Abstract
Na-jarosite dissolution rates measured at temperatures 277K, 295K, and 323K and at pH∼1, 2, 8, and 10 in dilute solutions yield the following rate equation: r=0.0946e-26,921RT(aH+)0.830+4.36e-52,272RT(aOH-)0.317Dissolution rates are minimized between pH 3 and 4 and increase with increasing activity of both H+ and OH−. Overall, Na-jarosite dissolution rates are comparable, but slightly faster than K-jarosite dissolution rates, suggesting that K–Na substitution in the 8-coordinated A site has a minimal effect on dissolution rate. Slightly faster Na-jarosite dissolution rates yielded shorter estimated lifetimes in aqueous systems, but similar activation energies compared to K-jarosite. Calculated Na-jarosite lifetimes for 1mm jarosite particles (maximum potential jarosite particle size observed at Meridiani Planum) range from less than 1year at pH 10 and 295K to 200years at 277K at pH 3–4. These calculated lifetimes represent a maximum far-from equilibrium fluid-Na-jarosite contact time for Meridiani Planum.
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