Study on the flotation separation efficiency of surfactants on the coal direct liquefaction residue raffinate

Given China’s coal-dominant energy structure, direct coal liquefaction (DCL) is vital for energy security, but it generates raffinate slag (RS) accounting for 20–30 wt% of input coal. RS features high carbon, sulfur, ash contents, and strong hydrophobicity, yet its utilization is hindered by intimate carbon-ash intergrowth and operational risks, necessitating efficient separation technologies. This study characterized RS via multi-dimensional analyses, revealing a bimodal particle size distribution (average 37.5 μm) and dominant 1.6–1.8 g/cm 3 density fraction (27.54 % ash), with partial dissociation in extreme density fractions indicating flotation potential. To improve hydrophobicity (untreated contact angle 126.5°), hydrophilic surfactants (HLB > 10: CTAB, SDBS, OP-10) were tested. OP-10 performed best, reducing contact angle to 84.6°by introducing C-O-C groups (boosting polar functional groups), despite lower adsorption capacity. At 2 kg/t dosage (no extra collectors/frothers), it achieved 74.45 % tailings ash, 58.5 % concentrate yield, and 89.3 % combustible recovery—outperforming CTAB/SDBS with lower reagent consumption. This provides a sustainable pathway for RS valorization, with future focus on carbon-ash complete liberation.