COMPARISON OF AQUEOUS ACETYLACETONE AND POTASSIUM PYROPHOSPHATE SOLUTIONS FOR SELECTIVE EXTRACTION OF ORGANIC-BOUND Fe FROM SOILS

Seven samples of iron oxyhydroxides, characterised by crystallinity and surface area (monolayer water content), were examined for solubility in aqueous acetylacetone (0.68 M), potassium pyrophosphate pH 10 (0.1 M) and acid ammonium oxalate pH 3 (0.2 M). Solubilities in acetylacetone and oxalate were dependent on surface area, being 30 per cent Fe or more for non-crystalline oxides in 40 h. Solubility in pyrophosphate was 2 per cent Fe or less in 40 h even when surface area was 300 m²/g. Pyrophosphate solution was more suitable than aqueous acetylacetone for selective extraction of iron-organic complexes from soils which contain amorphous or poorly crystalline iron oxides.