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Behavior of bromide, chloride, and phosphate during low‐temperature aqueous Fe(II) oxidation processes on Mars
Author(s) -
Zhao YuYan Sara,
McLennan Scott M.,
Schoonen Martin A. A.
Publication year - 2014
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2013je004417
Subject(s) - aqueous solution , bromide , mars exploration program , chloride , phosphate , inorganic chemistry , chemistry , astrobiology , organic chemistry , physics
The behaviors of bromide, chloride, and phosphate were studied experimentally under previously proposed Martian diagenetic conditions, involving jarosite (KFe 3 (OH) 6 (SO 4 ) 2 ), goethite ( α ‐FeOOH), and hematite ( α ‐Fe 2 O 3 ). Experiments evaluated (1) the behavior of Cl − /Br − with and without aqueous phosphate during oxidation of Fe 2+ to Fe 3+ , (2) the stability of halogen‐bearing jarosite, and (3) the uptake of Cl − , Br − , H 2 PO 4 − , and SO 4 2− by halogen‐free‐hematite, ‐goethite, and ‐jarosite through adsorption. Our results demonstrate that when precipitated from a solution, in which Cl − is higher than Br − , jarosite preferentially incorporated at least an order of magnitude more Br − than Cl − . Such enrichment of Br − over Cl − in the solids compared to initial solutions suggests that jarosite could be a host for elevated Br on the Martian surface, and the fluids from which jarosite forms could be depleted in Br − with respect to Cl − . Moreover, the incorporation of halogens in jarosite would affect its stability during aqueous alteration, and the dissolution rates of four types of jarosite at both 25°C and 70°C were in the same order: Br,Cl bearing > Br only > halogen free > Cl only. In addition, competitive adsorption of Cl − , Br − , SO 4 2− , and H 2 PO 4 − on halogen‐free‐hematite, ‐goethite, and ‐jarosite demonstrates that in a sulfate‐dominant aqueous system, Cl − , Br − , and H 2 PO 4 − could not compete with SO 4 2− . This observation suggests that the adsorption may not result in an enrichment of phosphate or halogens in Fe oxides in a sulfate‐dominant aqueous system like Meridiani Planum, consistent with the absence of significant correlations of Cl and P with nanoparticle Fe oxides found in Martian soils.