Research on adaptive flocculants for flocculation and sedimentation of difficult-to-settle coal slurry

Aiming at the widespread issue of poor sedimentation in coal slurry water treatment leading to high concentration in the circulating water system, this study takes the feed coal slurry water (with D₅₀ of 26.61 μm, high fine particle mass fraction, and difficult sedimentation) from the thickener at Zhaozhuang Coal Preparation Plant as the research subject. Using supernatant transmittance, initial sedimentation rate, and compressed layer thickness as the evaluation criteria for flocculation sedimentation, and combining methods such as Zeta potential and Focused Beam Reflectance Measurement (FBRM), the effects of cationic polyacrylamide (CPAM), anionic polyacrylamide (APAM), nonionic polyacrylamide (NPAM) alone and their combination with polyaluminum chloride (PAC) on coal slurry water sedimentation were investigated.The results show that PAC, as an inorganic polymer coagulant, possesses hydrolysis products with strong adsorption and bridging effects, which synergize with CPAM to significantly enhance the aggregation capacity of coal slurry particles. When PAC dosage is 50 g/t, the sedimentation rate reaches 75.38 cm/min, an increase of 6.7 cm/min compared to using CPAM alone; the compressed layer thickness decreases to 4.5 cm, and the transmittance improves to 96.2%. FBRM tests indicate that the floc size under the combined action of PAC and CPAM increases significantly. Therefore, the combination of PAC and CPAM achieves the best flocculation sedimentation effect, addressing sedimentation challenges through charge neutralization and bridging synergy. This study provides theoretical and practical support for coal slurry water treatment in coal preparation plants.