Improving Pumping Capacity And Reliability In The Mcclean Lake Leach Circuit

The McClean Lake mill is located approximately 850 kilometers north of Saskatoon, Saskatchewan, Canada and is operated by Orano Canada Inc. (Orano). The mill was designed to process high grade uranium ores, and in 2014 completed a multiyear expansion to increase its production capacity to 24 Mlbs U3O8 per annum. This expansion included significant changes to the mill’s secondary leach circuit in support of safely processing high grade ore directly from the Cigar Lake mine. In particular, inter-stage pumps were introduced for slurry transfer between the secondary leach tanks, replacing the original pressure feed forward operation. The design and selection process for these pumps was strongly influenced by the uncertainty related to actual radiation dose exposure when processing undiluted high grade ore (up to 30%U), and consequently the desire to maintain minimal occupancy in the vault enclosure containing the secondary leach tanks. These constraints resulted in the decision to install positive displacement pumps above the leach tanks in a suction-lift configuration. Operating experience with this design has shown that the pump capacity is significantly de-rated due to process solution gas-entrainment and pipe scale build-up, particularly in the front end of the secondary leach circuit where reagent dosage is high. Experience processing high grade ore also provided accurate radiation dose data to demonstrate that the level of occupancy in the leaching vault enclosure could be re-evaluated to accommodate alternate pump configurations. This paper reviews the lessons learned and improvements made to safely increase the capacity and reliability of the leach inter-stage pump system.