Characterization of natural and synthetic floating, mixed valent Fe-film (Schwimmeisen)

GEOC 180

Zeitel N. Gray,, Georg H. Grathoff,, and Robert B. Perkins. Geology Department, Portland State University, 1721 SW Broadway, 17 Cramer Hall, Portland, OR 97207
Schwimmeisen has been observed in wetlands, iron-rich seeps, and seasonally reduced soils. It forms when Fe(II)-rich groundwater oxidizes to Fe(III) at the air-water interface. The natural films are 100 to 300 nm thick and contain both Fe(III) and Fe(II) as well as Si. Energy-filtered electron diffraction patterns (EFED) show three diffraction rings at ~4.5, 2.6, and 1.4 .

`We synthesized films using Cornell and Schwertmann's (2000) recipe for Green Rust with and without the addition of humic acid and with surface oxidation using introduced air or photo-oxidation with 7% UVB light over periods of 8 to 600 hours. The few films that formed without organic acids were crystalline under TEM. The films that formed using 0.2% humic acid solutions appeared poorly crystalline as did the natural samples. Many of the synthesized films show similar diffraction rings and contain a similar ratio of Fe(II):Fe(III)as the natural films.