Clean low-rank-coal purification technique combining cyclonic-static microbubble flotation column with collector emulsification

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The flotation upgrading of low-rank-coal is more difficult to achieve than that of bituminous and/or anthracite coal, especially for micro-fine coal slime, because of developed porosity and a large number of oxygen surface functional groups and low collision probability between bubble and particle. In this paper, previous works on high-efficiency low-rank-coal flotation were reviewed first and a clean micro-fine low-rank-coal purification technique that innovatively combined a cyclonic-static microbubble flotation column with collector emulsification was proposed. The results show that a satisfactory separation performance for micro-fine low-rank-coal flotation can be obtained by using a cyclonic-static microbubble flotation column with collector emulsification. The collision probability between a coal particle and diesel increased because of the collector emulsification. The specific adsorption of the surfactant on the hydrophilic groups on the particle surface also increased the hydrophobicity. The improved micro-fine low-rank-coal flotation performance by cyclonic-static microbubble flotation column can be attributed to the high collision probability because of turbulent mineralization mechanism and micro-bubbles, and high attachment probability and low detachment probability because of the introduction of the hydrophobic attractive force due to the existence of the nanobubble. The outcome of this research provided a new insight into the flotation of low-rank-coal and other difficult-to-float coal.