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

Abstract

To improve the filter cake structure and efficiently dewater coal slime, CPAM and α-HH were designed for combined use in filtration experiments. The conditioned coal slime dewatering effect was measured using a newly designed pressurized dewatering device; the auxiliary mechanisms were analyzed from various perspectives, including hydrophobicity, electrostatic repulsion, coal slime composition and filter cake structure. A CCD experiment indicated that the optimal concentrations of the two additives in combination were 205.90 g/t CPAM and 56.25 mg/g α-HH. Under these conditions, the coal slime water CST decreased to 31.6 s, the filtration rate increased to 177.01 mL/(s·m2), the filter cake moisture content decreased to 16.46%. CPAM still acted as a polymer flocculant, causing the coal slime particles to form large flocs, while the addition of α-HH reduced the absolute zeta potential of the filtrate to 1.36 mV, thus decreasing the static repulsive forces between coal slime particles, promoting floc formation and increasing the floc chord length to 83–185 μm. These effects enhanced the CPAM flocculation effect. In the CPAM system, these phenomena accelerated the hydration reaction of α-HH and produced many CaSO4·2H2O crystals. These crystals formed an interwoven skeleton in the coal slime flocs, increasing the CDI increased to 1650.04, and increasing the filter cake porosity from 13.26% to 16.45% and effectively improving the filter cake pore connectivity and permeability, which improved the filtration effect. This study could provide a new method and perspective for the efficient pressurized dewatering of coal slime.