The Queneau-Schuhmann-Lurgi QSL Process

The slag formed is further treated by carbothermic reduction in an effective second stage to reduce its lead content before discharge from the reactor. 

Dusts from the boiler and gas cleaning system are recycled back to the reactor, but depending on the cadmium content part may be removed and leached to extract cadmium before recycling to prevent development of a large circulating load. 

The length of the reduction section of the reactor is at least twice the length of the oxidation section but is of reduced diameter. The relative slag volumes and residence times are the critical parameters and are determined by the relative amounts of sulfides and oxide lead materials in the feed mix, particularly the amount of lead to be reduced. The lead pool maintained in the reduction zone is minimal and merely provides a channel for the lead to flow back to the oxidation section. 

The cylindrical reactor can be rotated through 90° when the process is interrupted to lift the injectors clear of the slag bath. This also allows access to the injectors for maintenance or replacement. Injector life is relatively short and has been quoted for the Stolberg unit at 800 hours for the oxidation section and 1300 hours for the reduction section. Overall plant availability was given as 85 per cent. 

Design data for Queneau-Schuhmann-Lurgi (QSL) smelters (Mager and Schulte, 

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