New insights into the slime coating caused by montmorillonite in the flotation of coal

Slime coating is a considerable problem in the flotation of coal. Although many works have been done, there are still some problems that have not been clarified. In this work, the subtle behaviors of montmorillonite coating on coal surface under finely divided slurry pHs (from 2.7 to 10.6) were studied systematically through micro-flotation test, zeta potential distribution measurement, atomic force microscopy and scanning electron microscopy. Several interesting findings are summarized below. The flotation of coal even the highly hydrophobic one will be markedly depressed by montmorillonite once when the pH of the slurry is less than 6.5. However, under neutral condition, the degree of inhibition on the flotation recovery is related to the inherent hydrophobicity of coal itself, since only parts of the coal surfaces are covered by montmorillonite due to the unstable hetero-coagulation by the weak adhesion force. A good dispersion between coal and montmorillonite will be achieved when the pH of the slurry is greater than 8.2, which means good flotation performance restores. (c) 2019 Elsevier Ltd. All rights reserved.