Research and Application of the Rehbinder Effect in Coal Technologies

Abstract

This article explores how the Rehbinder effect manifests during the processing of low-metamorphosed coal from the Donetsk Basin. The authors distinguish between the classical primary Rehbinder effect (material weakening) and the secondary Rehbinder effect (a change in the zeta-potential of crushed coal) also known as the “adsorptive exposure of the pore space of the solid phase”), which accompanies the primary Rehbinder effect. The goal of the study is to examine how both primary and secondary Rehbinder effects manifest in Donetsk coal. Several methods were applied, including coal-sizing analysis, electroosmotic measurement of coal surface ζ-potential, the Tovarov method for determining the external specific surface area of dispersed material (coal), the authors’ own method for preparing polished sections of coal grains and analysing oxide films within pore walls and fractures, as well as the analysis of the results using Microsoft Excel. The experiments confirmed that the primary Rehbinder effect productively weakens the organic matter of low-metamorphosed Donetsk basin coal. The paper outlines several objectives for expanding future experimental work considering the following factors: pore parameters – their size and surface characteristics, the composition of the weakening liquid infiltrating into the pores, as well as infiltration kinetics. In the coal studied, the secondary Rehbinder effect appears as a shift in the hydrophilic–hydrophobic balance of the overall external surface of the crushed coal towards increased hydrophilicity. This shift results from the exposure of oxidised pore surfaces during the primary Rehbinder effect, as these surfaces contribute their oxidised fraction to the external surface when the pre-soaked coal is crushed. The experimental data show that it is possible to produce a stable, highly concentrated water-coal slurry (water-coal fuel) from the lowmetamorphosed Donetsk coal at рН ˃ 4 (ζ ˃ 30 mV) when the coal is pre-soaked and at рН ˃ 6.7 when dry-ground.