Thermal identification of goethite in soils and sediments by diffuse reflectance spectroscopy

Goethite (Gt) is an important iron mineral in soils and sediments. Conventional measurements cannot effectively identify it at the low concentrations typical of soils and sediments. In this paper we demonstrate that diffuse reflectance spectroscopy (DRS) in conjunction with thermal treatment provides a definitive technique for identifying Gt in soil and sediments. The DRS pattern of Gt exhibits diagnostic changes of the first derivative value (FDV) peaks after heating to 300 °C, whereas hematite (Hm) displays no shift in peak wavelength after heating. The degree of thermal changes induced in a sample depends on the concentration of both Gt and Hm. Application of this technique to natural soils and sediments demonstrates that it can effectively detect Gt even at very low concentrations in soils and sediments.