The Isasmelt Process

Initial application of this process to lead (and copper) was developed by Mount Isa Mines and was termed the Isasmelt process. Other applications and later also tin, copper and lead smelting and zinc fuming were developed by Ausmelt Limited, both as licensees of the Sirosmelt technology. 

Concentrates and flnxes are mixed in a paddle mixer and fed via a weigh feeder directly into the slag bath reactor. Wet feed is satisfactory, eliminating any need for drying, but high moisture will consume more fuel and increase the volnme of smelter gases. 

Flux additions are set to provide a slag with an Fe0 Si02 ratio of 2 1 and an FeO CaO ratio of 5 1. Higher levels of CaO will increase the activity of PbO and hence will aid subsequent reduction, but this will be offset by the increased volume of slag and greater lead loss at the same final lead in slag value. 

Air enriched to around 30 per cent oxygen is injected through the lance, and fuel in the form of pulverised coal, oil or natural gas is also injected as required to maintain the bath temperature at around 1150 to 1200°C. 

Off-gas containing eight to 12 per cent SO2 passes through a vertical membrane cooled offtake shaft to a waste heat boiler, electrostatic precipitator, gas scrubber and sulfuric acid plant. 

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The Isasmelt process uses a simple stationary, cylindrical, refractory-lined reaction vessel. The typical blended feedstock to the vessel is of a moist lumpy consistency and this feature greatly simplifies environmental control equipment requirements. 

Sirosmelt [CSIRO smelting] A copper smelting process developed in the 1970s by J. Floyd at the Commonwealth Scientific Industrial Research Organization (CSIRO), Australia. It formed the basis for the Isasmelt process. 

Direct smelting processes provide alternatives to the sinter plant-blast furnace above, up to the stage of crude bullion production, but still require the addition of refining operations to produce high-grade lead. Three alternatives have been evaluated - the Kivcet process, the QSL process and the Isasmelt process - as typical of the top submerged lance slag bath reactor. Evaluations are based on comparable feeds, predominantly lead concentrates with low residue inputs. 

Operating parameters for the Isasmelt process have been assumed as follows per tonne of product lead ... 

Table 17.7 gives the capital cost estimate for the production of 100 000 t/a of lead in bullion by the Isasmelt process. 

The two direct smelting technologies show similar overall direct operating costs, although the Isasmelt process may have lower capital cost. However, lead losses in slag are higher and recovery correspondingly lower for the Isasmelt process, which will raise raw material costs. This is covered in more detail below in the section on overall economics for refined lead production. 

The Isasmelt process functions in basically the same way as the QSL technology, processing moist feed in a submerged bath. However, in contrast, it uses two furnaces operated in series, for separate oxidation and reduction phases, and operates as a batch process. A key feature of the Isasmelt system is that air is blown into the oxidation furnace using a... 

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