Insight into filter cake characteristics of fine coal tailings assisted by CPAM and α-HH during pressure filtration

•CPAM still played its role as a polymer flocculant, the addition of α-HH promoting the formation of flocs.•In the CPAM system, the hydration reaction of α-HH could be accelerated to produce many CaSO4·2H2O crystals. The CaSO4·2H2O crystals could effectively play the role of skeleton support in the filter cake.•The CPAM and α-HH synergistic regulation effectively improves the dewatering performance of coal slurry.•The whole dewatering process was divided into four stages, and the filtering performance of filter aids was analyzed from the point of view of cake compressibility.•The conditioned coal slime dewatering effect was measured using a newly designed pressurized dewatering device.