Flotation behaviour of weathered coal in mechanical and column flotation cell

The low rank or oxidized coals show unpleasant flotation behaviour. The non-coking coal from Talcher, containing 26.8% ash, 4.9% moisture, 35.7% volatile matter and 1% oxygen was used for the investigation. The flotation performance of the weathered coal in a mechanical and column flotation cell was compared at low ash level of about 12%.

The oxidized coals possess negative surface charge due to the surface functional groups like carboxylic (− COOH) and phenolic (− OH). The surface charge could be determined by zeta potential study. The flotation at different pH values and pre-treatment of coal fines using a modifier were studied in a mechanical and column flotation cell. This type of coal is very difficult to float even at higher concentration of collector due to less dispersion of the collector molecules on the coal surface.

The surface charge determined by the zeta potential study appears to be negative. It designates the oxidation of the surface and makes the coal hydrophilic in nature. As a result, attachment of air bubbles with the particles gets reduced. Flotation performances, due to the modifier added in grinding mill, give encouraging results as it is inferred from the isoelectric point shifted towards the alkaline regime. Flotation studies carried out with promoter added in the mill followed by diesel oil in mechanical cell show that cleaning of the rougher concentrate is essential to reduce the ash content in the concentrate, whereas the single-stage flotation in a column is found to be better which yields 49.6% concentrate at 12% ash.