The Thermodynamic Modelling of the Zn Slag Fuming with the Use of Coal and Ammonia

Abstract

Slag fuming process is used to extract zinc from the lead blast furnace slags and recently for the extraction of multiple elements from the complex primary and recycling feed streams, making the thermochemistry of the process challenging. To meet new challenges, computer models with predictive powers outside of the range of normal process conditions are necessary. These models cannot rely exclusively on sets of existing process data and must have a foundation in thermodynamics combined with reasonable kinetic factors. The accuracy of predictions largely depends on the quality of thermodynamic data, including phase equilibria, elemental distributions, and calorimetry measurements. Present study demonstrates the recent developments of the self-consistent thermodynamic model for the gas/slag/matte/metal/speiss/solid phases within the Cu-Pb-Zn-Fe-Ca-Si-O-S-Al-Mg-As-Sb system, applied to zinc fuming, with attention to the phase equilibria and partitioning of minor elements in the process. As a demonstration of calculations far outside of normal operations, the use of ammonia as an alternative to coal is investigated. It was shown that from the thermodynamic point of view the process can reach the same final concentration of zinc and the heat balance of the reactor in the same amount of time when coal is replaced in the process by ammonia.