Selective extraction of amorphous iron oxides by EDTA from selected silicates and mixtures of amorphous and crystallline iron oxides

Abstract

Amorphous iron oxides in soil are often extracted by an ammonium oxalate solution (Schwertmann, 1964). This treatment may, however, also dissolve crystalline iron oxides and iron silicates (McKeague & Day, 1966; Baril & Bitton, 1969; McKeague et al., 1971; Arshad et al., 1972; Pawluk, 1972; Schwertmann, 1973; Taylor & Schwertmann, 1974; Borggaard, 1976).It has been shown that EDTA can selectively extract amorphous iron oxides from soils (Borggaard, 1979, 1981) and a synthetic mixture of amorphous iron oxide, goethite, and hematite (Borggaard, 1976). As pointed out previously (Borggaard, 1979), the EDTA method should also be tested on selected minerals to decide if it can serve as a reference method against which other less time-consuming methods may be tested.