Paramagnetic relaxation of ferric “oxyhydroxide” in Victorian brown coal and its structural implications

Abstract 

Mössbauer effect and magnetisation measurements show strong evidence that the principal form of native and introduced iron in Victorian brown coals is as isolated Fe³⁺ ions octahedrally coordinated to a range of oxygen-containing ligands. The mean iron-iron separation is less than expected from a uniform distribution, but there is strong evidence against 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 coupling between nearby Fe³⁺ ions causes slow paramagnetic relaxation in the low temperature Mössbauer spectra.