The thermodynamic behavior of magnetite in non-ferrous smelting

The problems of magnetite build up have plagued the non-ferrous pyrometallurgical industry for many years. Traditionally, solutions to this problem were brought about add-hoc, as a means of survival, and not necessarily based on rigorous fundamental work. Until now, no comprehensive fundamental studies were available, in the area of nickel pyrometallurgy, which addressed the thermodynamic principles and how the pertinent factors such as temperature, oxygen and sulfur pressure and activities of iron and magnetite influenced the age old problems of magnetite saturation.;One of the main objectives of this study was to provide a sound investigation and subsequent analysis, obeying the guiding principles of thermodynamics (phase rule) in order to understand the mechanisms behind magnetite saturation during nickel smelting. By fulfilling this goal, methods which could be used to control the behavior of magnetite as well as obtaining metallurgical benefits would naturally follow. Of perhaps equal and even more significance, was the manner in which these experimental data and fundamental understanding could be applied on an industrial level.;In order to fulfill these objectives a series of equilibration studies were performed in the systems matte-gas and matte-slag (silica saturation)-gas. The thermodynamic variables of temperature, sulfur and oxygen pressure and matte grade were examined and their relationships to the magnetite activity were defined. In general, a lower sulfur pressure and higher temperature operation was proven to enhance the metallurgical benefits of nickel smelting by decreasing the magnetite activity.;Comparison of actual industrial data, with those of this experimental study indicated that even by incorporating these data into theoretical process models (heat and material balances) no matter how reliable they may be, the real situations may end up radically different to those predicted from the models. It should be recognized that these types of studies only provide a guideline which can be used to pursue larger scale testwork in an attempt to prove out real and attainable benefits. Without these types of studies to form the basis for development, a clear direction and significant progress would never be possible.