Thermodynamic Analysis of Zinc Ferrite Decomposition in Electric Arc Furnace Dust by Lime

Abstract

Scientific basis of pyrometallurgical processing technology of dusts of electric steelmaking containing zinc ferrites was investigated. The thermodynamic analysis of the decomposition of zinc ferrite with lime was carried out. The analysis of calculated data has shown that, in order to decompose more than 90% ZnFe₂O₄, it is necessary to add no less than 46% CaO for dust, while to decompose more than 95% ZnFe₂O₄, no less than 60% CaO is necessary. The results of the calculation were verified experimentally using a laboratory furnace. The experimental calcination of dust in air with the addition of lime in an amount of 60% of the dust weight at 1000°C with a holding time of 4 h confirmed that the decomposition of zinc ferrite with calcium oxide with the formation of zinc oxide and dicalcium ferrite occurs. In addition, sublimates were also formed in an amount of 50 kg per 1 t of dust containing 29% of lead and 15% of zinc. Dust calcination with lime can be applied to transform zinc from ferrite into a soluble oxide form. Intermediate products for the recovery of zinc and lead can be obtained by the calcination. After zinc leaching, it is possible to obtain an iron-containing product, which can be used in ferrous metallurgy. This approach has a series of process advantages compared with the well-known Waelz technology. In particular, calcination with lime requires lower temperature (1000°C) than the known technology (1250°C), it eliminates the second stage of the Waelz treatment necessary to purify zinc oxide fed for leaching from halides, considerably reduces coke consumption, and significantly simplifies gas cleaning from dust due to a decrease in the amount of sublimates by a factor of 6–8.