As a highly efficient conductor, high-purity copper is essential to all energy transition plans of our society. Copper deoxidation is the final pyrometallurgical step of the copper production process, aiming at reducing the oxygen concentration in copper down to 0.15 %. However, currently used carbon-based reducing agents, such as natural gas, produce CO₂ as an output. Thus, the use of new reductant agents that avoid or reduce those process-related CO₂ emissions is a desirable target for the copper industry. In this context, the utilization of hydrogen gas as a reducing agent has promising potential.
This study explores thermodynamically the use of hydrogen gas as a reducing agent to replace natural gas currently used in copper deoxidation during fire refining. The objective is to maximize the removal of oxygen from the liquid copper phase while avoiding the CO₂ emissions. Process modelling of blister copper deoxidation (Cu-O-S system) was performed using the FactSage 8.2 software. Energy and mass balance calculations were obtained during the deoxidation of the input blister copper at 1200 °C by injection of variable amounts of hydrogen gas at room temperature. The results were compared with those obtained analogously by the addition of natural gas (CH₄).
A first approach to the process from a thermodynamic point of view shows the potential of oxygen and sulfur removal using H₂ and CH₄. Figure 1 displays the weight percent of impurities in liquid copper at 1200 °C against the amount (in grams) of reductant. The quantity of H₂ needed to reduce oxygen content to the target concentration of 0.15 Wt. % from a sample with 1.02 Wt. % O and 0.002 Wt. % S is considerably more favourable than using CH4.

The results of this study will allow us to understand the chemical reactions and the basic thermodynamic aspects of the processes occurring during the hydrogen-based deoxidation of blister copper. This knowledge sets the basis to substitute carbon-based reducing agents by hydrogen to eliminate the CO₂ emissions from the established fire refining process.