Top submerged lance direct zinc smelting

Abstract

A long history of zinc processing starting with pilot plant studies in the 1980s has progressed to the treatment of close to 800,000 tonnes a year of zinc bearing feeds in Top Submerged Lance (TSL) furnaces in the form of residues and slags. Whereas these Ausmelt TSL applications are end-of-pipe applications treating residues from classical Roast-Leach-Electrowinning (RLE) process routes, this paper discusses Direct Zinc Smelting (DZS) Process. In Stage 1 of this novel two stage TSL application the sulphide sulphur from the zinc concentrate is the energy carrier used to smelt the concentrate and fume 60–65% of the zinc content. Subsequently in Stage 2 zinc is fumed from the already molten Stage 1 slag to create a final discard slag with a total zinc recovery of 99%. The use of sulphide sulphur as fuel to smelt has economic advantage over the present end-of-pipe TSL applications, that require two steps (for smelting and sulphur removal) and then fuming using primary fuels. The slag product of the DZS process overcomes inherent environmental liability and ever increasing economic burden associated with the traditional RLE processes by eliminating the creation of large volumes of iron bearing residues (mainly jarosite and goethite) while complementing high recoveries of Zn with those of the valuable elements e.g. Cu, Ag, Au, Pb, Ge, and In. High levels of Fe, Mn, SiO 2, and MgO in some concentrates render them unsuitable for processing in RLE, however are elegantly directed by DZS to the benign slag. This paper will discuss Ausmelt’s applications in zinc processing with a focus on DZS to show how this process can extend the life of present RLE sites.