Study of the Effect of UShR Additives on the Pelletizing Process of Magnetite Concentrate

V. M. Vittogin, I. N. Landsman, A. K. Miskarli

In the practice of granulating iron-bearing concentrates, bentonite additions are usually used as a plasticizing component. However, when small amounts of dry bentonite are added to moist concentrate, it is difficult to mix the blend uniformly. Therefore, under practical conditions the consumption of bentonite is increased from the theoretically necessary 0.2–0.3% to 0.7–1.0%. This leads to a noticeable decrease in the iron content of the granulate and to deterioration of the properties of green and fired pellets.

It is more expedient to use water-soluble structure-forming agents of organic origin and, first of all, the coal-alkali reagent (UShR). UShR is one of the cheapest and most widespread reagents—stabilizers of clayey solutions used in drilling [1]. In recent years, powdered humate reagents have been produced by the Karadag (Azerb. SSR) and Aleksandriya (Ukrainian SSR) plants and widely introduced in oil drilling [2].

In this work we used magnetite concentrate from wet magnetic beneficiation of the Sokolovka–Sarbai Mining and Beneficiation Combine (SSGOK), with a particle size of 0.1–0 mm, of the following chemical composition:
$\mathrm{Fe}_{\text{tot}}$—67.6%, $\mathrm{FeO}$—28.29%, $\mathrm{S}$—0.15%, $\mathrm{SiO_2}$—1.98%, $\mathrm{Al_2O_3}$—0.54%, $\mathrm{CaO}$—1.31%, and powdered coal-alkali reagent /IO : 2.5/ from the Karadag plant. UShR additions were varied within the range from 0.1 to 0.5%. In this case, a dry reagent was introduced into the concentrate with a working moisture content of 9%. The uniformity of mixing was checked by measuring the electrical conductivity of suspension filtrates from samples of the mixture taken from different points. The electrical conductivity of the solutions was determined by the usual compensation circuit according to the Wheatstone-bridge principle. The null instrument was an oscillograph 30-7; the circuit included a ZG-34 sound generator, an R-326 resistance box, and a glass measuring cell with platinized platinum electrodes. Measurements were carried out at 20°C, a frequency of 1000 Hz, and an output voltage of 5 V.

The degree of uniformity of mixing of magnetite concentrate with UShR after 15-fold mixing is illustrated by the data in Table 1. The experiments showed that the average scatter of the specific electrical-conductivity values is 1.45%; thus, the uniformity of mixing fully meets the requirements of the practice of pelletizing iron-ore concentrates.

Table I

Value of the specific electrical conductivity of aqueous extracts from mixture samples at different sampling points

The structure-forming action of UShR was evaluated from the strength of vibro-briquettes made from mixtures with concentrate. Vibroforming of the mixtures was carried out at a frequency of 50 Hz, an amplitude of 2 mm, for 60 sec. The test results are given in Figure 1.

Figure axes: strength of wet vibro-briquettes, kg/cm²; strength of dry vibro-briquettes, kg/cm²; UShR concentration, %.

Fig. 1. Dependence of the strength of wet and dried vibro-briquettes on the concentration of UShR.

Table 2 gives, for comparison, data from tests of vibro-briquettes obtained without the addition of UShR. These data show that the strength of both dry and wet vibro-briquettes with the UShR additive is higher than that of briquettes prepared from ordinary charge mixtures. Moreover, the strength of briquettes at a UShR consumption of 0.25–0.3% exceeds the strength of wet fluxed briquettes without UShR by 11.7%, and that of briquettes made from concentrate alone by 235%.

Table 2

Effect of additives on the quality of vibro-briquettes made from magnetite concentrate

Of particular importance is the fact that the increase in pellet strength is accompanied by a noticeable increase in porosity. At the same time, the conditions for sulfur removal during firing of the granules are improved, which makes it possible to obtain a higher-quality final product. Thus, enlarged laboratory tests at SSGOK showed that, with the introduction of 0.3% UShR, the degree of desulfurization was 98.2%, as against 91% with the addition of 1% bentonite and 9% dolomite.

To clarify the mechanism of interaction of UShR with the concentrate, adsorption of it on the surface of magnetite concentrate and the electrokinetic properties of the mixtures were studied. Adsorption of UShR was assessed from the difference in the electrical conductivities of the UShR solution before and after contact with the concentrate. Since UShR is a two-component system consisting of humates and free alkali, the change in electrical conductivity was used to judge the total adsorption of these components. To determine the effect of UShR additives on the electrokinetic properties of the mixtures, the electroosmosis method was used. The electrokinetic potential was determined, \(p\), on an LGU instrument [3]. A universal UIP-1 power supply was used as the direct-current source. In the range of supplied current values of 0.5–5.0 A, invariance of the values of the \(\zeta\)-potential was established.

It had previously been established that the magnetite concentrate of the Sokolovsko-Sarbaisky Mining and Processing Plant should be classified as a relatively hydrophobic material, since the heat of wetting* by water was 0.209 cal/g, and by benzene, 0.56 cal/g, while the lyophilicity coefficient \((\beta)\) [4] was, respectively, 0.37.

The adsorption isotherm of UShR on magnetite concentrate (Fig. 2) is satisfactorily described by the Freundlich equation, which indicates the physical character of sorption on the surface of the iron-ore concentrate.

Fig. 2. Adsorption isotherm of UShR by magnetite concentrate.

The dependence of the \(\zeta\)-potential on the concentration of the introduced UShR is presented in Fig. 3.

Fig. 3. Effect of UShR additions on the \(\zeta\)-potential of magnetite concentrate.

* The heat of wetting was determined by junior research associate of NIINFB, Academy of Sciences of the Kazakh SSR, Candidate of Chemical Sciences S. B. Aslyanova.

With the addition of small amounts of UShR, the $\zeta$-potential increases as a result of the replacement of exchangeable $Ca^{2+}$ and $Mg^{2+}$ in the clay fraction of the concentrate by $Na^+$ ions, owing to a certain excess of alkali in the humate [5]. With an increase in the concentration of UShR /0.1–0.3%/, simultaneously with the process of adsorption of humates, there evidently occurs the formation of a second layer of molecules with reverse orientation, which leads to shielding of the double electric layer of ions on the surface and to a decrease in the electrokinetic potential. A further increase in the $\zeta$-potential up to a certain limit indicates the construction of the next layer with an orientation analogous to that of the first layer. It is natural to suppose that the compact coagulation that takes place with the addition of 0.3% UShR will most favorably promote the aggregation of dispersed materials. This supposition is also confirmed by the fact that the greatest strength of both wet and dried vibro-briquettes corresponds to the minimum value of the $\zeta$-potential.

Thus, the strengthening effect of UShR on vibro-briquettes and granules can be explained by adsorption modification of the surface of the magnetite concentrate and by the formation of strong coagulation and condensation bonds at the points of contact of magnetite particles, respectively, in wet and dry specimens.

Literature

1. V. S. Baranov and Z. P. Buks. Chemical Treatment of Clayey Solutions in Drilling Oil and Gas Wells. Gostoptekhizdat, 1945.

2. A. K. Miskarli. Colloid Chemistry of Drilling Clay Suspensions. Azerneftizdat, 1963. A. K. Miskarli et al. Author’s Certificate No. 116090 of August 25, 1958.

3. O. N. Grigorov, I. F. Karpova et al. Manual for Practical Work in Colloid Chemistry. Moscow–Leningrad, 1964.

4. P. A. Rebinder. Physicochemistry of surface phenomena and disperse systems in the USSR as applied to engineering. Mathematics and Natural Science in the USSR. Moscow–Leningrad, 1938, pp. 431–464.

5. Collection Electrokinetic Properties of Capillary Systems. Publishing House of the Academy of Sciences of the USSR, 1956.