Towards an Experimental Set-up for Measuring the Foaming Stability of Liquid Slags

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Vincent Cnockaert, Inge Bellemans, Evelien De Wilde, Bart Blanpain, Kim Verbeken

The use of liquid bath furnaces has been shown to be an energy efficient and environmentally friendly way for both the primary and secondary production of non-ferrous metals such as lead, nickel and copper. Typical for these kinds of furnaces is the injection or generation of reactive gases which occurs below the surface of the liquefied feed material. The large amount of rising gases during processing can cause foaming of liquid slag. This slag phase is in most cases present as the upper layer of the liquid bath. The formation of excessive amounts of slag foam can hinder the production and lower the available capacity of existing smelting and converting furnaces. It is, therefore, important to control this phenomenon and keep foaming to a minimum. It is generally accepted that the formation of slag foam is caused by the combination of a large amount of rising gases and the inherent foam stability of the slag, which in turn depends on the physical properties of the liquid slag. The measurement of this foam stability can be an important tool in predicting and comparing the foaming behaviour of different slags. In this work, a literature review is presented as the first step in the design of an experimental set-up for performing reliable measurements of the foaming stability of liquid slags at high temperatures, suitable for copper recycling and production. The simple model of Bikerman, on which the measurement of the foaming stability relies, is explained. In addition, the different suggested physical mechanisms for foam stabilization and breakdown are listed and the resulting influences of the physical properties of the liquid to the foaming stability are examined. It can be concluded that a general model that fully explains the phenomenon of foaming does not yet exist and the need for a reliable method of measuring foaming stability of slags is high.

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