Adsorption of toxic metal ions like Ni(II) and Zn(II) on fly ash and impregnated fly ash was studied in terms of different parameters like initial metal ion concentrations, pH, and temperature. Impregnated fly ash showed much higher levels of adsorption capacity for Ni(II) and Zn(II) as compared to untreated fly ash. The various rate parameters governing the adsorption process have been determined at different temperatures. Equilibrium modeling has been carried out using Langmuir isotherm, equations, and the corresponding constants have been evaluated. Thermodynamic studies have also been carried out and values of standard free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)) calculated. The adsorption was found to be exothermic for Ni(II) and endothermic in case of Zn(II) as determined by the values of enthalpy change.