Adsorption characteristics of Zn(II) from dilute aqueous solution by fly ash

This work examined the adsorption characteristics of Zn(II) onto fly ash, a waste produced from a coal-burning power plant. The results of batch equilibrium studies showed that the solution pH was the key factor affecting the adsorption characteristics. In general, the amount of Zn adsorbed increased as the solid concentration and pH increased, and sharply reached a 99% removal at a specific pH value, then it remained constant over a wide pH region. The Langmuir adsorption isotherm can describe well the equilibrium adsorption. The fly ash adsorption capacities of Zn ranged from 1.04 × 10−6 to 1.15 × 10−5 mol/g in the pH range of 6.0–7.5. Experimental results indicated that the adsorption was favorable at lower ionic strength, higher pH, and higher temperature. Values of ΔG° ranging from −6.86 to −7.41 kcal/mol suggest that the adsorption reaction is a physical process enhanced by the electrostatic effect. The values of ΔH° and ΔS° are 7.04 kcal/mol and 47.7 cal/(K mol), respectively.