Microwetting dynamic behavior and mechanism for coal dust based on low field NMR method—A case study

Abstract

With the gradual improvement of coal mine mechanization and automation, improving the production efficiency has also caused the dust concentration at the production site to increase significantly, which not only poses a great threat to the occupational safety and health of workers, but also affects the safe production and social stability of the mine. Therefore, based on the Low Field Nuclear Magnetic Resonance (LFNMR) experiment, combined with the micro molecular dynamic simulation, the micro wetting dynamic behavior characteristics and wetting mechanism of coal dust were explored. Second, based on LFNMR experiments, the wetting relaxation times of lignite under different surfactant conditions was studied, and the wetting mechanism of lignite was explored. It is considered that the sulfonic group, amino group and –COOH group in the surfactant can easily form hydrogen bonds with the abundant hydroxyl groups in lignite, which is conducive to wetting. However, there are more pores in lignite, and the pores are mainly smaller than 100 nm; this increases the specific surface area of the pores, which is conducive to the adsorption, condensation and diffusion of gas and liquid in coal. Then, the molecular dynamic behavior of lignite was simulated from the perspective of wetting dynamics, and the results show that: ① Lignite contains more oxygen-containing functional groups, which makes it difficult for sodium laurylsulfonate (SAS) and primary alcobol ethoxylate (JFCS) molecules to be absorbed and diffused on the coal surface. Instead, they spontaneously polymerize or combine with coal molecules to reduce the hydrophilicity. ② Cocoamidopropyl betaine (CAB-35)and stearyldimethylbenzylammonium chloride (1827) molecules have better adsorption properties than SAS and JFCS, and the former adsorbs on the coal surface in a gentle or inclined spatial configuration, which can not only spread effectively on the coal molecular surface, but can also actively diffuse in space, without self-polymerization of surfactant molecules, which is beneficial to wetting. Thus, the wetting dynamic characteristics and action mechanism of lignite are clarified at the micro level, which provides scientific guidance for the compounding of high-efficiency environmental protection composite dust suppressors to realize clean mine production.