Characterization of the Iron Phases in Some Soils from The Jabal Al–Akhdar Region of North–East Libya Using Mossbauer Spectroscopy

Abstract

A range of soils from the Jabal Al-khdar region of Cyrenaica in N.E. Libya have been investigated by Mossbauer spectroscopy with the objective of relating the mineralogical forms of iron to geographical location. All soils were of good agricultural quality and from three distinct types of locations; the coastal plain and north — or south-facing slopes on inland mountain ranges. After air-drying and sieving to remove stones and organic debris, the < 2mm clay fraction was separated and its major mineral components characterised by X-ray diffraction. Quartz, kaolinite and illite were the main components identified in all specimens. Chemical discrimination of the major groups of iron-containing phases was performed using the standard dithionite-citrate­bicarbonate (DCB) and the oxalate methods. Mossbauer spectroscopy, at ambient temperature and 77K, of whole clay fractions showed the presence of microcrystalline hematite and goethite, in combined amounts that were similar to the iron oxide fraction determined by the DCB method. There was, however, no systematic relationship between the relative proportions of hematite and goethite and the geographical origins of the soils. The iron in the illite components was principally in the Fe (III) form, although Fe (II) could also be detected in some specimens, particularly those from the south-facing mountain slopes. Spectra of the residues from both the DCB and oxalate treatments were also investigated and the spectral results related to primary minerals in the soils.