Abstract
Illite is one of the main components in coal slime water and it sometimes makes the water extremely difficult to clarify. In this study, the aggregation mechanism of coal and illite particles was investigated using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and settling experiments of slime water containing coal and illite. The results show that electrostatic energy plays a dominant role and manifests repulsive force in the long-range (>4 nm). However, the leading role becomes a hydrophobic force determined by the polar surface interaction energy in the short-range (<4 nm). A coagulant (Ca2+) can lower the surface electric potential to make all particles easier to coagulate, while the surface hydrophobicity of coal and illite determines whether the particles aggregate. Cationic polyacrylamide (CPAM) can promote the sedimentation of particles flocs effectively and makes the supernatant clearer due to attractive electrostatic forces while anionic polyacrylamide (APAM) flocculates particles through the bridge mechanism. Although the hydration shell on the hydrophilic surface of illite appears to be harmful for either coagulation or flocculation, illite can accelerate sedimentation when it is attached to the coal due to its higher density.
Highlights
Coal slime water is the waste-water produced during the wet processing of coal preparations
It is vital to understand how clays affect the aggregation and sedimentation of coal particles in order to make the clarification process more efficient. It was reported in reference [7] that for coal-kaolinite suspensions, the addition of Ca2+ decreases the repulsive electrostatic force between the kaolinite particles, allowing the attractive van der
Calcium chloride was used as the cationic coagulant; cationic polyacrylamide (CPAM; molecular weight 10,000,000; charge density 40%; with an effective pH range of 3–8); and anionic polyacrylamide (Xinbang Environmental Protection Technology Co., Ltd., Xinxiang, China)
Summary
Coal slime water (slurry) is the waste-water produced during the wet processing of coal preparations. Particles of rock, clay and coal are too small to float or sink [1,2,3]. It is vital to understand how clays affect the aggregation and sedimentation of coal particles in order to make the clarification process more efficient. It was reported in reference [7] that for coal-kaolinite suspensions, the addition of Ca2+ decreases the repulsive electrostatic force between the kaolinite particles, allowing the attractive van der
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