Ff. Peng, SURFACE-ENERGY AND INDUCTION TIME OF FINE COALS TREATED WITH VARIOUS LEVELS OF DISPERSED COLLECTOR AND THEIR CORRELATION TO FLOTATION RESPONSES, Energy & fuels, 10(6), 1996, pp. 1202-1207
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.