Since the Electric Arc Furnace (EAF) stepped into the industrial production of steel, this metal has become the most recycled material in the world. The benefits of recycling, reduced emissions, and the profit margins make it for a great case of circular economy.
Electric Arc Furnace Dust (EAFD) is the main by-product in this process. It is generated in a 1-3% ratio (ton EAFD/ton Steel), and it has always been a major point of concern given its chemical composition and physical condition.
The industry options in the past have been the disposal into landfills and various research efforts to transform this dust into an inert or usable material. All of this at high cost and no foreseeable economic return.
The Waelz Process became a real solution when EAFD was seen as a profitable raw material in the zinc industry: the dust is the collection of all volatile materials fed into the furnace at the melting shop, and this includes scrap metal containing high amounts of galvanized steel. EAFD typically amounts for a 15-30% Zinc weight composition.
Zinc, as an essential element, is used in the steel industry for galvanization (roughly 80% of the zinc worldwide is used for this). In addition, the Zinc Compounds industry serves ceramic, rubber, paint, fertilizer, food, and pharmaceutical processes. The focus on these figures and potential uses, is what makes the Waelz Kiln, together with the EAF, a pivotal process in the recycling of metals, substitution of primary production (reduced extraction of natural resources), and sustained profit margins in the Steel and Zinc industries.
The Waelz Process consists of a long rotary kiln (50+ meters) in which the EAFD is subject to specific heat and pressure conditions to separate zinc from iron through a combination of reducing/oxidizing atmospheres. Zinc and other heavy metals are vaporized and carried upstream in a gas/dust mix through a cooling and collecting process and the iron and inert materials stay solid and are discharged at the low end of the kiln. The main product of the system, the Waelz Zinc Oxide (WOx), is a market valuable concentrate that goes back to the Zinc industries mentioned before.