Continuous Separation of Hexavalent Chromium in a Packed Bed of Flyash Pellets

Abstract

The metal pollutant hexavalent chromium has been separated from flyash. Various types of flyash pellets were prepared by mixing flyash with different binders, such as cement, bitumen, kaolin, etc. Pellets containing 20% (w/w) kaolin were found to have satisfactory separation efficiency. Break through curves for a hexavalent chromium separation process at different bed heights, flow rates, and temperatures were evaluated. It was also observed that Cr (VI) removal in the packed bed increases with an increase in temperature and bed height but decreases with an increase in flow rate. Presence of other competing cations had no significant interference on separation. Desorption of adsorbed Cr (VI) from a packed bed of flyash pellets using H2SO4 and NaOH as eluants was also studied; it was found that sulfuric acid has better desorption efficiency. Leaching of Cr (VI) from flyash pellets to an aqueous phase at different temperatures was studied and it was observed that release of chromium (VI) is not a spontaneous process. The extent of leaching was markedly reduced when cement was present in the flyash as binder and temperature has little effect on the leaching. A model for break through curves has been established to co-relate the relative hexavalent chromium separation efficiency of flyash with other variables.