Effect of ultrasonic pretreatment on the flocs characteristics in the flocculation filtration process of coal slurry water

The enhancement of ultrasonic pretreatment on the flocculation filtration of coal slurry water has been reported. The structural characteristics of flocs are critical parameters in the flocculation and filtration process. In this paper, the effect of ultrasonic pretreatment on the flocs ' characteristics during flocculation and filtration was investigated. The flocs size, number, strength, and fractal dimension in the microstate were characterized through a polarized light microscope, PVM, and FBRM. The changes in flocs characteristics on the filter cake ' s pore structure and moisture distribution were analyzed using L -F NMR. The results showed that the optimal condition was an ultrasonic frequency of 30 KHz, ultrasonic time of 3 min, and the dosage of cationic polyacrylamide (CPAM) with ionicity of 60 at 50 g/t, under which the filtration rate was 597.42 mL & sdot; (m 2 s) - 1 and the moisture content of the filter cake was 27.03 %. Ultrasonic pretreatment increased the flocs ' size, with a decrease in the proportion of small flocs and an increase in the proportion of medium and large flocs, mainly medium flocs. The increase in the fractal dimension and strength of the flocs structure made the filter cake deformed less under pressure, formed a porous skeleton structure, and increased the total porosity of the filter cake, with the most significant variation in mesopores. Moreover, ultrasonic pretreatment could decrease the proportion of adsorbed and bound water while increasing the proportion of free water and effectively reducing the filter cake's moisture content. This study revealed the essential relationship between floc characteristics and flocculation filtration efficiency, filter cake pore structure, and moisture distribution and provided a new perspective for exploring the application mechanism of ultrasonic technology in enhancing flocculation filtration performance.