Removal of Nickel(II) from Dilute Aqueous Solution by Sludge-Ash

This work examines the adsorption of Ni(II) onto sludge–ash, a waste produced from a fluidized bed incinerator combusted primarily with biosolids. Results of kinetic experiments showed that the adsorption was rapid. The kinetic adsorption data can be well described by an empirical modified Freundlich equation. The rate of adsorption decreased with either increasing surface loading and ionic strength or decreasing solution pH. The results of equilibrium studies showed that the solution pH was the key factor affecting the adsorption. The modified Langmuir model fit revealed that the hydrogen ion acts as a competitive inhibitor for the adsorption of Ni onto ash. The maximum adsorption capacity for Ni is 5.41 μmol/g. Experimental results indicate that the adsorption is favorable at higher temperature. Thermodynamic adsorption parameters for $\Delta G°\text{,}$ $\Delta H°\text{,}$ and $\Delta S°$ are −7.41 kcal/mol, 7.25 kcal/mol, and 48.9 cal/mol K, respectively.