COMPARISON OF SYNTHETIC AND SOIL Al-SUBSTITUTED LEPIDOCROCITE

Abstract

The nature of Fe-oxides in the magnetic clay fractions of the Bt and Bs horizons of alpine forest soils in subtropical and tropical areas is not well defined. The objective of this study was to synthesize lepidocrocite incorporating Al in the laboratory and to compare its properties with soil lepidocrocite. Lepidocrocite and goethite were identified by differential X-ray diffraction and Mössbauer spectroscopy at 77 K in the magnetic clay fractions of the Bsm horizons and exhibited results similar to those of the products from a synthetic Fe(II) system with an Al/Fe molar ratio of 0.03. Several individual soil lepidocrocite particles can be identified in the magnetic clay fractions using high resolution transmission electron microscopy and selected area electron diffraction with the same (010) orientation as that of laboratory synthetic lepidocrocite. Weight percent of Al and Fe in the synthetic and soil lepidocrocite particles was determined by energy dispersive spectroscopy. The Al/Fe molar ratios in the soil lepidocrocite particles ranged from 0.005 to 0.095. This indicates the participation of Al(III) in the formation of lepidocrocite under acidic, udic, and mesic forest soil environments.