The resource utilization of coal gasification wastewater by co-slurry with lignite: Slurryability, dispersion/aggregation behavior, and co-slurrying mechanisms

Coal gasification wastewater (CGW) as a substitute for clean water to prepare coal water slurry, which serves as gasification/combustion feedstock, can simultaneously achieve wastewater management and resource utilization. The purpose of this work was to investigate the effects of internal components (i.e., oils, phenols, nitrogen heterocyclic compounds, and inorganic cations) in CGW on the slurryability and dispersion/aggregation behavior of lignite and their co-slurrying mechanisms through experimental and the extended DLVO (eDLVO) theoretical calculations. Results showed that compared to lignite water slurry (LWS), the maximum solids concentration (omega max) of coal gasification wastewater slurry (CWWS) increased by 0.80%, with a lower pseudoplasticity. The organic compounds adsorbed competitively on the hydrophobic regions of lignite improved the slurrying capability of CWWS by decreasing the wettability, Zeta potential, roughness and pore structure of the particles. By contrast, the static stability of CWWS decreased, and its kinetic stability index (TSI) increased from 0.23 to 0.33. From the backscattering spectra, dodecane caused the creaming process of the slurry, while the clarification process was attributed to phenol and nitrogen heterocyclic compounds. Inorganic cations, especially NH4+ and Ca2+, significantly reduced the hydrophilic and negative charges on the particle surface, which were the main unfavorable factors leading to particle aggregation and sedimentation. The eDLVO theoretical calculation results exhibited that inter-particle interaction in CWWS was determined by the hydrophobic energy (Eh) and electrostatic energy (Ee) and their dropped from 1.79 x 10-16 J and 5.16 x 10-17 J to -4.67 x 10-16 J and 2.59 x 10-17 J respectively.