Biological and Physicochemical Characters and Functions of Amorphous Iron oxides Produced by Iron-oxidizing Bacteria at Ambient Temperature in Hydrosphere

Abstract. The Rimicaris exoculata shrimp is considered a primary consumer that dominates the fauna of most Mid-Atlantic Ridge (MAR) hydrothermal ecosystems. These shrimps harbour in their gill chambers an important ectosymbiotic community of chemoautotrophic bacteria associated with iron oxide deposits. The structure and elemental composition of the minerals associated with these bacteria have been investigated by using X-ray microanalyses, light microscopy, and transmission, environmental scanning and scanning transmission electron microscopy. The nature of the iron oxides in shrimps obtained from the Rainbow vent field at 36°14.0' N, has also been determined by Mössbauer spectroscopy. This multidisciplinary approach has revealed that the three step-levels of mineral crust found in the Rimicaris exoculata shrimps consist of heavy concretions formed by nanoparticles of two-line ferrihydrite intermixed with minor inorganic SiO2, (Ca,Mg)SO4, and (Ca,Mg)3(PO4)2 minerals that may stabilise the ferrihydrite form of iron oxides. Morphological observations on the bacteria have revealed their close interactions with these minerals and, thus, indicate the biogenic origin of the iron oxide deposits. The evolution of the bacterial density in the three mineral crust levels is related to the amount of the iron deposits and it is proposed that the lower crust level is the most likely region for the location of the iron-oxidizing bacteria.

Download Full-text

Balneaves: Soil Thin Sections

Proceedings of the Prehistoric Society ◽

10.1017/s0079497x00079172 ◽

1992 ◽

Vol 58 (S2) ◽

pp. 23-25

Author(s):

Donald Davidson

Keyword(s):

Iron Oxides ◽

Fine Fraction ◽

Coarse Fraction ◽

Random Pattern ◽

Medium Sand ◽

Thin Sections ◽

Amorphous Iron ◽

Channel Pattern ◽

Mineral Components ◽

Quartz Grains

1. Structure: partially accommodated channels (0.16 to 0.80mm in width) above the pan; no aggregates; fewer channels below the pan; channel pattern - straight to curved; vughs (spherical to elongate, not normally connected) 0.4 to 0.8mm in diameter and are not orientated and have random pattern: above pan channels and vughs partially connected; pellicular grain microstructure - weakly developed.2. Mineral components: coarse fraction: quartz grains range in size from silt to fine/medium sand (<lmm). One large quartz (200mm). Dominance of single and compound quartz grains; instances of biotite and plagioclase; quartz grains -angular/subangular and smooth. Fine fraction: brown, optically amorphous iron oxides, isotropic.

Download Full-text

Tritium exchange studies on metal oxide colloidal dispersions

Australian Journal of Chemistry ◽

10.1071/ch9771655 ◽

1977 ◽

Vol 30 (8) ◽

pp. 1655 ◽

Cited By ~ 29

Author(s):

DE Yates ◽

F Grieser ◽

R Cooper ◽

TW Healy

Keyword(s):

Crystal Structure ◽

Heat Treatment ◽

Iron Oxide ◽

Metal Oxide ◽

Iron Oxides ◽

Colloidal Dispersions ◽

Water Interface ◽

Amorphous Iron ◽

Tio2 Rutile ◽

Exchange Technique

The tritium exchange technique has been used to detemine the maximum number of surface protons at the oxide-water interface for oxide colloids including silicas, TiO2 (rutile) and the iron oxides goethite, hematite and amorphous iron oxide. The effects of heat treatment, crystal structure and exchange conditions are considered and tritium exchange values for the number of surface protons are compared with values calculated from crystal structures.

Download Full-text

Photodegradation, interaction with iron oxides and bioavailability of dissolved organic matter from forested floodplain sources

Marine and Freshwater Research ◽

10.1071/mf07225 ◽

2008 ◽

Vol 59 (9) ◽

pp. 780 ◽

Cited By ~ 18

Author(s):

Julia A. Howitt ◽

Darren S. Baldwin ◽

Gavin N. Rees ◽

Barry T. Hart

Keyword(s):

Organic Matter ◽

Iron Oxide ◽

Dissolved Organic Matter ◽

Iron Oxides ◽

Photochemical Reactions ◽

Oxbow Lake ◽

Photochemical Degradation ◽

Fluorescence Excitation ◽

Amorphous Iron ◽

Leaf Leachate

Photochemical degradation of dissolved organic matter (DOM) can influence food webs by altering the availability of carbon to microbial communities, and may be particularly important following periods of high DOM input (e.g. flooding of forested floodplains). Iron oxides can facilitate these reactions, but their influence on subsequent organic products is poorly understood. Degradation experiments with billabong (= oxbow lake) water and river red gum (Eucalyptus camaldulensis) leaf leachate were conducted to assess the importance of these reactions in floodplain systems. Photochemical degradation of DOM in sunlight-irradiated quartz tubes (with and without amorphous iron oxide) was studied using gas chromatography and UV-visible spectroscopy. Photochemical reactions generated gaseous products and small organic acids. Bioavailability of billabong DOM increased following irradiation, whereas that of leaf leachate was not significantly altered. Fluorescence excitation-emission spectra suggested that the humic component of billabong organic matter was particularly susceptible to degradation, and the source of DOM influenced the changes observed. The addition of amorphous iron oxide increased rates of photochemical degradation of leachate and billabong DOM. The importance of photochemical reactions to aquatic systems will depend on the source of the DOM and its starting bioavailability, whereas inputs of freshly formed iron oxides will accelerate the processes.

Download Full-text

THE EFFECTS OF ORGANIC MATTER, IRON OXIDES AND MOISTURE ON THE COLOR OF TWO AGRICULTURAL SOILS OF QUEBEC

Canadian Journal of Soil Science ◽

10.4141/cjss79-019 ◽

1979 ◽

Vol 59 (2) ◽

pp. 191-202 ◽

Cited By ~ 13

Author(s):

S. CHOMCHAN ◽

R. G. LEGER ◽

G. J. F. MILLETTE

Keyword(s):

Organic Matter ◽

Iron Oxide ◽

Iron Oxides ◽

Agricultural Soils ◽

Area Ratio ◽

Oxide Coatings ◽

Soil Color ◽

Amorphous Iron ◽

Reflectance Curve ◽

Iron Oxide Coatings

A new spectrophotometric interpretation of the influence of organic matter, iron oxides and moisture on the soil color of the Ste-Sophie sand and the Ste-Rosalie clay is reported. The method is based on calculation of the area ratio of the reflected (area under the reflectance curve) against the absorbed (area over the reflectance curve). The higher the ratio the lighter is the soil. After treatment to remove organic matter and iron oxide coatings, both soils presented colors significantly lighter than those observed in untreated soils. Organic matter and amorphous iron oxide contributed for 78% and 64% of the color in the Ste-Sophie sand and in the Ste-Rosalie clay, respectively. Moisture tends to mask the effects of organic matter and iron oxides on soil color. Air-dried soils when compared to moistened soils were lighter in color.

Download Full-text