Flotation of low rank coal using dodecane after pretreatment by dielectric barrier discharge (DBD) air plasma

Abstract

Non-polar oils are commonly used as collectors for coal flotation but they are generally lack of collecting efficiency to low rank coals even at a high dosage. In this study, dodecane, a representative of the non-polar oily collectors, was treated by dielectric barrier discharge (DBD) air plasma and the product was employed in the flotation of a low-rank coal slime, attempting to improve its flotation performance. Results show that the dodecane treated by DBD air plasma led to a high concentrate yield and combustible material recovery. The mechanism underpinning the observed effect was investigated using gas chromatograph-mass spectrometer (GC–MS), Fourier transform infrared spectroscopy (FTIR) and contact angle measurements. The effect of UC (untreated collector) and TC (treated collector) on coal and gangue were detected, respectively. It was found that abundant polar substances were produced after the air plasma treatment. The functional groups including OCO and OH enhanced the adsorption of collectors onto the oxygenated surface sites of the coal and gangue, and thus increased the hydrophobicity of coal and gangue. According to the contact measurements, the increase of coal in hydrophobicity is stronger than that in gangue, as evidenced by their measured contact angle of organic matter increasing from 78.23° to 95.82°, and gangue increasing from 75.11° to 83.22° after conditioning with the TC. This implies that oily collectors after air plasma treatment is effective to improve low rank coal flotation performance, which may have great potential for industrial applications.