Washability and flotation charactersitics of two different coals reporting as feed to an operating coal washery.

Abstract

Coal washeries source their coal from various seams. Two such coal samples of different origin and source, namely seam IX coal and a mixed seam coal, reporting as feed to an operating washery, were characterised for their washability and flotation response. The washability characteristics of these two coal samples were studied by heavy media separation. The wettability properties of these coals were evaluated by measuring the ratio of carbon to hydrogen in them and their contact angles. The ash content of seam IX coal and mixed seam coal were 34.10% and 24.90% respectively. Washability studies indicated that at equivalent ash content of 15% in clean coal, yield in the case of mixed seam coal was higher at 29% as compared to that in the case of seam IX coal at 24%. Improved yield at lower ash levels in clean coal warranted grinding the samples for liberating the coal macerals followed by separation by flotation. 72.88% of clean coal analyzing 12.60% ash could be obtained at 0.13 kg/t of frother and 0.605 kg/t of diesel after 3-stage cleaning of finely ground mixed seam coal (85% -100 µm) which was superior to clean coal obtained by flotation on coal fines (-0.5 mm) of the same sample. Similarly, 49.15% of clean coal analyzing 14.49% ash could be obtained at 0.0108 kg/t of frother and 0.605 kg/t of diesel after 4-stage cleaning of finely ground seam IX coal (87.5% -100 µm) which was superior to clean coal obtained by flotation on coal fines (-0.5 mm) of the same sample. Better flotation in the case of mixed seam coal could be attributed to the higher hydrophobicity of mixed seam coal as borne out from the contact angle measurements and the higher carbon to hydrogen ratio (18.11) in its case as against that in the case of seam IX coal (16.91). Also, the flotation kinetics studies showed that the mixed seam coal floats faster (k= 0.00439 s-1) than seam IX coal (k=0.00343 s-1). Thus mixed seam coal is relatively easier to wash compared to seam IX coal and their yields and the ash content in clean coal could be predicted from these studies.