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Abstract
Mining of zinc demands the upgrading of different residues of the refining process. A method, which had been used over a period of several years, was based on the so-called Dörschel process. From the chemical point of view, the Dörschel process is a high-temperature redox process, combined with a flash distillation (sublimation) step.
This process is based on the reduction of zinc compounds with coke at elevated temperature. The metal is then evaporated, reoxidized, precipitated by filtration, and refined hydro-/electrochemically. Zinc, lead, cadmium, nickel, cobalt, germanium, and copper can be refined from solid feed material by this process.
Modern waste management also needs such methods for the treatment of hazardous waste from different industrial processes, and the applicability of the Dörschel process in the upgrading of galvanic sludge, dust from steel furnaces, and scrap of portable batteries has been investigated. The feed material used for investigation has a mean zinc content of 15 to 25 wt% and a mean lead content up to 10 wt%. The presence of sulfate determines the anionic nature of feed material from galvanic sludge.
The capacity of the kiln used in the investigation is about 10,000 metric tons per year. The efficiency of zinc recovery is about 95% to 98%. The matrix substances of the feed were dissolved in neutral to caustic slag. Sulfur dioxide was recovered by absorption, purification, and condensation.