STUDY OF THE EFFECT OF SODIUM HUMATES ON THE AGGREGATE PROPERTIES OF QUARTZ SAND

V. M. Vityugin, A. F. Karpovich

(Presented at the scientific final conference of the Faculty of Chemical Technology)

At present, the range of materials subjected to pelletizing is growing considerably; therefore the development of the theoretical foundations of pelletizing is acquiring ever greater importance. Enlargement of material by granulation is a complex mechano-physico-chemical process, and its study requires taking into account many factors that ensure pelletizing.

The particle size of the materials, their specific gravity, the nature of the surface, their hydrophilicity, and moisture capacity are important in pelletizing, as well as in the choice of the binding element.

The aim of the present work was to study the effect of sodium humates on the aggregate properties of quartz sand. As has already been shown by P. A. Rebinder and co-workers [1] and by V. I. Likhtman and co-workers [2], adsorption of polar molecules, which include sodium humate molecules, leads both to a decrease in surface hardness and to a decrease in the coefficient of friction between particles. A reduction in the coefficient of friction between particles and in their resistance to deformation facilitates the mutual displacement of particles. On the other hand, sodium humates, possessing adhesive ability, form a strong structure upon drying, as was noted earlier, in particular, in the works of P. V. Vershinin and co-workers [3].

I. S. Kainarskii showed that, in the case of pressing finely dispersed quartz, the use of surface-active additives, in its effect on reducing the porosity of samples, is equivalent to increasing the pressing pressure by more than a factor of 4 [4].

G. M. Volkov [5] investigated the possibility of using sodium humates as a binder in coal briquetting. To study the effect of humic acids on the aggregate properties of quartz sand, 4 sand samples of different granulometric composition were prepared.

Sample No. 1 — initial Tashlinskii sand, class — \(0.5 + 0\) mm.

Sample No. 2 — sand, class — \(0.25 + 0\), screened from the initial Tashlinskii sand.

Sample No. 3 and sample No. 4 — initial Tashlinskii sand ground for 10 and 20 minutes, respectively, in a vibration mill.

The granulometric composition of all samples is given in Table 1.

Sodium humates were obtained from peat of the Vasugan deposit by treating it, in an air-dry state and ground to a particle size of 1–0 mm, with a 1% solution of caustic soda.

The aggregability of the samples studied was evaluated by a modified method [6].

Table 3

Value of molecular moisture capacity when wetting sand with water and with humates

Air-dry sand was placed in a 100 ml beaker; then, into the central part of the layer, 0.5 ml of distilled water or of a sodium humate solution at a concentration of 1.66% was introduced by means of a syringe. The time for introducing the liquid phase into the sand was 5 seconds, and the holding time was 30 seconds. When the liquid phase is introduced into the sand layer, a spherical aggregate is formed, which is easily separated from the remaining sand. Aggregability (lumpiness) was evaluated by measuring its size, weight, density, moisture content, and crushing strength.

Since, for evaluating lumpiness, the value of the maximum molecular moisture capacity is of great importance, the latter was determined in parallel for all samples. The maximum molecular moisture capacity was determined by the method of moisture-capacity media developed by A. F. Lebedev [7]. The results of the studies are given in Tables 2 and 3.

Judging from the data presented in Table 2, it is evident that sodium humates have no pronounced effect on the aggregate properties of sand of classes −0.5 + 0 mm and −0.25 + 0 mm in comparison with water, since their specific surface area is small; however, even for these samples the moisture content of lumps with sodium humates is somewhat higher, and their strength in the wet state is lower. There is practically no difference in the value of the mean diameter.

With increasing dispersion of the sand, the effect of sodium humates on the aggregate properties of the sand is manifested to a greater degree than that of water. Because of the higher viscosity of humates, the rate of their propagation in the sand is considerably lower than that of water. Hence the smaller granule size and its higher moisture content. The crushing strength of wet lumps with humates is lower than with water, since the coefficient of friction between particles wetted with water is considerably greater. The reduction in the coefficient of friction between particles wetted with sodium humates affects the increase in density. The density of granules of samples 3 and 4 with humates is, respectively, 2.02 g/cm³ and 1.89 g/cm³, compared with the density of granules of the same samples with water, 1.85 g/cm³ and 1.77 g/cm³.

This is where the positive role of sodium humates is chiefly manifested. It is known that the strength of granules made of fine-grained materials is ultimately (after drying) determined by the density of the wet granules, since the interaction forces between the grains of material in the granule are determined by the distance between them. Indeed, the strength of lumps obtained by the above method from sand of samples 3 and 4 with wa-

Granulometric composition of the sand sample

Table 1

Yield of class, %

Aggregate properties of the sand

Table 2

...with water and with sodium humates at a concentration of 1.66%, dried at \(t = 55^\circ\mathrm{C}\) for two hours, is respectively 77 and 444 g, 93 and 479 g.

The second positive factor in the use of sodium humates instead of water in granulation is the increased plasticity of the raw mass, which makes it possible to intensify the rounding process. The improved lumping upon the introduction of humates is illustrated by the indices of maximum molecular moisture capacity. When water is replaced by sodium humates, the moisture capacity increases severalfold, as is evident from Table 3.

A certain drawback of replacing water with sodium humates is a decrease in the strength of the lumps because of the lower surface tension of sodium humate solutions in comparison with water. However, this drawback is completely offset by the higher quality of the finished granules and by more intensive granulation.

REFERENCES

1. P. A. Rebinder et al. Studies in the Field of Surface Phenomena, ONTI, 1936.
   P. A. Rebinder, L. A. Shreiner, K. F. Zhilach. Hardness Reducers in Drilling. Publishing House of the Academy of Sciences of the USSR, 1944.

2. V. I. Likhtman, E. D. Shchukin, P. A. Rebinder. Physicochemical Mechanics of Metals. Publishing House of the Academy of Sciences of the USSR, Moscow, 1962.

3. P. V. Vershinin, V. P. Konstantinova, N. V. Kirilenko. Study of adhesion phenomena in processes of structure formation in soil; P. V. Vershinin. Formation of soil structure. Bulletin of Agricultural Science. Fertilizers, Agrotechnics, Agricultural Soil Science, 1941.

4. I. S. Kainarskii. Physicochemical method for increasing the density of refractories from lean bodies. Refractories, No. 2, 1951.

5. L. L. Khotuntsev, V. L. Popov, G. M. Volkov. New types of binders for briquetting coal fines. Ugol’, No. 4, 1960;
   G. M. Volkov. On the plasticizing action of sodium humates in the process of compacting powdery materials. Engineering Physics Journal, No. 9, 1960.

6. A. M. Parfenov. Agglomeration of Iron Ores, Metallurgizdat, 1954.

7. A. M. Vasil’ev. Fundamentals of Modern Methods and Techniques for Laboratory Determinations of the Physical Properties of Soils. State Publishing House of Literature on Construction and Architecture, Moscow, 1953.