Influence of clays on coal flotation: Focusing on coal surface oxidization

[Display omitted] •Influence of oxidization on coal flotation in the presence of clays was studied.•Moderate oxidation is not conducive to coal flotation or particle-bubble adhesion.•AFM tests show that high oxidization increases the coal-clay repulsive force.•High oxidation is beneficial in reducing the influence of clays on coal flotation. This study is the first to investigate the influence of clays on the flotation of coals with different surface oxidization degrees. The results show that moderate oxidation is not conducive to coal flotation, regardless of the presence of clays. However, when the coal undergoes a high degree of oxidation, the presence of clay minerals has almost no influence on the coal flotation or is even beneficial when montmorillonite is present. This phenomenon is explainable, given that moderate oxidation is unfavorable for coal-bubble adhesion, whereas high oxidation is favorable from a single-bubble perspective when clays exist. Furthermore, atomic force microscopy tests show that a weak attraction force existed between unoxidized coal and clays, whereas a repulsive force always exists between highly oxidized coal and clays. These findings provide new enlightenment for oxidized coal flotation.