Aluminium recovery from NALCO fly ash by acid digestion in the presence of fluoride ion

•NALCO fly ash contains mullite the main phase bearing alumina.•A simple alternative method has been attempted to dissolve alumina from fly ash.•H2SO4 leaching in the presence of HF showed alumina leaching efficiency of ~ 92%.•The XRD data showed the dissolution of mullite grains during leaching.•The leaching condition is suitable for downstream operations to obtain alumina.

The safe disposal and utilisation of coal fly ash (CFA) for value addition are still major problems worldwide. Al2O3 is a major valued material associated with it. Till date no methods are available to treat CFA for recovering its valued materials. Leaching of alumina from CFA in an economical way is very difficult, which either requires higher chemical consumption or application of stringent reaction conditions such as high temperature and pressure. In this paper a simple alternative method has been attempted to dissolve alumina from CFA. Addition of fluoride ion as HF improved the acid leaching performance of fly ash to a large extent. XRD data showed mullite, the alumina bearing phase, as the major phase which gets dissolved during leaching operation. A standard procedure for the precipitation of alumina can be employed after the leached solution is obtained.

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