Acid leaching technique for the possible recovery of aluminium and other metal values from coal fly ashes

Abstract

The present study examines the rate of extraction of metals mainly aluminium and iron from coal fly ash collected from the captive power plant of Vedanta Aluminum Limited, Jharsuguda, Odisha by direct acid leaching method. The effect of different mineral acids, acid concentrations and solid : liquid ratios on rate of extraction of aluminium and iron have also been studied. The results presented in this paper shows sulphuric acid is the best leachant in comparison to other mineral acids. Aluminium extraction efficiency of 68.68% was achieved with sulphuric acid as leachant at 220 degrees C and at 1 : 3 solid to liquid ratios. It is also evident that extraction efficiency of aluminium and iron increases significantly with increasing concentration of acids and with solid : liquid ratio variation. The pre-leached and post-leached fly ash samples were analyzed for observing the morphological and mineralogical changes. Morphological and X-ray diffraction (XRD) analysis of post-leached residues indicated that the mullite inside fly ash was thermally decomposed during leaching with sulphuric acid due to the transformation of alumina and mullite into aluminium sulphate.