History and Development of Cobalt Production
As Sherritt was developing the hydrometallurgical process for refining nickel, they were also faced with the question of how to separate cobalt from nickel, and then what to do with the cobalt. The selection of hydrogen reduction technology to produce metallic nickel powder also provided Sherritt with a primary nickel-cobalt separation step. As long as the ratio of nickel to cobalt is large, nickel can be selectively reduced with hydrogen without reducing cobalt.
The Lynn Lake concentrate, with typical ore grades of 10% nickel and 0.5% cobalt, yielded nickel reduction feed solution with relatively low cobalt content (nickel/cobalt ratio greater than 30:1). Since the relatively small amount of nickel and cobalt remaining in the solution after nickel reduction could be precipitated from solution with hydrogen sulphide to yield a saleable intermediate nickel-cobalt sulphide product, development and construction of the nickel refinery was able to proceed without a final answer as to how to handle the cobalt.
Many alternative cobalt flowsheets were studied. The Ottawa pilot plant was closed in 1955 and some of the pilot plant equipment was shipped to Fort Saskatchewan where it was used in the assembly of a “commercial sized” cobalt refinery. Output of this plant, at less than 150 tonnes of cobalt per year, was so low that it was only utilized for commercial cobalt production for part of the year, and used for pilot scale development of other hydrometallurgical processes during the remainder of the year. Refining of nickel-cobalt sulphides, utilizing an acid leach of the sulphides, began on June 16, 1955.