POWDERY TALCITES OF THE ALGUI DEPOSIT

P. G. USOV, G. N. POPOVA

(Presented by the scientific seminar of the Department of Silicate Technology)

In the overall balance of industrial production, talc occupies a relatively small place; however, the scale of its extraction and, especially, the structure of its consumption may serve as a vivid indicator of the level of technical culture and industrial development of a country. At present, in terms of the amount of talc consumed, our country ranks third in the world, behind only the USA and Japan. But the consumption of talc in our country is determined almost entirely by its use as a filler for agricultural toxic chemicals (54.3%, 1959), whereas in the USA more than half of all mined talc (53.3%, 1959) is consumed by the ceramic and paint-and-varnish industries [1]. This lag in the structure of talc consumption in the USSR is explained mainly by the fact that high-quality talc is in short supply in our country. Therefore, the most important task of the domestic talc industry is the development and expansion of the base of iron-free talc. Of great interest is the Algui deposit of low-iron powdery talcites, identified in 1961 by work of the West Siberian Geological Administration (ZSGU). The deposit is located 9 km northeast of the Luzhba station on the Novokuznetsk—Abakan railway line, within the Kuznetsk District of Kemerovo Oblast. The thickness of the talc deposit in the central part of the occurrence, according to preliminary data from the magnesite party of the ZSGU, is 210 m; along strike it is traced for 950 m. Talc reserves that can be worked under the simplest hydrogeological conditions amount, according to data as of June 1, 1964, to 6.6 million tons. The enclosing rocks of the talc are monomineralic varieties of dolomite and quartzite.

This article presents the results of physico-mechanical and mineralogical studies of ten talc samples representing all the principal varieties of talc rock from the Algui deposit. According to macroscopic features, the material of all samples is identical and consists of a powdery, finely dispersed substance of grayish-white color, greasy to the touch. Analysis of the grain-size composition of the material of samples of the Algui rock, performed by sieve and sedimentation methods, establishes a high degree of its dispersion in the natural state: about 70–90% of the rock particles are represented by the fraction finer than 0.1 mm. Short-term grinding in a ball mill will be sufficient to obtain talc powder satisfying-

...meeting, in dispersion, the requirements of GOST 879-52 for talc of grades “A” and “B.” Chemical analysis of the talcites of the samples studied was carried out in parallel with chemical analysis of Onot talc taken from the radio-ceramics plant. The results of the analysis are given in Table 1.

Table 1

In its content of iron oxides, the Alguy talc compares favorably with the Onot talc; some of its samples contain practically none at all of this harmful impurity (Table 1). A distinctive feature of the Alguy talcites is the considerably lowered content, in a number of samples, of MgO in comparison with the Onot talc, and, correspondingly, the increased content of SiO₂.

Fig. 1. Interdependence of the MgO and SiO₂ content in the Alguy rock: — silica content, %----, magnesium oxide content, % (the chemical composition of samples 1, 2, 3, etc. is given in Table 1).

From Table 1 and Fig. 1 it is evident that changes in the MgO and SiO₂ content ...

are mutually dependent. The curves of variation of both components are symmetrical about the mean line separating them. The maximum MgO content corresponds to the minimum SiO₂ content, and vice versa. That is, the decrease in the content of MgO, and consequently of the talc mineral, in the Alguy talcites occurs exclusively at the expense of the introduction of quartz rock, which is the only appreciable mechanical impurity. Consequently, beneficiation of the Alguy rock must proceed by removal of the quartz material. However, it is impossible to beneficiate Alguy talc by mechanical methods alone, because, as investigations have shown, the talc mineral and quartz in the rock are represented by the same grain structure and occur in the same proportions in all fractions. By flotation, carried out in the laboratory of ZSGU and in the beneficiation laboratory of the Tomsk Polytechnic Institute, it proved possible to obtain a pure talc variety, exactly corresponding in chemical composition to the talc mineral.

Mineralogical investigations with the aid of the microscope and other methods establish in the Alguy rock a single magnesium-bearing mineral—talc in the form of flexible, but not elastic, plates and scales. The shapes and sizes of the scales are varied; elongated, irregular, and more rarely isometric ones predominate, with sizes from 0.01 to 0.003 mm. Extinction is straight; the refractive index is Ng—1.582 ± 0.003 and Np—1.538 ± 0.003. The refractive index of Onot talc is somewhat higher (Ng—1.590; Np—1.543), which is apparently due to the presence in its crystal lattice of iron oxides isomorphously replacing MgO. Microscopically, quartz is established in considerable quantities in the rock, in the form of sharp-angled and corroded grains of irregular shape, with an uneven, fissured surface. Feldspars and marcasite are recorded as isolated grains. X-ray and thermal methods of analysis of the Alguy rock, carried out for comparison in parallel with analysis of Onot talc, also confirm its talc character. All X-ray data for Alguy talc coincide with the standard. Here, too, the only impurity in the rock is recorded—quartz, with indices of interplanar spacings 4.16; 3.27 and 1.80. The differential heating curves for the Alguy rock, as also for Onot talc, record one endothermic effect in the temperature interval 850–1050° (Fig. 2), caused by the splitting off of chemically bound water. The same temperature interval corresponds to the maximum inflection on the weight-loss curves of Alguy talc, obtained by dynamic gravimetric analysis with the aid of a torsion balance (Fig. 3). Investigation of the ceramic properties of Alguy talcites was carried out on technological samples 439 and 372, corresponding to the average chemical composition of the Alguy talc rock for the deposit as a whole. Some data on the behavior of the rock during firing are given in Table 2¹).

It is apparent from Table 2 that Alguy talc is a difficult-to-sinter material, like any pure talc rock. After firing at a temperature of 1400°, the water absorption of the specimens remains high—9%; however, their compressive strength, despite the porosity, reaches 800–830 kg/cm². The absence of coloring oxides in the Alguy rock accounts for its high whiteness after firing—98–100%. The refractoriness of the rock is 1600°.

¹) Note: Specimen size \(d = 25\) mm, \(h = 25\) mm; semi-dry pressing at a pressure of 500 kg/cm².

Fig. 2. Thermograms of talcs:
1 — Onot talc; 2 — Alguy talc, sample 439; 3 — same, sample 372-20; 4 — same, sample 971-X; 5 — same, sample 971-XII; 6 — same, sample 971-XIII; 7 — same, sample 970-XIV; 8 — same, sample 970-XV; 9 — same, sample 970-XVII; 10 — same, sample 972-XIX; 11 — same, sample 970-XVIII.

Fig. 3. Weight-loss curves of talcs:
1 — Onot talc; 2 — Alguy talc, sample 439; 3 — Alguy talc, sample 372-20; 4 — same, sample 971-X; 5 — same, sample 971-XII; 6 — same, sample 971-XIII; 7 — same, sample 970-XIV; 8 — same, sample 970-XV; 9 — same, sample 970-XVII; 10 — same, sample 972-XIX; 11 — same, sample 970-XVIII; ordinate scale: 1 cm—1% weight loss.

Table 2

Conclusions

1. The Alguy talc rock is characterized by fine dispersion in its natural state and by the purity of its chemical composition. In terms of its low content of iron oxides, Alguy talc ranks first among the deposits of the Union and is not inferior to the best imported grades.

2. The only noticeable mechanical impurity to the talc mineral in the Alguy rock is quartz, which is completely separated by flotation.

3. In its natural composition, Alguy talc, containing not less than 27–28% MgO, after preliminary grinding satisfies the requirements of GOST 879—52, grade “B,” for the ceramic industry.

4. Flotated Alguy talc, representing a monomineral talc variety, will evidently satisfy all of its most demanding consumers.

5. The earliest possible industrial development of the Alguy deposit, located under favorable transport-economic and geological conditions and possessing large reserves of high-quality talc raw material, will to the extent practically necessary eliminate the shortage of low-iron talc in our Union.

Literature

1. P. P. Smolin. Questions of the development of the talc raw-material base and talc industry in the USSR. Proceedings of the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geology, issue 95, Publishing House of the Academy of Sciences of the USSR, Moscow, 29–47, 1963.