EFFECT OF THE COMPOSITION OF THE IRON-ORE BURDEN ON THE AMOUNT OF AIR ENTRAPPED IN GREEN PELLETS

T. G. Leont’eva, V. M. Vityugin

(Presented by the scientific seminar of the Department of General Chemical Technology)

Iron-ore pellets are a multiphase system consisting of fine-grained polydisperse mineral particles, pore liquid, and entrapped air. The character of the interrelation of these phases determines the properties of pellets at all stages of their production, i.e., during pelletizing, drying, and firing. The quantitative ratio of the liquid and solid phases is systematically controlled in the technological process and is maintained constant. The amount of the gaseous phase—air entrapped in green pellets—as a rule, is not measured. Moreover, the presence of entrapped air in pellets is unjustifiably ignored.

In the present work, investigations were carried out on the dependence of the amount of entrapped air in the structure of green iron-ore pellets on the composition of the burden. The following materials were used for the investigations: iron-ore concentrate from the Sokolovsko-Sarbaiskii mining and processing combine, with a size of 0.1–0 mm; limestone from the Kzyldzhar deposit, with a size of 0.25–0 mm; Azkomar bentonite, screened through a 44-micron sieve and, according to sedimentation analysis, consisting mainly of fractions from 1 to 5 microns; and magnetite slime, consisting of fractions with particle sizes below 20 microns. Pelletizing was carried out in a disk granulator whose diameter was 300 mm, rim height 100 mm, and angle of inclination 45°. The pelletizing time in all experiments was 7 min. The optimal working moisture content for each burden was calculated by the Vityugin–Bogma formula

\[ W_{r}^{\mathrm{opt}} = \mathrm{MCW} - \mathrm{MMW}, \quad \text{where} \]

MMW is the maximum molecular moisture capacity of the burden, %;
MCW is the maximum capillary moisture capacity of the burden, %.

The amount of entrapped air was measured in the following manner. An organic liquid immiscible with water (benzene or toluene) was poured into a burette with a division value of 0.01 mm and an internal diameter of 16 mm, up to a specified mark. Then several pellets were immersed in the burette and the new liquid level in the burette was measured. After complete disintegration of the pellets in the liquid, the amount of entrapped air, as a percentage of the pore volume, was calculated from the change in the liquid level in the burette before and after disintegration of the pellets. The averaged results of the experiments are given in Table 1.

From the analysis of the data obtained, the following conclusions were drawn.

1. As the dispersity of the burden increases, the amount of entrapped air increases.

Table 1

Effect of burden composition on the amount of air entrapped in green pellets

1. The increase in the amount of entrapped air is especially significant when moisture-absorbing, swelling additives are introduced into the burden.