Behavior of bromide, chloride, and phosphate during low‐temperature aqueous Fe(II) oxidation processes on Mars. Issue 5 (12th May 2014)

• Record Type: Journal Article
• Authors: Zhao, Yu‐Yan Sara; McLennan, Scott M.; Schoonen, Martin A. A.
• Is Part Of: Journal of geophysical research. Volume 119:Issue 5(2014:May)
• Page Start: 998
• Page End: 1012
• Publication Date: 2014-05-12
• Subjects: Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1002/2013JE004417
• Languages: English
• ISSNs: 2169-9097

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The behaviors of bromide, chloride, and phosphate were studied experimentally under previously proposed Martian diagenetic conditions, involving jarosite (KFe<sub>3</sub>(OH)<sub>6</sub>(SO<sub>4</sub>)<sub>2</sub>), goethite (<italic>α</italic>‐FeOOH), and hematite (<italic>α</italic>‐Fe<sub>2</sub>O<sub>3</sub>). Experiments evaluated (1) the behavior of Cl<sup>−</sup>/Br<sup>−</sup> with and without aqueous phosphate during oxidation of Fe<sup>2+</sup> to Fe<sup>3+</sup>, (2) the stability of halogen‐bearing jarosite, and (3) the uptake of Cl<sup>−</sup>, Br<sup>−</sup>, H<sub>2</sub>PO<sub>4</sub><sup>−</sup>, and SO<sub>4</sub><sup>2−</sup> by halogen‐free‐hematite, ‐goethite, and ‐jarosite through adsorption. Our results demonstrate that when precipitated from a solution, in which Cl<sup>−</sup> is higher than Br<sup>−</sup>, jarosite preferentially incorporated at least an order of magnitude more Br<sup>−</sup> than Cl<sup>−</sup>. Such enrichment of Br<sup>−</sup> over Cl<sup>−</sup> 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<sup>−</sup> with respect to Cl<sup>−</sup>. 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<sup>−</sup>, Br<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, and H<sub>2</sub>PO<sub>4</sub><sup>−</sup> on halogen‐free‐hematite, ‐goethite, and ‐jarosite demonstrates that in a sulfate‐dominant aqueous system, Cl<sup>−</sup>, Br<sup>−</sup>, and H<sub>2</sub>PO<sub>4</sub><sup>−</sup> could not compete with SO<sub>4</sub><sup>2−</sup>. 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.</p> </abstract>