The categories of ISW are closely related to the industrial
structure in China. The largest component of ISW is
mining gangue, which is 27.5% of the total.The other major
components of ISW are coal gangue (15.8%), coal ash
(14.4%), boiler slag (11.5%) and iron blast-furnace slag
(6.73%). These five categories of ISW make up 75.9% of
total ISW.6,7