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The QSL (Quenno Slag Lead) direct smelting technology represented a major advancement in primary lead production when commercial installations commenced in the 1990s, but actual operating experience provides the critical validation of any new metallurgical process technology. This publication documents operational results from two pioneering QSL installations: the Berzelius Stolberg facility in Germany and the Korea Zinc Company plant, providing the industry with comprehensive performance data from extended commercial operation. The documented experience covers process modifications implemented during startup and ongoing operation, actual operating results compared to design expectations, and overall technology validation for direct lead smelting applications.
The QSL process fundamentally differs from traditional sinter plant and blast furnace operations by reacting lead concentrates directly in an oxygen-enriched submerged combustion reactor containing molten slag. Lead oxide formed through oxidation of the sulfide concentrate is continuously reduced to metallic lead by carbon fuel injection, with the lead collecting beneath the slag layer for periodic tapping. Sulfur dioxide generated from concentrate oxidation exits in high-concentration off-gas streams suitable for conversion to sulfuric acid.
Operating experience from the German and Korean installations revealed both the technology's strengths and areas requiring refinement. Process modifications implemented during early operation addressed refractory wear in critical reactor zones, oxygen distribution optimization for improved sulfur capture and energy efficiency, and slag chemistry control to maintain appropriate lead-slag separation. The facilities achieved lead recoveries consistent with design expectations while producing sulfuric acid of commercial quality. Energy consumption per tonne of lead produced proved favorable compared to conventional routes, validating the QSL process efficiency claims.
For lead producers evaluating technology options or operating existing QSL installations, this documented experience provides essential reference data on achievable performance and typical operational challenges. Gas Cleaning Technologies' involvement with QSL and other direct smelting technologies encompasses the specialized off-gas handling requirements these processes demand, including high sulfur dioxide concentrations, elevated temperatures, and integration with acid plant operations.
