Thermodynamic properties of scorodite and parascorodite (FeAsO4·2H2O), kaňkite (FeAsO4·3.5H2O), and FeAsO4

Abstract

Iron arsenates, especially scorodite (FeAsO4.2H2O), are the usual phases of choice for arsenic immobilization in waste forms of variable origin. The thermodynamic properties of this phase, necessary for the prediction of its dissolution or precipitation, have been usually constrained by solubility experiments.

Here, we measured the thermodynamic properties of scorodite, its polymorph parascorodite, the mineral kaňkite (FeAsO4.3.5H2O), and the anhydrous FeAsO4 by a combination of calorimetric techniques, thus avoiding the inherent uncertainties of the solubility experiments.

Keywords

• scorodite
• ferric arsenates
• formation enthalpy
• entropy
• solubility