Freeze-thaw conditions effects on coals grain size composition and resistance to breakage

Far North and Arctic zones are the strategic regions for the Russian Federation economic development. This includes the current and future mining of coals, including those of the valuable brands. Extreme climate conditions of such regions, with seasonal and daily temperature transition through zero are considered to cause the coals products losses (fines formation, oxidation, etc.) when the latter is being delivered to the end consumers. The current paper is dedicated to investigation of the effects of low-temperature cyclic impacts on coals tendency to destruction and variation of their resistance to breakage depending on the freezing temperatures. Coals of various types (bituminous and lignites) from deposits confined to the regions of the Far North and the Arctic were selected as the objects of research. The alterations of the grain size composition (on samples with a size of 0—3 mm) and resistance to breakage (on pieces of 25—50 mm) were investigated after freezing at temperatures of –20, –40, –60 °C and subsequent thawing. It was found that the change in the grain size composition of coals (with particles size of 0—3 mm) after low-temperature treatments does not depend on the freezing temperature. At the same time, it was found that some coals are resistant to low-temperature impacts and do not change after freezing-thawing. Whereas, some others (from differing origins) are prone to destruction, since after freezing down to –20 °C and lower, there is a significant (by 20% or more) drop in the proportion of large particles. The resistance to breakage of the studied coals (of particles size 25—50 mm) after low-temperature treatment changes in different ways. The coals of the Pechora basin vary in the character of resistance changing depending on temperature. For one coal, there is a gradual decrease in resistance with the freezing temperature. Another one, on the contrary, hardens with a decrease in the freezing temperature. This may be connected with the known differences between the vitrinite structure of these coals. For coals of the Apsatsky deposit, whose organic matter is dominated by vitrinite, there is a significant decrease in resistance to breakage only after freeze-thaw cycle at the lowest temperature of –40 ° C. The latter is presumably associated with the formation and destruction of carbon dioxide hydrates. The resistance to breakage of coal of the same deposit, but with larger inertinite contents, there was practically no change in its resistance to breakage observed after freezing at all considered ending temperatures. The nature of the change in the resistance to breakage of lignites of the Kangalassky deposit is due to the differences in moisture content in them, as well as the intensity of its loss during freezing at different temperatures.

Keywords: coal, low-temperature treatment, grain size composition, resistance to breakage.
For citation:

Agarkov K. V., Epshtein S. A., Kossovich E. L., Dobryakova N. N. Freeze-thaw conditions effects on coals grain size composition and resistance to breakage. MIAB. Mining Inf. Anal. Bull. 2021;(6):72-83. [In Russ]. DOI: 10.25018/0236_1493_2021_6_0_72.

Acknowledgements:

The work was supported by the Russian Foundation for Basic Research grant 18-05-70002.

Issue number: 6
Year: 2021
Page number: 72-83
ISBN: 0236-1493
UDK: 552.57+54.03
DOI: 10.25018/0236_1493_2021_6_0_72
Article receipt date: 08.02.2021
Date of review receipt: 12.04.2021
Date of the editorial board′s decision on the article′s publishing: 10.05.2021
About authors:

K.V. Agarkov1, Graduate Student, Engineer,
S.A. Epshtein1, Dr. Sci. (Eng.), Head of Laboratory, e-mail: apshtein@yandex.ru,
E.L. Kossovich1, Cand. Sci. (Phys. Mathem.), Senior Researcher,
N.N. Dobryakova1, Cand. Sci. (Eng.), Researcher,
1 Laboratory of Physics and Chemistry of Coals, National University of Science and Technology «MISiS», 119049, Moscow, Russia.

 

For contacts:

S.A. Epshtein, e-mail: apshtein@yandex.ru.

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