Characterization of iron oxide compounds in soils by Mössbauer and other methods

Abstract

Iron oxide compounds in 12 selected Canadian soil samples have been characterized by Mössbauer, X-ray, chemical, infrared absorption, and differential thermal methods. Chemical differentiation provides useful information about the forms of iron compounds present such as crystalline, amorphous, inorganic, and organic complexed iron compounds. X-ray diffraction methods can generally identify mineral species of crystalline iron compounds. However, detection limits of goethite and hematite, which are iron oxide minerals commonly present in soils, are about 7% and 10%, respectively. The Mössbauer method is especially useful for identification of small amounts of these iron oxide compounds which are far beyond X-ray detection limits. In addition, information about grain size of hematite and goethite, the Fe³⁺/Fe²⁺ ratio and characterization of the 'amorphous' fraction are also available from Mössbauer spectra. Infrared absorption and differential thermal analyses provide supplementary data concerning organic complexed iron compounds.Hematite content in the soils examined is always lower than 10%, but goethite content varies widely and coexistence of both minerals appears to be common.