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.
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
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.
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.
© Fraunhofer ISI 2017