Regulation of coal flotation by the cations in the presence of clay

Abstract

The concomitant clay minerals in coal commonly have adverse effects on the coal flotation. In this work, the regulation of coal flotation by cations (Na+ and K+) in the presence of clay was investigated to abate this deterioration. It was observed by SEM-EDS that the clay particles coating on the coal surface in low pH condition, which significantly reduced the hydrophobicity of coal. However, after introducing the cations (Na+ and K+), the clay particles originally adhering to the coal surface fall off and form large aggregates. The addition of Na+ and K+ affected the DLVO interaction energy between coal and clay, making the attracting tendency between clays stronger than the attraction between clay and coal. Moreover, the cation species have different regulation behaviors. Na+ improves the combustible recovery by inhibiting clay coating. While, K+ mainly promotes the aggregation of clay and inhibits the recovery of clay. Thermodynamic simulating calculation shows that the combination of clay and coal in the presence of Na+ will release more heat than K+ which is also conducive to hinder clay coating. The obtained behavior rules and mechanisms using cations regulating the coal flotation in the presence of clay can help decouple the adverse effect of clay on clean production of coal, especially in water-deficient and coastal areas.