Study on the mechanism of anionic composite surfactant pretreatment to promote flotation of clay-rich coal slurry: Interfacial interaction

Clay-rich coal slurries suffer from low yield and high ash content during flotation. In this study, the effective recovery of clay-rich coal slurries was facilitated by pretreatment with sodium hexametaphosphate (SHMP) and sodium polycarboxylate complex surfactants. Contact angle and adhesion force tests show that complex surfactants reduce the wettability of the coal. Fourier transform infrared (FTIR) spectroscopy shows that the ring structure of SHMP leads to P-pi stacking with the benzene ring structure on the coal and hydrogen bonding with the oxygen-containing functional groups. Sodium polycarboxylate can combine with the hydroxyl groups on the coal and the oxygen-containing functional groups exposed after multipoint diffusion coverage of SHMP by the multihydroxyl structure on the chain. Atomic force microscopy (AFM) tests show that the complex surfactant is adsorbed on the coal surface by hydrophobic and electrostatic attraction. Adsorption occurs in the form of singleand double-layer adsorption. Zeta potential measurements and scanning electron microscopy (SEM) results show that the addition of a complex surfactant attenuates slime entrainment. Flotation tests show that after pretreatment with the surfactant complex, the cleaning coal yield is increased by 45.14% and the ash content is decreased by 7.92% compared with froth flotation. The flotation effect shows an obvious improvement. The above results help to elucidate the mechanism for composite surfactants to improve the flotation separation effect based on mesoscopic and microscopic aspects and strive to provide theoretical support for efficient flotation.