Preparation of coal-water slurry using high-concentration inorganic saline wastewater containing microplastics — A slurry performance and particle interaction analysis

In this study, high-concentration inorganic salt wastewater containing microplastics (MPs) was used to prepare MPs-coal wastewater slurry (MPs-CWWS). The rheological behavior, stability, and solid content of the slurry were discussed, and the interfacial interaction mechanism between particles was analyzed. Experimental results show that the presence of inorganic salts in the system will cause an increase in viscosity. This is because cations neutralize the negative charges on particle, resulting in a reduction in the electrostatic repulsion between particles. In addition, a large amount of water is adsorbed due to “ionic bonding”, resulting in a reduction in free water content and therefore a decrease in the solid loading of the suspended system. The enhanced stability is attributed to the thickening of the hydrated film. MPs have strong hydrophobicity and are easy to adsorb dispersants due to non-polar effects, which increases the negative charge and steric hindrance effect on the surface. MPs promote the dispersion of particles in the slurry. The extended-DLVO theoretical calculation results show that electrostatic repulsion and steric hindrance effect are the main forces promoting particle dispersion. Electrostatic repulsion plays a key role in promoting particle dispersion. The extended-DLVO theoretical calculations verify that the main reason for the increase in viscosity caused by inorganic salts is the decrease in electrostatic interaction energy. The existence of MPs can reduce the negative effects caused by inorganic salts.