Effective chemical leaching and ash depletion of low rank coal with EDTA and citric acid

Both physical and chemical methods are in practice to clean the coal and reduce its ash content. Mineral acids are used as chemical leachants, but because of their strong oxidizing power, they might have some disadvantages. In the present research work, demineralization of low grade coal with mild chemical leachents like EDTA and citric acid were studied. They were found as effective as mineral acids like HCI, HNO₃ HF, etc. They may be considered as preferred alternatives of the acids because Energy Dispersive X-ray Spectrophotometry (EDX) study has revealed that EDTA and citric acid leaching do not harm the carbon content of the coal as the acids did. Moreover, the environmental hazards due to use of acids may be avoided. In the current research, the coal samples were leached with HCI, HNO₃, CH ₃COONH₄, acid mixture (H₂O, HCI, HNO ₃, and HF), EDTA, buffered EDTA and citric acid. The treated coals were investigated for elemental analysis with EDX. The digestates of the ashes of treated coals were studied for metal contents with the help of Atomic Absorption Spectrophotometer (AAS). The coal under study was found to be high volatile lignite based on its Proximate and Ultimate analyses effectuated. The mild leachants investigated in the current research will be helpful to utilize low rank coals in an environment friendly way without deleterious effects associated with their combustion.