Study of the effect of sample preparation on the chemical composition and hydrophobicity of the coal surface

Abstract

Sample preparation for determination of the chemical and technological properties of coals is carried out using standard methods when coal samples come into contact with air. However, the outer surface of the resulting small particles is inevitably oxidized during grinding by the molecular oxygen present in air. Therefore, the physicochemical properties of the laboratory sample do not match the properties of the original native coal or coal of larger fractions. We present the results of studying the laboratory samples of low- metamorphized coal. Preparation of the native coal sample was carried out in a pure inert atmosphere (nitrogen) of a glove box. Methods of IR- and EPR- spectroscopy, chemical functional analysis of oxygen groups, determination of specific surface area, as well as methods for determining the wettability (determination of the wetting edge angle by a drop of liquid and the rate of absorption of a drop into a coal briquette) were used to characterize changes in the surface of coal particles. It is shown that the method of coal sample preparation significantly affects the functional composition and hydrophilicity of the outer surface of coal particles. The results obtained can be used in determination of the properties of native stratal coals, improvement of the technology of coal sample preparation, as well as in enrichment and processing of coals.