2009 Volume 50 Issue 2 Pages 321-331
The solubility of scorodite synthesized in a novel atmospheric process was investigated. Stable scorodite (FeAsO4·2H2O) particles were produced by introducing oxidizing gas into a reaction mixture containing ferrous sulfate and high-concentration arsenic (V) to convert ferrous ion to ferric ion. The obtained scorodite crystals released a very low, almost negligible concentration of arsenic in the pH range of 3 to 6, suggesting its long-term stability. The thermodynamic parameters for the dissolution reaction of scorodite, Ksp and ΔGf, were similar to those reported previously. The results show scorodite released a considerably high concentration of arsenic under specific leaching conditions. In particular, the combination of CaO and NaCl present in the alkaline leaching solution had a significant effect on the mobilization of arsenic. Although this study did not cover all possible natural environments in which scorodite would be stored, it seems practically impossible to develop conditions that would completely prevent the dissolution of arsenic from scorodite. It is crucial to develop scorodite storage methods that will minimize the risk of environmental arsenic contamination based on accurate evaluation of the conditions for the leaching of arsenic.