The removal of Cd(II) by adsorption on fly ash has been found to be contact time, concentration, temperature and pH dependent. The process of removal follows first order adsorption kinetics and the rate controlling step is intrap article transport into the pores of fly ash particles. The equilibrium nature of Cd(II) adsorption at different temperatures has been described by the Langmuir isotherm. The temperature dependence of Cd(II) adsorption on fly ash indicates the exothermic nature of adsorption. Alkaline aqueous medium favours the removal of Cd(II) by fly ash. The increase in adsorption of Cd(II) with pH has been explained on the basis of surface complex formation approach.
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