Multiscale influence mechanism of mechanical energy input on flocculation and sedimentation characteristics of coal slime and reagent optimization

As the source technology for the clean processing and utilization of coal, wet separation in coal preparation generates a large amount of coal slime water with a particle size of less than 0.5 mm. As a complex multiphase and polydisperse system, this coal slime water must undergo efficient sedimentation treatment to prevent environmental pollution and conserve water resources. The purpose is to explore the flocculation and sedimentation indicators of coal slime under different energy inputs, construct a comprehensive evaluation model for coal slime sedimentation efficiency under multi-scale energy input conditions, and provide guidance for the scientific on-site decision-making of coal slime concentration and sedimentation control measures. Coal slime from Guobei Coal Preparation Plant of Huaibei Mining Co., Ltd. was used as the research object, and instruments such as a viscometer, inverted fluorescence microscope, and industrial camera were employed to systematically measure indicators including residual flocculant (APAM), floc size, supernatant grayscale, and sedimentation velocity. The results show that energy input can be divided into four stages (0‒2479, 2479‒4948, 4948‒6597, and 6597‒8247 J) according to the variation trends of the indicators. In the first and third stages, the variation trend of residual APAM content is negatively correlated with the sedimentation characteristics of coal slime, which is manifested as a decrease in residual APAM content, an increase in supernatant grayscale, an increase in floc size, an increase in sedimentation velocity, and an enhancement of sedimentation efficiency. In the second stage, the residual APAM content increases sharply, while the supernatant grayscale, floc size, and sedimentation velocity also increase, and there is no significant correlation between residual APAM content and sedimentation characteristics. In the fourth stage, the residual APAM content rises again, the supernatant grayscale value drops sharply, excessive energy causes floc breakage, the sedimentation velocity is nearly stagnant, and the sedimentation efficiency deteriorates. Based on the principal component analysis (PCA) method and the entropy weight method, the weight coefficients of residual APAM content, floc size, supernatant grayscale value, and sedimentation velocity were determined, and a multi-index comprehensive evaluation model for coal slime water sedimentation efficiency was constructed. Verification experiments indicate that under the same sedimentation conditions, the APAM dosage can be reduced by 2 g/t by adjusting the energy input. A comprehensive evaluation model for coal slime water sedimentation efficiency based on residual APAM content, floc size, supernatant grayscale, and sedimentation velocity was established, which provides a theoretical basis for optimizing the energy input and reagent system in the coal slime concentration process.