Raffinate neutralization experiments at the McClean Lake Mill - removal of arsenic and nickel

Uranium ores at the McClean Lake Operation in the Athabasca Basin of Northern Saskatchewan can produce elevated levels of arsenic (up to 700 mg/L) and nickel (up to 500 mg/L) in acidic (pH<1.5) spent leaching solutions (raffinates). Prior to neutralization, if necessary, ferric sulfate is added to tailings slurries to increase their Fe/As (molar) ratio to greater than 3. The slurries are then neutralized with lime to pH 4, and subsequently to pH 7-8. After neutralization, As and Ni concentrations average less than 1 mg/L. Solids from bench scale experiments demonstrate that As is associated primarily with scorodite and annabergite, with small amounts adsorbed onto or co-precipitated with ferrihydrite.