Due to its excellent conductivity, high-purity copper plays a crucial role in our society's energy transition. During the blister copper deoxidation stage, the oxygen concentration in the metal is reduced to levels below 0.15 wt. % by bubbling a reducing gas (usually natural gas). In this process, the reaction of the reducing gas with dissolved oxygen generates water vapour and carbon dioxide (CO2). In this regard, the replacement of natural gas with hydrogen as a deoxidizer offers a promising alternative to reduce CO2 emissions from the copper production process. To evaluate the feasibility of the transition to hydrogen as a deoxidant, descriptive models capable of capturing the complexity of the process are needed.
This study presents a kinetic model of the blister copper deoxidation process based on the “Effective Equilibrium Reaction Zone” (EERZ) method and the thermodynamic databases of the FactSage 8.3 software implemented with the ChemApp Python module. The EERZ approach allows us to divide the complex heterogeneous system into several reaction zones where a local equilibrium is established under the following assumptions: 1) only a certain volume of phase participates in the deoxidation reaction at the reducing bubble/molten copper interface, 2) the volume of reacted (oxygen-depleted) copper is homogenized with the unreacted volume, 3) the reaction products generated at the interface are homogenized with the unreacted gas inside the bubble, and 4) the gas bubbles rise through the molten copper to the surface, where they are homogenized with the furnace atmosphere. The mass and energy balances derived from the model were validated with real industrial data obtained at Atlantic Copper's Huelva plant. The model allows the temperature and composition of liquid copper and gaseous products to be predicted satisfactorily during deoxidation.
The model presented will serve to improve our understanding of the deoxidation process of molten metals and will help lay the foundations for the substitution of carbon-based reductants for hydrogen, with the aim of mitigating CO2 emissions associated with metallurgical processes.