Abstract Nickel and copper values are separately recovered from coppernickel-sulphide matte by means of a multi-stage acid leach process. The matte is treated in a first leaching stage in which the acid to acid-reactive metals molar ratio and leaching time are controlled to selectively extract the bulk of the nickel values while the copper values remain in the leach residue. The residue containing copper values and a minor portion of the nickel values is then acid leached in one or more stages to substantially completely extract copper values and the residual nickel values. Precious metal contained in the matte are concentrated in the residue from the secondary leaching stages. Copper is recovered from the solution from the secondary leaching stages and the spent solution containing one mole of acid per mole of copper recovered is recycled as required to the first leaching stage to maintain the desired sulphur balance in that stage.
A process according to claim 1 in which the first stage leach is continued to extract from 70 to 90 percent of the nickel content of the matte.
Claim 2
Dependent Claim
42 words
A process according to claim 1 in which the recycling of spent solution from the copper winning step to the first stage leach is regulated to maintain the pH in the first stage leach within the range of about 3 to 4.5.
Claim 3
Dependent Claim
32 words
A process according to claim 1 in which the first stage leach is carried on under non-oxidizing conditions for a period of time after the major portion of nickel has been extracted.
Claim 4
Dependent Claim
31 words
The process as claimed in claim 1 in which the end slurry from the first stage leach is treated with a soluble sulphide to substantially completely precipitate any residual copper therefrom.
Claim 5
Dependent Claim
44 words
A process as claimed in claim 1 in which said matte initially contains nickel and copper values in a weight ratio of from about 1:1.5 to about 1:2.0 and from about 0.5 to about 0.8 mole of sulphur per mole of nickel plus copper.
Claim 6
Dependent Claim
23 words
A process according to claim 1 wherein the first and second stage leaches are conducted at a temperature between 270*F. and about 300*F.
Claim 7
Dependent Claim
31 words
A process as claimed in claim 1 in which said matte initially includes precious metal values which precious metal values are recovered in concentrated form in said second stage leach residue.
Claim 8
Dependent Claim
74 words
A process as claimed in claim 8 which additionally comprises leaching said second stage leach residue in a third stage leach with sulphuric acid and under oxidizing conditions to extract substantially all acid soluble metals therein, separating solution from said third stage leach end slurry and recovering a third stage leach residue rich in precious metal values and essentially completely free of nickel and copper and recycling said solution to said second leaching stage.