On the Intensification of Coal Flotation and a Methodology for Testing Industrial Flotation Machines

V. I. MELIK-GAIKAZYAN, A. A. BAICHENKO, V. A. BABENKO, B. A. DETINKO,
G. F. KOLINICHENKO, L. N. KURBATOVA, B. A. POPOV

(Presented by Prof. I. V. Gebler, Doctor of Technical Sciences)

Sparingly water-soluble nonpolar substances used in the industrial flotation of coal fines as flotation reagents increase the flotation activity of the surface of coal particles and thereby promote their recovery into the concentrate through selective adhesion to them in the form of fine droplets. Rock particles, on whose surface droplets of the reagent do not adhere, or adhere in a considerably smaller amount, are activated more weakly and are recovered into the froth product in a relatively smaller number because they adhere much worse to air bubbles. Although many details of this process of increasing the flotation activity of coal particles and particles of other nonpolar minerals by nonpolar reagents still remain controversial [1, 2], nevertheless the idea of the advisability of preliminary dispersion of the reagent and of feeding it into the pulp in the form of an aqueous emulsion with the aim of intensifying flotation was expressed long ago [3, 4, 5]. Attempts are also known to carry out emulsification of reagents under industrial conditions (for example, at Enakievo, Chumakovo, etc.); however, materials about them were not covered in the literature, and the method itself did not find application, apparently because the results obtained were not sufficiently satisfactory. The latter may have been a consequence both of poor control over the flotation operation, under which it is difficult to judge the results when the latter are not very significant, and of shortcomings in the emulsifying device—its unreliability in operation, bulkiness, or considerable cost. Believing, however, that emulsification of reagents should nevertheless intensify the process of coal flotation to some extent, we made an attempt once more to carry out emulsification under industrial conditions, but taking into account those possible shortcomings in the organization of the tests that were noted above.

As an emulsifier we used a metal water-jet pump [6], supplied by a portion of the process water fed into the conditioning tank for diluting the pulp before flotation. Industrial tests carried out at the Nikitovka Central Coal Preparation Plant [7] and at the coal-preparation plant of the Gorlovka Coke-Chemical Plant [8]¹,

¹ The work at the Gorlovka coal-preparation plant involved F. L. Pilyasov, E. M. Ioffe, and A. P. Moroz; at the Nikitovka Central Coal Preparation Plant, G. L. Livshits and A. I. Chubenko participated.

showed the complete advisability of emulsification and the suitability of the water-jet pump—an apparatus very simple and reliable in operation—for carrying out this operation. In order to conduct prolonged industrial tests, certain additions [9] were made to the emulsifying device, which made constant supervision of its operation unnecessary. Thus, the question of the emulsifier was practically resolved.

The solution of the second question, concerning testing of the flotation machine and control of the load on it, was begun with the development of the design and installation, in front of the flotation machines, of continuous-flow meters [10, 11], by means of which the amount of pulp, in \(m^3/\text{h}\), being fed to the flotation machine at a given moment was determined. Multiplication of this value by the density of the pulp, determined by the weight of a liter sample, gave the magnitude of the load in \(\text{t}/\text{h}\). This made it possible to maintain a constant load on the machine during experiments to determine the influence of emulsification of reagents on the process of flotation of coal fines. In addition, tests could be carried out at various loads on the machine, including limiting loads.

Testing of the machine was carried out by cells after two to three hours of normal operation of the flotation machine under the specified reagent regime and feed. Samples were taken over the course of an hour every 10 minutes, one froth scraper at a time, into a special tray whose length was equal to the width of the machine cell. From the tray the sample, with the aid of a brush-broom, was poured into a marked bucket.

After each such operation the brush-broom was washed in a bucket of clean water in order to exclude the possibility that individual particles remaining on it and belonging to the froth product from a given cell might enter the sample taken from the next cell. The froth scrapers were marked beforehand, and, in sampling, all the scrapers of the given cell took part successively, for greater representativeness of the overall sample from that cell; in the case of the “Giprokoks-52” machine, samples were taken from both of its sides. This subsequently made it possible, proceeding from the weight of the sample obtained from a given cell for a definite number of scrapers and knowing the total number of scrapers occurring during one hour of operation of the flotation machine, to calculate the productivity of each cell in \(\text{t}/\text{h}\).

The participation of all scrapers in sampling was dictated by the consideration that some of them could have different heights and therefore could remove different amounts of valuable product from the cell, which could subsequently distort the results of calculating the productivity of the cell. During sampling, the latter were continuously stirred in the bucket in order to break up the froth and reduce the volume of the sample; in this process, the coarse particles falling out of the froth settled mainly on the bottom of the bucket, forming a sediment, while the finer and lighter particles, firmly attached to bubbles, floated up together with the bubbles, forming on the surface of the liquid a froth “cap” several centimeters thick. At first, dewatering of the samples was carried out in the following way. The samples were left to stand for 12 hours, after which a slot was made with a tin spatula between the wall of the bucket and the dried froth “cap”; through this slot, by gently tilting the bucket, it was possible to pour off completely clear water. The sediment remaining at the bottom of the bucket and the froth “cap” were transferred to trays and dried in an electric drying cabinet at a temperature of 90–102°C.

Subsequently we used another, faster method of dewatering, which made it possible to process larger-volume and, consequently, more representative samples. For this purpose, a va—

... a batch-operated vacuum filter, which is shown schematically in Fig. 1.

The filter is a rectangular funnel 1, having the shape of an inverted truncated pyramid. A cylindrical receiver 2 for the filtrate is welded to its lower part. At some distance from the lower edge, a quadrangular frame 3, 40 mm wide, is welded into the funnel; into this frame is inserted a perforated sieve 4 with openings of 5 mm, covered with dense filter cloth 5. Before filtration of the sample, a certain amount of coarse-grained settled sludge is placed on this cloth from the bottom of the bucket; its layer prevents the filter cloth from being clogged by fine particles and thereby considerably facilitates and accelerates dewatering. Through valve 7 the filter is connected to the vacuum line. After filtration is completed, the cake, with a moisture content on the order of 20%, is transferred for quartering and drying, and the filtrate is drained through valve 6. The introduction of filtration brings the conditions of sample treatment closer to the conditions under which the froth product, arriving from the flotation machine through a froth breaker onto the filters, is treated, and makes it possible to compare the ash content of the cake from the filters with the mean dynamic ash content of concentrate samples taken from all cells. Thus, the results we obtained by this method, relating to the case in which the reagent was introduced into the pulp in non-emulsified form, are in good agreement with the monthly average data of the Technical Control Department on the operation of the flotation section under the same reagent regime and feed. This gives grounds to consider that the samples taken were sufficiently representative, and that the sampling procedure was entirely satisfactory. The dried samples were weighed and, after treatment with a magnet to remove scale that might accidentally have entered them from the quartering, were submitted to the plant chemical laboratory for ash analysis.

Fig. 1. Vacuum filter for dewatering samples

To determine the effect of emulsification on the flotation process, tests were conducted both with emulsification and without emulsification of the reagents, while the reagent consumption, feed points, and other parameters were kept unchanged. Figure 2 shows the flotation flowsheet and the reagent feed points during one series of tests at the Gorlovka coal-preparation plant.

Fig. 2. Flotation flowsheet and reagent feed points
1—contact vat, 2—pulpmeter, 3—“Giprokoks-52” flotation machine.

The results of flotation are given in Table 1. Sulfurized kerosene was used as a reagent, with a consumption of 1.2 kg/t; 50% of the kerosene was fed into the contact vat and 25% each into the third and fifth cells. Absorptive oil was used in an amount of 0.4 kg/t; 50% was fed into the first cell and 25% each into the fifth and seventh cells.

Table 1

Results of flotation of coal fines with emulsified and non-emulsified reagents at a pulp temperature of 20°C

A comparison of the data presented in the table shows that emulsification of the reagents increases concentrate removal from the first cells while simultaneously lowering its ash content and increasing the ash content of the flotation “tailings”; that is, emulsification of the reagents intensifies the flotation process of coal fines.

References

1. V. I. Klassen and I. N. Plaksin, DAN SSSR, 95, No. 4, 853, 1954; Izvestiya AN SSSR OTN, No. 3, 62, 1954.

2. A. F. Taggart, Fundamentals of Ore Dressing, Metallurgizdat, 1958.

3. J. A. Barr, Rock Products, 49, No. 10, 92, 1946.

4. V. I. Klassen, Elements of the Theory of Flotation of Coals, Ugletekhizdat, 1953.

5. D. S. Emelyanov, Theory and Practice of Coal Flotation, Ugletekhizdat, 1954.

6. V. I. Melik-Gaikazyan and A. A. Baichenko, Author’s Certificate No. 107652 with priority of June 8, 1956.

7. A. A. Baichenko, V. I. Melik-Gaikazyan, G. L. Livshits, and A. I. Chubenko, Ugol’, No. 11, 37, 1956.

8. V. I. Melik-Gaikazyan, A. A. Baichenko, F. L. Pilyasov, and B. M. Iosif, Koks i Khimiya, No. 8, 19, 1956.

9. V. I. Melik-Gaikazyan, A. A. Baichenko, F. L. Pilyasov, and A. P. Moroz, Koks i Khimiya, No. 8, 14, 1957.

10. V. I. Melik-Gaikazyan, A. A. Baichenko, F. L. Pilyasov, and A. P. Moroz, Koks i Khimiya, No. 6, 12, 1957.

11. V. I. Melik-Gaikazyan, E. Ya. Vintman, G. L. Livshits, and A. A. Baichenko, Ugol’, No. 7, 43, 1957.