TECHNOLOGY FOR PRODUCING SOLUBLE HUMATES FROM PEAT

N. M. Smolyaninova, S. I. Khoroshko, A. N. Moskalchuk

Recently, humic acids have been finding ever wider application in various branches of the national economy. In the form of soluble sodium salts—humates—they are successfully used as stabilizers for clay solutions employed in drilling oil wells, and also for producing dyes for wood. Owing to their good surface-active properties, humic acids are used in the storage-battery industry as an expander for the positive plates of storage batteries. Finally, the use of humic acids in the form of soluble humates in agriculture as growth stimulants is highly promising. Their high effectiveness has been demonstrated in numerous works by Professor L. A. Khristeva and her collaborators and by other authors [1, 2].

At present, industrial production of humic acids is carried out at the Tyumen Storage Battery Plant. Solid sodium humates for the needs of the furniture industry are produced in small quantities in Latvia at an industrial combine. Both products are in short supply.

Because of the increased demand for humic preparations, it is necessary to organize their industrial production on a large scale. This will make it possible to introduce humic acids and other preparations based on them more rapidly into industry and agriculture.

Existing technological schemes have a number of serious shortcomings, namely: 1) the batch nature of the process and, as a consequence, the cumbersome design of the equipment, the difficulty of automation, the low productivity of the installations, and high operating costs; 2) high heat consumption; 3) large product losses and a low extraction coefficient for humic acids.

Of course, if the question is posed of industrial production of acids at the modern level, then only a continuous process can be considered.

The principal difficulty in developing a continuous technology for producing humates or humic acids is the extremely long duration of the process of extracting them from fuel, caused by the low rates of diffusion of the active part of the alkaline reagent into solid particles and of the humates formed from the solid substance into the solution, as well as by the very specificity of humic acids as high-molecular organic acids possessing the properties of a colloid. In addition, oth—

the separation of the unreacted raw material from the humate solution is difficult, since pulverized fuel, especially peat, swells strongly and is partially peptized in the alkaline solution, forming a very stable suspension that settles very slowly and is practically impossible to filter.

Great difficulties also arise in carrying out the filtration and drying of humic acids. Hence there follows the need to seek ways of intensifying the process as a whole and, first of all, its first stage—the extraction of humic acids from the initial raw material in the form of soluble humates.

One of the factors that makes it possible to intensify this process is temperature. It is known that heating a peat–alkali suspension to a temperature of 80–100°C makes it possible to increase substantially the rate of formation and dissolution of humates. Our experiments showed [5] that, if during cold extraction for 30 min the yield of humic acids from peat is only 5.73%, then already at 50°C it is 12.74%, and upon boiling the mixture it is 29.72% over the same interval of time.

Of considerable interest is the so-called dispersion method of extracting humic acids, based on fine grinding of the initial raw material in an alkaline medium. According to G. M. Volkov [2, 3], this method ensures an increase in product yield and a reduction in the duration of the process, allowing extraction to be carried out cold.

The ultrasonic method of obtaining humates may have great prospects, since it makes it possible to intensify this process considerably. A. P. Grishin and V. Yu. Zorin [4] showed that, under the action of an ultrasonic field, the process of extracting humic acids from brown coal in an alkaline medium is accelerated approximately 20-fold.

In the peat problem laboratory of TPI, studies were carried out to determine the possibilities of the dispersion and ultrasonic methods of intensifying the process as applied to peat. The influence of the type, consumption, and concentration of the alkaline reagent, the temperature of the process, and the intensity of mixing of the peat–alkali mixture on the rate of extraction of humic acids was studied. In addition, methods of separating the peat–humate suspension were tested—settling, filtration, centrifugation, and the action of polyacrylamide (as a flocculant) [5, 6].

On the basis of a discussion of the results obtained by us, as well as data from an analysis of the operation of existing enterprises and literature data, the following conclusions were drawn:

1. Mechanical dispersion of peat in an alkaline medium makes it possible to intensify substantially the process of extracting humic acids from peat and may be used as the basis for the technological process under development, in combination with subsequent heating of the finely dispersed peat–alkali suspension to a temperature of 80–100°C. This will make it possible to reduce the duration of peat treatment with alkaline solution to 30–60 min and to carry out extraction with a lower alkali consumption, i.e., at a peat : alkaline-solution ratio of 1 : 10, as compared with 1 : 100, which is optimal in extraction by the conventional method.

2. Solutions of caustic soda or soda may be used as reagents; the latter is considerably cheaper, and its use is more economical.

3. To separate the humate solution from the peat residue, it is advisable to use a settling-type centrifuge.

4. If caustic soda is used as the reagent, its twofold use may be recommended: the first time—in the form of

of a pure solution, in the second—in the form of an alkaline humate obtained during the first extraction.

1. Intensification of the process of extracting humic acids by combining fine dispersion of peat in an alkaline medium with subsequent heating of the mixture to the boiling point under vigorous stirring provides a basis for developing a continuous technological scheme for the production of humates, and also, if necessary, humic acids.

2. It is advisable to construct a large installation for the production of solid humate or a concentrated solution intended for centralized supply to various consumers (agriculture, the furniture industry, oil fields). Concentration of the solution can easily be accomplished by evaporation.

Fig. 1. Technological scheme for obtaining sodium humates: 1—raw-material hopper, 2—elevator, 3—intermediate hopper, 4—hammer crusher, 5—screw mixer, 6—solution tank, 7—collector, 8—mechanical disintegrator, 9—reactor, 10—settling centrifuge, 11—evaporator, 12—surface condenser, 13—vacuum pump, 14—humate collector, 15—pump, 16—ejector.

The conclusions presented above were used as the basis for developing a continuous version of the technological scheme for the process of producing humates from peat of the Tagan deposit in Tomsk Oblast. The capacity of the installation was determined approximately on the basis of the demand for humates in the principal districts of the oblast with developed vegetable growing, since it is precisely for vegetable crops that the use of humic fertilizers is most effective.

On the basis of the application rates recommended by L. A. Khristeva [1], the annual demand for 100% humates was determined to be 60 t. With a yield of humic acids from air-dry peat of 20.6%, peat consumption is 260 t/year.

A 2% solution of calcined soda was used as the reagent. Despite its lower activity, soda ensures a sufficient degree of extraction of humic acids when combined with fine

dispersion of peat in an alkaline medium with subsequent heating of the mixture to 80–100°C for 0.5–1.0 hour while it is intensively stirred. The ratio of the weight of peat to the volume of the soda solution is 1:10.

For separation of the peat–alkali suspension, a settling centrifuge 2NOGSh-300 is used (7).

The technological flow sheet of the process is shown in Fig. 1.

Air-dry peat in the form of crumbs is fed from the bunker (1) by a bucket elevator (2), through an intermediate bunker (3), into a hammer crusher (4), where it is comminuted to pieces no larger than 1–2 mm. The comminuted peat is mixed in a screw mixer (5) with a soda solution supplied from a vessel (6). Then the peat–alkali mixture enters a mechanical disperser (8), from which it is fed to the reactor (9). In the reactor, final extraction of the humic acids takes place with heating and stirring of the suspension by live steam entering through an ejector. The unreacted peat is separated from the humate solution in a settling-type centrifuge (10). The latter has two screws, which makes it possible to wash the precipitate with separate removal of the wash waters, which (in order to reduce losses of humates) are fed to vessel (7) for preparation of the soda solution.

The washed precipitate goes to waste, while the weak humate solution (2.0%) is evaporated in an evaporator (11) to a concentration of 15% and enters a receiver (14).

Secondary steam from the evaporator is condensed in a surface condenser (12). The hot condensate can be used for washing the precipitate in the centrifuge. Vacuum in the system is created by a vacuum pump (13).

As the economic calculation showed, the total cost of humates was 465 rubles per ton. The high cost of the product is explained by the low productivity of the unit, since a large part of the costs (about 60%) falls on wages and operating expenses. These costs can be reduced by constructing larger units.

The economic effect from the use of sodium humates averaged 8–10 rubles per hectare of crops.

LITERATURE

1. Collection: Humic Fertilizers. Theory and Practice of Their Application, part I, Selkhozizdat of the Ukrainian SSR, Kiev, 1957.

2. Collection: Humic Fertilizers. Theory and Practice of Their Application, part II, Selkhozizdat of the Ukrainian SSR, Kiev, 1962.

3. G. M. Volkova, On the technology of production of humic acids. Proceedings of the Institute of Fossil Fuels, Academy of Sciences of the USSR, vol. XII, 65–76, 1961.

4. A. P. Grishin, V. Yu. Zorin, Ultrasonic method for isolating humic substances, Proceedings of the Grozny Petroleum Institute, collection 25, No. 3, 59–62, 1961.

5. N. M. Smolyaninova, A. N. Moskalchuk, Investigation of the process of obtaining humic acids from peat. Izv. TPI. In press.

6. Development of a technology for obtaining humic acids based on peat. Report on topic 162/63. Tomsk, 1965.

7. Centrifuges. Catalog-reference book. Mashgiz, 1955.