Complete recycling of filter dust containing zinc using melt bath injectionecyclability of the mineral fractions generated

© DK Recycling und Roheisen GmbH

More than half of the zinc produced worldwide is used to protect sheet steel or steel components against corrosion. At the end of the product life cycle, the galvanized steel products are usually melted down at steel works or in foundries to form new steel. The zinc contained in the filter dust is lost as are other process-specific elements such as iron oxide or carbon.

The process developed in the “Schmelzinjekt-II” project aims to recover zinc as well as other valuable components from the filter dust of the steel recycling process. The filter dust containing zinc is injected into the iron melt bath of an induction furnace using a submerged lance. The iron and zinc oxides in the filter dust are reduced to metal in the iron melt bath. The metallic zinc vaporizes selectively and oxidizes again to form solid zinc oxide. This is precipitated as a high-grade zinc-enriched main product in a filter system. The iron contained is turned into high-quality cast iron; the carbon is mainly used as a reducing agent.

An earlier project demonstrated that a high-quality zinc oxide product containing approximately 61 percent zinc can be produced from filter dust containing about 30 percent zinc using the melt bath injection method. The “Schmelzinjekt-II” project is now conducting longer field tests to establish a stable process that can be used in recycling plants, and especially in small and medium-sized smelting plants or foundries.

DK Recycling und Roheisen GmbH is the project coordinator and is designing and building the demonstration plant, which mainly processes the company’s own filter dust containing zinc from the blast furnace. VDEh-Betriebsforschungsinstitut GmbH is responsible for the accompanying research and process optimization.