Distribution of arsenic and nickel in uranium mill tailings, Rabbit Lake, Saskatchewan, Canada

The Rabbit Lake U mine in-pit tailings management facility (TMF) is located in northern Saskatchewan, Canada. The tailings body is approximately 425 m long x 300 m wide and 91 m thick at its centre. An investigation of the TM F was performed to collect tailings samples from depth to quantify the dist ribution of As and Ni in the tailings with respect to ore type and assess t he distribution of As and Ni with respect to tailings mineralogy. The taili ngs body consists of alternating layers of ice, frozen tailings and unfroze n tailings which varied in texture from a slurry to a firm silty sand. The tailings solids are predominately composed of quartz (16-36%), calcium sulp hate (0.3-54%) and illite (3 and 14%). Arsenic and Ni concentrations in the tailings show similar patterns with depth which were strongly related to h istorical changes in As and Ni concentrations in the mill feed. Mineralogy of the ore bodies indicated that As and Ni in the mill feed occurred primar ily as 1:1 molar ratio arsenides such as niccolite and gersdorffite. Arseni c and Ni concentrations in the tailings were also measured at a near 1:1 mo lar ratio. Mill process records showed that an average of 71% pf the As in the mill feed was solubilized during leaching. SEM analysis suggested that solubilized As is precipitated as Ca2+, Fe3+ and Ni2+ arsenates during the neutralization process. Mill records indicated that 17,000 tonnes of As wer e discharged to the TMF of which approximately 88% was as arsenates and 12% as primary arsenides. (C) 2000 Elsevier Science Ltd. All rights reserved.