Experimental measurement and prediction of complex phase equilibria in industrial non-ferrous slag systems

With increased emphasis on recycling and the need to treat materials from a range of sources it has become clear that further detailed information is required on the chemical behaviour of multicomponent slags used in non-ferrous processing. The data available on binary and ternary systems is no longer adequate to describe the liquidus temperatures, the phases formed at temperature or their compositions. New experimental methodologies and techniques have been developed that enable these properties to be accurately measured under controlled compositions, oxygen partial pressures and temperatures, importantly these techniques can be used to provide accurate information in the range of conditions of interest to industrial operations. The techniques involve novel approaches to equilibration of slag samples at high temperatures, followed by rapid quenching, the resulting phase assemblages are analysed using electron probe microanalysis (EPMA). Importantly these novel approaches enable measurements to be made in systems that could not previously be characterised, for example, due to uncontrollable reactions with container materials or changes in bulk composition due to vapour phase reactions. These data are then incorporated into thermodynamic databases, and used to ensure that model predictions accurately reflect the behaviour of these complex melts over a wide range of chemistries and conditions, providing confidence in the accuracy of these predictive tools. Examples of the application of these novel sophisticated techniques to the study and characterisation of complex copper, lead and zinc slag systems will be given, illustrating the potential to extend these approaches to other non-ferrous systems of industrial interest.