Efficient extraction of nickel from sintered alloy by stepwise leaching: Thermodynamic and kinetic studies

•More than 99.9% Ni was extracted from sintered alloy by stepwise leaching process.•Nickel oxides and passivation films prevented high-efficient extraction of nickel.•The nickel oxides were converted into water-soluble NiSO4 by an acid curing process.•The leaching process was controlled by the mixed control model within 60 min.