Aqueous speciation of lead and tin chlorides in supercritical hydrothermal solutions

Etsuo Uchida, Teppei Sakamori, Jin Matsunaga

    Research output: Contribution to journalArticle

    3 Citations (Scopus)

    Abstract

    In order to obtain the stepwise formation constants of tri-chloro complexes of Pb2+ and Sn2+, experiments on the effect of NaCl concentration on the ion exchange equilibria in the systems PbS - ZnS - PbCl2 - ZnCl2 - H2O and CaWO4 - SnWO4 - CaCl2 - SnCl2 - H2O were carried out. The experiments were conducted at 500°, 600°, 700° and 800°C (800°C is only for Sn2+), 1 kbar and also at 600°C, 0.5 kbar using 2 m aqueous chloride solutions. In all the experiments, the Σm(Pb)/(Σm(Pb)+Σm(Zn)) ratio of the aqueous chloride solutions in equilibrium with both PbS and ZnS and the Σm(Ca)/Σm(Ca)+Σm(Sn)) ratio of the aqueous chloride solutions in equilibrium with both CaWO4 and SnWO4 decrease with the increase of NaCl concentration. The experimental results were analyzed thermodynamically using the previously published dissociation constants for NaClaq, CaCl2aq and ZnCl3 - aq. As a result, the stepwise formation constants (log K) for PbCl3 - aq (PbCl2aq + Cl- aq = PbCl3 - aq) were obtained to be -0.1 at 500°C and 1 kbar, 0.9 at 600°C and 1 kbar, 1.4 at 700°C and 1 kbar, and 1.3 at 600°C and 0.5 kbar. The stepwise formation constants (log K) for SnCl3 - aq (SnCl2aq + Cl- aq = SnCl3 - aq) were obtained to be 0.5 at 500°C and 1 kbar, 1.4 at 600°C and 1 kbar, 2.0 at 700°C and 1 kbar, 2.6 at 800°C and 1 kbar, and 1.9 at 600°C and 0.5 kbar. The stepwise formation constants (log K) of tri-chloro complexes of Pb2+, Sn2+, Fe2+, Mn2+, Co2+, Ni2+, Zn2+ and Cd2+ vary with sixfold coordinated ionic radius showing a parabola-shaped curve with a maximum between Mn2+ and Cd2+. This may suggest that the best ionic radius for tri-chloro complex exists between Mn2+ and Cd2+.

    Original languageEnglish
    Pages (from-to)61-72
    Number of pages12
    JournalGeochemical Journal
    Volume36
    Issue number1
    Publication statusPublished - 2002

    Fingerprint

    lead chlorides
    tin
    Chlorides
    chlorides
    chloride
    Experiments
    Ion exchange
    parabolas
    radii
    experiment
    ion exchange
    stannous chloride
    lead chloride
    dissociation
    curves
    SnWO4
    ions

    ASJC Scopus subject areas

    • Geochemistry and Petrology
    • Geophysics

    Cite this

    Aqueous speciation of lead and tin chlorides in supercritical hydrothermal solutions. / Uchida, Etsuo; Sakamori, Teppei; Matsunaga, Jin.

    In: Geochemical Journal, Vol. 36, No. 1, 2002, p. 61-72.

    Research output: Contribution to journalArticle

    Uchida, Etsuo ; Sakamori, Teppei ; Matsunaga, Jin. / Aqueous speciation of lead and tin chlorides in supercritical hydrothermal solutions. In: Geochemical Journal. 2002 ; Vol. 36, No. 1. pp. 61-72.
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    AU - Matsunaga, Jin

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    N2 - In order to obtain the stepwise formation constants of tri-chloro complexes of Pb2+ and Sn2+, experiments on the effect of NaCl concentration on the ion exchange equilibria in the systems PbS - ZnS - PbCl2 - ZnCl2 - H2O and CaWO4 - SnWO4 - CaCl2 - SnCl2 - H2O were carried out. The experiments were conducted at 500°, 600°, 700° and 800°C (800°C is only for Sn2+), 1 kbar and also at 600°C, 0.5 kbar using 2 m aqueous chloride solutions. In all the experiments, the Σm(Pb)/(Σm(Pb)+Σm(Zn)) ratio of the aqueous chloride solutions in equilibrium with both PbS and ZnS and the Σm(Ca)/Σm(Ca)+Σm(Sn)) ratio of the aqueous chloride solutions in equilibrium with both CaWO4 and SnWO4 decrease with the increase of NaCl concentration. The experimental results were analyzed thermodynamically using the previously published dissociation constants for NaClaq, CaCl2aq and ZnCl3 - aq. As a result, the stepwise formation constants (log K) for PbCl3 - aq (PbCl2aq + Cl- aq = PbCl3 - aq) were obtained to be -0.1 at 500°C and 1 kbar, 0.9 at 600°C and 1 kbar, 1.4 at 700°C and 1 kbar, and 1.3 at 600°C and 0.5 kbar. The stepwise formation constants (log K) for SnCl3 - aq (SnCl2aq + Cl- aq = SnCl3 - aq) were obtained to be 0.5 at 500°C and 1 kbar, 1.4 at 600°C and 1 kbar, 2.0 at 700°C and 1 kbar, 2.6 at 800°C and 1 kbar, and 1.9 at 600°C and 0.5 kbar. The stepwise formation constants (log K) of tri-chloro complexes of Pb2+, Sn2+, Fe2+, Mn2+, Co2+, Ni2+, Zn2+ and Cd2+ vary with sixfold coordinated ionic radius showing a parabola-shaped curve with a maximum between Mn2+ and Cd2+. This may suggest that the best ionic radius for tri-chloro complex exists between Mn2+ and Cd2+.

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