Statistics – Applications
Scientific paper
Jun 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.2469g&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 11, pp.2469-2479
Statistics
Applications
4
Scientific paper
The solubility of the assemblage AgCl(s) + Ag-Pd alloy was measured in NaCl / HCl solutions at 300°C using the silica tube method. Oxidation state was controlled by the solid phases, according to the reaction . (A1) The Cl concentrations of the solutions ranged from 0.2 to 4.0 m, with calculated pH 300° C = 0.47 to 1.67. The surfaces of the alloys after the experiments were corroded and showed a substantial depletion in Ag relative to the initial compositions (either Ag .5 Pd .5 or Ag .7 Pd .3 ). Ag solubilities ranged from 0.026 to 0.39 m, whereas Pd solubilities were 3 to 4 orders of magnitude lower (max. of 10 -3.41 m). The results are in excellent agreement with previous studies of the solubility of AgCl ( , 1976; et al., 1986) and Pd-sulfide phases ( et al., 1992) in hydrothermal brines. For the following reaction: , (A2) a value of log K 300° C = 12.81 ± .18 was obtained, which compares with a value of 12.65 ± 0.5 obtained by et al. (1992). The agreement is strong evidence in favor of the validity of both experimental investigations. The results of the present study indicate that Ag will be far more soluble than Pd over most of the range of pH, f O 2 , and SCl concentration found in nature. Nonetheless, Pd-rich alloys may form, owing to the strong thermodynamic partitioning of Pd into the solid phase. Scavenging of dissolved palladium by pre-existing Au-Ag alloy is a viable precipitation mechanism and may limit PGE mobility to extremely low levels in many natural hydrothermal systems. Because this is the first detailed study of its type, the methods and results presented in this study have important applications to future experimental work in the hydrothermal geochemistry of precious metal alloys.
Bloom Michael S.
Gammons Christopher H.
Yu Yue
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