The production of steel in electric arc furnace (EAF) generates a by-product called EAF dusts. These steelmaking flue dusts are classified in most industrialized countries as hazardous residues because the heavy metals contained in them, tend to leach under slightly acidic rainfall conditions. However, and at the same time they contain zinc species which can be use as a source to obtain valuable by-products. The present investigation shown results on the processing of an EAF flue dust using ammonium carbonate solutions.
with other impurities (i.e. cadmium and copper), these are eliminated from the zinc solution via cementation with metallic zinc. The purified zinc solution was evaporated (distilled) until precipitation of a zinc carbonate species, which then was calcined to yield a zinc oxide of a high grade. For the unattacked dust residue from the leaching operation, mainly composed of zinc ferrite, several options can be considered: back-recycling to the furnace, further treatment by sodium hydroxide processing or a more safely dumping due to its relatively inertness.
(1) EAF steel dust is transported by road or rail to a steel dust recycling plant.
(2) The feed materials are provided in either dry compact-moist or pelletized form. The compact and pelletized moist materials, coarse fluxes and coke are stored in boxes while the dry dust is transported by pneumatic conveying systems to raw material silos.
(3) Typically 55 meters long with a four-meter diameter, the Waelz Kiln is slightly inclined 2-3% and has an approximate rotary speed of 1.0 rpm. As the moist material moves through the rotary kiln, it is dried and preheated by the kiln gas, flowing in a counter-current pattern. In the reaction zone, reduction of the metal oxides occurs around 1200°C as the zinc is vaporized as metal vapor into the gas cleaning system. Zinc is then re-oxidized in the kiln atmosphere that is operated with excess air (process air is injected from the kiln end). Chlorine and alkalis volatilize jointly with the heavy metals and the dust-laden off-gas is treated in a downstream off-gas system.
(4B) In the first stage, coarse particles mechanically entrained are separated in a dust settling chamber and returned to the kiln. The hot, dust-laden off-gas is cooled and Waelz Zinc Oxide is separated in a high efficiency collector.
(4A) The co-product, Waelz Iron Product, can be used directly in road construction, civil construction (backfilling), cement manufacturing or can be reprocessed to add more value to the iron content which is currently under research and development.
(5) The dust-free off-gas is then treated, filtered and discharged.
(6) The discharged air easily meets strict U.S. and European environmental regulatory standards and is a major supporting factor in the U.S. - EPA's designation as Best Demonstrated Available Technology and the E.U.'s designation as Best Available Technique.
(7) Waelz Zinc Oxide, the main product of the process, is delivered to zinc smelters for zinc production.
আপনার বার্তাটি 20-3,000 টির মধ্যে হতে হবে!
