Reduction of Nitrate By Fe2+ in Clay Minerals

Vibeke Ernstsen
Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400, Copenhagen NV, Denmark

Abstract: In the 12 km2 catchment area of Syv creek, Denmark, moderate to high concentrations of nitrate (NO3) occurred in the upper part of the oxidized zone (oxic-I), but dropped within the lower suboxic part (oxic-II), to below the detection limit in the unoxidized zone. Structural Fe2+ in the clay minerals made up 10 to 12% of the Fe in the oxidized zone and increased to approximately 50% in the unoxidized zone. Concurrent with changes in the distribution of structural Fe2+ the clay mineral constituents changed. Vermiculite was typically found in the oxidized zone whereas chlorite was found in the unoxidized zone only. A conversion of illite and chlorite into vermiculite seems to take place. A significant correlation between NO3 and the amount of reduced Fe2+ in the suboxic (oxic-II) zone, indicates that primary structural Fe2+ in the clay minerals is the reductant in a NO3 reduction process.

Key Words: Chlorite • Clayey till • Exchangeable ferrous iron • Illite • Mössbauer • Nitrate • Oxidized • Structural ferrous iron • Unoxidized • Vermiculite • Weichselian • X-ray

Clays and Clay Minerals; October 1996 v. 44; no. 5; p. 599-608; DOI: 10.1346/CCMN.1996.0440503
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)