Geo environmental assessment on abandoned mine filling with coal ash

Abstract

For minimizing surface subsidence, river sand is mostly used in abandoned coal mines filling. Due to increase in the use of the river sand in the construction industries, the mining industries are facing scarcity of river sand to fill abandoned mine. After extraction of coal from mines, large number of coal mines leave without filling, which creates surface subsidence. Therefore, the mining industry is searching for an alternate filling material which is easily available in large quantity and in minimal cost. The present work aims to characterize and utilize the largely available coal ashes in abandoned mine filling applications and to study the various issues related to geo- environmental aspects of the same. From the experimental results, it is concluded that coal ashes can replace the conventional river sand normally used for mine filling applications and thereby cost of the project as well as the environmental problems relating to coal ash can be reduced to a significant extent. It was observed that the water holding capacity of bottom ash considerably lower than pond and fly ashes. XRD results show that coal ash has more numbers of quartz, mullite and iron oxide peaks. The coal ash used in this study is classified under Class ‘F’ according to ASTM C618. However, in general Class ‘F’ fly ash can provide a better filler material than Class ‘C’ fly ash, because the calcium content is low. Heavy metal concentrations were leached more from fly ash as compared to bottom ash and pond ash. Initially, when neutral coal ash is mixed with acidic water, the pH value increases and after 24 hours it gradually decreases and attains value confirming to drinking water standard.