The chemistry of manganese is rather like that of iron since both metals participate in redox processes in weathering environments. However Mn has three oxidation states rather than 2 (for iron) (2+. 3+, 4+) and may form a wide range of missed valence oxides Mn 3+ species are unstable and may disproportionate (to produce one Mn 2+ and one Mn 4+ species) In waters, manganese is normally only present at trace amounts.
Mn2+ is present in many igneous and metamorphic minerals as a minor constituent and during chemical weathering, is released mainly as Mn2+ to waters. In carbonates it may also substitute for Ca (also as Mn2+) and may be released incongruently to waters. When released to waters it may remain stable as opposed to dissolved iron, but precipitating at high pH.
Measurement Techniques
Manganese is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectroscopy (ICP-MS)
Applications
Mn can be used as a tracer to indicate redox stsus of groundwaters. Also manganese is possibly used as an indicator for chemical weathering and groundwater residence time. In groundwater flow systems Mn may often increase with distance and time and can act as a qualitative indicator of residence time as seen in sandstone aquifers in the Uk and North Africa
References and Further Reading
- Hem, J.D., 1977. Reactions of Metal-Ions at Surfaces of Hydrous Iron-Oxide. Geochimica Et Cosmochimica Acta, 41(4): 527-538.
- Hem, J.D., 1985. Study and interpretation of the chemical characteristics of natural water. U.S. Geological Survey Water-Supply Paper 2254, 263 p.
- Edmunds, W.M. & Smedley, P.L. (2000). Residence time indicators in groundwaters: The East Midlands Triassic Sandstone aquifer. Applied Geochemistry, 15, 737-752.
- Edmunds, W.M. Guendouz, A.H., Mamou, A.., Moulla, A.S., Shand, P. & Zouari, K. (2003). Groundwater evolution in the Continental Intercalaire aquifer of Southern Algeria and Tunisia: trace element and isotopic indicators. Applied Geochemistry, 18:805-822.