ACID LEACHING PROCESS FOR TREATING HIGH GRADE NICKEL-COPPER MATTES

Nickel and copper values are separately recovered from copper-nickel-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.