Fireclay refractories in pyrometallurgical processes

In primary liquid metal production, the temperature of processing and the composition of the slag phase largely determine the selection of the refractories used to line the furnace. The objective of this work was to study the effect of temperature and FeO content on the dissolution rate of a clay refractory.50-g samples of synthetic, prefused iron oxide and silica were poured into slip cast crucibles of a high-duty fireclay. These were then placed in a preheated silicon carbide-element furnace and held at the required temperatures for known times. The cooled crucibles and their contents were broken and the amount of crucible wall thinning which had taken place at the slag-refractory interface was measured using a low-power microscope and a calibrated graticule.The study of the effect of process temperature was carried out over the temperature range 1100°–1400°C at 50°C intervals. Only two compositions, 65 and 75 wt.% FeO, were chosen for this part of the work.The effect of slag composition was next studied at 1300°C, the range of slag compositions being 60–80 wt.% iron oxide at 5% intervals in the iron oxide-silica system. Only one high-duty fireclay composition was studied throughout the tests.The outcome of the work was to show that for the iron oxide-silica compositions studied a high-duty fireclay refractory can be used to contain the melts if the temperature of the process is maintained below 1300°C and when the slag composition is less than the orthosilicate composition (2FeO.SiO₂).