Synergistic enhancing low-rank coal flotation mechanisms using nanocarrier collector through pore sealing and surface hydrophobicity

Low-rank coal (LRC) is difficult to float using conventional oily collectors due to the rich oxygen-containing functional groups and abundant pores on its surface. In this study, an effective nanocarrier collector containing both nanoemulsion and nanoparticle with droplet size of 10–70 nm was developed, through diesel-beeswax mixture and AEO-7 using low-energy shearing and rapid cooling emulsification to enhance the LRC flotation. The surface morphology and elemental compositions of LRC were firstly characterized using SEM and EDS, identifying its difficult-to-float mechanisms. Then, the macroscopic appearance and microscopic size distribution of nanocarriers, and flotation tests were conducted to determine the optimum formula of nanocarrier collector for LRC. The results indicated that the recovery rate of combustibles was first increased and then decreased, by increasing the mass ratio of beeswax to diesel. When the mass ratio of diesel, beeswax, and AEO-7 was 2:3:5, the recovery rate of combustibles could be achieved to 92.98 %. Finally, the BET specific surface area, water adsorption, contact angle and wrap angle experiments were conducted to clarifying the synergistic enhancing LRC flotation mechanisms of nanocarriers collector. The nanocarriers could permeate into and seal the LRC surface pores, thereby reducing the both surface pore volumes and specific surface area. In addition, the mixtures of diesel and beeswax synergistically improved the surface hydrophobicity. Consequently, this research provides new insight into the development of effective collectors for LRC flotation.