Permittivity measurements at high temperatures of selected pyrometallurgical minerals

Abstract

In pyrometallurgical processes, the temperatures attained are amongst the highest of all industrial chemical processes and consequently the energy requirements are considerable. Although in the last few decades there have been significant improvements in the thermal efficiencies of these processes, some limitations are imposed by the innate characteristics of both the energy sources and the pyrometallurgical raw materials. Currently, there exist significant incentives for innovative and efficient processes that harness electricity from renewable energy sources. Furthermore, this electricity can be converted into electromagnetic radiation, such as microwaves, which can be utilized as a source of thermal energy. The fundamental properties which determine the interaction of microwaves with any given material are the real and the imaginary permittivities. This data is required for microwave process development, particularly numerical modeling. In the present research, these permittivities were determined for a number of raw materials of pyrometallurgical interest as a function of temperature and frequency by the cavity resonance perturbation technique. The materials studied were oxides, carbonates and sulphides. Also, the permittivity changes during the reduction of hematite by hydrogen were investigated. In order to interpret the permittivity variations as a function of temperature and also in the reduction process, the changes in the composition were modelled using HSC Chemistry®7.1. Some conclusions are drawn regarding the utilization of microwaves for the heating of pyrometallurgical materials.