Exploring on aqueous chemistry of micron-sized lignite particles in lignite–water slurry: Effects of pH on humics dissolution

• The aqueous chemistry of lignite–water slurry was studied.
• The outer diffusion is the rate controlling step of humics dissolution.
• The particle size of lignite is decreased when the slurry pH is increased.
• Humics dissolution increases the surface hydrophilicity of the residual lignite.
• The dispersion stability of lignite is improved with humics dissolution.

The aqueous chemistry of lignite can change the properties of coal–water slurry. The aqueous chemistry of lignite–water slurry including dissolution kinetics of humics and properties of the residual lignite was studied using optical microscope imaging, SEM, FTIR, zeta potential and contact angle analysis. Also, the influence of humics dissolution on the interaction of micron-sized lignite particles was discussed by EDLVO theory. The dissolution kinetics demonstrates that humics concentration increases with increasing the slurry pH. The outer diffusion through the product layer is the rate controlling step according to shrinking unreacted core model. The value of D50 defined as the apparent particle size relevant to 50% of cumulative distribution is decreased when the lignite slurry pH is increased. The FTIR, zeta potential and contact angle results show that humics dissolution increases the surface hydrophilicity of the residual lignite. The total energy ET of the residual lignite particles at 10 nm of separation distance is enhanced from −0.70 × 10−17 to 0.34 × 10−17 J with the humics concentration is increased from 2.28 to 5.33 mg/L. The EDLVO calculation indicates that the dispersion stability of micron-sized lignite particles is improved with humics dissolution.

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