SURFACE-ENERGY AND INDUCTION TIME OF FINE COALS TREATED WITH VARIOUS LEVELS OF DISPERSED COLLECTOR AND THEIR CORRELATION TO FLOTATION RESPONSES

Separation of fine coal in froth flotation relies upon the wettability difference between the coal-rich and mineral-rich particles in the aq ueous solution. Two methods were used to measure the wettability of si x ranks of coal as well as coal samples treated with various levels of dispersed collector in aqueous solution. Wettability was determined b y measuring the distribution of critical wetting surface tension, i.e. , surface energy, using the film flotation technique and by measuring the induction time, i.e., bubble-particle attachment time, of the mate rial. The wetting of coal particles is strongly dependent upon the coa lification processes and can be affected by ash content. For anthracit e coal with a high ash content, very high surface energy and intermedi ate induction time were measured, but intermediate floatability with a very good ash rejection was obtained. Sub-bituminous coal with low mi neral inclusion was found to have a relatively low surface energy, and thus a high floatability, but very poor selectivity was observed, whi ch was reflected in lengthened induction time. When dynamics of flotat ion behaviors are involved, flotation results can be better interprete d by induction time. For dispersed collector-treated coal samples, an increase in collector dispersion (i.e., a decrease in kerosene droplet size), by direct liquid collector mechanical agitation, ultrasonic en ergy emulsification, or atomization, caused decreases in surface energ y and induction time and closely matched the increase of flotation rec overy and selectivity. With similar particle density, mineral liberati on conditions, and particle size, the induction time was found to be c losely related to the mean critical surface tension for untreated coal samples and for HV-bituminous coal samples treated by various levels of dispersed collector.