An overview of reverse flotation process for coal

• Detailed descriptions of the coal reverse flotation process and its present progress
• Discussion on the mechanism of adsorption of reagents used in coal reverse flotation
• Effects of important parameters: collector dosage, depressant dosage, pH and particle size on the performance
• Correlation of the coal type/rank and mineral matter on performance of reverse flotation process

Flotation is one of the most effective technologies for the up-gradation of coal fines of particle size below 0.5 mm because of the inherent hydrophobic nature of coal. Contrary to this, reverse flotation of coal in which coal particles are depressed and gangue particles floated, was developed as an alternative process to minimise the sulphur content in the coal. This method can also be applied to reduce the ash content of coal by floating the mineral matter present in coal. Therefore the mechanism and performance of this process treating different types of coal have become an active research topic and several literatures have also been published. Despite the research efforts, this process has yet to find application in the coal preparation industry which it deserves. In the present review article, an effort was made to understand the basic mechanism of this process along with the effect of variables and chemicals used on its performance. Finally, some challenging issues that need special attention are highlighted to further improve the process.