Solubility of KFe3(CrO4)2(OH)6 at 4 to 35°C

Details Solubility of KFe3(CrO4)2(OH)6 at 4 to 35°C Solubility of KFe3(CrO4)2(OH)6 at 4 to 35°C

Oct 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60.3815b&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 60, Issue 20, p. 3815-3824.

Computer Science

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Scientific paper

The solubility of KFe3(CrO4)2(OH)6, the chromate analog of the sulfate mineral jarosite, was studied in a series of dissolution experiments. Experiments were conducted at 4 to 35°C and pH values between 1.5 and 3.0 using synthetic KFe3(CrO4)2(OH)6. The solids were kept in the reaction vessel for up to 6 months. Equilibrium was established in the experiments between 2 and 4 months. The log Ksp for the dissolution reaction of KFe3(CrO4)2(OH)6 KFe()2(+6H⇄K+3Fe+2CrO42++6HO at 25°C is -18.4 ± 0.6. Based on this measured solubility product, the free energy of formation, ΔGf,298°, is -3305.5 ± 3.4 kJ mol-1. The dissolution experiments at 25°C indicate the formation of a FeCrO4+ complex. The dissolution experiments combined with previously published spectroscopic data between 0 and 25°C yield a formation constant of the form 2.303log KFeCrO4+ = -ΔH°/RT + ΔS°/R, where ΔH° = 19.1 ± 2.2 kJ mol-1 and ΔS° = 214 ± 8 J K-1 mol-1. At 25°C, log KFeCrO4+ is 7.8 ± 0.5. The equilibrium ion activity products calculated from the experiments at 4, 15, 25, and 35°C do not show a statistically significant trend indicating a weak temperature dependence of the solubility product over the temperature range of the experiments. The rate of the dissolution reaction can be described by a first-order model. The measured solubility indicates that the chromate analog of jarosite is stable over a wide range of conditions and could form in large parts of a Cr(VI)-contaminated aquifer.

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