Optimizing Confined-Turbulence Conditioning for Enhanced Flotation of Coal Gasification Fine Slag

Coal gasification fine slag (CGFS), a major solid by-product of coal gasification, contains substantial unburned carbon. However, efficient carbon–ash separation during CGFS flotation is often restricted by its complex surface properties. This study aims to enhance the flotation performance of CGFS by introducing a confined-turbulence pulp conditioning system. To clarify the role of conditioning pretreatment, the coupled effects of conditioning time and hydrodynamic intensity were systematically investigated. Flotation experiments were conducted to compare the separation performance under different conditions. Additionally, collector adsorption tests, wrap-angle measurements, zeta-potential analysis, and X-ray photoelectron spectroscopy (XPS) were performed to reveal the underlying interfacial modification mechanisms. The results indicate that within an appropriate time window, the intensified turbulence and high shear forces can effectively remove surface impurities and strengthen particle–reagent collision and adhesion, thereby improving flotation selectivity and combustible recovery. Specifically, an optimal conditioning time of 80 s achieves the maximum combustible recovery. Conversely, excessive conditioning induces an over-shearing effect, which leads to reagent desorption and a subsequent deterioration in flotation performance. In conclusion, the confined-turbulence pulp conditioning strategy successfully restructures the surface properties of CGFS and enhances its flotation efficiency. These findings provide fundamental data and a feasible technical approach for intensifying the carbon–ash separation of CGFS.