Surface modification of fine sodium bicarbonate for enhanced hydrophobicity and pulverized coal explosion mitigation

Pulverized coal explosions have threatened the mining industries for centuries. Its hazards are now usually mitigated by admixing powdered inert substances such as sodium bicarbonate (SBC). Literature confirmed the efficacy of SBC in suppressing coal dust explosions, while the bench-scale results may overlook the influence of on-site humidity in underground mines. The hydrophilic SBC is subjected to damp issues which lead to a reduction in dispersibility and thereafter a decline in explosion mitigation. The present work rendered the SBC powder hydrophobic via the mechanochemical coating method. The SBC surface was modified by two types silica nanoparticles (HB_NPs, HL_NPs) and polymethylhydrosiloxane (PMHS) to have good hydrophobicity with water contact angle approaching 120°. Explosion experiments in the 20-L chamber showed adding 60 % hydrophobic SBC in either dried or wetted form completely suppresses the coal explosions. The effects brought about by hydrophilic SBC were found weakened after 7-day exposure to a humid atmosphere, as an additional 10 % proportion was necessary for explosion suppression. Thermoanalysis suggested all SBC samples have a similar thermal sink and chemical inhibition mechanism on coal pyrolysis and combustion. The advanced performance of hydrophobic SBC was to maintain good dispersion, thereby effectively mitigating the explosion hazards over a longer period.