Indexing the washability characteristics of coal.

The washability data on coals of different origins have been analysed in terms of relation between the cumulative weight fraction of feed material floated and the recovery of non-ash and ash material in the float fraction at a given specific gravity. It has been noted that a unique recovery curve exists for both the recoveries of non-ash and ash material when plotted against the cumulative weight fraction of feed material floated. On the basis of this observation, a simple “Index of Washability” has been developed. An explicit mathematical expression has been derived to estimate the index value for a given coal