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_2O_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_2PO_4~-, and SO_4~(2-) by halogen-free-hematite, -goethite, and -jarosite through adsorption. Our results demonstrate that when precipitated froma 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 theMartian 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-), andH_2PO_4~- on halogen-free-hematite, -goethite, and -jarosite demonstrates that in a sulfate-dominant aqueous system, Cl~-, Br~-, and H_2PO_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.
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