tal, weakly clumping. A study of the kinetics of capillary saturation showed that, for the investigated powdered oxides, hydroxides, and carbonates, the rate of moisture propagation in the material is high, and the operating moisture contents for granulation are high. It is likely that simple mechanical granulation of these materials will be difficult. It is necessary either to add plasticizing and compacting additives, or to use other granulation methods, for example, forming pellets in an indifferent liquid or in a fluidized bed.

References

1. V. V. Nakhalov, N. F. Stas, G. G. Savel'ev, A. S. Guzenberg, A. M. Ryabkin, T. S. Gorina. On the adsorption of carbon dioxide by metal oxides. In the present collection.

2. N. F. Stas, G. G. Savel'ev, V. V. Nakhalov, A. S. Guzenberg, A. M. Ryabkin. Thermodynamics of the chemisorption of carbon dioxide and water vapor by metal oxides. In the present collection.

3. V. V. Nakhalov, N. F. Stas, G. G. Savel'ev. Study of the adsorption of carbon dioxide by aluminum oxide. In the present collection.

4. V. M. Vityugin, A. S. Bogma. Izvestiya vuzov, “Ferrous Metallurgy,” No. 4, 18, 1969.

5. V. M. Vityugin, A. S. Bogma, P. N. Dokuchaev. Izvestiya vuzov, “Ferrous Metallurgy,” No. 8, 42, 1969.

6. A. M. Vasil'ev. Fundamentals of Modern Methods and Techniques for Laboratory Determinations of the Physical Properties of Soils. Moscow, Stroiizdat, 1953.

7. B. V. Deryagin, N. N. Zakhavaeva, M. V. Talaev. An Instrument for Determining the Filtration Coefficient and Capillary Impregnation. Moscow, Nauka Publishing House, 1953.

ADHESIVE INTERACTION OF PARTICLES OF POLYDISPERSE MATERIAL IN WET AGGREGATION PROCESSES

V. M. Vityugin, E. N. Chulkova, I. N. Lanshchaya

In the practice of wet granulation, polydisperse materials are, as a rule, used. In this case, an active role in the process of granule formation is played by the finest fraction, comparatively small by weight, which concentrates in the pore liquid. The coarser particles, forming the framework of the granules, determine mainly the density

the structure and geometry of the pore space. During compaction of a granule, its framework undergoes deformations whose character has a decisive influence both on the rate of granule formation and on the strength of the granulate.

An effective aggregation process is possible only with sufficient development of plastic deformations, since the formation of granules in pan and drum pelletizers occurs with a high degree of freedom of volumetric deformations. Such plastic deformations are possible only when the pore space of the forming granule is filled with a coagulation-structured pore suspension. Indeed, as practice shows, effective pelletizing of magnetite concentrates deprived, during beneficiation, of the finest dispersed fraction requires the addition of small amounts of bentonite, which is capable of forming plastic coagulation structures when dispersed in the pore liquid.

During pelletizing of a loose, moistened disperse material, air is trapped in the pore space of the granules, and in greater quantity the higher the dispersity of the initial raw material. Thus, the granules being formed are three-phase multicomponent systems, and the resulting process indices will be determined by the properties and volumetric ratio of the interacting phases.

The principal index of the process is the strength of the granule structure. At present there is still no unified opinion on the nature of the mechanism of bonding of particles in a raw granule. Some researchers attach primary importance to capillary forces /1,2/. Others give preference to the molecular mechanism of particle bonding /3/. Analysis of the results of numerous studies and of pelletizing practice makes it possible to suppose a more complex capillary–molecular mechanism of granule cohesion. According to this mechanism, the framework particles are held mainly by the meniscus forces of the structured pore suspension, while the structural strength of the pore suspension is determined by van der Waals forces. Below are presented the results of a study of the adhesive interaction of particles in magnetite granules, confirming such a bonding mechanism.

During the destruction of raw granules under the action of external forces in

cracks first appear in their structure, localized in the places where the particles are least strongly bonded. Crack formation is due to the rupturing action of external forces overcoming the bonding of the particles in the granule. A quantitative characteristic of bonding can therefore be estimated from the force required to tear plates made of the granule framework material apart when there is a layer of pore suspension in the contact zone. The pull-off force will obviously be proportional to the wettability of the plates by the pore suspension, the surface tension, and the cohesive strength of the pore suspension. These parameters, in turn, will be determined chiefly by the nature and quantitative ratio of the components of the pore suspension.

Magnetite concentrates sent for pelletizing usually have a moisture content of 8.5–9.5%. If the strongly bound hygroscopic water amounts on average to 0.5%, then 8–9% water takes part in the formation of the pore suspension of the green granules. The bentonite addition, depending on its quality, usually ranges from 0.5 to 1.5%. Thus, the mass concentration of bentonite in the pore suspension lies within the limits of 10 to 20%. In addition to bentonite, the finest dispersed slime fraction of the magnetite concentrate passes into the pore suspension; its content in the concentrate usually varies within 1–3%.

As the objects of the present study, polished plates of pure magnetite from the Sokolovsko-Sarbaisky GOK, the slime fraction (with a particle size of less than 30 μm) from magnetite concentrate (2% of the concentrate weight), the filtrate after dewatering of magnetite concentrate, various bentonites, and hydrolyzed polyacrylonitrile (gipan) were used. Mineralogical analysis of the slime fraction showed the presence in it mainly of non-ore minerals of the epidote group and small amounts of chlorite and pyrite. The characteristics of the bentonites used are given in Table 1.

The adhesive interaction between the surface of magnetite plates and a layer of suspension simulating the pore suspension of iron-ore granules was evaluated from the force required to tear off a magnetite plate by means of torsion balances. The breaking load was applied at a rate of 15 mg/sec and expressed in newtons per m² of contact area. The weight of the plate being torn off was excluded from

the magnitude of the pull-off force. Suspension samples were prepared in the following manner. A definite amount of bentonite and of the silt fraction was introduced into the filtrate, mixed thoroughly, and, after holding for half an hour, a drop of the suspension was applied with a measuring pipette onto the lower magnetite plate. Then the upper magnetite plate was lowered onto the drop so that the entire polished surface of the plate was in contact with the suspension drop, and the pull-off was then carried out. In parallel, the surface tension and rheological parameters of the suspension under test were determined, respectively, by the ring pull-off method and on an RV-8 rotational viscometer.

Table 1

Characteristics of bentonites

The pull-off force of the magnetite plate was measured beforehand using pure filtrate as the liquid. The pull-off force at room temperature \((22^\circ\mathrm{C})\) was \(99.7\ \mathrm{N/cm^2}\) at a filtrate surface-tension value of \(75.9 \cdot 10^{-3}\ \mathrm{N/m}\). When the silt fraction was introduced into the filtrate in an amount of 20% by weight, the pull-off force of the magnetite plate practically did not change. The suspension was unstable. A series of samples of silt–filtrate suspensions was then investigated with the addition to them of various amounts of bentonites from the Dash-Salakhly and Cherkassy deposits. The results of these experiments are presented in Table 2, from which it is evident that the nature of the change in the pull-off force, surface tension, and limiting shear with increasing concentration of bentonite in the suspension is the same. A significant increase in these quantities occurs in the concentration range of 30–37% for Cherkassy bentonite and 14–20% for Dash-Salakhly bentonite. It is precisely these limits of bentonite concentration in the suspen-

correspond to the highest values of plasticity \((\psi)\), calculated by the equation \(\psi = \frac{e}{\eta}\), where \(\eta\) is the plastic viscosity, expressed in poises.

Table 2

Effect of bentonite concentration on the properties of an ore suspension and its adhesion interaction with magnetite.

The magnitude of the pull-off force for low-concentration (up to 10%) suspensions of bentonites of different quality is approximately the same. Thus, for example, for 10% suspensions of Dash-Salakhly and Cherkassy bentonites, the pull-off forces are, respectively, 1275 dyn/cm² and 1000 dyn/cm²; the strength of wet pellets with these bentonites also differs only slightly. With an increase in the concentration of the suspensions, substantial differences are observed in the magnitudes of the pull-off force for different bentonites.

Thus, at a bentonite concentration in the suspension equal to 17%, the pull-off force with Dash-Salakhly bentonite is 7.6 times greater,

than for a suspension with Cherkassy bentonite of the same concentration. The contact time of bentonite with the filtrate has a great influence on the detachment force. When the contact time was changed from 30 minutes to one hour, the detachment force for 10% suspensions with Dash-Salakhly and Cherkassy bentonites increased on average by a factor of 2.

The introduction into the suspension or into the filtrate of the structure-forming agent K-4 (hypan), at the rate of 500 g/t of concentrate, increases the detachment force from 100 N/m² to 160 N/m². This corresponds to the adhesive strength of a suspension with Dash-Salakhly bentonite at a concentration of 13%. In all experiments to determine the detachment force, rupture occurred through the layer of the porous suspension, i.e., the cohesion of the suspension, determined by van der Waals forces, was less than the adhesion of the clay-bentonite suspension to magnetite. Thus, the principal component of the cohesion of the system in this case is the capillary (meniscus) forces at the boundary between the magnetite plates and the coagulation-structured suspension. The results obtained explain the absence of any significant increase in the strength of green pellets when bentonite is added to the charge and show that the weak link of the structure is the porous suspension and that, evidently, destruction of the forming granules occurs in the zone of action of molecular forces.

Literature

1. Tgershild M., Hmon P.A., Amer. Inst. Min. Eng. Proceeding of the Blast Furnace and Coke Oven, Raw Materials Conference, V. 9, 1950, p. 18.

2. Y. Pajan, “Kohászati lapok,” 1963, köt. 96, No. 12, pp. 529–533.

3. V. I. Korotich. “Theoretical Foundations of Agglomeration of Iron-Ore Materials.” Metallurgiya, 1966.

4. Masayoshi Wada, Osumi Tsuchiya, Proceedings IX International Mineral Processing Congress, 1970, Prague, ČSSR.

APPLICATION OF METHODS OF EXPERIMENTAL DESIGN AND OPTIMIZATION TO THE ASSESSMENT OF THE RESOLVING POWER OF THE AMP METHOD

A. A. Zheltonozhko, A. F. Fedorov, A. A. Kalinin, A. G. Stromberg

With the simultaneous content in a solution of several elements with close potentials of anodic peaks, analysis by the amal-