Separation of cobalt from nickel and cobalt bearing ammoniacal solutions

Claim 1

In a process for treating nickel and cobalt bearing material in which the material is subjected to a leaching operation in which it is leached in one or more stages under oxidizing conditions with an ammonium salt leach solution in order to cause dissolution of nickel and cobalt values contained in said material after which said nickel and cobalt containing leach solution is separated from undissolved residue and said separated solution is subjected to a cobalt removal operation in which said separated solution is treated with a sulphidizing agent to preferentially precipitate cobalt values therefrom so as to provide a product liquor and a product precipitate composed of a mixed nickel-cobalt sulphide, said product liquor containing the bulk of the nickel values previously in said nickel and cobalt containing in which it is leached in at least two stAges under oxidizing conditions with an ammonium salt leach solution in order to cause dissolution of nickel and cobalt values contained in said material after which said nickel and cobalt containing leach solution from each said leaching stage is separated from undissolved residue and said separated solution from each said leaching stage is subjected to a cobalt removal operation in which said separated solu-tion is treated with a sulphidizing agent to preferentially precipitate cobalt values therefrom so as to provide a product liquor and a product precipitate composed of a mixed nickel-cobalt sulphide, said product liquor containing the bulk of the nickel values previously in said nickel and cobalt containing leach solution together with a small residual quantity of cobalt, said product precipitate containing the bulk of the cobalt values previously in said nickel and cobalt containing leach solution together with a quantity of co-precipitated nickel, the improvement to said cobalt-removal operation whereby the nickel-cobalt ratio in said product liquor is adjusted to a value above about 700:1 concurrently with an adjustment of the nickel-cobalt ratio in said product precipitate to a value below about 2:1, said improvement comprising the steps of: passing nickel and cobalt containing solution separated from one said leaching stage to a first cobalt-removal stage to which is added sulphidizing agent in controlled amount such that the ratio of nickel to cobalt remaining in solution following formation of a mixed nickel-cobalt sulphide precipitate therein is above about 700:1, removing solution from said first cobalt-removal stage and recovery thereof as said product liquor for subsequent treatment for recovery of nickel therefrom, removing from said first cobalt-removal stage the mixed nickel-cobalt sulphide precipitate formed therein and recycling at least a portion thereof to said first leach solution together with a small residual quantity of cobalt, said product precipitate containing the bulk of the cobalt values previously in said nickel and cobalt containing leach solution together with a quantity of co-precipitated nickel, the improvement to said cobalt-removal operation whereby the nickel-cobalt ratio in said product liquor is adjusted to a value above about 700:1 concurrently with an adjustment of the nickel-cobalt ratio in said product precipitate to a value below about 2:1, said improvement comprising the steps of: passing said separated nickel and cobalt containing leach solution to a first cobalt-removal stage to which is added sulphidizing agent in controlled amount such as to cause formation of a mixed nickel-cobalt sulphide precipitate having a nickel-cobalt ratio of less than about 2:1, removing from said first cobalt removal stage the mixed nickel-cobalt sulphide precipitate formed therein and recycling a portion thereof to said first cobalt removal stage and recovering the remainder thereof as said product precipitate, removing solution from said first cobalt-removal stage and recycling a portion thereof to said leaching operation and passing the remainder thereof to a second cobalt removal stage to which is added sulphidizing agent in controlled amount such that the ratio of nickel to cobalt remaining in solution following formation of a mixed nickel-cobalt sulphide precipitate therein is above about 700:1, removing solution from said second cobalt-removal stage and recovery thereof as said product liquor for subsequent treatment for recovery of nickel therefrom, removing from said second cobalt-removal stage the mixed nickel-cobalt sulphide precipitate formed therein and recycling at least a portion thereof to said second cobalt-removal stage and adding any unrecycled portion thereof to said first cobalt-removal stage.