Mechanism and experimental study on promoting coal slime dewatering based on weakening of hydration layer

The hydration of coal slime particle surface is an important reason for the difficulty in coal slime dewatering. Promoting the high efficiency dewatering of coal slime by weakening the hydration layer on the coal slime particle sur- face is a new technical method. To understand the mechanism of dewatering based on the weakened hydration layer on the coal slime surface,the density functional theory(DFT) was employed to study the adsorption mechanism of water molecules and surfactants on the kaolinite(001) surface,α-quartz (001) surface and montmorillonite (001) surface.The adsorption configuration,Mulliken bond populations and charge of long-chain alkyl quaternary ammonium salts on the main mineral particle surfaces were simulated and analyzed. Also,the effects of long-chain alkyl quaternary ammo- nium cations on the moisture content and surface wettability of coal slime particles were investigated by means of coal slime dewatering and contact angle tests. The results show that the adsorption stability of water molecule on different mineral surfaces is in the order of α-quartz (001) surface>kaolinite (001) surface>montmorillonite (001) surface, and the effect of quartz on the dewatering of coal slime is greater than that of kaolinite and montmorillonite. The ad- sorption stability of long-chain alkyl quaternary ammonium cations on the mineral surface is significantly higher than that of water molecule,and the order of competitive adsorption between surfactants and water molecules on the mineral surface is montmorillonite>quartz>kaolinite. The different long-chain alkyl quaternary ammonium cations adsorption on the mineral surfaces is via weak hydrogen bond and electrostatic attraction,and the electrostatic attraction is dominant. With the increase of the dosage of long chain alkyl quaternary ammonium salt,the moisture content of filter cake first decreases and then increases. When the dosage is 500 g / t,the dewatering efficiency reaches the optimum,wherein the moisture content decreases by 2. 25% . As the dosage and chain length of alkyl quaternary ammonium salt increase,the hydrophobicity of coal slime surface increases significantly. The key to achieve an efficient dewatering of coal slime is to control the dosage of surfactant. An appropriate dosage of surfactant is conducive to weakening the hydration layer on the mineral surface. Excessive long-chain alkyl quaternary ammonium salt would hinder the dewatering of coal slime. The hydrophobic modification of the coal slime particle surface based on the surfactant provides a theoretical ba- sis for the efficient dewatering of coal slime.