Method for treating alloy

An alloy processing method comprising:

• a leaching step that comprises subjecting an alloy comprising nickel and/or cobalt and copper to a leaching treatment with a sulfuric acid solution in the presence of a sulfurizing agent to obtain a leachate and a leached residue;
• and
• a reduction step that comprises subjecting a portion of the leachate to a reduction treatment by adding a reducing agent to the portion of the leachate to obtain a post-reduction solution and a reduced residue;
• wherein a remainder of the leachate, not subjected to the reduction treatment of the reduction step, is recycled for use in the leaching step as part or whole of the sulfuric acid solution added for the leaching treatment;
• wherein in the leaching step,
• an oxidative-reduction potential of the leachate is measured and controlled by addition of an oxidizing agent,
• the oxidative-reduction potential value of the leachate is controlled within the range of 240 mV or more and 300 mV or less as measured with reference to a silver-silver chloride electrode;
• the sulfuric acid solution is added in an amount of more than 1 equivalent and 1.2 equivalents or less based on the total amount of nickel and/or cobalt in the alloy for the leaching treatment;
• and
• the leaching treatment produces a leachate with a free acid concentration in a range of 0.1 mol/L or more and 0.4 mol/L or less.