Removal of Inclusions from Molten Aluminium by Flotation in a Stirred Reactor: A Mathematical Model and a Computer Simulation

Abstract

Inclusions removal by flotation in mechanically agitated vessels is widely used in liquid aluminium treatments. Originating from different sources (oxide skins, refractory or recycling wastes), inclusions may have disastrous repercussions, such as physical properties alterations of the final products or difficulties during forging processes.With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a mathematical modelling of the behaviour of the inclusions population has been set up. Agglomeration, flotation and settling of inclusions are considered here. The model is divided in two steps: a 3D calculation of the biphasic liquid aluminium/bubbles fluid flow based on an Euler/Lagrange approach and a population balance. The population balance is performed with the assumption of a perfectly stirred reactor, and the calculation of agglomeration and flotation rates relies on mean values of fluid flow properties provided by the CFD simulation. Kruis & Kusters' model is employed for the calculation of the agglomeration rate and Kostoglou's model is used for the flotation rate. The fixed pivot method of Kumar & Ramkrishna is employed for the resolution of the population balance equation.A laboratory scaled flotation vessel is modeled and results of a simulation are presented.