Solubility of jarosite at 4–35 °C

Abstract

The solubility of jarosite (KFe 3(SO 4) 2(OH) 6) was studied in a series of dissolution experiments. The experiments were conducted at 4–35 °C and at pH values between 1.5 and 3.0 using a synthetic jarosite with a composition very close to ideal. The solids were left in the reaction vessel for up to 6 months. Equilibrium was established in the experiments after approximately 3 to 4 months. The log K SP for the jarosite dissolution reaction KFe 3(SO 4) 2(OH) 6 + 6H +K + + 3Fe 3+ + 2SO 4 2− + 6H 2O at 25 °C is determined to be −11.0 ± 0.3. From this measured solubility product, the free energy of formation, Δ G f.298 o is calculated to be −3309.8 ± 1.7 kJ mol −1. Based on the temperature dependence of the solubility product, the enthalpy of reaction at 25 °C, Δ H r.298 o is −45 ± 5 kJ mol −1, the entropy of reaction, Δ S r.298 o, is −350 ± 40 J mol −1K −1, and the heat capacity of the reaction, ΔC p.r , over the temperature range of the experiments is determined to be −2.1 ± 0.2 kJ mol −1 K −1. The rate of the dissolution reaction can be described by a first-order model.