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Open Access item Manganese micro-nodules on ancient brick walls

Authors:López-Arce, Paula
García Guinea, Javier
García Fierro, José Luis
Keywords:Heritage preservation, Brick alterations, Manganese micro-nodules, Biofilm, XPS, XRD, SEM-EDS
Issue Date:13-Nov-2002
Citation:The Science of the Total Environment
Abstract:Romans, Jews, Arabs and Christians built the ancient city of Toledo (Spain) with bricks as the main construction material. Manganese micro-nodules (circa 2 μm in diameter) have grown under the external bio-film surface of the bricks. Recent anthropogenic activities, such as, industrial emissions, foundries or traffic and housing pollution have further altered these old bricks. The energy-dispersive X-ray microanalyses (XPS) of micro-nodules shows Al, Si, Ca, K, Fe and Mn, with some carbon species. Manganese atoms are present only as Mn4+ (pyrolusite phase, MnO2) and iron as Fe3+ (FeOOH-Fe2O3 mixtures). The large concentration of algae biomasses of the River Tagus and the Torcón and Guajaraz reservoirs suggest manganese micro-nodules are formed either from water solutions rich in anthropogenic MnO4K in a reduction environment (from Mn7+ to Mn4+) or by oxidation mechanisms from dissolved Mn2+ (from Mn2+ to Mn4+) linked to algae biofilm onto the ancient brick surfaces. Ancient wall surfaces were also studied by scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). Chemical and biological analyses of the waters around Toledo are also analysed for possible sources of manganese. Pyrolusite micro-nodules on ancient brick walls are good indicators of manganese pollution.
Description:8 pages.-- Printed version published on 20 Jan 2003.
Publisher version (URL):http://dx.doi.org/10.1016/S0048-9697(02)00398-4
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