Effect of gangue minerals on apparent viscosity and flotation of coal slime

In coal slime flotation, non-selective aggregation between fine gangue minerals and coal particles is a critical factor leading to the deterioration of coal floatability and a reduction in clean coal recovery. This study investigated the influence of three minerals commonly found in coal, quartz, kaolinite, and muscovite, on apparent viscosity and coal floatability. The results demonstrate that as the amount of gangue minerals increased, the apparent viscosity of the pulp increased to varying extents. Quartz exhibited the least impact on apparent viscosity, followed by kaolinite, while muscovite had the most significant effect. The addition of quartz, kaolinite, and muscovite decreased the flotation recovery from 79.46% to 74.09%, 62.50%, and 54.96%, respectively. The projected area of coal particles attached to bubbles decreased by 10.03%, 19.16%, and 30.14% compared to the blank test. These findings are consistent with the apparent viscosity results. Extended DLVO theoretical analysis revealed that the electrical double-layer repulsive forces between coal and quartz/kaolinite overcame the attractive van der Waals and hydrophobic forces, resulting in net repulsive interactions. In contrast, the net interaction force between coal and muscovite remained attractive under the experimental conditions, facilitating their aggregation and thereby impairing coal floatability. This observation aligns with the flotation and bubble-particle adhesion test outcomes. The study provides a theoretical foundation for regulating apparent viscosity in coal slime flotation and achieving efficient separation between coal and gangue minerals.