Na-jarosite dissolution rates: The effect of mineral composition on jarosite lifetimes

Na-jarosite dissolution rates measured at temperatures 277 K, 295 K, and 323 K and at pH ∼ 1, 2, 8, and 10 in dilute solutions yield the following rate equation: r = 0.0946 e - 26 , 921 RT ( a H + ) 0.830 + 4.36 e - 52 , 272 RT ( a OH - ) 0.317 ution 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 1 mm jarosite particles (maximum potential jarosite particle size observed at Meridiani Planum) range from less than 1 year at pH 10 and 295 K to 200 years at 277 K at pH 3–4. These calculated lifetimes represent a maximum far-from equilibrium fluid-Na-jarosite contact time for Meridiani Planum.