PARAMAGNETIC RELAXATION OF FERRIC OXYHYDROXIDE IN VICTORIAN BROWN-COAL AND ITS STRUCTURAL IMPLICATIONS

Mossbauer effect and magnetisation measurements show strong evidence t hat the principal form of native and introduced iron in Victorian brow n coals is as isolated Fe3+ ions octahedrally coordinated to a range o f oxygen-containing ligands. The mean iron-iron separation is less tha n expected from a uniform distribution, but there is strong evidence a gainst clustering. All experimental evidence is consistent with these iron ions being located in the water bridges between the coal micelles . Although the Fe3+ ions remain paramagnetic down to 4.2 K, magnetic c oupling between nearby Fe3+ ions causes slow paramagnetic relaxation i n the low temperature Mossbauer spectra.