E.p.r. study of paramagnetic metal ions in Victorian brown coal

Electron paramagnetic resonance (e.p.r.) spectra of some Victorian brown coals in the raw state possess absorbances attributable to metal ion radicals. E.p.r. signals at g≈4.3 and g≈2 (multiplet) have been assigned to iron(III) and manganese(II), respectively. The g≈4.3 signal intensity does not appear to vary directly with the total iron content of the raw coal. The amplitudes of the metal ion signals were found to change with drying of the coal, and were reduced to zero on removal of the metal ions by acid washing. Ion exchange of the sodium form of brown coal with iron(III) reintroduced the g≈4.3 signal and produced an additional broad signal centred at g≈2. The intensity of the latter signal was related to the total iron content of the iron(III)-exchanged coal. The extent of iron(III) exchange was shown to be pH dependent. Other paramagnetic ions, such as oxovanadium(IV), manganese(II) and copper(II) when exchanged onto brown coal produced their characteristic metal ion spectra.