The acid pressure leach process for nickel and cobalt laterite. Part II: Review of operations at Fort Saskatchewan

摘要

The nickel-cobalt sulphides produced from limonitic laterite ores by Moa Nickel S.A. in Cuba are shipped to the Corefco nickel-cobalt refinery in Canada. This refinery is the former Sherritt Gordon nickel refinery in Fort Saskatchewan, Alberta, which has been in operation since 1954. Major changes to the refining process were required to handle the Moa sulphide feed with its unusually high cobalt content. While the ammonia leach and hydrogen reduction circuits were retained with only minor modifications, major changes were made in the processes for the separation and recovery of cobalt. A totally new cobaltnickel separation was successfully developed, in which most of the cobalt is separated from the ammoniacal nickel sulphate leach solution by precipitation as a cobalt-nickel hexammine salt, using anhydrous ammonia as the reagent. This salt, which contains equal amounts of cobalt and nickel, is refined to a pure cobaltic hexammine salt by selectively leaching nickel with water, and recrystallizing the resulting impure cobaltic hexammine salt in ammonium sulphate solution. The recrystallized cobalt hexammine salt has a Co : Ni ratio of over 2000 : 1, and contains very low levels of copper, zinc and cadmium. It is redissolved in ammonium sulphate solution and coverted to cobalt powder by hydrogen reduction. This paper describes the changes made to the refinery processes since 1991, and reviews recent operating performance with emphasis on the treatment of Moa sulphides.