Properties of direct coal liquefaction residue water slurry: Effect of mineral matters by acid-leaching demineralization

The effects of demineralization treatment by acid leaching on the properties of direct coal liquefaction residue water slurry (DCLRWS) were investigated. The demineralized direct coal liquefaction residue (DCLR) with different mineral matter content and composition was prepared by leaching with the solution of HCl/HF, HCl, and HF, designated as DEM-1, DEM-2, and DEM-3, respectively. After demineralization, the slurryability of DCLR decreases but their effective solid loading (ash-free basis) increases. The results indicate that metallic minerals are the principal factor improving the slurryability of DCLRWS, mainly by increasing the dispersant adsorption capacity of DCLR. In addition, the decreasing density of DCLR after demineralization is not advantageous to its slurryability. DCLRWSs prepared by DCLR, DEM-1, and DEM-2 all have the same stabilization time (2 days), indicating that removal of metallic minerals could not deteriorate the stability. However, after removal of clay minerals, the slurries prepared by DEM-3 tend to form sediment after stopping high-speed stirring, attributed to its lowest zeta potential and loss of stability due to clay minerals. Except for DEM-3, the slurries prepared by other three samples all have a shear-thinning behavior, with the strongest behavior observed for DEM-1 slurry.