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The surface hydrophobicity of low-rank coal is meager, hindering the efficient adsorption of hydrocarbon oil on its surface. Consequently, the hydrophobicity modification of the coal surface is adversely affected, making flotation separation of the coal-gangue challenging. To achieve accurate separation of low-rank coal and gangue, this paper proposes the concept of a polar-nonpolar binary mixed collector to enhance the technology of flotation separation of low-rank coal. The study examined the effects of single polar/nonpolar collectors and compounded collectors on low-rank coal. The results showed that the flotation efficiency of oleic acid and lauric acid methyl ester as single collector was superior to all others. Moreover, the flotation efficiency of single nonpolar or polar collector was lower than that of nonpolar/polar compounded collector. Furthermore, the flotation yield of coal concentrate initially increased and then decreased with the increase of dodecane mass fraction. The ideal nonpolar and polar ratios ranged from 6: 4 to 8: 2. We analyzed the mechanism for boosting the floatability of low-rank coals using the combined collector through adhesion angle, contact angle, and X-ray photoelectron spectroscopy (XPS) tests. The adhesion angle displayed a much greater increase following treatment with the compounded collector than with the single collector. Within 10–20 seconds, the growth was swift. The adhesion angle significantly exceeded that of the single collector following treatment with the compounded collector. Furthermore, the inclusion of a suitable quantity of polar reagents proved effective in augmenting the coal samples' hydrophobic C-C/C-H chemical structure whilst decreasing the content of hydrophilic oxygen-containing groups. The use of alkyl acid ester addition in the composite reagent significantly improves the separation efficiency of a single flotation reagent and is expected to break through the current technical bottleneck of poor effect and high cost of flotation reagents.
Xue et al. (Fri,) studied this question.