Effective purification of the low-rank coal by the collaboration of the microemulsion collector and the CO2 nanobubbles

As the inferior hydrophobicity and low probability of bubble-particle collision, the low-rank coal has poor flotation performance. In this paper, an effective purification method that innovatively combined the use of the microemulsion collector and the CO2 nanobubbles was proposed. The procedure of the purification method and the reagent regime were established through flotation tests. And the flotation results showed that in the presence of the CO2 nanobubbles, a satisfactory separation performance with 83.97 % of combustible matter recovery was obtained at a microemulsion collector consumption of 3.5 kg/t. The collector consumption decreased signifi-cantly compared with the diesel oil. The interaction mechanism was elucidated through the Zeta potential measurements, the rheological behavior tests, the fractal dimension analysis, and the extended Derja-guin-Landau-Verwey-Overbeek theoretical analysis. On one hand, the microemulsion collectors can reinforce the adsorption of the oily collectors on the low-rank coal surface to improve its hydrophobicity. On the other hand, the agglomeration of the coal particles was strengthened and the probability of bubble-particle collision was increased due to the selective adsorption of CO2 nanobubbles on the hydrophobically modified surface of the low-rank coal. This research provided new insight into the improvement of the low-rank coal flotation.