Wet process for smelting nickel oxide ore

A process for smelting that can attain a high leaching ratio of nickel and cobalt and a high oxidation ratio of iron to trivalent iron, and, at the same time, can reduce energy cost by suppressing the amount of high-pressure air to be used as an oxidant and the amount of high-pressure steam to be used for maintaining temperature. In a smelting method comprising a first step for slurrying nickel oxide ore and a second step for adding sulfuric acid to the ore slurry and leaching the ore slurry while blowing high-pressure air and high-pressure steam therein, characterized by adjusting the carbon grade in a solid content of ore slurry so as to be 0.1 to 0.5% by mass depending on the blending ratio of the nickel oxide ore that constitutes the ore slurry in the first step and controlling oxidation-reduction potential (Ag/AgCl basis) of the leachate to 400 to 600 mV by adjusting the amount of the high-pressure air to be blown so as to be 700 to 800 Nm3 per ton of carbon in a solid content of ore slurry in the second step.