Rheology Behavior and Dispersion Mechanisms of Modified Wax Residue in Coal-Water Slurry

This study demonstrates the effective repurposing of a hazardous Fischer-Tropsch wax residue (containing 50% wax) from coal liquefaction as a performance-enhancing additive for coal water slurries. Through surfactant-assisted wet milling, we produced two modified wax residues: W<i>R</i>-1 (octylphenol ethoxylate OP-10 modified) and W<i>R</i>-2 (sodium dodecylbenzenesulfonate SDBS modified), which reduced the contact angle by 10° and increased ζ-potential to 25 and 27.2 mV. Remarkably, incorporating 5% W<i>R</i>-1 increased the maximum slurry concentration to 68.17% while maintaining low viscosity, attributed to enhanced electrostatic repulsion (<i>E</i> _T = 2 × 10^-10 J) per DLVO theory. In contrast, W<i>R</i>-2 addition decreased the slurry performance due to unfavorable particle size effects. The optimized W<i>R</i>-1 system formed a stable three-phase network of wax residue, coal particles, and water, offering a practical solution for both waste valorization and slurry quality improvement.