LOW-IRON TALC OF THE ALGUY DEPOSIT

P. G. Usov, G. N. Popova, N. F. Voronova

(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)

Thanks to its diverse valuable qualities, talc finds broad application in the most varied branches of industry, both in the Soviet Union and abroad.

In all industrially developed countries of the world there already exists a well-developed talc industry. Particularly characteristic is the rapid growth in the consumption of talc in ceramics. Ceramic materials produced on the basis of talc are distinguished by chemical resistance, heat resistance, and high mechanical strength.

High-frequency talc ceramics (steatite, forsterite) possess, with zero water absorption and high mechanical strength, very low energy losses in a high-frequency field and a number of other valuable electrochemical properties.

Cordierite ceramics, obtained from talc-clay compositions, are characterized, both in the porous and in the sintered state, by an exceptionally low coefficient of thermal expansion.

Therefore, in developed capitalist countries the ceramic industry is the principal consumer of talc. Thus, in 1931 the USA used 1.5 thousand tons in ceramic production, and in 1956—186.9 thousand tons; that is, in 25 years the consumption of talc in this branch of US industry increased by more than 120 times.

The structure of talc consumption that has developed in the USSR differs sharply from that in developed capitalist countries. Whereas in the USA the share of ceramics in the total volume of talc consumption in 1957 was 32%, in the Soviet Union in 1959 it was 5.6%. The main consumer of talc in the USSR (64.3%, 1959) is the production of insectofungicides, whereas in America this branch of industry uses less scarce raw material (pyrophyllite, etc.) [1]. In our country, numerous types of products manufactured abroad on the basis of talc are not produced at all. Such are, for example, chemically resistant, heat-resistant, frost-resistant ceramics, and others.

The limited development of the production of talc ceramics in the Soviet Union is explained mainly by the fact that domestic high-quality talc is still in short supply. Only since 1950, after the start of exploitation of the Onot deposit of iron-free talcs and as a result of imports of Chinese talc, has the domestic industr—

Table 1

Partial residues, in %, on sieves with openings, mm.

Table 2

Content of fractions, in %, with grain size in mm

...the industry has begun to receive high-quality talc raw material, but still in insufficient quantity. The use of Onot low-iron talc is hampered by the shortage of talc-grinding enterprises. The Kirgitei deposit of high-quality talcs is difficult to access.

Therefore, the new Alguy deposit of powdered low-iron talcs, discovered by a magnesite party of ZSGU in 1961, is of great interest; in composition and properties these talcs are close to the Kirgitei talcs. The deposit is located 9 km northeast of the Novokuznetsk—Abakan railway line, in the upper reaches of the Alguy River. These are fine-dispersed, disintegrated, white talcs with a grayish tint, occurring at the surface beneath insignificant alluvial deposits. According to preliminary estimates, talc reserves amount to more than 5 million tons only to a depth of 20 m from the surface. The enclosing rocks of the talcs are dolomite and quartzite.

This article presents the results of physico-mechanical and mineralogical studies of three representative samples of Alguy talc, selected by the geological exploration expedition of ZSGU from the central pit 439-62—sample No. 439-1—and from adit No. 372—sample No. 372-20 and sample a-372-20.

By macroscopic characteristics, the material of all the rocks is homogeneous; it is a grayish-white powder, greasy to the touch, and easily rubbed between the fingers.

Analysis of grain-size composition, performed by the sieve and sedimentation pipette methods (Tables 1 and 2), shows that the main mass of the rock is composed of fractions with grain sizes of 50 microns and smaller.

The chemical compositions of the rock are given in Table 3. For comparison, the chemical composition of Onot talc from a radioceramic plant is given.

Table 3

Spectral analysis establishes the following in the Alguy rock: Cu—up to 0.1%; Pb—up to 0.01%; Zn—up to 0.01–0.03%; La—up to 0.03–0.1%; Jb—up to 0.001%; Co—up to 0.001; and Cr—up to 0.001%.

Mineralogical studies by microscope and other methods establish in the Alguy rock a single magnesium-containing mineral—talc—in the form of flexible but nonelastic semitransparent scales and flakes. The shape of the scales and their sizes are very diverse; elongated, irregular, and more rarely isometric forms predominate. The size of the flakes varies from 0.01 to 0.033 mm. Extinction is straight. The refractive indices are \(Ng = 1.582 \pm 0.003\) and \(Np = 1.538 \pm 0.003\). Quartz is established in significant amounts in the rock, in the form of angular or corroded grains of irregular shape, with an uneven, cracked surface. Feldspars and marcasite occur as isolated grains.

Fig. 1. X-ray diffraction patterns of talcs. 1 — Alguy talc, 2 — Onot talc.

According to the magnesium oxide content, the amount of talc in the Alguy rock is about 85–90%. This content is also matched by the loss in weight on ignition as a result of the splitting off of chemically bound water by the talc molecule.

According to chemical and petrographic analysis, the rock contains 8–13% quartz and impurities, mainly feldspars—0.4–1.0%.

The refractoriness of the rock is 1600°. The talc material and quartz in the rock are represented by the same granular structure and occur in the same proportions in all fractions. The chemical compositions of the individual fractions do not differ substantially from the composition of the rock (Table 4).

Table 4

Consequently, it will be impossible to beneficiate the talc by mechanical methods. The talc composition of the rock is established by X-ray and thermal methods of investigation, carried out for comparison in parallel with Onot talc.

Fig. 2. Thermograms of talcs.
1 — Onot talc, 2 — Alguy talc, sample 439, 3 — Alguy talc, sample 372-20, 4 — Alguy talc, sample a-372-20.

Fig. 3. Curves of weight loss of talcs:
1 — Alguy talc, sample 372-20, 2 — Alguy talc, sample a-372-20, 3 — Alguy talc, sample 439, 4 — Onot talc.

In Fig. 1 are given the X-ray diffraction patterns of the Alguy and Onot talc, obtained under the same conditions on

on a URS-50-I unit with an ionization counter, from which it is evident that all the indices of the talc peaks coincide with the standard.

Here, too, the only impurity in the rock is recorded—quartz—with reflection angles \(\Theta = 12.06;\ 13.24\) and 25.12, corresponding to interplanar-spacing indices of, respectively, 3.66; 3.22 and 1.81 Å.

On the differential heating curves (Fig. 2), for the Alguy rock, as for the Onot talc, one endothermic effect is recorded in the temperature interval 900–1000°, which agrees with the data of Rudneva and Avgustinnik [2]. The bends on the weight-loss curves of the Alguy rock during heating (Fig. 3) also correspond to these same temperatures.

The rock in its natural state, and after grinding until it passes completely through a sieve of 4900 openings/cm² with water, does not form a plastic mass. It is shaped into articles in a semi-dry state, with a moisture content of about 5%. It sinters at temperatures above 1350°C. Of special value for the ceramic industry is the whiteness of articles made from the rock after firing.

In the raw state, the Alguy rock has a whiteness of 75–77%. The percentage of whiteness was determined on an FM-56 unit under the same regime. Some data on the behavior of the rock during firing are given in Table 5.

Table 5

Note: sample size \(d = 25.5\) mm, \(h = 25\) mm; semi-dry pressing at a pressure of 500 kg/cm².

Conclusions

1. The Alguy rock contains 85–90% talc, 8–13% quartz, about 0.4–1.0% feldspars, and very small amounts of iron-bearing minerals; it is a valuable raw material for the ceramic industry.

2. The deposit is located close to the railroad; the useful rock occurs as a thick bed close to the surface (the overburden is 1.0–1.5 m). All this creates favorable conditions for its development.

Literature

1. V. P. Petrov. Talc as a mineral and useful mineral resource. Trudy geologii rudnykh mestorozhdenii, pp. 13–14, issue 63, 1961.

2. Talc. Collection edited by I. D. Finkelshtein, Moscow, Promstroiizdat, pp. 81, 96, 1952.