Freeze lining formation in continuous converting calcium ferrite slags. I

The initial freeze-lining growth rate in calcium ferrite slags at copper saturation is high and comparable to iron silicate slags. The entire freeze-lining layer is crystalline, from the cold end to its hot-face in contact with the molten slag. Industrial copper converting slags from a continuous flash converting furnace, processing solid high-grade matte to blister copper, generate a thin calcium sulphate bonding layer against the water-cooled metal surface during the very first minutes of the slag-to-cooling element contact. The rare solidification behaviour was observed using the water-cooled probe technique in rotating MgO crucibles, at slag temperatures of 1325 degrees C when liquidus temperature of the flash converting slag was estimated to locate at about 1245 degrees C. The body of the freeze lining is mostly composed of magnetite, various mixed calcium-copper ferrites and delafossite embedded in an intergranular phase of metallic copper and some copper oxide. The arsenic oxides dissolved in the slag are precipitated as solid calcium arsenates in the freeze lining.