On the Effect of Bentonite on the Pelletization Process of Iron Ore Concentrates
Abstract Generated abstract
This paper examines how bentonite additions affect the pelletizing of iron ore concentrates and how the suitability of bentonites from different deposits can be evaluated. The authors argue that swelling capacity or electrokinetic potential of bentonite suspensions alone is insufficient, especially for fluxed burdens, and instead determine electrokinetic potentials by electroosmosis under conditions closer to pellet formation. Measurements on several bentonites show that higher swelling capacity corresponds to higher electrokinetic potential, while distilled and technical water give similar values, and conductivity changes of the dispersion medium strongly affect interpretation. The study concludes that bentonite assessment for pelletizing should combine measurements on both bentonites and the actual iron ore burdens, with electroosmosis as the preferred method.
Full Text
ON THE EFFECT OF BENTONITE ON THE PELLETIZING PROCESS OF IRON ORE CONCENTRATES
V. M. VITYUGIN, I. N. LANTSMAN
(Presented by the scientific seminar of the Department of General Chemical Technology)
In the practice of pelletizing iron ore concentrates, as a rule, small additions of bentonite (0.5–1.5%) are used to increase the efficiency of the pelletizing process. Studies of the influence of bentonites on the pelletizing process have been carried out both in our country [1, 2] and abroad [3, 4, 5]. However, the mechanism of the action of bentonite in the pelletized charges is still insufficiently clear. This substantially hampers the development of a rational method for evaluating the suitability of bentonites from various deposits for the process of pelletizing iron ore concentrates.
At the SSGOK it was proposed to evaluate the suitability of bentonite in the pelletizing of iron ore concentrates by the swelling index [2]. In the technological process this evaluation was confirmed, since the swelling of bentonite is associated with the degree of dispersion, with ion-exchange capacity, with the aggregate of surface properties, and with interaction with the dispersion medium. However, these relationships are by no means unambiguous, and therefore the swelling index alone is insufficient for explaining the mechanism of bentonite action.
American scientists [3] attempted to evaluate the quality of bentonite by the magnitude of the electrokinetic potential, determined by microelectrophoresis. This makes it possible to evaluate the aggregative stability of bentonite. However, depending on the composition of the other components of the iron ore charge, the behavior of bentonite will be different. For example, when only bentonite is added to an iron ore concentrate, the bentonite plays the role of a moisture-absorbing additive. In the case of the simultaneous addition of limestone and bentonite, in addition to the physical absorption of moisture, bentonite proves to be a structuring agent. Therefore, evaluation of the suitability of bentonite for pelletizing fluxed iron ore charges by the absolute value of the electrokinetic potential of a bentonite suspension is insufficiently substantiated.
We studied the electrokinetic properties of bentonites from various deposits. The determinations were carried out by the electroosmosis method on Gortikov’s apparatus [1], improved by Ovcharenko and Alekseev [2]. The electroosmosis method is used for powder diaphragms with a wide particle-size interval. The packing density of the powder in the finished diaphragm reaches the packing density of particles in a granule, i.e., in the process of determining the $\zeta$-potential, conditions are created that are close to the condi-
conditions of the pelletizing process. The use of the microelectrophoresis method for determining the electrokinetic potential of the components and of the burden is hardly expedient, since the determinations are made only for a narrow, fine-grained fraction of the materials in a dilute suspension.
The experiments were carried out as follows. A prepared 2.5% suspension of bentonite in water was aged for 1 day; a diaphragm 3 cm high and 0.5 cm in diameter was formed in a TsUM-1 centrifuge at 10,000 rpm. The cells of the main instrument were filled with filtrate from the suspension, the instrument and the electrical circuit were assembled. At the end of the experiment the electrical conductivity of the filtrate was determined and, from its value and the measured electroosmotic velocity, the electrokinetic potential was calculated.
The results of the determinations are presented in Table 1.
Table 1
Dependence of the electrokinetic potentials of bentonites and of burdens with their addition on the deposits of the bentonites and the composition of the water
| Bentonite deposit | Swelling capacity | Distilled water, $P_{\mathrm{э}}$ | Distilled water, $h$, mV | $x \cdot 10^{+3}$ | Technical water, $h$, mV | $h$, mV, concentrate +1% bentonite |
|---|---|---|---|---|---|---|
| Il’ichevsk . . . . . | 3.0 | 7.47 | 0.5 | 0.325 | 0.3 | 9.5 |
| Azkamar 1 . . . . | 4.5 | 27.0 | 6.35 | — | 6.75 | — |
| Oglanlinskii . . . . | 7.4 | 33.4 | 6.87 | 0.864 | 6.16 | 14.8 |
| Azkamar 2 . . . . | 17.0 | 49.0 | 12.9 | 1.284 | 11.7 | 18.7 |
As is evident from the table, the magnitude of the electrokinetic potential is higher for the more strongly swelling bentonites. The values of the electrokinetic potentials of bentonites in distilled and technical water change little, which is explained by the presence of the same ions in the exchange complex and in the dispersion medium. It is difficult to evaluate bentonite from the values of the electroosmotic velocity, since here the change in electrical conductivity also plays a major role. The specific electrical conductivity of the filtrates with a suspension of bentonites depends on their capacity for swelling, i.e., for osmotic binding of water with the crystalline structure.
Conclusions
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Determination of the electrokinetic potentials of bentonites for evaluating their suitability in the pelletizing process of iron-ore burdens is expedient only in combination with determination of the electrokinetic potentials of the burdens subjected to pelletizing.
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The electroosmosis method is the most acceptable for determining the electrokinetic potentials of bentonites and iron-ore burdens.
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When determining electrokinetic potentials, it is necessary to take into account changes in the electrical conductivity of the dispersion medium.
LITERATURE
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P. N. Dokuchaev, D. G. Khokhlov, I. E. Ruchkin. Effect of additions of bentonite and lime on the process of producing iron-ore pellets. TsNII ChM, series 4, information 23, 1966.
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P. N. Dokuchaev et al. Effect of bentonites from various deposits on the pelletizing of Sokolovsko-Sarbaisk iron-ore concentrates, TsNII ChM, series 3, information 15, 1967.
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Metell Bulletin, No. 5075, pp. 17–19, 1966.
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Mining Engineering, No. 10, V, 17, 1965.
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Stahl und Eisen. No. 79, 224, 1959.