Iron-rich minerals

Past depletions in dissolved inorganic phosphate may have also limited nitrogen-fixation and primary production due to high adsorption of phosphate by iron-rich minerals. Indeed, based on adsorption isotherms in banded iron formations, sea-water phosphate concentrations in the Archean have been suggested to have been more than ten fold lower than the present values (0.15-0.6 pM versus the modem value of 2.3 pM) (Bjermm and Canfield, 2002). Thus, present restrictions of phosphate on N2 fixers in some oligotrophic areas such as the western subtropical Atlantic (Mills et ai, 2004) and in the tropical Pacific (Moutin et al., 2007) may have correlations in the paleoceanographic records of the late Archean eon. 

Krot A. N., Petaev M. I., Zolensky M. E., Keil K., Scott E. R. D., and Nakamura K. (1998c) Secondary calcium-iron-rich minerals in the Bali-like and Allende-like oxidized CV3 chondrites and AUende dark inclusions. Meteorit. Planet. Sci. 33, 623-645. 

Berthierine is used to designate an essentially 7 A iron-rich mineral, chamosite, a 14 A chlorite with a wide range of Fe-Mg ratio. This is indicated by the combined data from Figures 8-10 shown in Figure 12. 

Alternatively, iron-rich sacrificial electrodes, which dissolve under acidic conditions generated at the anode by the application of electric field, may be used. The dissolved iron, in cationic form, migrates toward the cathode and then precipitates as iron-rich mineral phases (ferric iron oxyhydroxides, hematite, goethite, magnetite, and ZVl) near the cathode due to high-pH conditions. Contaminants such as Cr(Vl) can react with this iron and reduce into Cr(III). Cr(VI) transport may be limited by high sorption under low-pH conditions therefore, alkaline solution may be injected from the anode to increase the soil pH, and thereby reduce sorption and increase transport of Cr(Vl) to react with iron. 

Several experiments have shown that electrokinetically mediated iron mineralization is, in essence, a self-limiting process in which the current falls as an essentially impermeable (1 x 10" m/s or less) iron-rich lithilied soil mass develops (e.g. Hopkinson and Cundy, 2003 Cundy and Hopkinson, 2005). In the context of Cr(VI) stabilization, the generation of low-permeability zones, in which chemically stabilized Cr(III) is locked in iron-rich mineral phase(s), means that stabilized zones are likely to be resilient to reactive flow, with the low permeability also serving to limit potential loss of adsorbed Cr(VI) residue on the iron mineral phase(s). 

The two end members of this group with mainly tetrahedral substitutions are beidellite and saponite, which are di- and trioctahedral smectites, respectively. The corresponding end members with mainly octahedral substitutions are mont-morillonite and hectorite. Another common smectite, nontronite, is an iron-rich mineral. Chemical compositions of various smectite samples are provided in Table 2. Montmorillonite is the most common mineral of this group it is named for its location in Montmorillon, France. Figures 3d and 3e provide SEM views of the textural morphology of two montmorillonites. A common industrial mineral is bentonite, which is actually a montmorillonite of volcanic ash origin that contains a significant amount of impurities, such as cristobalite (a-quartz), that is intimately mixed with the clay. 

Red ochres form in the oxidised, weathered portions of iron-rich mineral deposits, especially those associated with so-called volcanic massive sulfide (VMS) deposits where they are derived from the breakdown of minerals such as iron pyrite and chal-copyrite and also from the direct weathering of hematite, the... 

Celadonite [71606-04-7] is an iron-rich dioctahedral micaceous mineral that is similar to glauconite. Celadonite has a composition of (Na,K)Q... 

The cycling of phosphorus in marine sediments is quite different from that of nitrogen in that its remineralized form, HPO , is readily sequestered in several mineral phases, namely carbonate fluoroapatite (CFA) and iron-rich clays and oxyhydroxides. 

Montmorillonite An iron-rich clay mineral that has a very high cation exchange capacity. Unlike the other clay minerals, a significant amount of sedimentary montmorillonite is hydrothermal in origin. 

Klupinski et al. (2004) report a laboratory experiment on the degradation of a fungicide, pentachloronitrobenzene (C Cl NO ), in the presence of goethite and iron oxide nanoparticles this study was intended to illustrate the fate of organic agrochemical contaminants in an iron-rich subsurface. To compare the effects of iron with and without a mineral presence, experiments were performed using... 

Intermediate members of the series that contain both Mg and Fe, may be identified as iron-rich cummingtonite, for example. Alternatively, a fibrous species whose composition and structure resembles grunerite occurs in South Africa. It is mined as asbestos and known commercially as amosite. Amosite is a varietal mineral name that has been used in the trade to describe mineral materials within the cummingtonite-grunerite series. The name is an acronym for asbestos mines of South Africa. Because it is not a proper mineral name, it may not be found in lists of minerals in standard miner-alogical texts. 

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