Zinc fuming kinetics in a bubble-stirred molten slag bath (for slag recycling)

SIM² KU Leuven – HiTemp researchers studied the Zn fuming kinetics in a bubble-stirred molten slag bath. The results were published in Metallurgical and Materials Transactions B. Based on laboratory-scale experiments, the kinetics of Zn fuming from a fayalite-based slag through stirring with air-CH4 gas mixtures have been studied, and a kinetic model has been developed. The outcome of this work provides a significant scientific basis for the recovery of Zn (ZnO) from the Zn-bearing metallurgical slags

Why Zn fuming?

Zn-bearing slags, containing a substantial amount of valuable elements (e.g., Zn, Fe, Cu and Ag), are an important secondary resource, and are also classified as potentially harmful wastes due to the presence of potentially harmful elements (PHEs). Recycling Zn-bearing slags sustains the production of the metal industry and reduces the use of virgin resources and environmental impact.

Zn fuming is a representative technology for the recycling of Zn-bearing slags. Understanding the Zn fuming kinetics allows metallurgists to develop a more efficient slag fuming process with high flexibility, economic gains, low carbon footprint, and low environmental impacts.

Zn fuming kinetics in a bubble-stirred molten slag bath

This paper reports the kinetics of Zn fuming from a fayalite-based slag through stirring with air-CH4 gas mixtures. The influence of process parameters on the Zn fuming rate is identified. A kinetic model is developed according to the understanding of the rate-controlling step of the fuming process, and the volumetric mass transfer coefficient is obtained by fitting with experimental data.

The theoretical volumetric mass transfer coefficient is further calculated to deepen understanding of the effect of the gas flow rate on the fuming kinetics. The results indicate that the fuming process consists of an unsteady fuming stage and a main fuming stage. The mass transfer of ZnO in the liquid phase, closely related to the gas flow rate, is likely to be the rate-controlling step.

Significance of Zn fuming and potential challenges

Zn fuming technology plays an important role in recycling Zn or Pb containing slags. It has been widely used to extract valuable metals and produce a clean slag for value-added applications. The Zn fuming kinetics is highly flow-related. However, the conventional mathematical and thermodynamic-transient models can not efficiently reveal the reactive multiphase flow in this process.

The understanding of slag fuming behavior from the perspective of multiphase flow is still limited, which becomes a bottleneck in designing and optimizing the process. Future work will focus on using Computational Fluid Dynamics (CFD) techniques to study the effect of process parameters on fuming behavior, thereby establishing the correlation between multiphase flow and fuming kinetics.

Full reference of the paper

Zhongfu Cheng, Abdul Khaliq, Bart Blanpain, Muxing Guo (2022), Zn fuming kinetics in a bubble-stirred molten slag bath, Metallurgical and Materials Transactions B, 53(2), 1308-1319, https://doi.org/10.1007/s11663-022-02449-x

Acknowledgments

The authors gratefully acknowledge support for this research by VLAIO (SIM Vlaanderen SuperMex project).

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