Floating iron
In mineralogy and hydrology, floating iron is the term used to describe fine films of oxidizing iron ( element symbol Fe) on the surface of shallow, mostly only temporary, still waters . It can be observed worldwide in wetlands , iron-rich seepage and seasonally reduced soils. The German term is also used in the technical-English context.
Swimming iron is created when iron (II) oxide settles out of the groundwater and oxidizes to iron (III) oxide at the water-air interface . The resulting layer - at first glance easily mistaken for oil or biofilms - is 100 to 300 nanometers thick and has a pH value that varies between 5 and 6 . The main components are the cations iron and silicon dioxide in a ratio of 3: 1 and the hydroxide ion (OH - ) as the main anion . Also halite and quartz can be detected in swimming iron. Near the coast, moreover, finer due to the entry spray - aerosols , higher values for chlorine and sodium measurable. As a result of the ongoing oxidation process, floating iron deposits are usually mixed-valence , with Fe (II) and Fe (III) in a ratio between 1: 3 and 1: 5.
Analyzes with the aid of atomic emission spectrometry and ion exchange chromatography reveal reduced iron in an average concentration of 9 ppm , silicon dioxide with 7 ppm, sodium with 60 ppm and chlorine with 85 ppm for the water of waters that carry swimming irons . When examining floating irons with an FTIR spectrometer , the results indicate hydrogen bonds , and there are peaks similar to those of ferrihydrite . The diffraction results in X-ray diffractometry and transmission electron microscopy are also very similar to those of 2-line ferrihydrite - with diffraction at 2.6 and 1.5 Å ; however, some swim irons also have an additional peak at 4.5 Å. In fact, as the oxidation proceeds, it changes to 2-line ferrihydrite. When the oxidation is complete, the film sinks as flocculation to the bottom of the water.
Similar to iron (II) hydroxide and iron (III) hydroxide ("green rust"), floating iron can also be synthesized in the laboratory - either with air introduced for surface oxidation or with seven percent radiation from a UV-B lamp over a period of eight to 600 hours for photo-oxidation . Optionally, humic acids can be added. The few iron films that form without these organic acids are crystalline under the transmission electron microscope . Those that develop after adding 0.2 percent humic acid solutions appear to be as sparsely crystallized as the natural occurrences. Many of the artificial films also have approximately the same diffraction disks and Fe (II) / Fe (III) ratios as in nature.
literature
- Heather R. Easterly: Characterization of Iron-bearing films found on ephemeral pools, Central Coast, Oregon. Portland State University , Master's thesis, 2005.
- Georg H. Grathoff, John E. Baham, Heather R. Easterly, Paul Gassman, Richard C. Hugo: Mixed-valent Fe Films ('Schwimmeisen') on the Surface of Reduced Ephemeral Pools . In: Clays and Clay Minerals . tape 55 , no. 6 , December 2007, pp. 635-643 , doi : 10.1346 / CCMN.2007.0550610 .
- Robert B. Perkins, Zeitel N. Gray, Georg H. Grathoff, Richard C. Hugo: Characterization of natural and synthetic floating iron surface films and their associated waters . In: Chemical Geology . No. 444 , December 2016, p. 16–26 , doi : 10.1016 / j.chemgeo.2016.09.027 .
Individual evidence
- ^ Easterly (2005), p. 1.
- ^ Easterly (2005), p. 2.
- ↑ Zeitel N. Gray, Georg H. Grathoff, Robert B. Perkins: Characterization of natural and synthetic floating, mixed valent Fe-film (swimming iron). Abstract from the 235th ACS National Meeting , New Orleans , June 6-10 . April 2008. Retrieved from oasys2.confex.com on November 9, 2016.