STUDIES ON THE PHASE MINERALOGY AND LEACHING CHARACTERISTICS OF COAL FLY-ASH

The phase mineralogy and leaching characteristics of some Indian coal fly ashes were studied to assess their safe disposal in abandoned coal mines. Since, fly ash contains a number of toxic trace elements, the leaching of fly ash was tested using strong acid/alkali solutions and distilled water under different conditions (solid-liquid ratio,leachin g time, pH) in the temperature range of 30-100 degrees C. It was found that the concentration of various metals in leachates depends on thei r chemical nature, association with mineral phases of ash and follows the almost similar concentration profile to that of iron, especially i n acidic medium. The distribution of toxic trace elements in fly ash a nd their leachability were found to depend on the amount of unburnt ca rbon and iron in fly ash. In alkaline medium, leaching of iron and tox ic trace elements (except As) from fly ash was very negligible. Hence, alkali treatment of coal By ash is desirable for its safe use in refi lling of coal mines.