CONTINUOUS SEPARATION OF HEXAVALENT CHROMIUM IN A PACKED-BED OF FLY-ASH PELLETS

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 conta ining 20% (w/w) kaolin were found to have satisfactory separation effi ciency. Break through curves for a hexavalent chromium separation proc ess at different bed heights, flow rates, and temperatures were evalua ted. It was also observed that Cr (VI) removal in the packed bed incre ases 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 w as also studied; it was found that sulfuric acid has better desorption efficiency. Leaching of Cr (VI) from flyash pellets to an aqueous pha se at different temperatures was studied and it was observed that rele ase of chromium (VI) is not a spontaneous process. The extent of leach ing was markedly reduced when cement was present in the flyash as bind er and temperature has little effect on the leaching. A model for brea k through curves has been established to co-relate the relative hexava lent chromium separation efficiency of flyash with other variables.