New tools for viscosity measurement and modelling of fully liquid and partly crystallised slags

As process feedstocks to pyrometallurgical operations become more varied, and complex control over the viscosity, one of the key properties of the slag system, becomes more challenging. To ad-dress this problem new slag viscosity measurement and modelling tools have recently been devel-oped. The viscosity measurements are undertaken using a rotating bob technique; however the design of the apparatus differs significantly from conventional commercially-available instruments. This new design enables i) Control of the gas atmosphere, in particular the oxygen partial pressure of the system. ii) Quenching of the samples at any stage of the viscosity measurements. The new design makes it possible to measure slag viscosities over a wide range of chemical compo-sitions, oxygen partial pressures and temperatures. In addition, it is possible to measure the viscosi-ties of partially crystallised slags, and to directly determine the proportions and chemical composi-tions of the phases present in these slags using electron probe X-ray microanalysis (EPMA). New mathematical models have also been developed enabling the viscosities in complex slag sys-tems to be predicted. The quasi-chemical viscosity model is valid for liquids at all compositions and temperatures within the system Al-Ca-Fe-K-Mg-Na-Si-O under reducing conditions. Used in con-junction with the FactSage program and its associated thermodynamic databases, the viscosities of solid/liquid slurries commonly encountered in industrial slag systems can be predicted. Examples of recent experimental measurements and viscosity predictions relevant to recycling tech-nologies used in non-ferrous metal smelting systems are presented