Computational Thermo-Fluid Dynamic and Mass Transfer Simulation of Anodic Oxidation in Copper Refining by Arc Electrolysis Using COMSOL Multiphysics

Abstract

Metals such as copper and iron are commonly refined through pyrometallurgical processes, where air serves as the oxidizing agent to remove impurities. The final traces of residual oxygen are typically eliminated by adding deoxidizers to the molten metal, producing inclusions that either float to the surface or become trapped during solidification. An alternative approach consists of supplying oxygen to molten copper via anodic oxidation of oxyanions present in the slag, while cathodic reduction occurs at the arc-slag interface, under conditions that favor oxide valence reduction and evaporation. This paper presents a mathematical formulation describing the physics of arc electrolysis, including the spatial and temporal evolution of electric current, fluid dynamics, heat transfer, and mass transport—particularly the transfer of oxidizing agents from arsenic to copper. A three-dimensional finite element model was developed in COMSOL Multiphysics to couple direct current conduction, fluid flow, heat transfer, and mass transport for oxygen transfer from slag to synthetic blister copper in a DC arc furnace. Thermal balance results indicated an arc temperature of 2067 K, which generates natural convection driven by temperature gradients that also produce concentration gradients. The effect is more pronounced in the slag near the heat source, where velocity reaches 6.75 × 10 − ⁷ m/s, compared with a maximum of 9.72 × 10 −10 m/s in molten copper. Oxygen transport simulations showed that an initial homogeneous concentration of 2446 mol/m 3 evolves after 2000 seconds into a profile ranging from 1840 mol/m 3 at the slag-gas interface to 759 mol/m 3 at the metal-slag interface, where electrochemical oxidation occurs. In copper, oxygen—initially absent—develops a profile with a maximum of 291 mol/m 3 at the metal-slag interface and 184 mol/m 3 at the crucible bottom.