ABRASIVE STRIPPING VOLTAMMETRY AND ESR SPECTROSCOPY OF MANGANESE IN CARBONATES

A combined approach using solid state electroanalysis (abrasive stripping voltammetry) and ESR spectroscopy was made to characterize the different species of manganese which are present in natural and synthetic calcium carbonates. Abrasive stripping voltammetry permits identifying MnO2 and MnCO3, but the method fails when it comes to detecting unambiguously MnCO3 in the presence of MnO2. Neither can this method detected Mn2+ ions in mixed crystals of Ca1-xMnxCO3 because of their low concentrations. ESR spectroscopy can show that Mn2+ ions are present in calcite on Ca2+ sites. Additionaly, information about the state and symetry of Mn2+ sites and the local dynamics of the lattice can be obtained. In aragonite, only extremely small amounts of individual Mn2+ ions are present and most of the manganese is found in the form of MnO2 agglomerates. Solid state electroanalysis and ESR spectroscopy allow a rather complete qualitative specification of manganese in calcium carbonates.