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The use of in situ neutron diffraction methods to determine the kinetics of mineral reactions in iron nickel sulfides
Goldschmidt Conference Abstracts 2006
A505
Thermal evolution of several sulfate-rich brines and hydrated sulfate minerals at the environmental conditions of the martian surface
The use of in situ neutron diffraction methods to determine the kinetics of mineral reactions in iron nickel sulfides
O. PRIETO-BALLESTEROS1, D. FERNANDEZ-REMOLAR1, M. FERNANDEZ-SAMPEDRO1, J.S. KARGEL2, R.E. ARVIDSON3, R. AMILS1,4
ALLAN PRING Department of Mineralogy, South Australian Museum, Adelaide, SA, Australia ([email protected])
1
Centro de Astrobiologı´a-INTA, Spain ([email protected]) Department of Hydrology and Water resources, University of Arizona, Tucson, USA ([email protected]) 3 Washington University in St. Louis, USA (ardvidson@wunder. wustl.edu) 4 Centro de Biologı´a Molecular, CSIC-Universidad Auto´noma de Madrid, Spain ([email protected]) 2
Recently, sensors from different missions to Mars have detected spectroscopic signals of magnesium, calcium and iron sulfates on different locations of the surface of this planet (Arvidson et al., 2005; Gendrin et al., 2005, Langevin et al., 2005). These minerals have been taken as an evidence for supporting the presence of liquid water over the surface in the past of Mars. It is believed that kiesserite, as the lower hydrated phase is the most likely magnesium sulfate, but the stability of higher hydration states at the environmental conditions of the martian surface must be explored (Vaniman et al., 2004). Furthermore, considering the restricted stability of aqueous liquids under low pressures, the thermal evolution of brines should be studied experimentally under expected current and past atmospheric conditions on Mars and compared with the theoretical models (Tosca et al., 2005). We have performed calorimetric analysis at 1, 7, 15 mbar and 1 bar from 100 °C–100 °C of the higher hydrated sulfates and for sulfate-rich brines, including those from (a) the binary systems MgSO4 Æ H2O, FeSO4 Æ H2O, Na2SO4 Æ H2O at eutectic and peritectic compositions and (b) the natural water of Rio Tinto at different concentrations. The analysis have been done in a 2900 TA Instrument DSC equipment. Calorimetric data have determined the vapor pressure of the different hydrated phases in the range of the atmospheric pressure of Mars. The thermal behaviour of the brines and the hydrated minerals at low pressure has been compared to the evolution at atmospheric pressure. Results indicate that in some cases the endothermic process of melting in eutectic or peritectic points is almost simultaneous with the evaporation to the resulting liquids. Results are used to provide updates to the relevant phase diagrams for expected martian conditions.
References Arvidson, R.E. et al., 2005. Science 307, 1591–1594. Gendrin, A. et al., 2005. Science 307, 1587–1591. Langevin, Y. et al., 2005. Science 307, 1584–1586. Tosca, N.J. et al., 2005. EPSL 240, 122–148. Vaniman, D.T. et al., 2004. Nature 431, 663–665.
The penetrating power of a beam of neutrons together with its scattering interactions with minerals offers a number of advantages over alternative techniques such as synchrotron and conventional laboratory sources for the study of the kinetics and mechanisms of mineral reactions. Pentlandite is a primary mineral that forms as an exsolution product from the breakdown of the monosulfide solid solution (mss), an immiscible sulfide melt, from mafic and ultramafic magmas. Violarite, is an abundant supergene alteration product in massive and disseminated Ni sulfide deposits, where it replaces pentlandite and can be a significant part of the ore. To measure the kinetics of the exsolution of pentlandite from mss we undertook a series of in situ cooling neutron diffraction experiments and anneal/quench experiments. These showed that the temperature at which exsolution commences, upon cooling, decreases from 873 K for Fe0.7Ni0.3S–823 K for Fe0.9Ni0.1S and that exsolution effectively between 598 and 548 K. Both high Ni content and high M:S ratio served to facilitate nucleation rate, indicating that nucleation occurs at S vacancies within mss crystals rather than at grain boundaries. Having a low M:S ratio (M0.97S) in the starting mss revealed makes the kinetics of the system is more complex and a refined Avrami model kinetic model had to be employed (Wang et al., 2005). The lowest rates of reaction are observed for the more S rich compositions. The activation energy (Ea) varies from 49.6 to 20.7 kJ.mol 1 with reaction extent (y). The decrease in Ea with y is related to the increasing vacancy concentration in the host phase during the course of exsolution. The kinetics and mechanism of the transformation of pentlandite, (Ni, Fe)9S8, to violarite, Ni2FeS4, have been studied using a specially built flow through cell for in situ neutron diffraction under hydrothermal conditions. The reaction was studied at constant values of pH (range 3–5) controlled by an acetic acid/sodium acetate buffer. At 353 K 20(4) wt% of the pentlandite transforms to violarite in 33 days; with the addition of small amounts of FeIII(CH3COO)2(OH) and H2S the reaction reaches 40(4) wt% completion in this time. At 393 K and a pressure of 3.5 bar the reaction is complete in 3 days at pH 3.9. Electron backscatter diffraction and backscattered electron imaging reveal that the reaction textures are typical of a coupled dissolution–reprecipitation reaction, rather than a solidstate electrolytic process as has been previously reported (Tenailleau et al., 2006).
References doi:10.1016/j.gca.2006.06.1471
Tenailleau, C., Pring, A., Etschmann, B., Brugger, J., Grguric, B., Putnis, A., 2006. Am. Mineral. 91, 706–709. Wang, H., Pring, A., Ngothai, Y., O’Neill, B., 2005. GCA 69, 125–415. doi:10.1016/j.gca.2006.06.1472
A505
Thermal evolution of several sulfate-rich brines and hydrated sulfate minerals at the environmental conditions of the martian surface
The use of in situ neutron diffraction methods to determine the kinetics of mineral reactions in iron nickel sulfides
O. PRIETO-BALLESTEROS1, D. FERNANDEZ-REMOLAR1, M. FERNANDEZ-SAMPEDRO1, J.S. KARGEL2, R.E. ARVIDSON3, R. AMILS1,4
ALLAN PRING Department of Mineralogy, South Australian Museum, Adelaide, SA, Australia ([email protected])
1
Centro de Astrobiologı´a-INTA, Spain ([email protected]) Department of Hydrology and Water resources, University of Arizona, Tucson, USA ([email protected]) 3 Washington University in St. Louis, USA (ardvidson@wunder. wustl.edu) 4 Centro de Biologı´a Molecular, CSIC-Universidad Auto´noma de Madrid, Spain ([email protected]) 2
Recently, sensors from different missions to Mars have detected spectroscopic signals of magnesium, calcium and iron sulfates on different locations of the surface of this planet (Arvidson et al., 2005; Gendrin et al., 2005, Langevin et al., 2005). These minerals have been taken as an evidence for supporting the presence of liquid water over the surface in the past of Mars. It is believed that kiesserite, as the lower hydrated phase is the most likely magnesium sulfate, but the stability of higher hydration states at the environmental conditions of the martian surface must be explored (Vaniman et al., 2004). Furthermore, considering the restricted stability of aqueous liquids under low pressures, the thermal evolution of brines should be studied experimentally under expected current and past atmospheric conditions on Mars and compared with the theoretical models (Tosca et al., 2005). We have performed calorimetric analysis at 1, 7, 15 mbar and 1 bar from 100 °C–100 °C of the higher hydrated sulfates and for sulfate-rich brines, including those from (a) the binary systems MgSO4 Æ H2O, FeSO4 Æ H2O, Na2SO4 Æ H2O at eutectic and peritectic compositions and (b) the natural water of Rio Tinto at different concentrations. The analysis have been done in a 2900 TA Instrument DSC equipment. Calorimetric data have determined the vapor pressure of the different hydrated phases in the range of the atmospheric pressure of Mars. The thermal behaviour of the brines and the hydrated minerals at low pressure has been compared to the evolution at atmospheric pressure. Results indicate that in some cases the endothermic process of melting in eutectic or peritectic points is almost simultaneous with the evaporation to the resulting liquids. Results are used to provide updates to the relevant phase diagrams for expected martian conditions.
References Arvidson, R.E. et al., 2005. Science 307, 1591–1594. Gendrin, A. et al., 2005. Science 307, 1587–1591. Langevin, Y. et al., 2005. Science 307, 1584–1586. Tosca, N.J. et al., 2005. EPSL 240, 122–148. Vaniman, D.T. et al., 2004. Nature 431, 663–665.
The penetrating power of a beam of neutrons together with its scattering interactions with minerals offers a number of advantages over alternative techniques such as synchrotron and conventional laboratory sources for the study of the kinetics and mechanisms of mineral reactions. Pentlandite is a primary mineral that forms as an exsolution product from the breakdown of the monosulfide solid solution (mss), an immiscible sulfide melt, from mafic and ultramafic magmas. Violarite, is an abundant supergene alteration product in massive and disseminated Ni sulfide deposits, where it replaces pentlandite and can be a significant part of the ore. To measure the kinetics of the exsolution of pentlandite from mss we undertook a series of in situ cooling neutron diffraction experiments and anneal/quench experiments. These showed that the temperature at which exsolution commences, upon cooling, decreases from 873 K for Fe0.7Ni0.3S–823 K for Fe0.9Ni0.1S and that exsolution effectively between 598 and 548 K. Both high Ni content and high M:S ratio served to facilitate nucleation rate, indicating that nucleation occurs at S vacancies within mss crystals rather than at grain boundaries. Having a low M:S ratio (M0.97S) in the starting mss revealed makes the kinetics of the system is more complex and a refined Avrami model kinetic model had to be employed (Wang et al., 2005). The lowest rates of reaction are observed for the more S rich compositions. The activation energy (Ea) varies from 49.6 to 20.7 kJ.mol 1 with reaction extent (y). The decrease in Ea with y is related to the increasing vacancy concentration in the host phase during the course of exsolution. The kinetics and mechanism of the transformation of pentlandite, (Ni, Fe)9S8, to violarite, Ni2FeS4, have been studied using a specially built flow through cell for in situ neutron diffraction under hydrothermal conditions. The reaction was studied at constant values of pH (range 3–5) controlled by an acetic acid/sodium acetate buffer. At 353 K 20(4) wt% of the pentlandite transforms to violarite in 33 days; with the addition of small amounts of FeIII(CH3COO)2(OH) and H2S the reaction reaches 40(4) wt% completion in this time. At 393 K and a pressure of 3.5 bar the reaction is complete in 3 days at pH 3.9. Electron backscatter diffraction and backscattered electron imaging reveal that the reaction textures are typical of a coupled dissolution–reprecipitation reaction, rather than a solidstate electrolytic process as has been previously reported (Tenailleau et al., 2006).
References doi:10.1016/j.gca.2006.06.1471
Tenailleau, C., Pring, A., Etschmann, B., Brugger, J., Grguric, B., Putnis, A., 2006. Am. Mineral. 91, 706–709. Wang, H., Pring, A., Ngothai, Y., O’Neill, B., 2005. GCA 69, 125–415. doi:10.1016/j.gca.2006.06.1472