<p>Improving the efficiency of copper (Cu) fire refining is essential for reducing energy consumption and environmental impact. Although methane (CH₄) gas is often used as a reducing agent in the Cu fire refining processes, the kinetic mechanism of deoxidation using CH₄ (<i>g</i>) remains insufficiently understood. This study aims to elucidate the rate-controlling step of the deoxidation of a Cu (<i>l</i>) melt using a methane-argon (CH₄–Ar) gas mixture bubbled in the temperature range of 1423–1523&#xa0;K. The effects of total gas flow rate, partial pressure of CH₄, and reaction temperature on the deoxidation rate were investigated. The overall deoxidation reaction of the Cu melt comprises the mass transfer of CH₄ in the gas boundary layer, mass transfer of dissolved oxygen (O) in the liquid boundary layer, oxygen-promoted decomposition of CH_<i>x</i> (1 ≤ <i>x</i> ≤ 4) at the reaction interface, and the subsequent deoxidation by carbon (C) and hydrogen gas (H₂). From the analysis of the first-order reaction rate equations, the decomposition of CH_<i>x</i> at the reaction interface was determined to be the rate-controlling step of deoxidation under the investigated conditions. The activation energy of deoxidation reaction was calculated to be 183.1&#xa0;kJ⋅mol^–1 in the range of 1423–1523&#xa0;K.</p> Graphical Abstract <p></p>