THERMODYNAMIC ANALYSIS OF ZINC FERRITE DECOMPOSITION IN ELECTRIC ARC FURNACE DUST BY LIME

The paper studies the scientific basis of the pyrometallurgical treatment process for electric steelmaking dust containing zinc ferrites. Thermodynamic analysis of zinc ferrite decomposition by lime was performed. According to the calculated data analysis, dust requires adding at least 46 % of CaO to decompose more than 90 % of ZnFe2O4, and at least 60 % of CaO to decompose more than 95 % of ZnFe2O4. The calculation results were verified by the laboratory furnace experiments. Experimental dust calcination in air with lime added up to 60 % of dust mass at a temperature of 1000 °C and a holding time of 4 h confirmed that zinc ferrite is decomposed by calcium oxide with the formation of zinc oxide and dicalcium ferrite. In addition, 50 kg of sublimates per 1 ton of dust were obtained containing 29 % of lead and 15 % of zinc. Dust calcination with the addition of lime can be used to transform zinc from ferrite to a soluble oxide form. Intermediate products resulting from calcination can be used for zinc and lead recovery. After zinc leaching it is possible to obtain the iron-containing product applicable in ferrous metallurgy. The approach has a variety of technological advantages in comparison with the known Waelz process. In particular, calcination with lime requires lower temperature (1000 °C) than the known technology (1250 °C), it eliminates the second stage of Waelz treatment necessary to purify zinc oxide fed for leaching from halides, significantly reduces coke consumption and simplifies gas cleaning from dust due to the 6–8 times lower quantity of sublimates.

zinc ferrite, dicalcium ferrite, calcium oxide, zinc oxide, thermodynamic analysis, Waelz process

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