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An experimental study of solubility and speciation of NdF3 in F-bearing aqueous solutions
Goldschmidt Conference Abstracts 2006
An experimental study of solubility and speciation of NdF3 in F-bearing aqueous solutions ART. MIGDISOV, A.E. WILLIAMS-JONES
A419
Geomicrobiology of an Antarctic subglacial brine: A plausible Martian ecosystem J.A. MIKUCKI1, J.C. PRISCU2, W.B. LYONS3, K.A. WELCH3, M. TRANTER4, A. PEARSON1 1
Deparment of Earth and Planetary Sciences, McGill University, Montreal, Canada ([email protected]) The solubility of neodymium fluoride was investigated at 150, 200 and 250 °C and saturated water vapour pressure. Experiments were performed in Teflon test tubes sealed by Teflon stoppers and placed in the autoclaves. In order to prevent failure of the test tubes due to the internal pressure developed during runs, an aliquot of distilled water was introduced into the autoclaves. Crystals of neodymium fluoride (NdF3) were equilibrated with solutions containing HF in concentrations ranging from 0 to 0.15 mol/l. The pH (1.34 ± 0.1 at 25 °C) and ionic strength (I) of the solutions were controlled by perchloric acid and sodium perchlorate, respectively. The solubility of neodymium fluoride was determined for sets of experiments with ionic strengths of 0.01, 0.05 and 0.15. Control experiments were also performed at ionic strengths of 0.5 and 1. After equilibrium was attained, the autoclaves were quenched, the crystalline NdF3 was removed, any Nd species precipitated were dissolved by adding sulfuric acid to the experimental solutions and the concentrations of Nd and F were analysed using ICP-MS and NAA.
Earth and Planetary Sciences, Harvard University, UK ([email protected]; [email protected]) 2 Montana State University, UK ([email protected]) 3 Byrd Polar Research Center, UK 4 Bristol Glaciology Centre, UK ([email protected]) The dry valleys of Antartica are host to an assortment of brines at various stages of cryoevaporation (Lyons et al., 2005). It has been suggested that brines formed by similar processes exist on Mars (Burth and Knauth, 2003). Here, we present geomicrobiological data on an Antarctic brine that exists below the Taylor Glacier in the Taylor Valley. Geochemical analyses of subglacial discharge collected at the surface site known as Blood Falls, indicates that the brine is of marine origin and has had limited contact to the atmosphere since it was covered by Taylor Glacier. The brine contains high concentrations of iron oxides (3.8 mM), dissolved inorganic (50 mM C) and organic carbon (400 lM C), and is depleted in sulfate relative to is source waters (SO42 :Cl ratios in seawater = 0.052; in Blood Falls = 0.035). The microbial diversity associated with this feature, described using molecular and culture techniques, reflects the in situ geochemistry with members known to cycle iron and sulfur compounds (i.e. Thiomicrospria sp., Geopsychrobacter sp., and Desulfocapsa sp.). Combining our geochemical and biological data on the Taylor brine allows for the theoretical modeling of both physical and geochemical constraints on microbially mediated processes in this subglacial system. Importantly, the physical and chemical nature of Blood Falls brine provides a model system for assessing the biological potential for similar ecosystems on Mars.
References Burth, D.M., Knauth, L.P., 2003. J. Geochem. Res. 108, 22–33. Lyons et al., 2005. Geochim. Cosmochim. Acta 69, 305–323. doi:10.1016/j.gca.2006.06.844
The results of our experiments show that Nd3+ and NdF2+ are the dominant species in solution at the temperatures investigated. The data obtained were used to derive formation constants for NdF2+ and values of the solubility product for NdF3. Dependence on ionic strength was modelled using the extended Debye–Hu¨ckel equation. The parameter bc (NaClO4) for this equation and the distances of closest approach for Nd3+ and NdF2+ were also optimized based on the experimental data. The results of this study show that published theoretical predictions significantly overestimate the stability of NdF2+ and the solubility of NdF3. doi:10.1016/j.gca.2006.06.843
An experimental study of solubility and speciation of NdF3 in F-bearing aqueous solutions ART. MIGDISOV, A.E. WILLIAMS-JONES
A419
Geomicrobiology of an Antarctic subglacial brine: A plausible Martian ecosystem J.A. MIKUCKI1, J.C. PRISCU2, W.B. LYONS3, K.A. WELCH3, M. TRANTER4, A. PEARSON1 1
Deparment of Earth and Planetary Sciences, McGill University, Montreal, Canada ([email protected]) The solubility of neodymium fluoride was investigated at 150, 200 and 250 °C and saturated water vapour pressure. Experiments were performed in Teflon test tubes sealed by Teflon stoppers and placed in the autoclaves. In order to prevent failure of the test tubes due to the internal pressure developed during runs, an aliquot of distilled water was introduced into the autoclaves. Crystals of neodymium fluoride (NdF3) were equilibrated with solutions containing HF in concentrations ranging from 0 to 0.15 mol/l. The pH (1.34 ± 0.1 at 25 °C) and ionic strength (I) of the solutions were controlled by perchloric acid and sodium perchlorate, respectively. The solubility of neodymium fluoride was determined for sets of experiments with ionic strengths of 0.01, 0.05 and 0.15. Control experiments were also performed at ionic strengths of 0.5 and 1. After equilibrium was attained, the autoclaves were quenched, the crystalline NdF3 was removed, any Nd species precipitated were dissolved by adding sulfuric acid to the experimental solutions and the concentrations of Nd and F were analysed using ICP-MS and NAA.
Earth and Planetary Sciences, Harvard University, UK ([email protected]; [email protected]) 2 Montana State University, UK ([email protected]) 3 Byrd Polar Research Center, UK 4 Bristol Glaciology Centre, UK ([email protected]) The dry valleys of Antartica are host to an assortment of brines at various stages of cryoevaporation (Lyons et al., 2005). It has been suggested that brines formed by similar processes exist on Mars (Burth and Knauth, 2003). Here, we present geomicrobiological data on an Antarctic brine that exists below the Taylor Glacier in the Taylor Valley. Geochemical analyses of subglacial discharge collected at the surface site known as Blood Falls, indicates that the brine is of marine origin and has had limited contact to the atmosphere since it was covered by Taylor Glacier. The brine contains high concentrations of iron oxides (3.8 mM), dissolved inorganic (50 mM C) and organic carbon (400 lM C), and is depleted in sulfate relative to is source waters (SO42 :Cl ratios in seawater = 0.052; in Blood Falls = 0.035). The microbial diversity associated with this feature, described using molecular and culture techniques, reflects the in situ geochemistry with members known to cycle iron and sulfur compounds (i.e. Thiomicrospria sp., Geopsychrobacter sp., and Desulfocapsa sp.). Combining our geochemical and biological data on the Taylor brine allows for the theoretical modeling of both physical and geochemical constraints on microbially mediated processes in this subglacial system. Importantly, the physical and chemical nature of Blood Falls brine provides a model system for assessing the biological potential for similar ecosystems on Mars.
References Burth, D.M., Knauth, L.P., 2003. J. Geochem. Res. 108, 22–33. Lyons et al., 2005. Geochim. Cosmochim. Acta 69, 305–323. doi:10.1016/j.gca.2006.06.844
The results of our experiments show that Nd3+ and NdF2+ are the dominant species in solution at the temperatures investigated. The data obtained were used to derive formation constants for NdF2+ and values of the solubility product for NdF3. Dependence on ionic strength was modelled using the extended Debye–Hu¨ckel equation. The parameter bc (NaClO4) for this equation and the distances of closest approach for Nd3+ and NdF2+ were also optimized based on the experimental data. The results of this study show that published theoretical predictions significantly overestimate the stability of NdF2+ and the solubility of NdF3. doi:10.1016/j.gca.2006.06.843