98/00083 Structural changes induced by thermal treatment of deashed coals

Abstract

Frothers are surface active molecules and facilitate to produce more mechanically stable froth by reducing the surface tension at air–water interface. It adsorbs at the air–water interface and serves to reduce the loss of water from the lamellae of bubble. In this investigation weak and powerful frothers, like methyl isobutyl carbinol (MIBC) and polyethylene glycol-600 (PEG) were used for studying the surface tension of frother blends at various concentrations. Gibb's surface excess adsorption and surface area were determined from the rate of change of surface tension with logarithm of concentration. The high surface area per molecule of PEG signifies that little amount is enough to significantly reduce the interfacial tension at the air–water interface. The foam volume and its stability were measured for single frothers and their blend. The foam stability (foaminess) of single MIBC is very less however; it could be improved significantly using a small amount of strong frother (PEG).Flotation studies of coal fines from eastern part of India were carried out with the above two types of frothers and their blend. The performances were compared with reference to recovery of combustibles for clean coal and rejects. It was found that coal concentrate contains high ash with single PEG due to high froth stability that results the entrainment of the gangues, while single MIBC produces high grade concentrate with low recovery. It was observed that the recovery of carbon value increases significantly when a 10% (w/w) of powerful frother was added with MIBC. The recovery of carbon at 90:10 ratio of frother blend is 77.6% at 17% ash. The recovery could be increased to 86% when ash in clean coal increases to 19.7% and loss of combustibles in the tailing could also be reduced to 14%.