Direct-to-blister smelting of copper concentrates: the slag fluxing chemistry

Abstract

The fundamental feature of the flash smelting process is its capability to utilise the combustion energy of sulphidic raw materials, by conducting a carefully controlled roasting and subsequent smelting in a single furnace. Its furnace and equipment design is implemented so that the reaction enthalpy released in the suspension oxidation is fully used for melting the reactive and non-reactive particles of the feed mixture. Since the first industrial application in 1940s, flash smelting has been developed for other applications than copper matte smelting, including the oxygen enriched smelting, continuous converting to blister copper with low sulphur concentration, and direct-to-blister smelting. Along with actual evolution in the processing equipment, the basic metallurgy has been under careful evaluation and development. In spite of many favourable features of iron silicate slags, they become problematic in the direct-to-blister copper smelting environments, at oxygen partial pressures higher than in matte smelting. These conditions typically locate beyond thermodynamic stability range of the homogeneous, fully molten iron silicate slags, which are more or less fully degraded ‘internally’, precipitating their solid constituents, silica and/or magnetite.