Study of Three-Phase Flow Field Characteristics in a Multi-Stage Friction–Shear Cavitating Waterjet for Flake Graphite Liberation

Flake graphite is a natural non-metallic material with excellent electrical and thermal conductivity and good lubricity. This study proposed a multi-stage friction–shear cavitating waterjet method to enhance the liberation of flake graphite from gangue minerals. A corresponding nozzle was designed and fabricated by integrating liquid–solid two-phase transport, grinding kinetics, profile-based design, and similarity design. Fluent simulations were conducted with the Eulerian multiphase model to analyze the water–vapor–flake graphite three-phase flow field at different inlet pressures, focusing on vapor volume fraction, water phase flow, and flake graphite particle phase behavior. A distinct cavitation region appeared in the outlet diverging section, mainly near the wall. At inlet pressures of 25 MPa and above, the maximum vapor volume fraction was maintained above 99%, suggesting strong cavitation-inducing capability. Jet liberation experiments showed that the fixed carbon content increased from 49.11% in the feed sample to 78.77% in the waterjet-treated flotation concentrate, while D90 decreased from 121.36 to 103.33 μm and the average particle size decreased from 62.78 to 55.02 μm. These results indicate that multi-stage friction–shear cavitating waterjet treatment facilitates the liberation of flake graphite from gangue minerals, thereby improving the fixed carbon content of the flake graphite concentrate.