نتایج جستجو برای: goethite
تعداد نتایج: 1100 فیلتر نتایج به سال:
The impact spherules from the distal K–Pg boundary sections are considered to represent silicate droplets condensed and solidified from a laterally expanding, cooling vapor plume formed upon hypervelocity impact. In the present-day Cretaceous– Paleogene boundary (K–Pg) spherule population of the Umbria–Marche region in Italy, three texturally and compositionally distinct types of impact spherul...
The reversíbilíty of the adsorption of phosphate on goethite was measured by dlluting suspensions of goethite on which phosphate was adsorbed with large volumes oí phosphate-frce solution at the same ioníe strength. The effect on the reversibility of various adsorptíon and desorption conditions was studied, particularly pH, temperature, ionic strength and time of reaction. The apparent irrevers...
Madrid, L. and De Arambarri, P., 1978. Adsorption isotherms and hysteresis of proton adsorption by goethite. Geoderma, 21: 199-208. The adsorption of H+ions by goethite is only partially reversible and the adsorption process is faster than desorption. The adsorptian isotherm shows two inflexion points at pH y,alues 7.5 and 9.5, which can be attributed to the existence of two ar more types of OH...
The microbiologic reduction of a 0.2 to 2.0 mm size fraction of an Atlantic coastal plain sediment (Eatontown) was investigated using a dissimilatory Fe(III)-reducing bacterium (Shewanella putrefaciens, strain CN32) to evaluate mineralogic controls on the rate and extent of Fe(III) reduction and the resulting distribution of biogenic Fe(II). Mössbauer spectroscopy and X-ray diffraction (XRD) we...
The equilibrium Fe isotopic fractionation factors of goethite and jarosite have considerable importance for interpreting Fe isotope variations in low temperature aqueous systems on Earth and possibly Mars in the context of future sample return missions. We measured the b-factors of goethite FeO(OH), potassium-jarosite KFe3(SO4)2(OH)6, and hydronium-jarosite (H3O)Fe3(SO4)2(OH)6, by Nuclear Reson...
U(VI)-phosphate interactions are important in governing the subsurface mobility of U(VI) in both natural and contaminated environments. We studied U(VI) adsorption on goethite-coated sand (to mimic natural Fe-coated subsurface materials) as a function of pH in systems closed to the atmosphere, in both the presence and the absence of phosphate. Our results indicate that phosphate strongly affect...
Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25 degrees C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard stat...
[1] The Mössbauer spectrometer on Spirit measured the oxidation state of Fe, identified Fe-bearing phases, and measured relative abundances of Fe among those phases for surface materials on the plains and in the Columbia Hills of Gusev crater. Eight Fe-bearing phases were identified: olivine, pyroxene, ilmenite, magnetite, nanophase ferric oxide (npOx), hematite, goethite, and a Fe-sulfate. Adi...
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