National University of Science & Technology (MISIS), Moscow:

V. V. Korovushkin, Leading Researcher, Doctor of Geologo-Mineralogical Sciences
S. A. Epshtein, Head of Laboratory of Physics and Chemistry of Coals, Doctor of Engineering Sciences, e-mail: apshtein@yandex.ru
N. M. Durov, Senior Lecturer
N. N. Dobryakova, Engineer, Post-Graduate Student

The paper is dedicated to issues concerning effects of mineral iron compounds at processes of coal oxidization and self-ignition. The given in literature data indicates an important role of pyrite and iron carbonate within the mineral matter of coal in processes leading to coals selfignition. We provide a review of methods for quantitative estimation of iron carbonates and sulfides. It was demonstrated that for the quantitative estimation of mineral and valence forms of iron it is preferably to use Mössbauer spectroscopy method. In the paper we studied mineral and valence forms of iron in coals of various minefields, and also the features of their mineral matter composition. The representative samples of coals were collected at manufacturing plants and kept under the conditions of maximal excluding of oxidization. According to the growth of the degree of carbon contents, the coals collection included three main types: brown, bituminous coals and anthracite, and also bituminous oxidized coals. In order to study mineral and valence forms of iron we used methods of inductively coupled plasma emission spectral analysis and Mössbauer spectroscopy. Studies of mineral and valence forms of iron for coals of different minefields allowed finding sulfides as pyrite as well as carbonates as siderite. Contents of pyrite and siderite within the considered coals do not exceed 1%. The only exception was anthracite of Donetzk coal field with pyrite contents of 3.2%. Comparison of oxidized bituminous coals and not oxidized coals revealed that oxidization leads to substantial increase of hydromica contents and appearance of finely dispersed iron oxide. Study of mineral and valence forms of iron allowes to establish potential hazard of heat formation caused by siderite and pyrite oxidization at contents of the latter larger than in studied coal samples. In order to reveal the effect degree of sulfides and carbonates on coals self-heating, it is necessary to investigate alteration of composition of mineral and valence forms of iron at various oxidizing conditions. Control of such processes may be performed by emission spectral analysis and Mössbauer spectroscopy.
The study was supported in the framework of the Federal Targeted Prorgam on R&D in Priority Areas of Scientific and Technological Complex Develpment of Russia for 2014-2020, Agreement No. 14.575.21.0062, Unique Agreement Identifier RFMEF157514X0062.

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