Design, construction, commissioning and operation of the Key Lake uranium mill

After crushing and grinding, the uranium ore is treated in a two-stage leach circuit followed by countercurrent decantation, clarification and filtration. The pregnant solution proceeds to mixer-settlers for the recovery of U3O8 by solvent extraction. Coextracted arsenic is then removed from the organic phase in acid-scrub mixer-settlers. The scrubbed organic phase passes to stripping mixer-settlers, from which loaded strip solution at 20-25 g/l U3O8 passes to the yellow cake precipitation circuit, where uranium is precipitated as ammonium diuranate. The (NH4)2SO4 generated by the yellow cake circuit is crystallized for sale as fertilizer. The effluent treatment circuit incorporates a multistage precipitation system. Treated water is discharged to the environment only after sampling in monitoring ponds. Throughput is now 760-800 t/day at a grade of 2.2% U3O8, 2.3% Ni and 1.3% As. The recovery in the leach circuit is 99% and overall recovery is 97.5%, given an annual production of 5675 t U3O8. (author)