Study on low-rank coal surface wettability effect and recyclability of different anionic magnetic ionic liquids

Abstract

Three types of magnetic ionic liquids (MIL) ([C12mim]FeCl4, [C12mim]2CoCl4, and [C12mim]2NiCl4) were chosen to study the enhancement of the quality and utilization of low-rank coal (LRC). The mechanism of coal wettability modification was explained from the macrocosm and microcosm points of view by contact angle, adhesion work, and adsorption studies, and the recovery of MIL was realized by salting out the separation-strong magnetic recovery (SMR). The contact angle and adhesion work results showed that [C12mim]FeCl4 had the greatest effect on coal wettability. The adsorption on the LRC surface was as follows: [C12mim]FeCl4 > [C12mim]2CoCl4 > [C12mim]2NiCl4. The adsorption thermodynamics indicated that MIL conformed to the Langmuir isotherm model, which is a spontaneous reaction of exothermic entropy minus physical adsorption. The adsorption kinetic process belong to the pseudo-second-order kinetic model and was influenced by the combined action of intraparticle and liquid film diffusion. From the contact angles and adsorption thermodynamics, it can be inferred that [C12mim]FeCl4 has the highest activity and can better adsorb onto the LRC surface, covering the oxygen-containing functional groups and reducing the wettability to achieve efficient quality improvement and utilization of LRC. Through the research of salting-out separation-SMR, the most suitable salting-out reagent was found to be NaCl, and the highest recovery was obtained when the concentration reached the solubility level. As the magnetic field strength increases, the recovery rate gradually increases. The recovery of [C12mim]FeCl4 was more than 90% when it reaches 1.5 T, and it could be recovered by magnetic separation.