ON THE PRODUCTION OF EARTH MINERAL PIGMENTS FROM RAW MATERIALS OF TOMSK OBLAST*

M. E. Efendi

The rapid growth of construction and the presence of an ever-increasing quantity of metal equipment, machines, and means of transport—all this requires a considerable quantity of paints for the preservation of this equipment and of structures; with the high rates of mechanization of agriculture, saturated with tens of thousands of tractors, combines, seeders, and other agricultural machines, protection is required against the destructive action of atmospheric precipitation, to which they are inevitably subjected in the field.

The assortment of paints consumed by the various branches of the national economy is very diverse, but nevertheless some representatives of them sometimes have predominant importance, owing to their mass consumption. Thus, for example, of the total quantity of ground paints planned for consumption in the prewar years, more than 50% consisted of ocher, mummy, and iron red. These paints, bearing the general name “earth pigments,” are comparatively cheap.

This is what makes their transportation unprofitable, since often the cost of transporting them may approach or even exceed the factory cost.

Therefore, in every district or oblast, especially those possessing developed industry and agriculture, the question of the possibility of producing earth pigments, their assortment, and methods of production must be worked out seriously. Reserves of raw material for paints and their quality must be clarified. A rational distribution of the paint-production industry, bringing it closer to the sources of raw material, gives an undoubted economic effect.

Tomsk Oblast at present does not have any significant industrial enterprises for the production of earth pigments, while the need for them here is very great. The delivery of earth pigments from other regions of the USSR, where the production of these paints is concentrated on the basis of significant deposits of raw materials for them, is irrational in view of the existing reserves of such raw material in Tomsk Oblast.

In the present work, the possibility of producing earth pigments in Tomsk Oblast is examined; analyses are given of samples of raw material found by a geological-prospecting party organized in 1945 and 1946 by the West Siberian Geological Administration in Tomsk Oblast, and experiments on processing it into paints are presented; the paths along which the production of earth pigments in our oblast may proceed are also indicated.

It is necessary to note here that Tomsk Oblast also possesses other broad possibilities for the production of paints from clays. The first

* Reported at a meeting of the Tomsk Branch of the All-Union Chemical Society named after D. I. Mendeleev on January 9, 1947.

one of them is that the white clays of Tomsk Oblast are an excellent raw material for the production of the extremely scarce pigment ultramarine.

In addition, the use of clays for producing colored pigments (green, blue, pink, and protective) is of considerable interest. Some clays have the ability to absorb basic aniline dyes well and form lakes with them; moreover, these aniline dyes do not tint the material superficially, but form stable compounds [1]. Very beautiful shades of various colors are obtained depending on the added dyes. The dyes may be malachite green, brilliant green, methylene blue, auramine, and fuchsin. The resulting green colors, when mixed with ocher and umber, give all possible shades of protective color. Blue shades from methylene blue may partially replace ultramarine for interior work.

The chief advantage of these pigments is that, in the presence of lime, they do not fade; therefore they are called lime-resistant pigments.

According to the review of Malyarstroy, the lakes obtained, especially the green ones, proved lime-resistant for interior work using glue, casein, and lime, and can replace the greens hitherto used, which are unsuitable in glue paints (for example, carriage green, containing Prussian blue, which, decomposing in an alkaline medium, forms brown iron oxide). Good results have also been obtained with the pigments described above when they are used in wallpaper manufacture.

These colored clays are of little use for oil painting, but green lakes mixed with umber, ocher, and white lead give all possible protective-color paints and may also be used for oil paints. By combining green lakes obtained from clays by the above-described method with glauconite, all possible colors for oil paints can be obtained; this makes it possible to replace the more expensive chrome pigments.

In Tomsk Oblast, which possesses a variety of clays, the study of this question, with the aim of organizing production of the pigments described above, is, in our opinion, highly expedient and desirable, since it makes it possible, from local raw materials and with the import of only a small quantity of aniline dyes, to organize the production of green, blue, red, and yellow pigments. The first experiments we have conducted with clays of Tomsk Oblast have shown that some of the clays absorb aniline dyes well, forming beautiful tones.

Returning to the production of earth pigments, it should be noted that the latter has existed on the territory of the USSR for more than one hundred and thirty years. In 1814, about 160 tons (10,000 poods) of red iron oxide and mummy were obtained. The main center was Moscow; in addition, there were factories in Yaroslavl and Petersburg. In 1912–13, there were up to 125 enterprises in Russia producing various pigments. Enterprises operating on imported raw materials were wholly dependent on foreign countries both with respect to raw materials and with respect to formulas. The assortment had a targeted character—production was limited to painters’ pigments. In general, the paint-and-varnish plants of prerevolutionary Russia were technically backward and extremely primitive.

After the October Revolution, the paint-and-varnish industry in the USSR developed rapidly. During the years of the first five-year plan, the Zhuravka ochers, the earth pigments of Leningrad Oblast, and others were explored and brought into production.

In the second five-year plan, a shift took place toward the use of local reserves and the establishment of a new technical basis for processing, in place of the existing irrational methods for producing dry earth pigments. Earth pigments will continue to occupy one of the chief places, in terms of their specific weight, in the assortment of the paint-and-varnish industry.

Earth Pigments and Methods of Their Production

Among earth pigments, the most widespread and important are iron red, mummy, and ocher [2]. Natural iron red is a dark-brown paint with a reddish tint. This paint consists of a considerable amount of iron oxide with an admixture of clay. The content of $\mathrm{Fe_2O_3}$ in natural iron red ranges from 60 to 90%. Iron red should contain as little clay as possible. Red used for painting iron must not contain free acids, sulfur compounds, gypsum, ferrous sulfate, chalk, etc. [3,4].

Mummy contains less iron oxide than red. The content of $\mathrm{Fe_2O_3}$ in it is from 30 to 55%. It occurs in various shades—from yellow-red to dark violet. In addition to iron oxide, mummy contains clay and gypsum, but not chalk.

Ochers are natural pigments consisting of clays colored by iron oxides. The composition of the latter in ochers ranges from $\mathrm{Fe_2O_3 \cdot H_2O}$ to $\mathrm{Fe_2O_3 \cdot 3H_2O}$.

The color of ocher depends on the amount of impurities, which include manganese oxides, basic ferrous sulfate, ferrous-ferric oxide, free iron oxide, organic substances, calcium carbonate, etc. The red shade depends on the presence of free iron oxide. Manganese oxides give ochers a brown shade. The color of a darker ocher can be improved by mixing in some white material (heavy spar, limestone spar, gypsum, lithopone).

It should also be noted that ochers containing a considerable amount of clay—fatty ochers—require a larger amount of drying oil, dry more slowly, and give a softer film than lean ones (with calcium compounds). Good ochers should have not less than 17% iron oxides and, as far as possible, fewer calcium and magnesium compounds; otherwise the oil absorption of the paint increases. In ochers with a high $\mathrm{Fe_2O_3}$ content, the hiding power is greater.

When calcined, ocher changes its color, acquiring a reddish shade. This occurs because hydrated iron oxide is converted into anhydrous oxide and because organic substances burn out. During calcination, ocher loses weight. The smaller the loss in weight of the ocher, the better it is considered.

The technology for producing dry earth pigments is basically reduced to their beneficiation by various methods and, in some cases, to heat treatment in order to improve their properties and change their color.

Tomsk Oblast and the adjacent districts possess several separate deposits of raw material for the production of earth mineral pigments. One of the best deposits [5] of mineral pigments within the Tomsk district is considered to be the Barentsevo deposit. Testing of the ocher from this deposit showed its high covering properties and complete suitability for the preparation of oil paints of reddish-brown and brown shades. The total reserves of ochers at this deposit are quite large. Samples of rocks colored yellow, red, and greenish-blue (delivered to the analytical chemistry laboratory of the Tomsk Polytechnic Institute from other deposits by engineer P. T. Sazonov) were studied both for chemical composition and for the properties characterizing these rocks as pigments. A corresponding conclusion was made regarding the proper process for processing the raw material to produce paints from it.

Most of the rocks have a yellow or dark-yellow color. After firing, owing to the decomposition of iron hydrates, the color of the rocks becomes red or orange-red. Greenish-blue clay after firing becomes dirty yellow.

Chemical analysis was carried out in accordance with OST 229; in some cases a complete analysis of the paints was made.

Below we give the results of the study of the rocks, indicating where the samples were taken (Tables 1 and 2).

Table 1

Table 2

¹ Analysis of the 1946 samples was carried out by Assistant Z. N. Tereshkova.

Far from all of the rock samples cited above for the production of earth paints meet the requirements imposed on them with respect to their chemical composition and, first of all, with respect to iron content. Dividing iron paints into ocher, mummy, and red lead, we have approximately the following iron content in them: ocher—10–25%; mummy—30–55%; natural iron red lead—60–90%.

Comparing these figures with the results of the analyses of the rocks, we see that the main part of the rock samples does not meet these requirements for iron content. According to OST 229, dry ocher must contain: iron oxide not less than 12%, loss on ignition not more than 10%, moisture not more than 3%, residue insoluble in hydrochloric acid not more than 75%. The reaction of the paint must be neutral.

Considering the analyses of paints given above, and disregarding the moisture content, since in the course of processing the raw rock it can be dried, we may note that, in terms of calcium oxide content and the magnitude of loss on ignition, all the rocks almost meet the requirements of OST 229—dry ocher. In terms of iron content, the rocks, with the exception of the bog iron ore of the Luchanovo deposit, do not meet the requirements of OST 229—dry ocher. Luchanovo ore may be used for preparing mummy. All the other rocks listed may be used for preparing from them a mineral paint of the “ocher type.”

However, the chemical analysis of paints can by no means always serve as the final criterion of their quality and of the suitability of the rocks from which they are obtained for the production of natural earth paints.

Of great importance for the quality of a paint are the degree of hiding power (paint consumption per unit of surface) and oil absorption (the amount of drying oil required to form, with the paint, a mass suitable for painting) [6].

An increase in the content of ferric oxide hydrate raises the hiding power of the paint. The content of clay in ocher (fatty ochers), as many indicate, also leads to an increase in hiding power in comparison with lean clays (containing lime). However, this proposition is disputed. Fatty ochers always require more oil (drying oil); they have a higher oil-absorption value. Hiding power increases noticeably after calcination of the rock.

Hiding power is determined by repeated applications of the test paint to a previously weighed plate of white glass measuring 10·30·2.5 mm, on the reverse side of which two stripes—black and white—have been painted. The test paint is applied until, in reflected light, the black and white stripes on the reverse side cease to be noticeable.

The oil absorption of paints is determined by adding drying oil, whose specific gravity is precisely known, from a burette to a weighed portion of paint, which is stirred with a glass rod until the paint reaches painting consistency.

In order to supplement the chemical analyses of natural paints given above, and to determine their quality, we carried out tests of them for hiding power and oil absorption. In order to ascertain the quantity of paints as a function of the method of processing the raw material, these determinations were made both for a washed and calcined sample and for rock that had undergone no preliminary treatment other than grinding and sieving through a sieve with the corresponding number of openings per 1 sq. cm.

Below, in Table 3, we present the results of measurements of oil absorption and hiding power for the rocks studied by us.

If we compare the values of oil absorption for washed and unwashed paints, we observe a certain tendency toward an increase, although a very slight one and not in all cases.

For calcined rocks there is a sharp increase in oil absorption. The opposite phenomenon is observed with hiding power. If after washing the hiding power of the paint shows some tendency toward improvement, although not equally expressed for different rocks, then after calcination the amount of paint required per unit of covered surface falls sharply.

Thus, owing to the reduction in paint consumption, we shall not have, despite the increased oil absorption, any noticeable increase in the consumption of drying oil per unit of surface covered with calcined paint. Consequently, as a result of calcination we shall not obtain any economy, judging by the values of oil absorption and hiding power. Calcination can only be regarded as a method of making paints that makes it possible to change their color.

Table 3

Oil absorption and hiding power of ochres

In approaching the choice of a production method, we must first of all select those samples whose reserves are very considerable and sufficient to supply the plant with raw material. Such raw material for the production of ochre is represented by the clays of the Khaldeevskoe (1) deposit. We see, for example, that with the use of washing no particular change in the quality of the paint is observed; therefore paint can also be prepared from this rock without washing it.

Thus the process of producing ochre may be adopted as follows. The raw material is delivered to the warehouse, where it is partly subjected to natural drying, being placed on boards in thin layers. Final drying is carried out in a drying chamber. Next, the paint passes through a hopper by gravity to be ground in a crusher, where it is thoroughly comminuted, and is then separated from coarse particles in a separator.

In the case of producing mummy (the Luchanovskoe raw material), the above process is changed so that after drying the product it is calcined in an appropriate furnace.

Conclusions

1. In the present study we have established the suitability of certain local rocks for producing ocher, golden ocher, and mummy from them.

2. Under thermal treatment the color of the clays becomes red or orange-red.

3. Although the paints obtained from the above-listed clays do not fully meet the requirements of the all-Union standard (dry ocher, OST \( \frac{7815}{754} \)) and are merely paints “of the ocher type” (pale yellow, golden, light brown, red, dark red, and gray-blue), they may be used in painting work for putties and primers, for painting wooden structures (walls, floors, doors, windows), iron objects, and stone structures.

4. As a result of the study of the quality of the paints, depending on the method of processing the rock, a scheme for the production of paints has been given.

References Cited

1. M. E. Effendi, V. F. Negreev, and I. V. Filippaki. Study of the properties of Azerbaijani raw materials for obtaining dry earthy mineral paints. Proceedings of the Chemical Institute of the Azerbaijan Branch of the Academy of Sciences of the USSR, 1, Baku, 1937.

2. N. F. Baikov. The Mineral-Paint Industry of the USSR. Goskhimtekhizdat, 1931.

3. V. A. Naumov. Production of Ocher. Goskhimtekhizdat, 1932.

4. E. F. Belenskii. Technology of Pigments and Varnishes. ONTI, Khimteoret, 1938.

5. L. P. Zhukov. Mineral Paints. Useful Minerals of the West Siberian Territory. II, Tomsk, 1934.

6. T. I. Tolstikhina. Methods of Physico-Mechanical Investigation of Ocher. Gostekhizdat, 1930.