Study on the preparation of coal wastewater slurry from salt/alkali wastewater

Abstract

Combining experimental research and simulation calculation, the effect of high-concentration salt/alkali wastewater on the preparation of coal wastewater slurry (CWWS) was studied. The research on the slurry-ability of CWWS shows that Na+ in NaCl will be electrically neutralized with the negative charge on the coal, the electrostatic repulsion of particles will decrease, and the viscosity will increase. In the presence of HCO3c, negative charge increases on coal particles, the apparent viscosity decreases by 42 mPa·s compared with the absence of HCO3−. In the CO32− systems, the pH is 8.25. Higher pH indicates that there are more OH−. Because CO32− is easy to combine with water to form a stable structure, and the strong polar effect of OH− is also easy to bind water molecules, forming a stable water molecule layer configuration on the coal, which hinders the adsorption of sodium lignosulfonate (SL), resulting in a decrease in steric hindrance effect, which is not conducive to the dispersion of particles. The molecular dynamics (MD) simulation results confirmed the existence of the neutralization of Na+ and the negative charge on coal in the NaCl system. The adsorption energies (Eadsorption) of each system were negative, indicating that the dispersant was easily adsorbed on the coal. However, in the CO32− system, the absolute value of Eadsorption was lower than that the pure water system, indicating that the presence of CO32− is not conducive to the adsorption of SL. The self-diffusion coefficient(D) of Na2CO3 system is lower than that of coal/water/SL system, NaCl system, and NaHCO3 system. It shows that the presence of CO32− can significantly reduce the migration rate of water molecules and is easy to bind water molecules. The presence of HCO3− is also easy to bind water molecules, but it is weaker than CO32−. The migration and diffusion rate of water molecules in the saline-alkali mixed system decrease. This may be mainly affected by CO32−, which easily binds water molecules on the coal surface and hinders the adsorption of SL.