphous Al(OH)3, goethite, hematite, and ferrihydrite show a relative increase of the band intensity of carboxyl groups compared to NOM in the initial solution, confirming the importance of those groups for the sorption to mineral surfaces. The spectra also indicate reactions of carboxyl groups with metals at the mineral surfaces. The extent to which the carboxyl groups are bound depends on the surface coverage with NOM and the type of mineral. At high surface coverage, less carboxyl groups seem to be involved in binding reactions. Sorption on amorphous Al(OH)3 and goethite is stronger than on hematite and ferrihydrite since the predominand proportion of carboxyl groups are bound.