Optimized reagent dosage effect on rock dust to enhance rock dust dispersion and explosion mitigation in underground coal mines

Rock dust consisting of ultrafine calcium carbonate particles is required in underground coal mines to suppress the potential for coal dust explosions. When the dust is applied in a moist mining atmosphere or placed in the mine in wet form, caking of the rock dust particles occurs which negatively effects dispersion of the dust during an event thereby creating the potential for an explosion. An earlier investigation found that sodium oleate was effective in rendering the surfaces of rock dust particles hydrophobic thereby allowing the water to drain, eliminating the caking effect and enhancing their dispersive properties. However, subsequent research has shown that increasing the sodium oleate concentration above a specific value reverses the positive impact on dispersion by inducing particle agglomeration through hydrophobic particle-particle interactions. A detailed investigation found that monolayer adsorption of sodium oleate occurs most likely within the oleate concentration range of 0.1% and 0.15% by weight. A further increase in the oleate concentration resulted in a corresponding rise in the surface contact angle to a maximum of 126°. As a result, the inter-particle interactions become dominated by the attractive hydrophobic interaction force which results in spontaneous particle agglomeration upon contact between the rock dust particles. In addition, precipitated calcium oleate nucleated on top of the hydrophobic dust surface as nanoparticles and tended to agglomerate at high oleate concentrations. As a result, the benefits of hydrophobizing rock dust particles are limited to lower reagent dosages to maintain the desired dispersion characteristics.