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Removal of Cadmium Ions from Waste Water using Raw and Treated Coals as Adsorbents

Aparna Mukherjee, S. K. Srivastava and G. Udaybhanu

Studies on the adsorption of cadmium (II) ions from waste water on two raw coals viz. North Tisra and South Tisra collieries, along with their eight chemically treated coal samples (which were used as adsorbents) were carried out. The chemical treatments adopted were (a) alkali treatment, refluxing – 72 BS mesh size coal with 25% w/v NaOH solution for 6 hrs., (b) acid treatment, refluxing – 72 BS mesh size coal with 50% v/v HCl for 6 hrs, (c) alkali-acid treatment, refluxing alkali treated coal with 50% v/v HCl for 6 hrs. and (d) acid-alkali treatment, refluxing acid treated coal with 25% w/v NaOH solution for 6 hrs. These treatments have shown changes in the moisture, ash volatile matter and fixed carbon values. FTIR & SEM spectra of treated coals were compared with the corresponding spectra of raw coals indicating structural and morphological changes in coal after the treatment. Adsorption studies reveal that acid treatment reduced the adsorption capacity of coal whereas alkali treatment improved it. Alkali-acid treatment, which gave the highest ash reduction, also did not improve the adsorption capacity substantially. The best results, as far as the improvement in adsorption capacity is concerned, were obtained from acidalkali treated coals. This clearly indicates that it is not the reduction in the mineral mater content of coal by acid, which is important for the improvement in the adsorption capacity, but it is the alkali treatment, which changes the chemical character of both; the organic and mineral matter part of coal, which ultimately results in improvement in its ion exchange capacity.