Study on the variation law of geometric and surface properties of ultrafine coal particles with particle size

The variation of particle properties and surface physicochemical properties during coal crushing was studied. The geometric properties of coal particles were explored by analyzing the particle size distribution curve under the dual-domain fractal rule and the surface morphology under the scanning electron microscope. With the increased refinement degree, the fine particle size gradually concentrated and uniform, and the population difference of coarse particle size increased. The dominant force for particle refinement transitioned from shear force to crushing force, and the angular coal particles gradually had roundness and aggregation of ultrafine particles appeared. The surface properties of the particles were analyzed by the surface pore structure, the surface functional group content and the charge state. The specific surface area and average pore size of the coal particles gradually increased, and the adsorption kinetic constant gradually decreased, indicating that the crushing exposed the new surface and made the micro pores more developed. The oxygen-containing functional groups on the surface gradually decreased and the isoelectric point gradually increased, indicating that the hydrophobicity of the particles decreased gradually during the refinement process.