Mechanism of oxides reduction during bubbling of copper-smelting slags by CO–CO<sub>2</sub> gas mixtures

Abstract

The paper suggests a mechanism of simultaneous oxide reduction from multicomponent copper-smelting slags during their bubbling with CO–CO2 reducing mixtures and provides a numerical algorithm developed to implement this mechanism as a mathematical model. The first feature of the suggested mechanism is a statement that the total speed of the overall reduction process is determined by CO consumption during its interaction with oxygen ions formed in slag oxide dissociation. The second feature is a statement about equilibrium achieved between slag, alloy and gaseous phase according to the system oxidizing potential reached at every instant. The paper demonstrates a satisfactory agreement between calculated and experimental data obtained when reducing industrial coppersmelting slags at 1300 °С and СО/СО2 = 4, 6, 156, and using the first-degree kinetic equation regarding the difference between initial and equilibrium CO contents in the gaseous phase. A generalized kinetic constant of the multicomponent slag reduction reaction rate is calculated as k = 2.6·10–7, moles CO /(cm2 · sec·%) at 1300 °С. It is shown that during industrial multicomponent slag reduction, reduction speed of copper (I) oxide and magnetite are high and close to maximal ones as early as at the first minutes of slag bubbling with reducing gas. At the same time, for Fe(II), lead and zinc oxides they are low at the first minutes of the process, and increase gradually to reach their maximum, and then decrease again up to near-zero values as the supplied gas and melt come to equilibrium. Generally, oxide reduction speed naturally decreases with approaching to equilibrium between the initial gas and liquid phases, and this should be taken into account when designing continuous slag depletion processes.