Water jet-enhanced supergravity separation for pre-enrichment and deashing of coal-series oil shale

Conventional beneficiation of fine-grained coal-series oil shale is constrained by low efficiency and selectivity. This study proposes a recoil-jet-enhanced supergravity pre-enrichment method. Operational parameters (rotational speed R, jet pressure P, feeding rate Q, and feeding concentration C) were systematically optimized via single-factor experiments and Box-Behnken RSM, while providing insight into the interplay between centrifugal layering and hydraulic scouring. Results demonstrate that the recoil jet substantially upgrades separation: compared to no-jet conditions, concentrate yield and combustible recovery increased by 35–60% and 42–60%, respectively. Conversely, jet hole blockage (0–40%) induces instability, reducing yield by ~20% points. Parameter significance followed R >p >C, featuring a critical P × R interaction where strong centrifugal fields amplify jet-induced fluidization. A quadratic model (adjusted R2 > 0.98) was established to map the empirical relationship between recovery, ash removal, and the tested operational parameters (p =0 .048 MPa, R ≈589 r/min, C ≈185 g/L), combustible recovery reached 81.70% and ash removal achieved 20.09%, closely mirroring predictions. By sequentially integrating centrifugal stratification and jet-induced elutriation, this reagent-free approach shows potential to mitigate fine-particle stratification bottlenecks in supergravity fields, demonstrating its feasibility as a pre-enrichment strategy for coal-series oil shale.