Solubility and stability of scorodite, FeAsO4•2H2O: new data and further discussion

The solubility of crystalline samples of scorodite, synthetic and natural, was found to be about two orders of magnitude lower than those reported by earlier authors for apparently amorphous ferric arsenate. Congruent dissolution was observed between pH 1.0 and 2.4. Congruent dissolution data obtained with the synthetic sample were used to calculate the solubility product of scorodite at 23 o C and the free energy of formation