THE PH-DEPENDENCE OF SCORODITE DISSOLUTION KINETICS

Scorodite (FeAsO₄ * 2H₂O) occurs naturally as an arsenic-bearing alteration product of arsenopyrite (FeAsS). It is important to understand what controls the release of arsenic into natural systems, as arsenic is a human carcinogen and toxin. The purpose of this research is to evaluate the dissolution kinetics of scorodite as a function of pH. Previous studies of scorodite dissolution have shown that scorodite is stable around a pH of 2 (Dove and Rimstidt 1985; Demopoulos 2005). The dissolution kinetics of scorodite as a function of temperature was studied by Harvey (2004) and was found to increase with temperature. In the current study, the rate of scorodite dissolution is being examined at pH values between 2 and 7, as this pH range is typical in sulfide mine settings. Preliminary results for pH 3 and 5 show that the rate of scorodite dissolution is approximately 10^-10.51 mol/m²sec at pH 3, and increases to 10^{-10. 11} mol/m²sec at pH 5, indicating that the rate of scorodite dissolution increases with pH.