Abstract

Dolomite from the Jhamarkotra phosphate mine (India) contains 680 ppm Mn 2+ as indicated by electron-spin resonance spectroscopy (EPR). Dipolar broadening of the EPR signal prevents a quantitative assignment of Mn 2+ to the Ca and Mg sites. Upon heating to 700 °C, over 99% of the dolomite is decomposed and all the Mn 2+ is released from the dolomite structure. Approximately 95% of the original Mn 2+ is oxidized and forms Mn-oxide. The remaining Mn 2+ preferentially migrates into CaO. This behavior is interpreted by the Goldschmidt rule stating that smaller ions are taken up at the sites of larger ions. During subsequent hydration of CaO into Ca(OH) 2 , the Mn 2+ remains stable. The protection of Mn 2+ against oxidation is explained by the topotaxical alteration of the host minerals. Carbonation of the Ca(OH) 2 leads to Mn 2+ oxidation caused by the dissolution of the hydroxide prior to the formation of CaCO 3 . Divalent Mn monitored by EPR can be used to unravel the behavior of trace elements on the molecular level during mineral alteration

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