Slag-Metal Separation in Mn Ferroalloy Production

Abstract

The separation of slag and metal in the ferroalloy production process is an important issue that has an impact on both the ecological and environmental considerations of the entire production process. The extensive mixing of metal and slag during the tapping into ladles leads to the formation of a considerable amount of metal droplets in slag due to interfacial interaction and turbulence of the molten flow from the tap-hole. The entrainment of metal droplets into the slag phase causes ferroalloy losses with the slag, creating additional difficulties in the removal of metal from the slag. It is known that the separation of metal and slag is strongly influenced by interfacial phenomena and for this reason they were studied in this thesis, and the influence of interfacial tension and surface tension were also discussed for ferroalloy-slag systems.

The main goal of this research work was to understand interfacial phenomena between ferroalloy and slag. This has been achieved by developing a methodology for investigating the interfacial interaction in ferroalloy-slag systems, modelling the separation of molten slag and metal in OpenFOAM, and assessing operational parameters and physical properties affecting the formation of metal-slag emulsion and metal droplets in slag. The microstructure of slag and metal phases under different conditions has also been extensively addressed.

This thesis demonstrates a novel methodology for estimating the interfacial tension between metal and slag which combines experiments in the sessile drop furnace and multiphase modelling in OpenFOAM. It was concluded that the interfacial interaction can be significantly altered by surface-active elements such as sulfur in ferroalloy-slag systems, as well as by changing the composition of the slag, which causes to the transfer of species or elements across the interface, creating interfacial instability and reducing the interfacial tension. As a consequence, the significant instability of the interface leads to higher losses of metal with the slag.