The transformation of ferrihydrite under a range in pH (2-10) and temperature (25-100 ^oC)

Ferrihydrite, a form of iron in mill tailings, is a dominant sorption complex for elements of concern (EOC) such as arsenic (via adsorption or co-precipitation) within uranium mine tailings at the Key Lake Operation. As ferrihydrite is unstable under oxic conditions, and can undergo dissolution and subsequent crystallization to hematite and goethite over time, the impact of crystallization on the long-term stability of EOC within tailings needs to be investigated. Here, studies were undertaken to assess rates of pure ferrihydrite recrystallization in relatively dilute aqueous solutions which serve as baseline for upcoming studies that more closely simulate uranium mine tailings solutions. The results are also used to assess the impacts of recrystallization on porewater concentrations of sorbed sulfate and arsenate. At present, these preliminary results indicate the rate of crystallization is controlled by solution pH, temperature, and reaction time. (author)