Treatment method for alloy

An alloy treatment method for obtaining a solution containing nickel and/or cobalt from an alloy containing nickel and/or cobalt and copper, the method comprising:

• a leaching step of adding an acid solution to the alloy and performing a leaching treatment in a state where a sulfurizing agent coexists, thereby obtaining a leachate comprising nickel and/or cobalt and a leached residue containing cupper sulfide formed by sulfurization of copper with the sulfurizing agent, wherein
• in the leaching step, a divalent copper ion source is added and the leaching treatment is performed while maintaining a copper concentration in a reaction solution in a range of 0.5 g/L or more and 15 g/L or less, and
• sulfurization of the divalent copper ions by the sulfurizing agent is controlled by maintaining an oxidation-reduction potential of the reaction solution after the divalent copper ions are added, at 50 mV or more in terms of a value using a silver/silver chloride electrode as a reference electrode.