Microstructural, thermochemistry and mechanical evaluation of self-reducing pellets using electric arc furnace (EAF) dust containing zinc for Waelz process

Resumo

The increment of recycling of steel using electric arc furnace and the tendency to coat of steel products with
zinc, in order to prevent corrosion, has increased the proportion of galvanized scrap used worldwide in the
recent years. Approximately 10 to 20 Kg/t of cast steel is generated in casting arcs. These collected dusts
electric arc furnace (EAF dust) contains iron, zinc, lead, and cadmium. Mainly in the form of oxides and their
wastes are considered hazardous typically in countries such as Brazil, U.S., Japan and Germany. It is
estimated that from the total of 7.5 million metric tons of EAF dust generated worldwide only 45% is
recycled. With Waelz process, the EAF dust can be treated to recover zinc by means of reductionvolatilization-
oxidation reactions occurring within the rotary kiln. In this work the thermodynamics of the
Waelz process is studied to optimize the recovery of volatiles especially zinc. Kinetic parameters were
evaluated trough series of ten experiments, comprise the major process factors such as type of reductants
(charcoal and petroleum coke), time (20 – 120 minutes) and temperature (450 - 1150°C). The mechanical
behavior of the pellets was evaluated by compressive cold strength and drop tests. Characterization was
performed using scanning electron microscopy, microanalysis EDS, X-ray diffraction, X-ray fluorescence,
granulometric analysis by laser diffraction, as well as measurements of moisture, bulk density and percentage
of volatiles, fixed carbon and ash. The small pellets (10mm) with charcoal used as a reductant, presented a
higher compression and higher recovery of volatiles than those with petroleum coke.
Keywords: Self-reducing pellets; recovery of zinc; treatment of steelmaking waste; Waelz process.