MISE EN EVIDENCE DE GOETHITE EN SUSPENSION DANS LES EXTRAITS PYROPHOSPHATE ET TETRABORATE DE CERTAINS SOLS GRESEUX DU PORTUGAL

Five chemical reagents (citrate-bicarbonate-dithionite, oxalate, EDTA, pyrophosphate and tetraborate), generally used for studying iron forms, were applied to sandy soils from Portugal. The results emphasized anomalies in the order of efficiency of these reagents. In deep horizons particularly, a greater extractibility of iron by pyrophosphate, and sometimes by tetraborate, than with oxalate was noted. After separating particles in suspension in pyrophosphate and tetraborate extracts, it was shown that these particles were not entirely soluble in oxalate, and that they consisted of goethite, well-identified by X-ray diffraction and infra-red spectroscopy. It was concluded that iron, present as particles in the peptising reagents, such as pyrophosphate and tetraborate, was not only in the amorphous organic complex state. These results confirm those obtained by Schuppli et al. (1983) for pyrophosphate, but are new for tetraborate. Key words: Chemical extraction (Fe, Al), iron forms, flocculation, ethanol </jats:p