OJSC «Uralmekhanobr», Yekaterinburg, Russia:

E. G. Dmitrieva, Leading Researcher, Candidate of Engineering Sciences
G. I. Gazaleeva, Head of Department, Doctor of Engineering Sciences, gazaleeva_gi@umbr.ru
E. V. Bratygin, Head of laboratory, Candidate of Engineering Sciences
I. A. Vlasov, Senior Researcher

The mineral and chemical composition of oxidized iron ore of the Abail deposit, Republic of Kazakhstan is analyzed, and the degree of goethite and hydrogetite dissociation is studied. We choose the method of magnetizing roasting. The thermogravimetric ore analysis has shown that the preliminary magnetizing roasting is necessary for the oxidized iron ore beneficiation to convert non-magnetic iron minerals to magnetite. The results of the thermogravimetric studies show that with change in the temperature from 221.0 to 365.6 °С, the decrease in sample mass is observed by 6.83%. This effect occurs with heat absorption and corresponds to the decomposition of iron hydroxides to hematite. The analysis of the obtained results also shows that the processes of dissociation of iron hydroxides and carbonates completely stop at the temperature of 775 °C. This temperature is sufficient for complete burning of carbon in coal of the Ekibastuz deposit, which is used as a reducing agent, and for reduction of hematite to magnetite. Experimental verification of these thermograms in the Tamman kiln makes it possible to recommend optimal parameters of magnetizing roasting : - carbon content in the charge is 11%, the roasting time is less than 10 minutes, the roasting temperature is 900 °C. Studies into the nature of this phenomenon using a scanning electron microscope reveal the presence of floccules of rock and magnetite particles in the annealed and magnetic products, which pass into the magnetic fraction and worsen its quality. The probable reason for the formation of floccules is the rapid cooling of the product with water after roasting. The two-stage process circuit with milling, desliming and wet magnetic separation is recommended for application. This process circuit produces iron concentrate with iron content of 67 % at the recovery of 76.5 %.

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