Investigation of seasonal metallurgical shift at incoʹs clarabelle mill

The seasonal metallurgical shift at Incoʹs Clarabelle mill, Copper Cliff, Ontario represents a significant variation in pentlandite and precious metals recovery from summer to winter. The decrease in metals recovery in winter has been a subject of research and debate in the past decades. To understand this seasonal phenomenon, on-site testwork using a portable batch flotation column was conducted in two winter seasons and two summer seasons. On-site batch tests on the main flotation feed were used to obtain flotation rate and selectivity data. Other data such as dissolved ions and thiosalts in process and feed waters that could affect flotation was also collected. the most important findings from the present investigation was that both sulfide and gangue minerals were floated significantly faster in winter than in summer. The pentlandite /pyrrhotite and pentlandite / rock selectivity was, however, considerably decreased in winter. The process and feed water analysis indicated that the high concentration of dissolved nickel ions in the winter process water could have activated all minerals, leading to the higher flotation rates. The increase in pyrrhotite and rock flotation rates was, however, larger than the increase in pentlandite flotation rate. This resulted in the reduced pentlandite /pyrrhotite and pentlandite / rock selectivity in winter, which was the main cause for the seasonal metallurgical shift.