Isotope fractionation adsorption

Isotope fractionation between the vapor phase and the dissolved aqueous phase has been studied only for toluene and trichloroethylene (carbon only [545, 690]). Fractionation associated with adsorption has been quantified only for toluene in regard to sample extraction using a poly(dimethylsilo-xane)-coated solid-phase microextraction fiber [373] and qualified for benzene, toluene, and ethylbenzene based on high-pressure liquid chromatography analyses of isotopically labeled and unlabeled compounds (carbon and hydrogen [692]). Isotope fractionation associated with the reductive dechlorination of chlorinated ethylenes by zero-valent iron and zinc has been... 

Adsorption of Mo to Mn oxyhydroxides produces an isotopic fractionation that appears to follow that of a closed-system equilibrium model as a function of the fraction of Mo adsorbed (Fig. 8). Barling and Anbar (2004) observed that the 5 TVlo values for aqueous Mo (largely the [MoOJ species) were linearly correlated with the fraction (/) of Mo adsorbed (Fig. 8), following the form of Equation (14) above. The 5 Mo-f relations are best explained by a MOaq-Mn oxyhydroxide fractionation of +1.8%o for Mo/ Mo, and this was confirmed through isotopic analysis of three solution-solid pairs (Fig. 8). The data clearly do not lie... 

Barling J, Anbar AD (2004) Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett 217 315-329... 

Recent experiments have determined that the isotopic fractionation between adsorbed and dissolved Cr(VI) is very small (Ellis et al. submitted). In batch experiments, dissolved Cr(VI) was equilibrated with finely ground alumina or goethite. The results of these experiments should be appficable to natural settings, as oxides chemically similar to alumina and goethite provide the main adsorption sites for Cr(VI) anions. Because the analytical precision of the measurements was 0.2%o, it was necessary to amplify any isotopic shifts so that effects smaller than 0.1 %o could be detected. This was accompfished by repeating the sorption step ten or more times, so that a fractionation between dissolved and adsorbed Cr(VI) of 0.04%o was detectable at the 95% confidence level. 

Adsorption to Mn oxides. The only thorough experimental study of Mo isotope fractionation to date focused on adsorption to Mn oxides (Barfing and Anbar 2004). The intent of this study was to examine the possibility that Mo isotopes are fractionated during this process. In these experiments. Mo dissolved in aqueous solution of defined iorfic strength at room temperature was exposed to synthetic 5-Mn02. pH (6.5-8.5) and solution-solid contact... 

The major isotopic findings are summarized in Figure 8. Amean 8 Mo offset of 1.8%o was observed between dissolved and oxide-bound Mo in all experiments. The data do not fit the expectations of a Rayleigh model, as might be expected from irreversible adsorption. Instead, the data closely approximate closed system exchange between adsorbed and dissolved Mo, suggesting that Mo isotope fractionation in this system is an equilibrium process. 

Aveston J, Anacker EW, Johnson JS (1964) Hydrolysis of molybdenum (VI). Ultracentrifugation, acidity measurements, and Raman spectra of polymolybdates. Inorg Chem 3 735-746 Baes Jr. CF, Mesmer RE (1986) The Hydrolysis of Cations. Krieger Publishing Company, Melbourne, EL Barling J, Anbar AD (2004) Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett, in press... 

Isotope effects of this kind are relevant for an understanding of the isotope composition of clay minerals and absorption of water on mineral surfaces. The tendency for clays and shales to act as semipermeable membranes is well known. This effect is also known as ultraliltration . Coplen and Hanshaw (1973) postulated that hydrogen isotope fractionations may occur during ultraliltration in such a way that the residual water is emiched in deuterium due to its preferential adsorption on the clay minerals and its lower diffusivity. 

BaUstrieri L, Borrok DM, Wanty RB, Ridley WI (2008) Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide experimental mixing of add rock drainage and ambient river water. Geochim Cosmochim Acta 72 311-328... 

Figure 17 shows schematically the major transformations of sulfur in aquatic systems and their related isotopic fractionations. Processes that do not significantly fractionate sulfur isotopes include (i) weathering of sulfide and sulfate minerals, (ii) adsorption-desorption interactions with organic matter, and (iii) isotopic exchange between S04 and HS or H2S in low-temperature environments. Precipitation of sulfate minerals is accompanied by only slight isotopic fractionation, and the precipitates are generally... 

Pokrovsky, O.S., Viers, J., and Freydier, R., Zinc stable isotope fractionation during its adsorption on oxides and hydroxides, J. Colloid Interf. Sci.. 291, 192, 2005. 

Benz W, Cameron AGW (1990) Terrestrial effects of the giant impact. In Origin of the Earth. Newsom HE, Jones JH (eds) Oxford University Press, New York, p 61-67 Bematowicz TJ, Keimedy BM, Podosek FA (1985) Xe in glacial ice and the atmospheric inventory of noble gases. Geochim Cosmochim Acta 49 2561-2564 Bematowicz TJ, Podosek FA (1986) Adsorption and isotopic fractionation of Xe. Geochim Cosmochim Acta 50 1503-1507... 

It has been shown that B incorporation into carbonates occurs predominantly via B(OH)4 adsorption on the growing mineral (Hemming et al, 1995) and results in an isotopic fractionation between carbonate and seawater which is thus grossly that between dissolved B(0H)4 and seawater. A few permil variations of this isotopic fractionation have been observed among biogenic carbonates such as foraminifera, brachiopods and corals (Sanyal et al, 1996 Lecuyer et al, 2002 Rollion-Bard et al, 2003) these variations are not well understood but could result, in the case of corals for instance, from some small scale pH variations in the calcifying fluid (Rollion-Bard et al, 2003). 

Palmer M. R., Spivack A. J. and Edmond J. M. (1987) Temperature and pH controls over isotopic fractionation during adsorption of boron on marine clay. Geochim. Cosmochim. Acta 51(9), 2319-2323. 

Schwartz H. P., Agyei E. K. and Mcmullen C. C. (1969) Boron isotopic fractionation during adsorption from... 

In the general case, the set of Equation 51.6 is solved by differential methods. If a step of reactant adsorption is irreversible, then the equations that describe the changes in isotope transfer in the gas phase are solved analytically. Further solution of the primal problem is based on the numerical search of eigenvalues and eigenvectors of the matrix at the right side of the equations describing changes of isotope fraction in the intermediate substances. In this case, the procedure of numerical analysis is performed much faster. 

Wasylenki, L.E., Rolfe, B.A., Weeks, C. L., Spiro, T.G., and Anbar, A.D. (2008) Experimental investigation of the effects of temperature and ionic strength on Mo isotope fractionation during adsorption to manganese oxides. Geochim. Cosmochim. Acta, 72 (24), 5997-6005. 

Siebert et cd. [12] and Barling and Anbar [13] suggested that the equUibrium isotope fractionation effect during adsorption of Mo on birnessite could result either from equUibration of two chemical species of Mo in solution, followed by adsorption of just one of them, or from fractionation during the adsorption reaction itself, between one aqueous species and one adsorbed species not present in solution. In order to address this, Tossell [21] used quantum mechanical calculations to explore which trace species of aqueous Mo might fractionate from the... 

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